Dichotomous table for gallers on Qercus

by Hans Roskam

FF agamic generation of gall wasps; FM ditto, sexual generation.
Galls on different plant parts have been subdivided in different keys:

Deciduous oaks
(Quercus robur, Q. petraea, Q. pubescens; with reference to Q. frainetto and galls occurring occasionally on exotic oaks)

On roots

1a Galls ± rotund, about pea-size or much larger, larval chambers inside => 2

1b Galls smaller, nodular or elongated spindle-shaped, without chambers: Meloidogyne sp.

2a Single galls ± globular; pea-, more rarely cherry-size up to 8 mm across, one-chambered; initially whitish-reddish to red-brown, glabrous, succulent, later woody, black-brown and rough on the outside. Usually on the filamentous roots down to 50 cm and deeper underground. Often in a bunch of grape-like or bulb-clustered groups, up to 30 mm across, mutually flattened or more rarely ± coalescing. Gall containing one larva per chamber. Q. petraea, pubescens, robur, pyrenaica, lusitanica: Biorhiza pallida FF

2b Galls much larger; irregular rotund or oval, ± crenate, up to 70 (80) mm across, many small chambers; initially succulent, later woody, with flaked cortex. On thicker roots close to the surface, more rarely at stem base. Containing one larva per chamber. “Truffle gall”. Q. petraea, pubescens, robur, lusitanica and some close allies. Andricus quercusradicis FF

= Inquiline gall wasps: Saphonecrus conatus and Synergus apicalis.

On stems, branches, twigs or shoots
(For galls developing from latent buds on stems, often directly on the bark, see Section C)

1a Inducers completely or partially on the outside of the galls => 18

1b Inducers inside the galls => 2

2a On old oaks => 3

2b Predominantly on seedlings. The caterpillar mines in the cortex, and damaged tissue regenerates with diffuse proliferations, causing curving of the seedlings. Q. petraea, pubescens, robur: Spulerina simploniella

3a Swellings on shoots of current or the preceding year => 8

3b Variously shaped malformation erupting from the bark on perennial twigs or stems, more rarely on old stems or on coppice; often hidden in herb layer, more rarely in the soil => 4

4a Single galls rotund or cone-shaped, about pea size or up to 1 cm across; basal part hidden in bark => 6

4b Galls about cherry- to fist size => 5

4c Midge larvae cause necrosis of cambium and bark- or timber damage to trunks of young oak trees and upper branches of older trees. Q. petraea, robur: Resseliella quercivora

5a Galls rotund or ± oval, walnut- to chicken egg size, multi-chambered. At the base of perennial stems, often in the soil. Q. petraea, pubescens, robur, etc.: Andricus quercusradicis FF

5b Partially fissured, later woody massive tumours of often considerable size have also been found on younger stems of Q. petraea. Probably partially caused by bacteria, although in many cases these have not been verified: Agrobacterium tumefaciens

= The small to expanded “wood crops”, cancers, occurring on perennial branches are not true galls; the causes may be various.

6a Mature galls cone-shaped to cylindrical => 7

6b Mature galls ± semi-globular, 2–6 x 3–5 mm, single or some galls clustered, protruding from the bulging bark. When young, with red fleshy wall, later brown, woody, at the base with longitudinal ridges. At top with emergence hole. Containing a single larva per gall. Q. petraea, pyrenaica, robur, lusitanica, etc.: Andricus rhyzomae FF

6c An extremely cryptic gall induced beneath the bark of branches and shoots; monolocular, often aggregated. The small larval chambers are induced just beneath the bark, without any visible external deformation of the shoot. The galls are most easily located by the emergence holes made by the adults. Q. robur, petraea, pubescens: Callirhytis erythrocephala FM

7a Galls developing deep in the woody tissue; outer half upwardly narrowed, wide cone- or ± pear-shaped, initially reddish, soft; later, after losing its outer envelope, brown, hard. Gall wall, compared with the large larval chamber relatively thin; in dry condition ridged from base to top with lateral emergence hole. Often protruding from rather swollen stem, ± covering thinner parts on all sides. One larva per gall. “Barnacle gall”. Q. petraea, robur, pyrenaica, lusitanica, etc.: Andricus testaceipes FF

7b Gall initially slender egg-shaped, ± acuminate, white or reddish, 6–10 mm long, about 4 mm across; with socket part sunk into otherwise damaged old stems or branches; single or more often in dense clusters and mutually flattened to ± three-sided pyramids. Before maturity covered by fleshy semi-globular to oval, yellow-green or –reddish, 3–4 mm long lid, drying out later on and dropping. The remaining cup-shaped part woody, protruding from the stem as a short cylindrical stub. Larval chamber separated by a thin hard, arched scale; the ± circular rim with deep pits (remains of vascular bundle). Containing a single larva per gall. Q. petraea, pubescens, pyrenaica, robur, lusitanica, etc.: Andricus quercuscorticis FF

7c Similar gall, differs by a ± cylindrical funnel which leads to the larval chamber. Q. pyrenaica: Andricus quercuscorticis FF

7d Gall shallowly embedded in the bark. Galls found on bark crevices, sometimes close to the ground; on branches 2‒5 years old buried in leaves and covered with moss; on regrowth shoots; in the axils of suckers around stumps. Rarely singly, generally in dense aggregations of galls at different stages of development. Galls conical in shape and found in tight groups, pea-sized with a grooved surface and a pear-shaped apex. Gall outer wall is reddish purple and fleshy, and is cast off as the gall develops. The wall of the gall beneath is initially whitish and soft-structured, hardening later and becoming brown, longitudinally grooved from the tip. Exit hole at the side. The galls can be confused with those induced in a similar location by the agamic generations of A. quercuscorticis and A. rhyzomae. A. quercuscorticis galls are frequently smoothly rounded and paler, and lack radiating grooves on the gall surface. Galls of A. sieboldi project further from the stem than those of A. rhyzomae, and the emergence hole is often in the side of the gall rather than at the summit as in A. rhyzomae. Galls of A. sieboldi also more frequently retain a cap of the external gall tissue usually shed in A. quercuscorticis and A. rhyzomae. Q. robur, petraea, pubescens, macranthera, iberica, lusitanica, pyrenaica: Andricus sieboldi FF

8a Small, 2–3 mm long, nodular swellings, partially protruding from the cortex => 16

8b Often expanded swelling of the shoot, on either the tip or sometimes on lower parts of young shoot => 9

9a Galls distinct from the exterior => 10

9b Shoots externally hardly changed. A terminal gall at maturity with a hardly distinct emergence hole may be found between the densely clustered lateral buds at shoot end are on the sometimes stunted shoots. Containing a single larva: Andricus turionum FF

10a Galls spindle-shaped, elongated or curved and crooked => 12

10b Swellings plump club-shaped, directly situated on the distinctly stunted top. Leaves clustered, leaf blades developed normally => 11

11a Galls at tip of twig, 15 (20) x 8 (10) mm. Centrally with longitudinal narrow cavity, eventually open above; at its base a small, oval, only terminally free inner gall. A single larva. Q. petraea, pubescens, robur, rubra, rubra var. maxima, lusitanica: Andricus inflator FM

11b Galls similar but smaller, only 6 mm long and 5 mm across. One larva. Q. pubescens, robur, pyrenaica, lusitanica, etc.: Andricus pseudoinflator FM

12a Galls not conspicuously curved => 13

12b Young shoots angularly curved, sometimes strongly deflected. Inside the stunted, thickened knee a pea-size swelling, sometimes 2–3 mutually coalesced, cartilaginous, green, initially succulent, each hiding an inner gall. Each containing one larva. All deciduous oaks: Andricus curvator FM

13a Development of galls in first year shoots => 14

13b Larvae in terminal part of previous year shoots which are swollen at the site of infestation; upward parts diseased and withering early. A single larva in pith. Q. petraea, pubescens, robur: Janus femoratus

14a Larvae in pith => 15

14b Stems with tubercular spindle-shaped swellings, pervaded by a screw-like ascending tunnel, which in cross-sections may be gall-like swollen by callus-proliferations. Larvae between sapwood and cortex. All deciduous oaks: Agrilus biguttatus

15a Shoot at tip almost evenly 2- to 3-fold swollen over a length up to 6 cm. In pith a white caterpillar with bright chestnut brown head. Q. petraea, pubescens, robur: Stenolechia gemella

15b In similar galls on same oak species: Epinotia festivana

15c Spindle-shaped gall, 2 mm long, emerging from a slit in the bark of a young twig. Q. petraea, robur: Pseudoneuroterus saliens FF

15d Large subglobular gall embracing the twig. Q. petraea, robur, pubescens: Aphelonyx cerricola FF

16a Galls on scars of bud scales or outside the buds in the leaf axils => 17

16b Galls usually with several on nodes, also on internodes, often at the base of one-year, ± shortened and locally thickened shoots. Solitary galls in bark, often hard to find, flat, often very slight spindle-shaped, up to 2 mm large, with a hardly 1 mm large internal gall. Chambers inside twigs have flat, circular rims, best seen if bark removed. Q. petraea, pubescens, robur, cerris, etc.: Andricus quercusradicis FM

16c Similar, but usually solitary galls. Q. petraea, robur. GW: Andricus testaceipes FM

16d Similar, inconspicuous, slightly arched cortex galls on young twigs. Q. petraea: Plagiotrochus marianii FF

= Three other cynipid species (Callirhytis glandium FM, C. rufescens FM and C. hartigi FM) cause similar galls in twigs and young shoots on Q. robur. There is no external sign of these galls

= The oak bark phylloxera Moritziella corticalis causes cancerous bark on the previous year’s growth. Known at a few localities in S- and E-England since 1972.

17a Galls with broad base attached on the scars of bud scales at the base of just extending shoots; oblong-oval, up to 1.5 mm thick and 2–3 mm long, white-yellow to bright brown. Containing a single larva. All deciduous oaks: Neuroterus anthracinus FM

17b Galls two- or three together, on young shoots, often close to axils of just extending leaves; attached with narrow base, elliptical, 1–2 mm long, initially green, later brown, bold, glabrous, very thin-walled. Containing a single larva. Q. petraea, pubescens, robur, cerris, lusitanica, etc.: Andricus quercuscorticis FM

18a Galls in the still glabrous bark of young stems and twigs => 21

18b Malformations usually on older organs, already developing bark => 19

19a Branches with conspicuous malformations, developing mistletoe => 20

19b Coppiced stem parts with open proliferations with bulging rims. “Nectria-cancer” Q. petraea, robur, etc.: Neonectria ditissima

19c Cancer-like rimmed malformations on young twigs, still lacking bark.
FUNGUS: Caudospora taleola

20a Affected twigs locally swollen; base of mistletoe stem dome-shaped margined. Mistletoe deciduous. Q. cerris, petraea, pubescens, robur, etc.: Loranthus europaeus

20b Local, often conspicuous swelling of twig; typical “rose-formation” absent. Mistletoe evergreen. Q. petraea, pubescens, robur: Viscum album

= Similar witches’ brooms have sporadically been recorded from endemic oaks, and, on various occasions, on red oaks. The cause is unknown, parasites have not been found.

21a Bark of the thinner twigs usually of younger plants with smaller, oval, flat-grooved, bulging-rimmed depressions, harbouring a scale insect => 22

21b Bark of the two-year old and perennial twigs, usually on the underside with expanded, 2–3 mm thick, later with longitudinal fissures bursting proliferations of the cambium. Q. petraea, pubescens, robur: Lachnus pallipes

22a Insects with flat scale => 23

22b Scale usually rotund-oval, about 1.5 x 2 mm across, ± strongly convex, greenish, brownish or yellowish. Scales in various densities usually keeping some distance apart, many in profile on the ± disfigured young shoots. On many oaks, predominantly on Q. robur: Asterodiaspis variolosa

22c Similar lifestyle, apparently more sparse: Asterodiaspis minus and/ or A. quercicola

23a Similar depressions, often more irregular. Scale insect with pear-shaped, whitish to grey-white shield, about 2.5–3 mm long. Females wine-red. All deciduous oaks: Chionaspis salicis

23b Malformations similar to above. Rim often less distinct. Shield of the females rotund, about 3.5 mm long, dark. Females vivid yellow. Q. petraea, pubescens, robur, etc.: Diaspidiotus zonatus

23c Stunting and branching of young shoots. Q. robur: Parthenolecanium rufulum

On buds or on ± extending terminal shoots

1a Buds unopened, only slightly changed externally or completely to partially transformed into often conspicuous closed galls of various shape => 3

1b Galls on shoot tips => 2

2a Shoot axis distinctly stunted, club-like, swollen. Gall up to 15 (20) x 8 (10) mm, bearing clustered, mostly normal leaves. Galls centrally with a narrow, cylindrical, soon apically opening cavity; at base with an oval sessile inner gall. Containing a single larva: Andricus inflator FM

2b Buds on extended and ± stunted shoots. Young leaves clustered almost ± artichoke-like. Their leaf blades, only 10–30 mm long, folded upwards, irregularly twisted and curled. Veins, especially midrib, ± thickened and sometimes haired. Several yellowish-white jumping larvae. Q. petraea, robur, etc.: Contarinia quercina

2c In similar malformations, whitish larvae also gregarious, non-jumping: Arnoldiola quercus

2d Larvae bright orange to reddish yellow: Dasineura dryophila

3a Buds completely or partially transformed into particular, distinctly recognizable, small to sizeable galls => 5

3b Buds unchanged externally or only slightly transformed => 4

4a Buds slightly enlarged, not opening. Containing usually several red larvae. Q. faginea, petraea, robur, ? pubescens, lusitanica: Arnoldiola quercus

