Plant Parasites of Europe

leafminers, galls and fungi

gallers on Crataegus

Dichotomous table for gallers on Crataegus

by Hans Roskam

1a On flowers => 23

1b On vegetative plant parts => 2

2a On buds, leaves and thinner twigs => 4

2b In root, trunk or on thicker branches => 3

3a Irregular lumpy swelling on root, 10 mm across or much larger; soft at first, later woody; contains red, purple or brown woolly aphids covered with copious white wax; gall persists long after aphids have left; rare. Crataegus spp.: Eriosoma lanigerum

3b Branches or stems often with conspicuous, club- or barrel-shaped swellings. Crataegus spp.: Viscum album

4a Malformations of various shape, soon occupied by fructifications of fungi => 20

4b Malformations caused by animals => 5

5a Aphid galls => 15

5b Other causers => 6

6a On younger stems, shoot tips or leaves => 7

6b Buds slightly swollen, not opening, occasionally abnormally pubescent. C. laevigata, monogyna: Eriophyes calycobius

6c Vegetative bud unopened, transformed into a rotund mass of small, strongly folded leaves, about 5 mm wide, the external ones making a sort of hood enveloping a shell of aggregated dying leaves. Crataegus spp.: Anthonomus bituberculatus

7a Malformations on single, or several terminal leaves, loosely arranged => 9

7b Galls on thin stems or on shoot tips => 8

8a Leaves on distinctly stunted, slightly thickened shoot tip often in many densely tuft-like clusters. Leaf blades sessile, ± stunted, rugose, occupied by many bolt-shaped or globular green or reddish proliferations. Between the inner, very small leaves are many white, later orange larvae. C. azarolus, coccinea, laevigata, monogyna, rhipidophylla: Dasineura crataegi

= Associated are the yellowish larvae of the inquiline gall midge Prolauthia circumdata.

8b Shoot axis with brown-green swelling, sometimes extending onto the petiole, with easily loosening epidermis. C. laevigata, monogyna: Unidentified gall midge

= The “Hawthorn twig gall midge” Resseliella crataegi, with larvae living gregariously under bark, has not been observed to cause galls.

8c Bark of younger twigs usually with several, ± distinctly rimmed depressions, which contain a rotund, whitish- to brownish-grey scale insect, the inducer. C. rhipidophylla: Epidiaspis leperii

9a Leaves curled or with many small swellings or pocks => 12

9b Leaf margin rolled or leaf blade abnormally pubescent => 10

10a Rolls of leaf margins => 11

10b Underside of leaf with white or violet-red erinea of slightly club-shaped hairs. C. coccinoides, laevigata, macrocarpa, monogyna, nigra, rhipidophylla, sanguinea: Phyllocoptes goniothorax

10c Upper side of leaf slightly protruding at junction of midrib and side vein; corresponding area on underside weakly pubescent. Crataegus spp.: Eriophyes albaespinae

10d Underside of leaf with a longitudinal groove, abnormal pubescence absent. C. laevigata, rhipidophylla: Aculops crataegumplicans

11a Leaf margin tightly rolled downwards, with short club-shaped, at first white, then brownish hairs sometimes extending as erinea into the leaf blade or developing there as isolated patches. C. coccinoides, laevigata, macrocarpa, monogyna, nigra, rhipidophylla, sanguinea: Phyllocoptes goniothorax

11b Leaf roll, containing several red larvae. C. monogyna, laevigata: Unidentified gall midge

12a Leaf blade with many pocks or small swellings => 13

12b Several leaves of suckers on curved stems bent together into a loose aggregation. Leaf blades ± crumpled. Containing a froth-covered nymph. Crataegus spp.: Philaenus spumarius

13a Leaf blade with one-sided archings => 14

13b Leaf blade with many pocks protruding on both sides, often pale green; with narrow opening on underside, occasionally also on upperside. C. laevigata, monogyna: Eriophyes crataegi

14a Leaf blade with many small bulging swellings, yellowish or often carmine-red. Froth-covered nymphs in grooves on underside. C. laevigata, monogyna, rhipidophylla: Cacopsylla melanoneura

14b Leaf blade browned by vagrant gall mites. C. macrocarpa, monogyna, rhipidophylla: Calepitrimerus armatus

14c In similar malformations on hawthorns during the same period also lives Cacopsylla peregrina

14d Leaf blade with small depressions on the underside, and corresponding tiny bulges, often coloured red, on the upper side. In each cavity is one flat froth-covered nymph. C. laevigata, monogyna: Cacopsylla affinis

= The psyllid Cacopsylla crataegi is only weakly cecidogenic, and often reported only as inquiline, or successorium (secondary inhabitant) in aphid galls.