4b An egg-shaped gall completely covered by scales, up to 2 mm long, inside an externally hardly transformed bud. Eventual exit hole laterally. Containing a single larva. Q. petraea, pubescens: Callirhytis bella FM

5a Galls develop in terminal- or lateral buds on young, one- or also two-year, especially lateral, free-standing shoots => 17

5b Galls arise on thin- or thicker perennial, usually basal, shoots or older stems, here on latent buds => 6

6a Gall body with lateral enlargements, sometimes with spines or with thread-, club-shaped or conical appendages => 10

6b Shape of gall body uniform; surface glabrous or pubescent => 7

7a Galls about 3–5 mm long, slender egg-shaped or cylindrical => 8/p>

7b Galls rotund, usually short acuminate, pea-, exceptionally up to cherry-size, ± whitish or on above-ground parts often shining coral-red, cowberry-like, glabrous or with some brown scales; thick-walled, succulent, one-chambered. Separate or in groups. Each containing a single larva. Q. petraea, pubescens, robur: Trigonaspis megaptera FM

8a Galls up to 3 mm long; on Q. petraea, robur => 9

8b Galls on Q. pubescens, pyrenaica, 3–5 mm long, egg-shaped, greenish or reddish, surface densely covered with small hairs, usually red distally; thin-walled, soft, one-chambered, covered by bud scales at base. Containing a single larva: Cynips quercus FM

9a Galls slender egg-shaped, 2–3 mm long, rotund on top or slightly depressed. Initially red, later dark-violet, densely velvet-like pubescent, thin-walled. At base with bud scales. A large chamber containing a single larva. Q. petraea, pubescens, robur, cerris: Cynips quercusfolii FM

9b Gall similar, 4 mm high, 2 mm in diameter, terminally rounded, brownish when mature, glabrous or very finely pubescent. Usually several galls are clustered, but not coalesced. Q. petraea: Biorhiza cecconiana FF

9c Gall similar, but grey-green or grey-brown, smaller, only about 2 mm long; slender egg-shaped, ± acuminate. Hairs slightly longer, whitish; bud scales absent at base, thin-walled. A large chamber containing a single larva. Q. petraea, robur, lusitanica: Cynips longiventris FM

10a Appendages on the entire gall surface => 12

10b Appendages limited to parts of the gall => 11

11a Appendages on the basal half of the gall, very irregular, short and thick, like an uneven humped bulge closely appressed to the shoot axis; upper gall half obtusely conical, with rounded end. Gall 10–12 mm long, with same width at base. Surface net-like checkered, brown, with white stellate hairs or almost glabrous. Outer wall spongy, chamber in the under part, large; protective layer woody. Containing a single larva. Q. petraea, pubescens, robur, frainetto: Andricus conificus FF

11b Gall consists of two parts; distal parts is 7‒8 mm high, 5‒6 mm wide, brownish, almost woody, cup-shaped opened and separated by a narrow circular groove from the distal part which envelopes the twig, but is only narrowly attached. Basal part of gall pubescent; gall chamber rotund, thin-walled, situated in basal part of gall. Q. pubescens: Andricus korlevici gen. unknown

11c Galls with a sharp-edged, ± undulate shallowly lobed corolla, urn- or bell-shaped, 6–9 mm high, yellowish-green, reddish or bluish. Outer wall a little tough; inner wall hard. Containing a single larva. Q. petraea, pubescens, robur: Andricus polycerus FF

12a Appendages ± filamentous, at least terminally setose or conspicuously pubescent => 16

12b Appendages more rough, sometimes terminally slightly haired, but without setae => 13

13a Protrusions not contacting one another, obtusely conical or papillate, sometimes spine-like or also comb- to ridge-like => 15

13b Protrusions enlarged in middle- or upper part, hence touching one another => 14

14a Appendages initially stalk-like, then suddenly pyramidally enlarged and closely touching, covering the actual gall body. Gall body one-chambered, globular, about pea-size, including protrusions, walnut-size. Containing a single larva. Q. petraea, pubescens, robur, frainetto, pyrenaica, etc.: Andricus hartigi FF

14b Appendages stalked, terminally disc-like enlarged, covering completely the woody gall body, like a tortoise shell. Shields of the under half three- to four-angular, of about equal size on all sides; on the upper half converging like long equal-sided triangles. Galls one-chambered, incl. appendages, about pea-size. A single larva. Q. petraea, pubescens, robur, lusitanica, etc.: Andricus truncicolus FF

15a Galls sessile, 3–4 mm across, rotund, with many sturdy papillae or conical tubercles, increasing abruptly from base to top, terminally rounded, often red, with fleshy outer layer, later yellowish or brown and woody. In the basal part is a wide- oval inner gall containing a single larva. Q. petraea, pubescens, robur, etc.: Andricus gemmeus FF

15b Gall c. 60 x 45 mm; white spots. Q. conferta, farnetto, hungarica:
Andricus quercustozae

15c Galls globular, about 8 mm across, with many thick conical spines, up to 1.5 mm long, similar to a horse-chestnut fruit, having a stalk about 1 mm long. A single larva. Adults in spring, Q. robur: Andricus hedwigia FF

16a Single galls egg-shaped to globular, white to red, later brown, 4–5 mm across, often several united to about cherry-size agglomerations. Surface with thread-like radiating appendages, tapering apically and about 5–10 mm long which are distantly white pubescent over their whole length. Wall thin and fragile. One larva per chamber. Q. petraea, pubescens, robur: Andricus serotinus FF

16b Galls rotund, 3–4 mm across; solitary or sometimes in unified clusters of 2–4; with densely covered bristles, 3–4 mm long, from a broad base gradually narrowed, glossy, white, bluish-red on tip, with 3–4 longitudinal grooves. Gall wall thin, woody. Containing a single larva. Q. infectoria, petraea, pubescens, robur: Andricus hystrix FF

17a Bud scales are not transformed or disappear partially or completely => 19

17b Bud scales are completely or partially involved in the gall development and are recognisable as modifications or remains => 18

17c Bud galls terminally on a thin twig in groups of 2–4. Q. robur:
Andricus quercuspyramidalis
gen. unknown

18a All scales on the strongly broadened bud base are considerably enlarged, resembling a larch- or a hop-cone, comprising a ± egg-shaped envelope, up to 20 (30) x 10–12 (20) mm. Outer scales brownish, dorsally usually glabrous, short and wide, triangular-rotund to egg-shaped, connected by intermediate forms to the inner, at first elongate-lanceolate, then short filamentous, white and pubescent leaf rudiments. In the middle an eventually brown, hard, egg-shaped, acuminate, one-chambered inner gall, up to 6 (9) mm long. “Artichoke or hop gall, oak rose”. Containing a single larva. Q. petraea, pubescens, pyrenaica, robur, frainetto, lusitanica, etc.: Andricus foecundatrix FF

18b Only the inner scale leaves strongly enlarged and coalesced. Gall rotund- to oblong-oval, slightly larger than pea-size, up to 10 mm long, greenish-white to reddish, succulent, with fleshy wall and (1) 2–3 (5) large larval chambers. Apical scales transformed into brown lobes, basal scales normal. One larva per chamber. “April gall”. All deciduouys oaks: Neuroterus politus FM

19a Gall body in profile bell- to jar shaped, conical or variously structured, but not rotund or egg-shaped. Sometimes compartmentalised with several long protruding appendages => 41

19b Profile of galls, very different in size, ± uniform, globular, rotund- or oblong-oval, egg- to lemon-, cylindrically or also spindle-shaped, sometimes provided with tubercles, bumps or flat ridges => 20

20a Galls not differing substantially in longitudinal- or cross section, or acorn-shaped to cylindrical => 24

20b Galls distinctly spindle-shaped => 21

21a Short-stalked or sessile; stalk often to a large extent covered by bud scales => 23

22b Galls long petiolate, the stalk protruding far beyond the unopened bud. Petiole longer than the longitudinally ridged one-chambered gall => 22

22a Gall body about rice-grain size, 3–5 mm long, 2–4 mm thick, broadest in the middle, gradually tapering at both ends, ending in an elongated tip; initially yellow-green, eventually brown; on Q. petraea, robur glabrous, on Q. pubescens initially with distant, obliquely deflected hairs, which ± fall off later; usually with conspicuously red, protruding longitudinal ridges. Wall thin, almost woody. Gall from 5 onwards, dropping 7‒8. ‘Large spindle gall’. In the middle is a sizeable chamber containing a single larva: Andricus callidoma FF

22b Gall similar, but with short conical, papilla-like bare tip; with or without longitudinal ridges, green, later red to brown. Gall and stalk bear scattered shorter or longer deflected bristle hairs. Gall wall thin; large chamber in the inflated upper half of the gall, with a single larva. Q. petraea, pubescens, robur: Andricus amenti FF

23a Gall rice-grain size, stalk slender, shorter than gall or absent; gall developing from end- or lateral buds of lammas shoots, slightly thickened in the middle, green to brown with longitudinal ridges and an obtuse conical shiny tip, which reaches about a third of the length of the thin-walled, one-chambered gall body; develops in 9, dropping off in 10. ‘Little spindle gall’. Containing a single larva. Q. petraea, pubescens, robur, pyrenaica, lusitanica: Andricus malpighii FF

23b Gall body spindle-shaped to conical, about 10–12 (16) mm long and 3 mm wide, thin-walled, hard, with large chamber. Initially green, later brown-felt-like pubescent, eventually glabrous and glossy brown, ridges absent. Under part with short, thick, stalk (sometimes absent) inserted only between the small bud scales; tip of various length, usually bill-like or bent. “Brown felt gall”. Containing a single larva. Q. petraea, pubescens, robur. frainetto, lusitanica, etc.: Andricus solitarius FF

24a Galls globular, ± egg-shaped or rotund- to oblong-oval => 25

24bGalls ± slender acorn-shaped to cylindrical; 5–6 (8) mm long, 3–4 mm broad, sometimes narrowing gradually from the base to the tip; small blunt tip, in the middle with papilla-like little warts, glossy, glabrous. Wall rigid and thin, initially fragile succulent, soon drying out; outer layer green or reddish, with longitudinal ridges and whitish streaks or spots, later brown. At base enveloped by scales. Chamber large, containing a single larva. “White-spotted oak gall”. Q. petraea, pubescens, robur: Andricus paradoxus FF

25a Galls ± globular, usually less than 2 cm => 27

25b Galls not globular; when mature much larger than 2 cm => 26

26a Developed galls usually (1) 2–4 cm large; rotund, tuberculate or ± flattened and bulging bulb-shaped; apple- or potato-like. ‘Potato gall, oak apple’. Up to maturity succulent spongy, rather soft, whitish- to yellowish brown, sometimes reddish suffused, later darker brown and papery. Occasionally with mark of bud scales. Predominantly close to the attachment many tough-walled, oblong, ± radiating chambers. Each chamber with a white larva. All deciduous oaks: Biorhiza pallida FM

= Inquiline: Synergus gallaepomiformis.

26b Galls rotund to concave cup-shaped; (10) 17–35 (40) mm long; with somewhat distended tip; upper half with a distinct, equatorial rim of ± smaller to larger tubercles. Wall thick, spongy; outside brownish, sometimes coated silver-grey. Inside is an oblong eventually loose inner gall containing a single larva. Q. petraea, pubescens, robur, frainetto, pyrenaica: Andricus quercustozae FF

= Galls of Andricus insanus strongly resemble those of A. quercustozae but they are permanently viscous (those of quercustozae only when young) and the spines are not arranged in a neat circle, but rather scattered in several circles.

27a Galls only cherry stone-size => 34

27b Galls about 8–10 mm long or larger => 28

28a Surface always with wart- to tubercle-like, ± regularly arranged protrusions. Galls with flat conical basal part => 31

28b Surface glabrous, at most irregularly reticulate or with inconspicuous, irregularly scattered warts => 29

29a Galls about 8–10 mm long, globular or unequal rotund-oval, wall compact spongy or woody => 30

29b Galls almost spherical, 10–25 (30) mm long, glabrous or with very slight warts, occasionally finely striated; initially green and short pubescent, later yellow to dark brown, completely glabrous. Outer layer thin-walled, ± spongy and soft. Centrally an oblong chamber with fragile protective layer. “Marble gall”. Containing a single larva. All deciduous oaks. Andricus kollari FF

= Inquiline cynipid wasps:

1Synergus gallaicus

2 Synergus hayneanus

3 Synergus ibericus

4 Synergus pallidipennis

5 Synergus pallipes

6 Synergus radiatus

7 Synergus reinhardi

8 Synergus thaumacerus

9 Synergus tibialis

10 Synergus umbraculus

= Inquiline gall midge: Arnoldiola gemmae.

30a Galls usually globular, about 8–10 mm long; solitary or 2–5 together. Surface initially grey-green, later very hard, grey to red-brown, coarse, as result of covering of the upper layer with grey-whitish, irregular reticulate coating. Single chamber off-centre, exit hole always close to the point of attachment. “Cola-nut gall”. Containing a single larva. All deciduous oaks: Andricus lignicolus FF

30b Galls very similar to previous ones, but gall chamber situated closer to the gall wall. Solitary galls ± rotund, 8–10 mm long; usually in groups of 3–5 or more; gregarious galls smaller, flattened at contact area, ± pear-shaped. Surface glabrous, rarely rugose, green, later dirty yellowish-brown. Wall rough-porous, not woody. Chamber laterally, usually under a wart-like protruding pin-prick scar. Containing a single larva. Q. petraea, pubescens, robur, frainetto, etc.: Andricus conglomeratus FF

31a Galls irregularly coarse rugose or with isolated sometimes ridge-like connected tubercles => 32

31b Surface of 7–10 mm long galls subdivided into regular fields, similar to a closed acorn cup. Each small shield bearing a tubercle. Green in the beginning, then brown, short scale-like pubescent; with thick-walled, enclosed, one-chambered inner gall. Containing a single larva. Q. petraea, pubescens, robur, etc.: Andricus caliciformis FF

32a Galls with solitary tubercles or tuberculate ridges => 33

32b Galls spherical, 7–15 mm long, slightly narrowed at base, surface brownish-yellow. with coarse, irregular, tuberculate wrinkles. Protective layer of the gall chamber hard, wall softer. Containing a single larva. Q. petraea, pubescens, robur, frainetto, etc.: Andricus infectorius FF

33a Galls like the preceding ones, not rugose; red- to grey-brown, glabrous, hard and woody, 15–20 mm long. Larval chamber coalesced with the gall tissue; with irregularly placed, scattered coarse tubercles, especially apically. A single larva. All deciduous oaks. Andricus gallaetinctoriae FF

33b Gall more or less spherical, but with a slight elongation to the point of attachment, reaching 10‒15 mm in diameter when mature, unilocular. The gall surface is sparsely covered with pointed protuberances, each 2‒3 mm long in the mature gall, and sometimes joined by raised ridges. Galls greenish-yellow when young, and a uniform pale sandy brown when mature. The wall of the mature gall is extremely hard and woody and it does not dehisce from the host. Q. infectorius

33c Galls globular, usually 20–25 (45) mm, rarely only 13–20 mm long, dull brown, tubercles irregularly reticulate connected by ± protruding longitudinal ridges. Tissue inside brown, spongy, with large, irregular cavity, which containing a small, thin-walled inner gall, narrowly attached. Containing a single larva. Q. robur, pubescens: Andricus hungaricus FF

34a Gall oval- or egg- to lemon-shaped, thin- and ± tough-walled => 36

34b Galls ± globular, fleshy => 35

35a Galls globular to short rotund-oval, 4–7 mm long, with short tip, ± whitish to pale red. Surface glabrous, with scattered scale-like appendages. Wall thick, succulent; gall with central chamber. Containing a single larva. Q. petraea, pubescens, robur, frainetto, etc.: Trigonaspis megaptera FM

35b Galls similar to the previous ones; not different from the agamic generation. Adults somewhat later than those of the previous species, still emerging in 7 of the first year, or also not before the second year. Q. petraea, pubescens, robur: Trigonaspis synaspis FM

36a Galls rounded at top; without wart-shaped appendage; ± ellipsoid to egg-shaped => 39

36b Galls at top with a distinct papilla; often ± lemon-like => 37

37a Gall narrowed at base, ± markedly attached by short stalk => 38

37b Galls mounted on a broad base, short, rotund-oval, usually somewhat broader than long, 3–4.5 mm long, single-chambered, about half enveloped by bud scales, on top with a yellow to rust red wart. Outer wall green, slightly succulent, later drying out, then with netlike surface. Inner wall woody, longitudinally furrowed, later blackish. often on small twigs sprouting from trunk. Containing a single larva. All deciduous oaks: Andricus inflator FF

37c Gall shape and size similar, but surface longitudinally ridged at maturity. Q. lusitanica: Andricus pseudoinflator FF

38a Galls mounted on wart-like base, at base enveloped by bud scales, looking like a globular lemon, up to 5 mm across, brown-yellow, darker on top, finely rugose, with deflected small hairs, single-chambered, wall thinner, with a free, completely spherical inner gall in the cavity. A single larva. Q. petraea, robur: Andricus clementinae FF

38b Galls lemon- to acutely egg-shaped, often 3–4 mm long and 2 mm wide, hard, glabrous, reddish, later brown. Below the dark tip is a narrow, whitish, belt-shaped ring. Predominantly solitary, sometimes pairs in a single bud. With only the upper third or fourth part protruding from the bud scales. Initially connected by a short stalk which reduces later on. ‘Collar gall’. Containing a single larva. Q. petraea, pubescens, robur, pyrenaica, etc.: Andricus curvator FF

38c Gall green, glabrous, thin-walled, ovoid, 2 mm long, 1.5 mm in diameter; protruding from the bud by a third only or completely hidden. Gall dropping off. Q. petraea, pubescens, robur: Andricus gemmicola FM

39a Galls egg-shaped, green or ± reddened, glabrous => 40

39b Galls in spring, ± egg-shaped, 3–5 mm long, at base with inconspicuous bud scales, green or ± reddish, thin-walled, soft. Surface densely covered with usually brownish-red, distal small hairs. Containing a single larva. Q. pubescens: Cynips quercus FM

40a Galls egg-shaped to rounded cylindrically, in autumn; 3.5–5 x 2.5–3.5 mm, sometimes with short little warts at the tip; basal part halfway to two-third enclosed in bud scales, whitish coloured. Outer layer thin, glabrous, somewhat succulent, the exposed part olive-green, later rose-red to violet, eventually drying out, brown and longitudinally keeled like the inner layer. Wall thin. Chamber elliptical. Containing a single larva. “Whitefoot gall”. Q. petraea, pubescens, robur: Andricus quercusramuli FF

40b Gall body at base not enclosed by bud scales, usually ± obliquely protruding on short stalk; elliptical, width about 2–3 mm and length 2–2.5 mm, sometimes smaller. Wall glabrous, thin, dark-coloured with irregular brighter stripes, appearing slightly roughened. In the conspicuously large cavity is a single larva. Q. pubescens, rare on Q. petraea: Andricus trotteri FF

41a Galls appearing deeply subdivided into an upper and basal part, respectively acute transversely constricted, or with several conspicuous protrusions or appendages => 47

41b Gall body not deeply subdivided, of different shape, ± conical, cup-, or urn-shaped, sometimes with bulges => 42

42a Galls glabrous, sometimes viscose => 44

42b Galls velvet-like pubescent => 43

43a Galls on younger shoots in late summer, length 3–6 mm, width 2–4 mm; green to dark red, occasionally on the same shoot; quite variously shaped, bell-shaped to obtusely conical, on the tip with small hairless brown warts, at base with an inward curved bulge; in other cases at base cup-like widening, on top ± rounded, more rarely flattened, the wart on top ± countersunk. In all cases covered in a deflected, white or ± violet, silk- to velvet-like pubescence. Wall rather soft; one larval chamber with distinct cavity above or very loose parenchyma. Q. petraea, pubescens, pyrenaica, rare on robur, etc.: Andricus glandulae FF

43b Galls bell-shaped, similar to the previous ones, but with long, cylindrical, thick stalk. Upper part elongate, ± cylindrical; basal part with thick, rounded tubercles at base. Containing a single larva. Q. petraea, pubescens, robur: unidentified subsp. of Andricus glandulae FF

44a Overall shape of galls rotund, cup-, urn-like, or consisting of a broad basal part with a narrow cylinder on top => 45

44b Galls slender conical, with abruptly narrowing, usually hollow apical part, about 5–6 mm long and 4 mm wide, brown, glabrous or with rather long deciduous hairs, longitudinally striate up to tip. Wall hardly thickened, slightly woody. No inner gall. Chamber containing a single larva in basal part. Q. petraea, robur: Andricus paradoxus FF

44c Gall oblong-ovoid, almost cylindrical, 6–8 x 3 mm, woody, glabrous, the upper half longitudinally striate, a little but distinct navel on apex; larval chamber large, thin-walled. Q. petraea, pyrenaica: Andricus lichtensteini DM

45a Galls up to only10 mm => 46

45b Gall 17–40 mm long, rotund or ± cup-shaped. In the upper part with a belt-shaped circle of smaller and larger tubercles, about 5–6 mm long. The lid-like apical part weakly arched with somewhat extended tip. Glossy brown, ± silver-grey coated. Wall thick, brown, spongy. At the level of the ring centrally is an oblong, transversely situated inner gall in a flat, wide cavity. Containing a single larva. All deciduous oaks. Andricus quercustozae FF

= Galls of Andricus insanus strongly resemble those of A. quercustozae but they are permanently viscous (those of quercustozae only when young) and the spines are not arranged in a neat circle, but rather scattered in several circles

45c Gall rotund, one-chambered, 20–30 mm across, a small spongy, surface covered with flat pyramidal warts. The tip of these warts is bluish when young, The base is red and the middle part yellowish. Q. robur, lusitanica, pyrenaica: Andricus curtisii FM

46a Gall urn-shaped, up to 10 mm long, broadly attached to the twig, ± enveloping and overtopping it laterally Basal half swollen, without interruption, passing over into a narrower, apically slightly narrowing upper half. Terminal part groove-like depressed, in the middle with wart-like tubercles. Fresh yellow or red and ± sticky, or dry yellow and hardly sticky. In a large central cavity is an initially attached, later free, thin-walled egg-shaped inner gall. Containing a single larva. Q. petraea, pubescens, pyrenaica, robur, etc.: Andricus glutinosus FF

46b Gall oblong-conical 12–28 mm across, embracing the twig and some petioles; surface brownish deciduous pubescent, eventually the upper part of the cone is slightly broadened, the centre with a navel-like depression. One large basal chamber containing a single larva. All deciduous oaks. Andricus tomentosus FF

46c Gall bowl-shaped, pale yellow, glossy, stalked. Stalk about 6–8 mm long and 1.5–3 mm thick. The bowl is 15–22 mm in diameter, the margin deflected, sometimes fimbriate; at the place of attachment is a cavity with ovoid inner gall. Q. petraea, pubescens: Andricus stefanii FF

46d Gall up to 10 mm long, bipartite. Basal part flat expanded, ± lobed, enveloping the shoot axis, up to 3 mm long and 10 mm wide. The centrally mounted cylindrical or ± obtuse conical gall, flattened at tip and ± depressed, up to 7 mm long and 3–4 mm wide. Whole gall red- to chestnut brown, ± sticky, glossy. With an oval inner gall in the basal part. Containing a single larva. Q. dalechampii, petraea, pubescens, robur: Andricus mitratus FF

47a Gall body undivided, with conspicuous, stalked or several variously shaped appendages => 51

47b The gall body appears ± subdivided => 48

48a Subdivision in longitudinal direction => 49

48b Length of gall body about 8 mm, abruptly transversely subdivided. Basal part rotund-oval, 4–5 mm wide, 2–3 mm long, brown red, ± occupied by rather long, fine, woolly, white hairs. The hollow onion-like upper part, up to 5 mm wide running on top into several simple or forked, short, thread-like appendages. Appendages short pubescent, longitudinally grooved, with pith inside. An oval larval chamber in the basal part containing a single larva. Q. petraea, pubescens, robur: Andricus galeatus FF

49a Under part of the early woody galls short cylindrical; appendages on the upper part only => 50

49b Galls with wide oval basal part, about 3–4 mm long, fleshy during longer time, at their free surface occupied by many papillae from gall base to tip rapidly increasing in length, obtuse-conical, terminally pubescent; in the basal part is a large wide-oval chamber containing a single larva. Q. robur, more rarely Q. petraea, pubescens, lusitanica: Andricus gemmeus FF

50a Basal part of the early woody galls cylindrical, 4–6 x 2.5–4 mm, usually standing on a strongly swollen branch stump. Upper part usually divided into 2–4 (5) conical or rotund, 2–4 mm long, acutely-angular erect, glabrous lobes, between them laterally the actual tip showing a flat, coarse little ‘rosette’. Surface red-brown to bark-coloured, glabrous, ± glossy, irregularly disrupted. Wall woody. Gall chamber in basal part with a single larva. “Lappet gall”. Q. petraea, pubescens, robur, etc.: Andricus corruptrix FF

50b Basal part of the gall short cylindrical; standing on the not thickened twig. Upper part with (2) 3–4 (6) usually obtusely-angular upward and outwardly directed projections, short conical, with papillate appendages, between the actual tips, a small wart provided with a dense, woolly hairline. Gall hard, 4–6 mm long; surface grey to red-brown, fissured, fine velvet-like pubescent and dull. With a large, transversely situated, oval chamber lacking a particular protective layer in the basal part. Containing a single larva. Q. petraea, pubescens, robur: Andricus amblycerus FF

50c Galls similar, rotund, but about 7–8 mm long; appendages much shorter and broader, glabrous at tip, provided with a wart. With distinct inner gall. Containing a single larva. Q. petraea, robur: Andricus corruptrix FF

51a Galls multi-chambered, with appendages all over the surface => 54

51b Galls one-chambered, with thinner or thicker crown-like arranged appendages => 52

52a Appendages extending from a disk-like apical plate => 53

52b The basal gall body, with broad basal attachments, slender onion-shaped, 5–8 mm long and 4–6 mm wide, one-chambered, then passing into two tapering, conspicuous horn-shaped projections, up to 50 mm long, hollow, to the tip sometimes repeatedly subdivided, which may be fused into a single strap, or reduced to two points. Containing a single larva. “Ramshorn gall”. Q. petraea, pubescens, robur: Andricus aries FF

= Inquiline gall wasp: Ceroptres clavicornis

53a Gall body rotund, cup-shaped or inverted bell-shaped, 10 to 12 mm long, at top 12–15 mm wide; flattened here and in the middle with groove-like depression, passing into several coarse horn-like projections, the terminal half narrowed, usually deflected upward and outward, 5–8 mm long, occasionally with a similar double crown. In fresh condition yellow, here and there ± reddened, basal part sticky; when dry, brownish and not sticky. Inside a small central cavity is an inner gall, attached above and below. Containing a single larva. Q. petraea, pubescens, robur, frainetto: Andricus coronatus FF