14e Leaf blades usually bent downwards along the venation. Malformations without abnormal pubescence. C. laevigata, rhipidophylla: Aculops crataegumplicans

15a Leaves variously curled, leaf blades not discoloured or sometimes marbled yellow. Malformation usually with many leaves, loosely arranged on shoots or ± clustered on shoot tips => 17

15b Leaves swollen, bladder-like, and conspicuously discoloured yellowish or reddish. Galls caused by several Dysaphis species, all host alternating and difficult to separate => 16

16a Leaf blade usually keel-shaped, curved downwards; segments between the veins especially close to the midrib strongly inflated, bladder-like, discoloured yellowish, not red. Galls mainly on several leaves distributed over the plants. C. laevigata, monogyna: Dysaphis ranunculi

16b Galls usually strongly reddened, otherwise not different from previous species. Often on several neighbouring leaves occurring already during unfolding of leaves. Larvae usually greenish or pink. Aphids mainly distinguished by their different host alternation. Aphids interbreed on Crataegus. Exules on roots, at stem base or sheaths, rarely on leaf blades of basal leaves of various Apiaceae:

a Migrating to Daucus carota, sativus (Anthriscus, Aegopodium): Dysaphis crataegi

b Migrating to Aethusa cynapium: Dysaphis crataegi subsp. aethusae

c Migrating to Angelica: Dysaphis angelicae

d Migrating to Apium graveolens and Petroselinum crispum: Dysaphis apiifolia subsp. petroselini

e Migrating to Heracleum, Conium: Dysaphis lauberti

f Migrating to Laserpitium, Anthriscus: Dysaphis laserpitii

g Migrating to Petroselinum, (Levisticum officinale, Conium): Dysaphis apiifolia subsp. petroselini

h Migrating to Pastinaca sativa: Dysaphis crataegi subsp. kunzei

17a Leaves not conspicuously discoloured => 18

17b Several leaves at shoot tip loosely arched, marbled yellow, soon drying. C. laevigata, monogyna, rhipidophylla, sanguinea: Prociphilus pini

17c Cherry-red to crimson curled-leaf galls in spring. Crataegus laevigata, monogyna: Dysaphis apiifolia

17d Red curled-leaf galls on leaves. C. curvisepala: Dysaphis incognita

17e Pale green or red curled-leaf galls. C. orientalis: Dysaphis virgata

18a Aphids green => 19

18b Aphids black; rolling and curling of young leaves. Crataegus spp.: Aphis fabae

19a Leaves on the unshortened shoots normally distributed or sometimes loosely clustered at shoot tip. Midrib conspicuously bent, screw-like, leaf blade sometimes undulate, nested, loosely or more compactly bent downwards. Aphid with short, thick green siphunculi. C. coccinea, laevigata, monogyna: Rhopalosiphum oxyacanthae

19b Leaves at stunted ends of shoots bent downwards over tip and margins rolled. Aphid with rather long black siphunculi. Crataegus spp.: Aphis pomi

20a Leaves curled or swollen, bladder-like, also young stems partially ± thickened and curved, occupied by grey-white fungal fructifications => 22

20b Considerable yellowish, also reddened, pad- or bulge-shaped swellings on leaves, young stems and even fruits. Galls occupied by spermogonia and aecia => 21

21a Peridium cylindrical, 2–3 mm long, lacerated brush-like later on, divided from the tip into many long lobes. Lateral walls of peridium cells with many, irregularly shaped tubercles of different size. Crataegus spp.: Gymnosporangium clavariiforme

21b Aecia similar. Lateral walls of peridium cells with strong transversely and obliquely running tubercles and ridges. Crataegus spp.: Gymnosporangium confusum

22a Leaves with yellowish-green or reddened bladder-like swellings, at maturity appearing white-frosted because of presence of many asci. Sori occasionally slightly arched, usually on one side, and ± curved swellings on young shoots, flower peduncles and even floral parts; sporadically developing almost witches’ broom-like malformations. C. laevigata, monogyna, nigra, sanguinea: Taphrina crataegi

22b During development of infected young shoots, according to response ability, the internodes partially appearing shortened, slightly thickened, partially etiolated, elongated and in case of mainly one-sided infestation ± conspicuously curved and often ± reddened. Diseased organs covered with a loose white mycelium. Crataegus spp.: Podosphaera clandestina

23a Malformations caused by fungi on flower parts or young fruits => 21, 22

23b Malformations caused by animals => 24

24a Outer parts of flower buds, especially basally, slightly swollen, not opening. Between the inner parts occur larvae with inconspicuous head capsules => 25

24b Receptacle and ovaries sometimes facultatively slightly swollen. Flowers remain closed, corolla distinct between healthy flowers because of its premature browning. Inside is a single larva with distinct head capsule. C. laevigata, monogyna: Anthonomus pedicularius

25a Larvae ivory-coloured, jumping. C. laevigata, monogyna: Contarinia anthobia

25b Larvae red, non-jumping. C. crus-galli, laevigata, monogyna: Dasineura oxyacanthae

= Inquiline of Dasineura oxyacanthae, larvae orange-coloured, non-jumping: Dasineura fusca

Last modified 24.viii.2020