53b Gall inverted conical to bell-shaped, 12–15 mm long and almost of same width above; not sticky. Upperside almost disc-like, in the middle somewhat elevated, with a central wart; the margin ± sharp-edged, with 3–5 outwardly directed lappets, ± upwardly and downwardly bent, flattened and gradually tapering, up to 10 mm long, sometimes extending starfish-like. In fresh condition greenish and ± reddened, later brownish-yellow. Inner gall large, spherical, cartilaginous with coarse longitudinal striations. Containing a single larva. Q. petraea, pubescens, robur, frainetto, fruticosa: Andricus polycerus FF

53c Galls similar, about 8 mm long; in the bell-shaped part finely striate, brick-coloured. Upper part more brightly coloured, with four elevated, flat-triangular protruding appendages, which form a wide, slightly cross-shaped disc, with a papilla in its middle. A single larva. Q. petraea, pubescens: Andricus stefanii FF

53d Gall generally bell-shaped, 12‒15 mm in length when mature. The upper, distal surface of the gall is a flat or slightly concave surface from the rim of which radiate 3‒6 (most frequently 4) stout spines, often curved at their tips. The upper surface usually has a small tubercle at its centre. The young gall is green, and sometimes matt in texture due to a coating of fine white powder. In other cases, the gall can be shining, or pubescent, or even (very rarely) glutinous. As it matures the gall turns a reddish brown. The single globular larval chamber is located in the upper part of the gall, 7‒8 mm across, with a thick, hard wall. Though the peripheral tissue in young galls can be quite soft, when mature the central parts are very woody, and bisection reveals a structure of radiating fibres around the larval cell. The gall remains on the tree for a long time after emergence of the adult insect. Q. petraea, pubescens, robur, hartwissiana, lusitanica: Andricus subterraneus FF

54a Appendages of various size and appearance, scattered => 55

54b Appendages of almost similar appearance, very many, covering the globular to oval, cherry- to hazelnut-sized gall bodies, spiny, 4–8 mm long, sticking out rigidly radiating, tipped with a small knob, often red and sticky. Old galls persist but lose spines. Inside the livid yellow, thick-walled woody gall are several larval chambers each containing a single larva. “Hedgehog gall”. Q. petraea, pubescens, robur, frainetto, lusitanica, etc.: Andricus lucidus FF

= Inquiline gall wasp: Synergus umbraculus.

54c Galls much smaller, up to 8 (10) mm across with spines only 2–4 mm long, with rounded tips and appearing longitudinally striate. Andricus lucidus FF

55a Basal part of the brown gall about 10–20 mm wide, irregularly rotund-oval, apically often widening, only rarely narrowing; at the end flattened and predominantly bearing many rigid, 5–10 mm long, irregular, usually strongly curved, compressed, longitudinally grooved horn-like tapered appendages, sometimes ± coalesced at their bases. Inside many, ± oval chambers each containing a single larva. All deciduous oaks: Andricus coriarius FF

55b Galls similar. However, appendages straight or only weakly curved, not horn-like and tapered, compressed, longitudinally striate, yellow-green, sticky, 5–15 mm long, 2–4 mm wide. Q. petraea, pubescens, robur, frainetto, pyrenaica, etc.: Andricus pictus FF

= Andricus grossulariae FF develops exclusively on catkins in similar, but smaller galls.

= Andricus bulgaricus FF causes a bud gall on Q. pubescens, usually solitary. The gall is unilocular, elongated, narrower at the base broadening towards the apex. Galls are 11‒23 mm long and 7‒9 mm in diameter in their broadest apical part, gradually narrowing towards the base.

On leaves

1a Galls are open and often of undefined shape. Openings of many galls often only recognisable with difficulty => 34

1b The inducer develops during all its immature stages in galls completely closed on all sides => 2

2a Galls of defined, distinct shape on the leaf blade, on the leaf margin, or distinctly breaking out of the hardly modified venation => 7

2b Swellings of petiole or of leaf venation, but not clearly protruding => 3

3a Caused by gall wasp larvae. Larval head hardly contrasting, thoracic legs absent. Galls predominantly on the venation; on petioles only simultaneously appearing with those on leaf surface => 4

3b Petiole ± shortened and bent, distinctly swollen over all its length. Gall often far more pronounced on short stalked oaks than on long stalked ones. The mature larva cuts an oblong-oval shelter terminally from the gall. Larva with distinctly contrasting head and with thoracic legs. On deciduous oaks: Heliozela sericiella

4a Galls ± spindle-shaped, considerably longer than wide; recognisable on the leaf veins usually only on the underside; with membranous-leathery wall => 5

4b Galls on main and subordinate veins; ± globular to rotund-oval, 5–8 mm across; in adjacent leaf blade areas protruding on both leaf sides; sometimes with several ± coalesced and distorting the leaf. Upperside glabrous, underside sometimes weakly pubescent; on Q. pubescens both sides ± haired. Wall succulent. Centrally a thin-walled cavity with an eventually detached inner gall. about 2 mm long. Containing a single larva. Q. petraea, pubescens, robur, frainetto, lusitanica and many other cultivated deciduous oaks” Andricus curvator FM or, southern localities: Andricus curvator var. lusitanica FM

5a Swellings on petiole and midribs, predominantly on underside, mostly ± expanded spindle-shaped, up to 8 mm long, yellowish, later brownish, sometimes multi-chambered; occasionally on smaller veins but then smaller, ± short spindle-shaped and one-chambered, several per leaf and sometimes coalescing => 6

5b Galls also on petioles and main veins, always small and one-chambered, about 1.5 mm wide and 2.5 mm long, with small inner gall. Containing a single larva. Q. petraea, robur: Andricus testaceipes M

5c Swelling of a main vein or the petiole, 2.5 mm long, fusiform; the gall has an inner gall. Q. petraea, robur: Andricus nodifex FM

5d Midrib of very young leaves locally swollen, with oval egg capsules (procecidia, oviposition scars, not true galls). Larva living externally on the leaf blade, initially pale green with black head capsule, provided with 5 rows of bifurcating setae; standing on black warts later on orange-yellow, eventually losing their setae. Q. robur, less frequent on Q. petraea, also on Q. rubra, rubra var. maxima, etc.: Periclista lineolata

6a Galls slightly arched, usually solitary, also on lateral veins; up to 5 mm, whitish or brownish, occasionally, if several, forming a longitudinal bulge. Each chamber with a single larva. On deciduous oaks: Andricus quercusradicis FM

6b Galls similar but greener; predominantly clustered. Solitary galls often stronger arched, only exceptionally on axial parts. Each chamber with a single larva. On many deciduous oaks, also on evergreen species: Andricus testaceipes FM

6c Gall within leaf petioles, has a straight axis in the petiole, and a smooth surface. A longitudinal swelling along the petiole axis, many times wider than the original width of the vein. Individually monolocular galls may fuse along the vein. When young, the galls are slightly paler in colour than the petiole. The gall surface is smooth when young, but with age may become longitudinally ridged. The tissue of the gall is soft and moist at first, later drying and becoming harder. The galls fall with the leaves. On many deciduous oaks: Andricus sieboldi FM

Note Many authors attributed the agamic generation of sieboldi to testaceipes. Unravelling the literature is complicated – see WNE

= Callirhytis tumifica FM, native to N-Am, has been recorded on leaf ribs and acorns of Q. rubra. The agamic generation might very probably be attributed to C. fructuosa FF, galling acorn cups of Q. rubra and also native to N-Am on Q. rubra

7a Galls on leaf blade or venation => 12

7b Galls on sometimes heavily notched or bent-in leaf margin => 8

8a Galls usually with narrow base attached on margin at site where leaf vein ends => 9

8b Galls with longitudinal side attached on leaf margin, often in ± deep indentation or tear of the leaf blade, at end of main- or side vein. Oblong-ovate, 1.5–2 x 1–1.5 mm, pale green to yellowish-white; the early phase with distant hairs; later on glabrous, thin-walled; on the free side often with small warts. Containing a single larva. On many deciduous oaks: Neuroterus albipes FM

= The procecidia (oviposition scars, not true galls) on veins of developing leaves of the sawfly Periclista lineolata are sometimes similar to the preceding galls ‒ comp. HB. 5471

9a Galls with distinct longitudinal rims => 11

9b Galls without such rims, with granulate or tuberculate surface => 10

10a Galls appearing flat-lustrous, covered with tiny liquid-filled pustules, blunt cone-shaped to cylindrical, 3–5 mm long, 2–2.5 mm wide, the basal third somewhat widened; green-yellowish or reddish, thin-walled. Containing a single larva. On many deciduous oaks: Cynips divisa FM

10b Galls without such pustules; finely tuberculate, ± conical or slender egg-shaped, up to 5 mm long and 2.5 mm wide, thin-walled; very similar to the previous species. Containing a single larva. “Red wart gall”. On many, also exotic, deciduous oaks: Cynips disticha FM

10c Similar galls, difficult to distinguish from previous two species, rearing of adults necessary: Cynips agama FM

11a Galls egg- to pear-shaped, 3–4 x 2–3 mm, sometimes slightly curved, glabrous, thin-walled, initially green, later on brown, slightly grooved and with several irregular red or pale green longitudinal ridges. Containing a single larva. “Rimmed leaf margin gall”. Q. petraea, robur: Andricus quadrilineatus FF

11b Gall spindle-shaped, about barley-corn size, sessile or ± long petiolate, in that case 6–14 mm long; green, with red or pale green longitudinal ridges, with scattered short hairs; often in deep indentations, almost situated on the midrib. Terminally a wart possessing a crown of hairs. Thin-walled, containing a single larva. Q. petraea, robur: Andricus seminationis FF

12a Galls on the leaf blade or on the subordinate venation => 14

12b Galls almost exclusively on or lateral to the main venation => 13

13a Galls flattened rotund-oval; laterally protruding on the main venation, the longitudinal axis parallel to the venation. The outer gall soon stops its growth, dries out, tears open and embraces by two valves the basal part of the further growing inner gall. The latter is 2–4 x 2–3 mm, glabrous, glossy, tough-walled, initially green or yellow, later on with many red to violet dots or spots. “Oyster gall”. Containing a single larva. On many deciduous oaks: Neuroterus anthracinus FF

13b Gall irregularly kidney- or bean-shaped, rarely ± ovate, 2–4 mm long, pale green or partially ± reddened, glabrous. Often arranged in rows, attached with a minute stalk on the mid- or main lateral veins. Longitudinal axis along the vein, flatly appressed to the leaf blade; thin-walled; inner gall absent. “Kidney gall”. Containing a single larva. On many deciduous oaks: Trigonaspis megaptera FF

13c Little spindle-shaped gall, 4 mm long, 1.5 mm thick, almost woody, white, attached by a thin stalk to the underside of the lateral veins and parallel to these; the distal side of the gall covered with long hairs, underside almost glabrous; thin-walled elliptic larval chamber. Adults emerge in spring of the following year. Q. faginea, pyrenaica: Trigonaspis brunneicornis FF

13d One, often more, elongate-starlike galls on the underside of a leaf, lengthwise attached to a thick vein; the end points are free. The longest axis is about 3 mm long. The surface has irregular ridges and is white-hairy. Q. canariensis, lusitanica: Trigonaspis baetica FF

13e Oval, 3.5 mm long swelling of the underside of the midrib, covered by long, whitish hairs. Q. robur: Andricus gallaecus gen. unknown

13f Strong swelling on the underside of a leaf, attached to a vein. The gall measures 15 mm and is multilocular. Q. ithaburensis subsp. macrolepis: Andricus melikai gen. unknown

14a Galls usually point-wise attached on a side vein, protruding on a single leaf side => 21

14b Gall in the leaf blade or attached with a broad base, protruding on both sides => 15

15a Galls spherical or pustular- sometimes lenticular flattened; on both leaf sides similarly protruding => 17

15b Galls on underside almost globular, only flat disc-shape emerging on the opposite side => 16

16a Galls vitreous berry-like, almost spherical; with thick, very succulent translucent wall; 4–7 mm across, glabrous or in case of Q. pubescens with scattered short hairs; pale green, sometimes ± reddish marbled. On the upperside visible as a slightly arched, broad disc. “Currant gall”. Containing a single larva. On many deciduous and evergreen oaks: Neuroterus quercusbaccarum FM

16b Galls a flattened sphere, often several coalescing, initially with erect, long, white, also violet hairs which drop off later on; usually smaller than the previous ones, only 4–6 mm across, appearing a little later; wall not vitreously translucent as in the previous species; thick, succulent, milk-white or grey-green, sometimes with a reddish-violet gloss. “Bristly globular gall”. Containing a single larva. On many deciduous oaks, even on evergreen species: Neuroterus tricolor FM

17a Lenticular- or pustule-shaped parenchyma galls => 18

17b Galls close to a vein, protruding ± hemispherically on both sides of the leaf blade; up to 7 x 12 mm long. Often coalesced in clusters and ± disfiguring the leaf. Green, succulent, ± cartilaginous. Glabrous above, on the underside pubescent, in Q. pubescens on both sides long-haired. Mature galls with large cavity and about 2 mm long, whitish-yellow to pale brown, free inner gall. Containing a single larva. On many, also cultivated deciduous oaks: Andricus curvator FM

18a Galls contain larvae => 19

18b The hour glass-like arched, especially recognisable on the underside, pustule-shaped, solitary swellings each contain an egg. “Procecidia”, oviposition scars, not true galls. The emerging, slime-covered larva feeds on the leaf blade. Q. petraea, robur: Caliroa annulipes

19a Galls induced by gall wasp larvae with powerful biting mouth parts on the small, but clearly eyeless head => 20

19b Malformations caused by midge larvae lacking such mouthparts. Rotund, about 2–4 mm long, slightly arched, slightly discoloured, irregular, inconspicuous pustules. The single larva leaves the gall by a centrally situated exit hole on the leaf underside. On many deciduous oaks: Janetia panteli

19c Distinct blister on upper surface of leaf blade (central depression may appear in old gall); containing white gall midge larva which escapes via a hole in lower surface. Q. petrea, pubescens, robur: Polystepha malpighii

19d Similar galls. Q. robur: Polystepha quercus

20a Rotund, up to 3 mm x 1 mm, initially green, later on ± browned parenchyma gall. Inside is a minute, inner gall coalesced on all sides. Containing a single larva. Q. pubescens, robur, frainetto, lusitanica: Andricus gallaeurnaeformis FM

20b Galls similar, pale green, also later hardly discoloured. On the upperside rather distinctly arched, radially striated, with central, small tubercles, on the underside only flatly protruding. Inner gall absent. Containing a single larva. Q. petraea, pubescens, robur, cerris, etc.: Neuroterus numismalis FM

21a Galls either much wider than high, disc-shaped or lenticular, broadly attached to the leaf, or the galls beaker- or urn-shaped => 28

21b Galls ± spherical or rotund-oval => 22

22a Mature galls only up to 8 mm across, glabrou => 25

22b Mature galls about 8–10 mm across or larger, glabrous or bulging => 23

23a Gall wall glabrous, especially when young, ± finely tuberculate => 24

23b Mature gall 8–10 mm across, rotund-oval, flattened on the underside, yellow or mostly red; with lighter, variously spiralling or annular broad- and flat-bumped bands; thick and tough-walled; with a large transversely-elongate chamber. “Striped pea gall”. Containing a single larva. Q. petraea, pubescens, robur, dalechampii, frainetto: Cynips longiventris FF

24a Galls (10) 15–20 (25) mm across, yellowish or on the sun side ± reddened, glabrous. Surface smooth or with little warts. Wall very thick, till maturity ± succulent, spongy, later on brown, partially shrinking. Centrally a small, rotund chamber, with a thin but tough layer. “Cherry gall”. Containing a single larva. Q. petraea, pubescens, robur and other deciduous oaks: Cynips quercusfolii FF

= The snout beetle Archarius pyrrhoceras lives as an inquiline in agamic galls of Cynips quercusfolii.

24b Galls about 10 mm across, spherical, pale brown, dull, with some flat warts and sometimes ± white frosty; thick-walled; missing an inner protective layer. A rotund, about 4 mm wide central chamber containing a single larva. Q. pubescens, lusitanica, much rarer on Q. petraea, frainetto and some other, even evergreen oaks: Cynips quercus FF

24c Little spherical gall, smooth, not shining, yellowish sprinkled with brown-black round spots. Q. pubescens: Andricus giardias gen. unknown

25a Wall only initially soft, soon dry and hard, galls in late summer and autumn => 26

25b Galls only present in spring and early summer. The thick wall is succulent until maturity with exception of a thin, hard inner layer. Galls spherical, 5–7 mm across, initially ± pale green, reddened when mature, sometimes yellow dotted. With central larval chamber, its size equalling almost the wall width. Containing a single larva. Q. petraea, pubescens, robur, lusitanica and other deciduous oaks: Trigonaspis synaspis FF

26a Galls with only one cavity => 27

26b Galls rotund-ovate, above the larval chamber a second empty one. Usually with several on the side veins; 4–6 mm across, smooth or bumpy surface; narrowed at base, flattened at top and often with ± depression and centrally a navel-like protuberance. Wall hard. Containing a single larva. Predominantly on Q. petraea, much rarer on Q. pubescens, robur, lusitanica, also on other deciduous, even evergreen, oaks: Cynips disticha FF

27a Galls rotund-ovate, 4–6 x 5–8 mm wide, at base and top slightly flattened; initially green, soon reddish, later on brown, glossy; almost woody. Often many on mid- and side veins. Chamber elongate transverse, relatively thick-walled. Containing a single larva. “Pea gall”. On many deciduous oaks: Cynips divisa FF

27b Galls egg-shaped to oblong-elliptical, 3–4 mm high, initially yellowish-white, later on brownish-yellow, not reddened, almost dull, glabrous or slightly tuberculate. Wall thin, hard, brittle. A relatively large chamber containing a single larva. Predominantly on Q. petraea, more rarely on Q. robur, pubescens: Cynips agama FF

28a Galls beak- or urn-shaped; species from SE Europe => 33

28b Galls disc-shaped or lenticular, dropping off in autumn; on indigenous oaks, sometimes in large numbers on the leaf underside => 29

29a Galls variously, ± densely pubescent => 31

29b At least the older galls completely glabrous => 30

30a Gall flat, disc- to cup-shaped, 3–4 (5) mm across. Underside flat, upperside with raised centre, ± distinctly radially striate. Margin often irregularly rim-like, bent upwards. Initially upper surface with scattered stellate hairs, soon completely glabrous. Yellow, ± reddish to dark purple-red. Often in clusters mainly on the leaf underside. “Smooth spangle gall”. Containing a single larva. On many deciduous oaks: Neuroterus albipes FF

= The inquilinous gall midge Xenodiplosis laeviusculi, living between gall underside and leaf surface may cause additional malformations.

30b Galls similar, only the margin with 3–4 or more lobes tricorn- or star-like broadly bent upwards, sometimes consisting of only the central bump. Otherwise like the previous gall; on same hosts. Neuroterus albipes f. sp. reflexus FF

30c Flat gall, little pubescent, 5 mm across. Q. faginea, pyrenaica, robur: Neuroterus albipes f. sp. lusitanicus FF

31a Galls ± flat, rotund, lenticular; densely covered with stellate hairs. Upperside with raised centre; cross section triangular or bowl-like. Larval chamber short lenticular, protective layer absent => 32

31b Galls relatively thick disc-like; flattened on the underside. On the upperside with deep central pit; surface hidden by flat golden silky hairs. About 2–3 mm wide and 1.5–2.5 mm high. Inside is an expanded acuminated, broad oval chamber provided with a protective layer. “Silk-button gall”. Containing a single larva. On many deciduous oaks. Neuroterus numismalis FF

= Inquiline gall wasp: Synergus albipes. – Occasionally the galls develop together with Neuroterus quercusbaccarum , the galls of which may become disfigured

32a Gall lenticular, brownish-yellow, initially reddened; underside flat and glabrous, upperside smoothly rising towards the obtusely angled mound; in cross section flat triangular; up to 4–6 mm wide, about 2 mm high; densely covered with large red-brown stellate hairs; the margin often white spotted. Underside appressed to the leaf. Dropping off. “Frequent spangle gall”. Containing a single larva. On many deciduous, also cultivated, oaks: Neuroterus quercusbaccarum FF

32b Similar gall, 6 mm across, sparsely covered with reddish hairs. Adults 2 of the following year. Q. robur, pyrenaica: Neuroterus quercusbaccarum FF

= Inquiline gall midge: Parallelodiplosis galliperda

32b Galls lenticular to bowl-shaped, 2–3 x 1–1.3 mm, brown-yellow to reddish; margin blunt, ± bent upwards, without white dots. Middle part clearly arched. On the upperside with scattered, large rust-brown stellate hairs, on the underside more sparsely pubescent. “Cupped spangle gall”. Containing a single larva. On many deciduous oaks: Neuroterus tricolor FF

33a Galls cornicular, up to 10 mm high, rarely larger, middle or basal part ± constricted, at base broadened, however the leaf underside attached with only a short, thin stalk. Green, later on brownish-yellow and ± reddened, glossy, hard. Chamber in the basal part, containing a single larva. Q. lusitanica, petraea, pubescens: Cynips cornifex FF

= Cross-matings between C. cornifex and C. quercus may result in galls of intermediate shape

33b Galls urn- to barrel-shaped, about 3 mm across; gradually narrowed upwards from basal third; terminal part flat, with central flat tubercle surrounded by a slightly elevated annulus. Wall green, red or red-brown, longitudinally grooved. With large, oblong-oval, inner gall, attached on all sides; containing a single larva. On many deciduous oaks: Andricus gallaeurnaeformis FF

33c Gall shuttle-shaped, 4–5 mm long, red, glabrous, woody, attached on the midrib (rarely on a secondary vein) with a cylindrical, slightly striated, stalk; larval chamber ovoid. Q. faginea, lusitanica: Trigonaspis mendesi FF

34a Galls on leaf blades delimited locally; sometimes with many together => 37

34b Large part, or whole leaf blade disfigured (somewhat ± crumpled malformations on developing leaves caused by gall mites or aphids) => 35

35a Leaf margin ± rolled. Leaf blade ± mottled discoloured to browned, often with other malformations, which represent merely stunted malformations rather than true galls; caused by mites => 36

35b Leaves of spring shoots deflected, rolled or curled, hardly discoloured; contain aphids. Q. petraea, pubescens, robur: Thelaxes dryophila

35c Leaf underside with scattered blister-like swellings, containing uredinia and telia of rust. Quercus spp.: Cronartium quercuum

36a Shape of leaf blade ± changed, with irregular, yellowed spots; venation irregular. Q. petraea, pubescens, robur etc.: Rhyncaphytoptus massalongoianus

36b Leaf margin undulate; ± upwardly reflexed. Q. pubescens, robur and other oaks: Acaricalus cristatus

37a Leaf blade with groove-like or bladder-shaped depressions, folds along the veins or with erinea => 41

37b Leaf blade with localised roll, or leaf margin folded => 38

38a Leaf margin folded up- or downwards => 39

38b Margin usually in the indentation of the lobes mainly upwardly and narrowly rolled, tube-shaped. Roll thickened, not- or only slightly discoloured; inside 1–3 (5) initially white, later on orange, especially at the ends, midge larvae. On many deciduous oaks: Macrodiplosis roboris

39a Margin of young spring leaves mostly bent downward along short length and width; bowl- or mussel-shaped. The inducer is located on the bend on the somewhat widened and ± discoloured vein. The insects leave the galls from end of 5 onwards and live freely on the leaf blades which are soon strewn with dried-out spots close to the suction sites. Dwarf aphids host-specific, identification difficult and only on microscopic characters => 40

39b End of lobe broadly downward deflected, closely appressed to the leaf surface; slightly thickened, slightly discoloured and sometimes yellow to red spotted. Containing one (to several) yellowish-white to yellowish larvae. On many deciduous oaks: Macrodiplosis pustularis

= Outwardly similar are the leaf margin folds caused by spinning activities of mining caterpillars which belong to the microlepidopterons Caloptilia alchimiella and C. robustella

40a Aphid distinguished by the minor development of the dorsal tubercles, the marginal ones are slightly elevated. Q. robur: Phylloxera glabra

40b Aphid distinguished by a conspicuous latero-dorsal row of dorsal tubercles; spinal and pleural rows may be distinctly weaker. On many deciduous oaks: Phylloxera coccinea

40c Dorsal tubercles of the aphid arranged uniformly. On many deciduous oaks: Phylloxera foaae

= Phylloxera confusa. Fundatrices feed from veins on undersides of oak leaves, causing the lobe of the leaf distal to the feeding point to fold inwards

= Phylloxera quercus, S-Europe, alternates between evergreen and deciduous oaks

41a Leaf blade with groove-like depressions, elongate leaf folds or pustule- to bladder-like archings => 43

41b Leaf blade often with extensive erinea => 42

42a Erinea on the underside; rust-brown. Hairs partly longer and strongly twisted, partly shorter, slightly bent or cylindrical and slightly club-shaped. Q. petraea, pubescens, robur and other deciduous oaks: Aceria quercina

42b Erinea on Q. frainetto: Aceria suberina

43a Depressions groove-like, rotund, about 3 (4) mm across => 45

43b Leaf blade with bladder-like swellings or folds along the side veins => 44

44a Leaf blade alongside vein of seedlings with a downwardly protruding fold. The respective vein swollen and slightly bent. Q. petraea, robur: Dasineura panteli

44b Leaf blade usually with several, inconspicuous swellings or bladder-like malformations of various dimensions, arched on the undersides and showing clearly on upper side. In the cavities, predominantly on the underside develop downy mycelia of the fungus: Taphrina caerulescens

45a Depressions about 3 mm wide, containing the inducer on the leaf underside; usually many per leaf blade => 46/p>

45b Depressions only about 1 mm wide, usually several per leaf blade; contain flat froth-covered nymph. Q. macranthera, petraea, pubescens, robur, rubra:
Trioza remota

46a Galls already in early spring just after unfolding of leaves, usually many per leaf. The leaf tissue is ring-like and swollen around the sucking larva. The mature fundatrix soon moves into the bark furrows of branches and stems. Q. petraea, robur and other deciduous oaks: Acanthochermes quercus

46b Underside of leaf with round flat depressions, 3 mm across, containing a gall midge larva. Q. petraea, pubescens, robur: Arnoldiola libera

On male inflorescences (catkins)

1a Malformations of only parts of the catkins => 2

1b Complete catkins disfigured, shortened, swollen. Several red larvae between the flower parts. Q. pubescens, robur: Contarinia amenti

2a Gall glabrous or with hairs which are shorter than the galls => 4

2b Actual gall 1–3 mm long, bearing very long, ± distant, woolly pubescence => 3

3a The galls develop from the male buds on stumps of stunted axial parts; often 10–20 in a single bud. Each of the about 2 mm long, oblong and hard galls bears on its free surface long, initially turgid white-, later dried, flattened, twisted and ± browned hairs, forming together a 20 mm long ball which largely conceals galls and buds, sometimes overtopped by ± short tufts, some bearing anthers. “Cotton-wool gall”. Each gall containing a single larva. Q. petraea, pubescens, robur, frainetto, pyrenaica, lusitanica, ? cerris: Andricus quercusramuli FM

3b The roughly egg-shaped galls, up to 2 mm with tufts of long, white hairs, develop solitarily or clustered from a single pollen chamber, usually on stunted, markedly shortened catkins which, in cases of heavy infestation, remain hidden in the bud. Distinguished from the preceding species by hairs which only incompletely cover the gall base, hence protruding paint-brush-like from the bud. Q. petraea, robur: Andricus callidoma FM

4a Galls less than 5 mm long, unilocular, spindle of catkin not thickened => 7

4b Galls about 5–10 mm long => 5

5a Galls rotund to globular => 6

5b Galls spindle-shaped, barley grain-like. ± distinctly ridged longitudinally, 6–8 mm long, initially green, later brown; apically framed by a collar of hairs. Usually already before the appearance of this gall with a short stalk attached and locally thickened, often ± bent spindle. Containing a single larva. Q. petraea, robur: Andricus seminationis FF

6a Galls almost globular, vitreous, grape-like, 5–7 mm long; with thick, very succulent wall; unilocular. “Currant gall”. Containing a single larva per gall. Q. petraea, pubescens, robur: Neuroterus quercusbaccarum FF

6b Shiny swelling at the base of the catkin stalk and bending the rest of the catkin (visible at the tip) through 90 degrees; up to 5 mm across; bright green: Andricus curvator FM

6c Galls rotund, 6–10 mm across, multilocular. With many, densely standing, unequal, edged, obtusely acuminate, on top red, viscous, 3–5 mm long appendages. Rachis shortened, bent and thickened. Anthers absent. Not dropping. Containing one larva per chamber. Q. petraea, robur, frainetto:
Andricus grossulariae

7a Galls glabrous, sometimes either with a tuft or collar of hairs, or only locally loosely pubescent => 11

7b Galls completely, or on major part pubescent or uniformly and pubescent => 8

7c Solitary galls or in small groups of 2‒4; globular, 1.7 mm in diameter, surface initially green becoming grey-brown, covered with small tubercles or projecting spines, and many white hairs of varying lengths: Andricus paradoxus FM

8a Galls develop on receptacle => 9

8b Galls develop from pollen loculi. The remains of the anthers rest on a bulge. Galls bearing two distinct longitudinal ridges on each side meeting below the tip ± egg- or cone-shaped, about 2 x 1 mm, with a broad base attached to the bulge, initially green-yellow, later brownish, thin-walled, unilocular and uniformly covered by short, obliquely distant, pale yellow hairs. Not dropping to the ground. Containing a single larva. Q. petraea, pubescens: Andricus amenti FM

9a Galls covered by distinctly distant, gradually tapering, slender hairs => 10

9b Galls densely pubescent with short, rough, apically ± club-shaped, translucent, broadened hairs giving the gall a vitreous appearance. Galls ± cylindrical; rounded at both ends, base somewhat broadened, about 4 mm long and 2 mm thick, green or ± reddish. A single larva. Q. petraea, robur: Cynips divisa FM

10a Gall egg-shaped, acute, up to 2 mm long, initially green, later pale brown, uniformly occupied by rigid, distant whitish hairs. Sometimes with several in the clusters of hardly distorted catkins; occasionally framed by some anthers of the same flower. Catkins remain attached to the plant until emergence of the wasps. Containing a single larva. Q. petraea, robur, pyrenaica: Andricus foecundatrix FM

10b Gall egg- to cone-shaped, 2–3 mm long, 1 mm thick, red-brown; the basal, covered, part glabrous, the apical part covered with rather long, yellow to brown hairs; laterally often with dried perianth; up to 1–3 cm of the markedly shortened rachis, ± protruding from the bud, on which the stunted anther fascicles form a bottle brush-like cluster. Occasionally the catkin does not protrude from the bud, however the spreading scales aid recognition of the enclosed parts. Containing a single larva. Q. pubescens, pyrenaica, cerris: Andricus solitarius FM

11a Galls with smooth and dry wall, ± bifid or oblong- to egg-shaped, sometimes locally pubescent, usually smaller than 2.5 mm => 13

11b Galls glabrous, often with only slight, but always distinct, elevated, irregular, often interrupted and converging longitudinal striae. Rachis ± changed; dropping => 12

12a Galls oval to wide lemon-shaped, 3–4 (5) x 2–3 mm, initially greenish, the exterior fleshy and glabrous, later red-brown and dry. At the base of the gall are several anthers and remains of the perianth. A single larva. Q. petraea, robur: Andricus quadrilineatus FF

12b Galls similar, about 3.5 mm across. Quercus spp.: Andricus flavicornis FF

12c Pfützenreiter recorded the early glabrous, smooth- and thin-walled oval, about 2 x 1 mm long galls of Neuroterus albipes FM

13a Galls generated by receptacle => 15

13b Galls very small, developing from a single anther, or even a part of it, attachment broad-based => 14

14a Galls only 1–1.5 x 1 mm, green to yellowish, locally sometimes reddened, glabrous; basal part stalk-like or sometimes egg-shaped or almost globular; the about equal upper, cone-shaped parts with a paler ridge, consisting of remains of the pollen chambers. Containing a single larva. Q. petraea, pubescens, robur, pyrenaica. Neuroterus politus FF

14b Gall ± egg-shaped, about 1.5 (2) mm across, initially green, later yellowish-grey, eventually brown, glabrous or with several short, white, deflected hairs at base. Protruding from the filament; remains of pollen chambers usually unrecognizable. Containing a single larva. Q. petraea, robur: Andricus glandulae FM

14c Gall oblong- to egg-shaped, 1.5–2 mm long and about 1 mm in diameter. The dark ridges, remains of the anthers, are distinct on the gall. Surface glabrous, just below the apex are a number of white hairs about 1 mm long. The yellow-brown galls are inconspicuous among the mature anthers, but may nevertheless be present in large numbers, simultaneously with the agamic generation. Q. iberica, petraea, robur, pubescens, pyrenaica: Andricus quadrilineatus FM

14d The filament is modified into an obpyriform, short hairy, 2 mm long, thin-walled, unilocular gall that apically seems to bear a small cap. Q. petraea, pubescens, robur: Andricus floridus FM

15a Galls slender egg-shaped, with distinct apical wart; inconspicuous, 1.5 mm across, initially green, later yellow-brown, glabrous or with an apical tuft of short, fragile hairs; situated on the receptacle and usually enclosed by normal anthers. Catkins developing normally; dropping after emergence of the adults. Containing one larva. Q. petraea, robur, pyrenaica: Andricus malpighii FM

15b Gall ± oblong-ovate, thin-walled, 2–2.5 (3) x 1.5 mm, greenish to yellowish, with brown tip, at base with collar of white to brown hairs; surface finely longitudinally striated, glabrous or sparsely occupied by short, appressed hairs. At base of stunted catkins, emerging from the receptacle, ± visible just above the bud scales. Containing a single larva. Q. petraea, robur: Andricus solitarius FM

On acorns or acorn cups

1a Galls only on acorn cups => 4

1b Galls on acorns, including cup, or on developing flowers => 2

1c Very small (3 x 2.5 mm) ovoid gall, slightly bent at tip, glossy, glabrous, straw-coloured, hidden between the scales of the cupule; acorn stunted. Q. lusitanica: Andricus nobrei gen. unknown

2a Galls on acorns only => 3

2b Ovary and cup adnate in the developing flowers producing a uniform large fleshy mass pea-size to even hazelnut size, surmounted by the converging cup rims and centrally bearing a stick-shaped thickened style. Side- and upper parts of the cup with many green and succulent red scales, so that the gall is distinguished by its red colour from the similar looking healthy acorns. In the ovary tissue are several, ± egg-shaped chambers each containing a single larva. Q. petraea, robur, cerris: Pseudoneuroterus saliens FM

3a Acorn remaining small, externally otherwise not changed. Hardened seed scale without internal embryo, but with a round cavity containing a round, woody, single-or multi-chambered inner gall. Each chamber with a single larva. Q. petraea, pubescens, robur: Unidentified gall wasp

= From the Iberian Peninsula, but also from NL the gall midge Dasineura squamosa has been recorded on Quercus robur. The larvae develop in atrophied acorns. The same holds, but from F and NL, for the midge larvae of Contarinia cf. aprilina

3b Acorn remaining small and completely enclosed by cup. Containing one egg-shaped gall, 5–6 x 2.5–3 mm, with a single larva. Sexual generation unknown. Galls infected by inquilines are multi-chambered. ‒ Comp. next lead. Q. ? faginea, petraea, pubescens, ? pyrenaica, robur: Andricus legitimus FF

3c Seed scale or cotyledons, rarely the embryo, with several or often many, hard, ± egg-shaped chambers, up to 3 mm long. Development of affected acorns sometimes only slightly stunted, but ± crookedly; usually smaller, sometimes ± curved or only locally swollen. Early infected acorns usually do not protrude from the upper margin of strongly narrowed cups. Each chamber containing a single larva. Q. petraea, pubescens, pyrenaica, robur: Callirhytis cf. glandium FF

= It is uncertain whether the polyphagous and frequent acorn weevil Curculio glandium, similar to Curculio nucum on Corylus, is responsible for the facultative development of “kaptocecidia” after oviposition on suitable acorns.

4a Galls laterally on the acorn cup; SE-Europe => 5

4b The galls develop in early summer from the base of the acorn cup, growing between the ± malformed acorn and the wall of the cup. Base obtuse cone-shaped with broad apical part; 15–20 mm high; at the base 18–25 mm across, initially green and sticky, later grey-brown and dry; with about 5–8 strongly protruding, ± interrupted longitudinal ridges or wings. At top is a narrowed rotund opening, widening conically into a cavity, separated by a thin cross-wall from a smaller basal chamber, containing the globular 3–5 mm long, single-chambered inner gall, attached only at a single point. “Knopper gall”. Containing a single yellow larva. Q. robur, more rarely faginea, macrolepis, petraea, pubescens, x rosacea, turneri: Andricus quercuscalicis FF

= Four inquiline Synergus species have been recorded from knopper galls: S. gallaepomiformis, pallicornis, umbraculus, and pallipes

= Furthermore the tortricid Pammene fasciana has been recorded

5a Galls developing isolated on the distinctly recognisable acorn cup => 7

5b Galls to a large extent enclosing the acorn cup => 6

6a Galls arising externally at the base of the cup; cross section similar to a compact double-T beam. Woody, brown-red, glossy, sticky; up to 25 mm high and 20 mm wide. Basal dilatation semi-globular bent downwards, covering cup and under part of the acorn; variously cleft at the margin. The narrowed, but broad central part with mortar-like cavity and smaller, thin-walled inner gall, attached at one point. Upper enlargement broadly disc-shaped, the central part elevated, running into a flat, ± lacerate rim. Containing a single larva. Q. petraea, pubescens, robur, frainetto, etc., also evergreen oaks: Andricus dentimitratus FF

6b Base body of the gall mounted laterally on the acorn cup like a thick, red disc which bears on the outside many, 2–3 (4) cm long, thick filamentous, branched, acuminate appendages. In the middle is a thin-walled inner gall, up to 5 mm long, which is subdivided by a cross wall. “Medusa-head gall”. Containing a single larva. Q. petraea, pubescens, robur, frainetto, pyrenaica, lusitanica, cerris and other species, as well as evergreen deciduous, oaks: Andricus caputmedusae FF

6c Acorn gall, woody, one-chambered, subcylindrical, 4–7 mm high, 5–9 mm wide, slightly attenuate and rotund at attachment, more or less flattened and with a central navel apically. Half-way up its height or higher is a little crown with short but tight reddish hairs. Q. lusitanica: Cynips fortii gen. unknown

7a Galls with variously shaped appendages, multi-chambered => 8

7b Appendages lacking; lemon-shaped to almost rotund, 5–6 mm high, ± 5 mm thick; glabrous or appressed silky pubescent, initially green or red, brown at maturity. Single or with several on the rim of the acorn cup. Containing one larva. Q. petraea, x hispanica, pubescens, robur. Andricus superfetationis FF

7c Hard spherical structure, limited at both poles, 6–8 mm across, one-chambered, surface green, covered with abundant white-yellowish or brownish hairs with length of about 6–10 mm. The whole structure resembles a large cotton ball of 20–30 mm across. Andricus theophrasteus gen. unknown

7d Large blunt-conical gall (20 mm high, 20–25 mm wide at base and the upper part 11–13 mm wide; provided with two basal envelopes of appendages of about 15 mm long and one corolla of shorter and more irregular appendages around the apical opening. This opening corresponds with a conical cavity situated above the inner gall. Surface initially violet coloured and sticky becoming brownish at maturity and losing its sticky substance. Q. lusitanica, pyrenaica: Andricus pictus FF

8a Appendages 4–8 mm long, straight, spiny, each spine tipped with a red, sticky knob; standing in a regular and dense pattern. Gall rotund, cherry- to walnut-sized, pale yellow, thick-walled. Containing one larva per chamber. Q. petraea, pubescens, robur, frainetto and other deciduous species. “Hedgehog gall”: Andricus lucidus FF

8b Gall on acorn cup, often enclosing immature acorn; woody ovoid and radiating blunt rectangular spines, sometimes with longitudinal striations; up to 15 mm total diameter (body of the gall up to 10 mm, spines up to 5 mm long); bright green and sticky at first, later red, then brown and hard. Andricus grossulariae FF

8c Appendages 2–4 mm long, situated in circles; almost cylindrical, irregularly curved, the upper half red, sticky, acuminate. Gall rotund, 10–25 mm across, green or red, later brown, glabrous, woody. Containing one larva per chamber. Q. petraea, pubescens, robur: Andricus senckendorffi FF

Quercus cerris – turkey oak

On stems, branches, twigs or shoots
(For galls developing from latent buds on stems, often directly on the bark, see Section B)

1a Galls on various sites on axial parts below inconspicuously disfigured shoot tips => 6

1b Galls develop from shoot tips or on severely stunted short shoots => 2

2a Gall ± barrel- or egg-shaped; ± considerable size, often provided with some scale-like- or ± normal leaves => 3

2b Internodes stunted, short. Young leaves in tufts, brittle along the thickened veins. Several yellowish-white jumping larvae. Also on Q. petraea, robur, etc.: Contarinia quercina

2c Gall irregular thick disc-shaped, up to 15 mm wide, developing from the severely stunted and widened shoot tip and broadened leaf cushions. Gall hard, strongly pubescent, sometimes deeply grooved. In the central part of the upperside protrude many yellowish one-chambered inner galls, originating at the leaf base. The complete gall is ± completely surrounded by a tuft of many reduced, often heavily disfigured leaves and overtopped by some appendages. Each chamber containing a single larva. Andricus multiplicatus FM

2d Gall develops on the shoot opposite a developing leaf, causing retardation of this leaf’s development. This gall causes a hollow swelling of the shoot 5‒6 mm thick at a junction with a leaf petiole, although the axis of the shoot is not distorted. Gall surface uneven. An elliptical inner cell with a thin, brown wall is situated within the gall’s inner chamber. Plagiotrochus marianii FF

3a Galls one-chambered => 4

3b Gall multi-chambered up to 15 mm long, rotund- to oblong-oval, greenish, weakly pubescent, woody; large jar-shaped, with wide open cavity, above the basal half with many egg-shaped inner galls. Galls, especially in the upper part, with almost chaffy scale-like leaves. Each chamber containing a single larva: Andricus cydoniae FM

4a Galls less than 10 mm long => 5

4b Shoot apex shortened, club-like, swollen. Galls up to 20 mm long and 10 mm wide; in the middle with an oblong, eventually open cavity, on the bottom with a small oblong-oval inner gall. The ±normally developed leaves on the gall close to one-another. Containing a single larva. Also Q. lusitanica: Andricus inflator FM

5a The rotund-oval gall, 3–5 mm across, initially green, at maturity brown, originates on the axis of a longitudinally completely stunted short shoot and bears on its tip bud-like arrangements of leaf rudiments. Containing a single larva: Andricus gemmeus FM

5b Galls in small twigs, located apically; the host bud gall is integral to the twig as well as the larval chamber and thus typically a tiny swelling is visible where the larval chamber is located. Rarely the gall is spherical, 3–5 mm across; may also be found on petiole and leaf midrib: Synophrus hungaricus gen. unknown

5c Galls 6–8 mm long, ± globular or pear-shaped, weakly pubescent, hard, one-chambered; on the outside with 2–3 (4), ± normally developed as well as scale-like leaves. Inner gall egg-shaped, brown, hard, only free at apex. Connected to the outside by a thin canal. Containing a single larva. Andricus singularis FF

6a Galls usually well delimited, ± distinctly protruding or bark with groove-like, rimmed depressions => 7

6b Young twigs swollen on all sides, 2–4 times the normal breadth over a length of 10–50 mm. Gall surface glabrous or ± tuberculate. In the woody part of the gall are many oblong-oval chambers, which are at right-angles to the pith and each containing a single larva: Pseudoneuroterus macropterus FF

7a Bark with shallowly bulging, rimmed depressions, containing gall causer covered by a shield => 12

7b Galls protruding from the bark of solitary twigs or thinner branches, ± well defined => 8

8a Single galls less than 5 mm across => 9

8b Gall up to 15 mm long, short-stalked, rotund, initially pale green and ± with short felt-like pubescence, later on brownish and glabrous, thick-walled, dry and hard; predominantly on thin, not disfigured twigs; ± embracing these. Occasionally many groups up to 70 mm long, mutually flattening one-another; sometimes shortly tuberous, up to walnut-size. A large cavity with one, more rarely, two separated rotund-oval inner galls, attached only at base. Containing a single larva. Aphelonyx cerricola FF

= Inquiline cynipids: Saphonecrus undulatus and/ or Synergus flavipes.

9a Galls with tough or membranous wall, dry at maturity, without separate inner gall => 10

9b Up to about pea-size, succulent to cartilaginous one-sided swelling of young shoot, bent at infestation site. Containing an eventually detached inner gall with a single larva: Andricus curvator FM

10a Galls about 2–3 mm across; appearing solitary or in small irregular groups on young twigs => 11

10b Many galls in groups protruding on all sides from the bark of stronger twigs or thinner branches. Single gall ± egg-shaped, up to 5 mm long, attached with an acute base; pale green to reddish. Surface viscose, oily. Each chamber containing a single larva: Dryocosmus cerriphilus FF

= Inquiline gall wasps: Saphonecrus haimi, undulatus and/ or Synergus variabilis

11a Gall elongate spindle-shaped, 2–3 mm long; attached over its length; green, later on red-brown; one-chambered. Often several to many, separated, in the outer bark of not thickened young shoots. Each gall containing a single larva: Pseudoneuroterus saliens FF

11b Single galls rotund, flat, nodule-shaped, up to about 2 mm wide; often with several on the nodes, sometimes appearing on the internodes at base of one year old ± shortened and swollen shoots. Solitary galls form sometimes only a barely recognisable nodule. Containing a single larva: Andricus quercusradicis FM

11c Galls rotund to elliptical, up to 2 mm long, wall very thin. In leaf axils of young shoots, but not in buds. Containing a single larva. Andricus quercuscorticis FM

12a Bark with bulging thickened ridge surrounding depressions. Below a rotund-oval convex shield, about 1.6–2 mm wide: Asterodiaspis variolosa

12b Similar, but less conspicuous malformations. Shield flat lid-shaped, rimmed, 1–2 mm wide: Diaspidiotus zonatus

On buds

1a On terminal and lateral buds of young shoots => 3

1b Galls on older branches or stems, emerging from adventitious or dormant buds => 2

2a Gall transversely egg-shaped, up to 2 mm long, with finely granulate surface, greenish, also ± reddened or crimson-violet. Wall very thin, leathery. Galls usually with several together on older branches or stems. Containing a single larva: Neuroterus aggregatus FM

2b Galls egg-shaped to cylindrical, up to 3 mm long; rounded or weakly depressed at the tip, dense- and short velvet-like pubescent; initially red, later dark violet; thin-walled, often surrounded at base by bud scales. A large chamber containing a single larva. Andricus quercusfolii FM

3a Galls completely or partially transformed into closed galls of distinct shape. Gall wasp galls => 7

3b Buds swollen and ± not opening => 4

4a Galls on young shoots, caused by gall midge larvae => 5

4b Lateral buds or perennial shoots swollen: Aceria cerrigemmarum

5a Buds usually distinctly opened => 6

5b Buds enlarged and slightly swollen, up to 10 mm long and 5 mm in diameter; usually not opening and surmounted by the free tips of the scales; only occasionally developing further together with the smallest, irregularly developed leaves. Larvae bright yellow Contarinia quercicola

6a Galls often very similar to the preceding ones. Buds enlarged and swollen, of the same size as the preceding one, but often slightly opened. Several orange-red to red larvae: Arnoldiola dryophila

6b Malformation similar. Containing a single larva: Unidentified gall midge

7a Single galls about 1.5–6 mm long. Wall leathery or succulent. Several galls are often partially coalesced; however, ± deep furrows indicate the separate galls => 11

7b Galls often more than 6–10 mm long, uniform in outline. Wall thick, succulent or wood => 8

8a Galls 8–15 mm long, uniform in outline. Wall tough and woody, dried out. Inside is a larval chamber => 10

8b Galls usually larger than 15 mm => 9

8a Gall 15–30 (40) mm long; rotund to flattened oblong-oval, initially whitish, later on brownish, tuberculate, nodule-like. Wall succulent, spongy. Inside are many hard larval chambers. Mature in 6; not dropping off. The soft parts dry out up to the separate chambers after the adults have emerged. Each chamber with a single larva. “Oak apple: Biorhiza pallida FM

9b Galls up to 20 mm across; rotund. Wall hard, woody, provided with ± wart-like tubercles. Mature in autumn. The central chamber, surrounded with a protective layer, containing a single larva: Andricus infectorius FF

9c Gall oblong-ovoid (1.5 x 1 mm), thin-walled, terminally with a small curved apex, one-chambered, covered with long erect hairs; usually solitary in a leaf axil. Callirhytis meunieri FM

9d Gall conical, with dense and short pubescence: Andricus tomentosus FF

10a Gall broadly coalesced with twig; variously shaped, usually rotund, (6) 10 (15) mm across; initially green, also bark-coloured to dark grey; glabrous or with minute warts. The thick wall with an outer, greenish bark layer and a thicker, inner ± whitish woody tissue. The central chamber containing a single larva: Synophrus politus FM

10b Gall spherical, 4–5 mm across, surface with some little whitish protuberances. Synophrus pilulae FM

10c Gall in small twigs, located apically; a tiny swelling is visible where the larval chamber is located; rarely the gall is spherical, 3–5 mm across. Occasionally also on petiole and midrib: Synophrus hungaricus FM

10d Gall almost spherical, 6–10 mm across; solitary or often with several together. Surface reticulate, rough, ± pale grey. Wall woody, in cross section uniform radially striate, rust-brown, only the protective layer paler close to the larval chamber situated at the attachment point. Containing a single larva. “Cola-nut gall”: Andricus lignicolus FF

10e Gall globular, 5–10 mm across, covered with tubercles: Andricus caliciformis FF

11a Galls 2–3.5 mm across, one-chambered, if in clusters, then not coalesced => 12

11b Single galls rotund-oval to conical, about pea-size, up to 6 mm long; glabrous or ± warty, pale green, partially violet-red, initially glossy, with very sticky coating, later on dull. Inside spongy-succulent, brownish; with usually several, hard-walled, brighter inner galls. Two to several galls coalesce often into irregular, cherry-size structures, more or less distinctly showing by furrows the number of participating galls. Each chamber containing a single larva: Chilaspis mayri FM

11c Gall thick-walled and woody, bright brown, sticky when fresh. From a basal disc of 10 mm in diameter, embracing the twig, rises a truncate cone which ends in an apical navel. Total height 8–10 mm: Andricus mitratus FF

11d About 3–4 mm long, sometimes coalesced into larger structures. The unilocular, solitary gall, 2.8 mm x 1.3 mm, usually hidden by the bud scales, is barely visible. Gall surface smooth, and medium to pale brown or orange-brown. The gall is usually twice as tall as broad, with lateral longitudinal ribs, the tip of the gall tapering into a blunt irregular point: Andricus hystrix FM

11e Gall subglobular (20–22 x 18–20 mm), hard, smooth, conical at base, the distal region flattened and with 7–10 blunt appendages. Larval cavity rotund and large. Andricus bulgaricus FF

12a Galls developing from the centre of the bud => 13

12b The galls develop from the inside of the soon unfolding bud scales. Gall oblong-oval, 1.5–2 mm long, yellowish, almost glabrous, thin-walled. Usually 2–3 galls per bud. Each containing a single larva. Neuroterus obtectus FM

13a Gall egg- to barrel-shaped, round in cross section, 2–3 mm across, glabrous, solitary or many per bud => 14

13b Gall similar to an apple seed, flattened in cross section, attached with rounded base; upper part acute conical; 3–3.5 mm high, brown, with paler tip. Surface finely warty, rugose; with upwardly directed hairs which are more dense towards the tip. Corolla-like surrounded by several ± smaller leaves. Containing a single larva. Andricus cryptobius FM

14a Galls barrel-shaped, glabrous, up to 2 mm long and 1 mm in diameter, narrowed upwards, with obtuse apical part, usually solitary, rarely paired, only showing its tip => 15

14b Galls rotund-oval, about 2–3 mm long and ± 2 mm in diameter. Surface finely granulated, yellow-brown to grey. Usually several in a terminal- or lateral bud on previous-year shoots; rarely solitary, in that case larger and oblong-oval. Containing a single larva: Andricus kollari FM

15a Thin-walled bud gall, 2‒2.5 mm long, pointed, usually single, lower half covered by bud scales. Its surface is ± velvety-glossy greyish brown; the very tip often has a small black spot: Andricus improprius FM

15b From almost identical galls, but developing 1–3 per bud, and, contrary to the preceding gall, apically mucronate: Andricus lignicolus FM

On leaves

00a Galls open or connected externally by a small, only point- or slit-like entry, sometimes hidden and rarely visible to the naked eye; curls, marginal folds or rolls, or erinea. Galls caused by fungi, mites or insects, gall wasps excepted => 31

00b Galls closed on all sides (galls usually caused by gall wasps) => 2

2a Galls on the petiole or on subsidiary veins. Larvae in gall chambers => 11

2b Galls in or on the leaf blade or on the main veins, sometimes attached terminally => 3

3a Larvae living in closed cavities until maturity. Gall wasp galls => 4

3b Petiole stunted, conspicuously swollen, sometimes curved. Inside a caterpillar, producing short ellipsoid mine next to the midrib, this for the most part falling out later on: Heliozela sericiella

4a Galls of various shape; with broadened or narrowed base attached to the leaf, or even stalked => 6

4b The rotund- or oval galls are situated, inside the petioles or veins, surrounded by host tissue. Usually several galls coalesce into sometimes ± bulged swellings; on the venation mainly conspicuous on the underside (in immature stages visible galls sometimes ± similar, on both sides of the leaf blade => 5

4c Large spherical gall, 10–30 mm across, succulent, surface slightly irregular. Dropping off with leaves. Containing a single larva: Cynips quercusfolii FF

5a Single gall rotund- to oblong ovoid; one-chambered 2–3 (4) mm across. Usually several galls are variously coalesced to ± expanded bulging swellings. Solitary galls occasionally also in the main lateral veins. Each gall with a single larva. Andricus quercusradicis FM

5b In similar, sometimes more markedly bulging galls developing on Q. cerris also are the larvae of Andricus testaceipes FM

6a Galls directly attached to the petiole or leaf blade veins => 8

6b Galls terminally attached to the midrib, or with a longer stalk to the venation => 7

7a Galls on the stunted tip of the midrib of a usually severely stunted leaf. Gall rotund, about pea-size, glossy and sticky. Containing a single larva: Chilaspis mayri FM

7b Smaller, only about 1.5–2 mm long, ± egg-shaped, pale green to yellowish galls which are distantly sparsely pubescent; usually terminally on main veins with leaf margin often ± emarginate. Containing a single larva: Neuroterus albipes FM

7c Galls usually located on a main lateral vein which leads to the outer edge of a lobe, globular with a short, blunt tip; 5‒8 mm diameter; fleshy. The gall makes a small hump on both sides of the leaf blade. If located at the end of a vein, the gall has a small, curved tip. Pale green, with a pubescent surface. Thick-walled; central chamber large, unilocular: Dryocosmus cerriphilus FM

7d Gall half spindle-shaped to funnel-like, green, glabrous; with long slender drooping stalk attached to the mid-rib; reaching the leaf margin. Containing a single gall: Amphibolips mernyensis gen. unknown

8a Galls usually only on the underside, one-chambered, glabrous => 9

8b Ovoid, about 2 mm long and 1–1.5 mm broad swelling on petioles or, visible on both sides of the leaf blade, on main veins. Initially yellowish, later on brownish, with distant whitish hairs which may be somewhat longer on the upperside; thin-walled; one-chambered. Containing a single larva: Andricus schroeckingeri FM

9a Galls spindle-shaped or flat rotund-ovoid => 10

9b Galls urn-shaped; up to 3 mm long, green to red-brown, longitudinally grooved; terminally flat, with protruding margin. On swollen parts of the midrib often with several together. Containing a single larva: Andricus gallaeurnaeformis FF

10a Galls kidney-shaped, up to 3 mm long, attached to the leaf over the complete length of the gall. Containing a single larva. Also on Q. lusitanica. Galls kidney-shaped, up to 3 mm long, attached to the leaf over the complete length of the gall. Containing a single larva. Also on Q. lusitanica. Pseudoneuroterus saliens FF

10b The full-grown gall, about 4 mm long, laterally flattened, rotund- to oblong-ovoid, yellowish, densely red- to violet-spotted protrudes laterally from the leaf veins. Surrounded by two valves and dropping off. Containing a single larva. “Oyster gall”. Neuroterus anthracinus FF

11a Galls visible on both leaf sides; one chambered => 19

11b Galls visible on only one side of leaf, point-like attachment => 12

12a Galls predominantly on underside of leaf => 13

12b Galls predominantly on leaf upper side, rarely on underside and then on smaller veins. Globular, ± 1.5 mm across. Initially white to green, later on rust-brown, glabrous; densely covered by short rounded tubercles, red at maturity; tough-walled. Often with several together; one-chambered, containing a single larva: Neuroterus minutulus FF

13a Gall distinctly wider than high, ± disc- or kidney-shaped; point-like attachment; one-chambered => 16

13b Galls rotund, about as long as broad; ± thick-walled => 14

14a Galls 4–6– (20) mm across, pubescent or glabrous => 15

14b Galls oblong-rotund, 2–2.5 mm long and 1.5–2 mm broad. White or pale reddish. Surface densely covered with acute, dark red tubercles. Wall hard and thick. Larval chamber large, oblong-oval. Solitary or with several scattered on the underside of the lateral veins; one-chambered. Mature in autumn. Containing a single larva. Unidentified gall wasp

15a Gall rotund-oval, about 1 mm across, with large larval chamber, very short stalked, provided with many, distant, 3–5 mm long, filiform, multi-cellular hairs. Often several coalesced into a wine-red complex. Neuroterus sp., gen. unknown

15b Gall oblong-oval, 4–6 mm across; covered by short, dense stellate hairs, green, later on grey-brown, thick spongy-walled; with one or two transverse-oval larval chambers., Attached to leaf underside with short thin stalk on secondary vein. Containing a single larva: Chilaspis nitida FF

15c Gall similar to the gall of the agamous generation of C. nitida, but smaller (1-3 mm) and with a relatively thinner wall. Also on Q. suber: Chilaspis trinacriae FF

15d Gall on apical and accessory buds, rotund, 5–10 (20) mm across, greenish to grey-green, upperside rough because of minute warts. Wall very thick, tough, with a greenish outer- and a somewhat thicker, paler, inner layer. Larval chamber relatively small, with coalesced protective layer on all sides. Containing a single larva. Synophrus politus FM

16a Galls disc-shaped in outline, of various height => 17

16b Galls flat kidney- or bean-shaped, up to 4 mm across; pale green or ± reddened. Often with several together on the underside of lateral veins. Older galls browned, eventually ± rounded; dropping off. “Kidney gall”. Containing a single larva. Trigonaspis megaptera FF

17a Galls flat disc-shaped, rotund, 4–6 mm across; glabrous or with stellate hairs => 18

17b Galls flattened, thick disc-shaped, rotund, 4–5 (6) mm broad, 3–4 mm high, white or ± red, flat above, with slightly elevated centre, margin below curved. Whole surface provided with long silky hairs, which are longer in the centre of the gall and yellow-brown and shorter and whitish towards the margin. Periphery with flat cavities, separated by small plates. Inner part consisting of uniform tissue surrounding a small larval chamber. Containing a single larva: Neuroterus lanuginosus FF

18a Galls up to 5 mm wide, slightly curved upwards at margin, hence flat bowl-shaped; radial striate, with slightly elevated central part. Margin sometimes slightly undulate. Galls yellowish to deep red, glabrous, or with scattered stellate hairs. One chamber containing a single larva: Neuroterus albipes FF

18b Galls up to 6 mm across; brownish-yellow or ± reddened, especially when young. Upperside densely covered with large rust brown stellate hairs; often white-spotted on the margin, underside glabrous. Closely appressed with its entire disc. In cross section a flat, blunt triangle. Containing a single larva in a central larval chamber. Neuroterus quercusbaccarum FF

19a Galls protruding on both leaf sides; however, predominantly only on one side => 24

19b Galls ± globular or pustule-shaped; in about equal amounts on both leaf sides => 20

20a Gall developed as low, up to 2.5 mm wide, glabrous, one-chambered, pustule-shaped swelling of the leaf blade => 22

20b Galls ± globular, to ovoid, one-chambered, ± pubescent; on, or next to, a vein => 21

21a Galls ± oblong-oval, about 2mm long and 1–1.5 mm high, longitudinal axis in the leaf blade, usually next to a main vein and leaf margin emarginate towards the vein. Yellowish to brownish, with distant simple, whitish hairs, thin-walled. Containing a single larva. Andricus schroeckingeri FM

21b Globular gall, 5–8 mm across, pea-size, translucent green, with short stellate hairs, thick-walled, succulent. Attached on the swollen end of a lateral vein. Larval chamber rotund, diameter equals the wall thickness. Containing a single larva. Dryocosmus nervosus FM

22a Larvae in closed chamber where they complete their development; pale with distinctly darker head => 23

22b Larvae lacking conspicuous mandibles, in round pustule, about 2.5 mm wide, very flat with a small wart on upper and on underside. Larvae pale red: Janetia pustularis

23a Leaf blade with one-chambered pustules, about 2 mm across. Containing a single larva with contrasting head. Unidentified gall wasp

23b Similar galls, 5 (6) mm across, on the upperside with radiating striations: Neuroterus numismalis FM

24a Pustule-, conical, cornicular, sometimes bulge-like galls are only apparently closed on all sides. Midge galls => 25

24b Galls oblong-ovoid 2–2.5 mm high, about 1.5 mm wide, with their longitudinal axis at right-angles to the leaf surface; protruding mainly on the upperside, underside only ± half-globular. Closed on all sides, thin-walled, one-chambered, glossy or dull, provided with long, distant stellate hairs and simple hairs in between. Often clustered on hardly stunted, but often ± heavily curled leaf blades. Containing a single larva: Andricus crispator FM

25a Galls in the leaf tissue, on both sides of leaf but developed to different extents => 26

25b Midrib, sometimes also all major veins, with 3–4 mm long, blunt spindle-shaped, predominantly laterally arched, glabrous swellings, sometimes visible on the leaf upperside as rather flat, pale green bulge. Often occurring on the underside on both sides of the midrib in a compact sequence behind- or next to one another and ± mutually coalescing to a varied extent. Each gall containing a longitudinal larval chamber, closed until maturity and later on with a slit-like opening towards the leaf blade. Containing a single larva: Janetia nervicola

26a When mature, only a part of the gall drops off, or opens by valves => 29

26b The gall remains complete, the larval chamber is connected to the outside by a ± thin channel, closed until maturity by a net-like barrier of upwardly directed small hairs => 27

27a Galls more conspicuous on the underside or thick disc-shaped => 28

27b On the upperside cornicular protruding, up to 6 mm high and 1 mm in diameter, ± bent, sometimes provided with some stiff bristle hairs. On the underside with a collar closing the gall exit, with yellowish hairs on the inside. Often many per leaf blade. Containing a pale yellow larva. Contarinia subulifex => 29

28a Upperside ± half-globular; up to 1.5 mm high and 2 mm broad, yellowish, glabrous. On the underside with thin, ± bent tube up to 2.5 mm long; exit closed by hairs on top. Wall hard. Containing a single yellow larva: Dasineura tubularis

28b Rotund to kidney-shaped gall on the underside, up to 6 mm wide and 2.5 mm high, provided with distant, yellow or grey, hairs. On the upperside a sparsely pubescent disc, surrounded by a slightly bulged rim with a central ± fish trap-like barred pore. Larval chamber expanded, running into the pore spirally. Often many per leaf blade. Containing a single larva: Dryomyia circinans

29a Galls up to 3 mm across => 30

29b Gall flattened, hard, almost woody, up to 5 mm across, with a thick (2–3 mm) base, slightly convex in the middle with a small tubercle; on the leaf upperside a round yellowish pustule, the middle conical, provided with some hairs. The under part, a lid which drops off when mature, is felt-like pubescent. The larval chamber is situated at base in the thickened disc. Containing a single red larva: Janetia homocera

30a Upper part with broad base, acuminate-conical; about 2 mm high, glabrous, yellow-brown. The somewhat narrower, on the underside only weakly protruding basal part is flat, disc-like, with central channel and densely covered with distant, fine yellowish hairs. Between both parts is the elongated larval chamber. At maturity the basal part becomes lid-like detached and drops off. Containing a single orange-red larva: Janetia cerris

Inquiline gall wasps: Saphonecrus haimi and Synergus variabilis

30b Leaf blade usually with several rotund, somewhat darker coloured, differently appearing, weak bladder-like swellings. On the upperside ± lenticular, glabrous, with central, point-shaped tip. On the underside a densely pubescent, central valve-like opening in autumn. Containing a single larva: Janetia szepligetii

= From GR, southern I the gall midge Janetia plicans has been recorded in crowded young leaves, containing a white larva

31a Galls situated in leaf blade => 34

31b Galls on leaf margin => 32

32a Leaf margin without conspicuous thickening, variously folded downwards => 33

32b Margin of expanded leaves narrowly tubular and rolled upwards between the lobes. In the hardly discoloured, clearly thickened ± leathery-brittle roll are one to several white larvae: Macrodiplosis roboris

33a Margin of the young leaves with sometimes several narrow, scale- or mussel-like downward, rarely upward, indentations. The respective vein slightly thickened and discoloured at the site of infestation. Each gall initially containing an aphid: Phylloxera coccinea

33b Margin of the leaf lobes broadly folded downwards. Outside of the gall slightly thickened, often marbled. Containing usually only a single yellowish-white larva per gall: Macrodiplosis pustularis

34a Leaf blade with smaller to larger, up to bladder-like swellings => 35

34b Leaf blade folded upwards over the midrib, the affected venation, especially of the basal part, thickened, abnormally pubescent. Unidentified gall midge

35a Usually upwardly directed protrusions several mm wide => 36

35b Small upward protrusions; containing a froth-covered nymph in the cavity on the underside. Trioza sp.

36a Leaf blade bulging upwards, swollen. In the depressions abnormal felt-like pubescence, composed of longer, ± twisted, and shorter, club-shaped or cylindrical hairs: Aceria cerrea

36b Leaf blade with 4–8 mm wide, rotund, slightly protruding upward archings, rarely also arched downwards. Infections initially ± pale- to grey-green, later on browned. Developing asci at maturity: Taphrina caerulescens

On male inflorescences (catkins), acorns and acorn cups

0a xxxxxxxxx => 00

0b xxxxxxxgxx => 00

0a xxxxxxxxx => 00

0b xxxxxxxgxx => 00

0a xxxxxxxxx => 00

0b xxxxxxxgxx => 00

0a xxxxxxxxx => 00

0b xxxxxxxgxx => 00

Evergreen oaks, Quercus coccifera, ilex, lusitanica and suber

On branches, twigs or shoots

On buds

On leaves

On male catkins

On acorns and acorn cups

mod 11.xi.2019