Plant Parasites of Europe

leafminers, galls and fungi

gallers on Betula

Dichotomous table for gallers on Betula

by Hans Roskam

1a On parts above ground => 2

1b Roots, especially close to stem, with conspicuous, irregular, ± nodule-shaped, massive proliferations. B. pendula, pubescens: Agrobacterium tumefaciens

2a On catkins or fruits => 51

2b On vegetative plant parts => 3

3a On leaves => 18

3b On shoots or buds => 4

4a On shoots => 6

4b Bud galls => 5

5a Buds greatly enlarged; scales loosely adpressed, with outward tips, brownish, grey-silky pubescent. Gall often persistent, sometimes already developing early into small, compact witches’ brooms. Betula spp.: Acalitus calycophthirus

5b Leaf buds swollen, disfigured to a variable extent. B. pendula: Eriophyes leionotus

5c On buds of B. pendula is also reported: Unidentified gall midge

6a On thinner twigs => 12

6b On older stems or branches => 7

7a Bushy malformations in or on the branches => 8

7b Bark of thicker stems or branches with nodule-shaped or open, rim-like margined cancers. Neonectria ditissima

= Globular, several cm large wood balls or the giant wood cancers, observed occasionally have unknown causes and are not true galls.

8a Complete shoot systems are disfigured into conspicuous witches’ brooms, or young twigs with ± pronounced malformations. Usually only the leaves are covered by a short lanuginose grey-white layer of asci => 9

=Regarding compact small witches’ brooms => 5

8b Branches with nodular swellings which give rise to Viscum album

9a Fungi only exceptionally cause witches’ brooms. Northern species => 11

9b Fungi usually cause pronounced witches’ brooms => 10

10a Fungus scattered on many birches. Witches’ broom persistent. Leaves usually lighter coloured than the normal ones, occasionally enlarged but hardly thickened. Betula spp., incl. cultivated foreign species. Taphrina betulina

10b ngus frequently causes pronounced witches’ brooms, but may also develop on many disfigured, ± yellowing leaves without conspicuous malformations of the branches. Taphrina nana

11a Asci with stalk cells. Witches’ brooms only caused exceptionally; the fungus is merely located on darker green areas, on the underside sometimes ± rust-brown discoloured, usually on undisfigured leaves. Taphrina splendens

11b Asci without stalk cells. The fungus is located on often many, sometimes slightly enlarged, soon yellowing leaves of the infected plant, only exceptionally do witches’ brooms disfigure shoots. B. glandulosa, nana, pubescens, x alpestris. Taphrina bacteriosperma

12a Inducer inside the malformations => 14

12b The flat inducers are located in rim-surrounded depressions in the bark and, in case of heavy infestation, sometimes additionally on swollen or disfigured twig => 13

= Minute elevations on twigs of B. pendula, caused by the damselfly Chalcolestes viridis, are not true galls

13a Scale ± pear-shaped, 2.5–3 mm long, white to grey-white, females wine-red. Betula spp.: Chionaspis salicis

13b Scale ± rotund, 1.2–1.6 mm across, whitish to brownish-grey, with dark-yellow median spot. Insect red. Betula spp.: Epidiaspis leperii

14a Shoots with elongated spindle-shaped or ± distinctly separated, nodule-shaped swellings, up to 1 cm wide => 15

14b Young shoots with various proliferations of walls of wounds. Betula spp.: Cryptorhynchus lapathi

= Large nodular outgrowths up to several cm, like those found laterally on young shoots, cannot be attributed to a particular cause and could be considered as teratologies.

15a Inducers inhabit only galls on first-year twigs; galls on woody twigs vacated or occupied by successoria (secondary inhabitants) => 16

15b Older shoots with spindle-shaped thick swelling, up to 50 mm long and 15 mm wide. Gall extending over several internodes, broadest in the upper part caused by a swelling of the woody part; bark only slightly swollen. Inside a long tunnel. B. pendula, pubescens: Unidentified lepidopteran

16a Axis swollen at the top of the shoot => 17

16b Swelling situated below a node, rotund or more or less spindle-shaped, 5–10 mm long; broadest at the node. In a long tunnel inside the pith is a pale-green to greenish-yellow caterpillar with a pale brown head capsule. Exit hole in the leaf axil. Betula spp.: Epinotia tetraquetrana

17a Axis swollen at the top of the shoot. B. pendula, pubescens: Acleris notana

17b Young shoot with a slender swelling on all sides which usually starts below the top and expands downwards over several internodes. Internodes sometimes ± shortened. A tunnel in the pith contains a single caterpillar. B. pendula, pubescens and related species. Heliozela hammoniella

18a Galls on the leaf blades => 23

18b Malformations only on petioles and leaf veins => 19

19a Swellings hardly 2 mm across or smaller => 21

19b Galls several mm long => 20

20a Petiole shortened, over its whole length thickened; at the base of the leaf blade an oblong-elliptical excision. Betula spp.: Heliozela hammoniella

20b Main-, or more rarely lateral veins, occasionally also the petiole, with spindle-shaped, glabrous, hard, pale-green or often also ± purple-red swellings especially visible on the undersides. Each gall contains one single larva; in largely coalesced galls several white, later on pale red larvae. B. pendula, pubescens, x intermedia: Massalongia rubra

20c Much weaker, only up to about 3 mm long, pale green, thin-walled swellings, developing usually solitary per leaf blade on first or second order lateral veins. Containing a single white larva. B. pendula: Unidentified gall midge

21a Each swelling contains a single egg; the emerging larva leaves the rapidly collapsing egg capsule. “Procecidium” (oviposition scars, not true galls ) => 22

21b Up to 2 mm long, corn-like or more wart-like galls, up to 1 mm high, on petioles and veins. Cavity with some short, 1-celled hairs. B. pendula, pubescens: Cecidophyopsis betulae

22a Petiole, more rarely also the midrib, with two rows of egg capsules. B. pendula, pubescens: Hemichroa crocea

22b Egg capsules arranged in one row on the midrib or also on the side veins. B. pendula, pubescens: Craesus septentrionalis

22c In similar way develops on birches Craesus latipes

23a Leaf blade with weak to strong spoon- or bladder-like swellings caused by mites, aphids or fungi, whose asci develop on the galls => 40

23b Malformations different => 24

24a Galls mainly on unfolded leaf blades => 27

24b Leaves folded or rolled upwards => 25

25a Malformations without abnormal pubescence => 26

25b Leaf margin rolled upwards; on older leaves often only at the leaf base; early infected leaf blades may be completely taken up in a leaf roll with densely pubescent surface. Unidentified gall mite

26a The leaf blades of young leaves do not develop completely and remain mostly folded upwards. Midrib and basal part of the side veins thickened, pale green or ± reddened. Several yellowish-white larvae. B. pendula: Resseliella betulicola

= The white larvae of the gall midge Dasineura betuleti live, probably as inquilines, in similar galls which may be caused by the previous specie

26b Leaves close together at the tips of young shoots, severely stunted, rolled, curled and yellow-green. Unidentified thrips

= Stunting of leaves are occasionally caused by the thrips Mycterothrips consociatus

27a Galls situated in the leaf blades => 28

27b Teeth of the leaves with rapidly collapsing egg capsules after the larvae have emerged. “Procecidia” (oviposition scars, not true galls). B. pendula, pubescens: Pristiphora testacea and/or Arge pullata

27c redominantly on Salix, occasionally on Betula: Pristiphora melanocarpa

28a Leaf blade with ± expanded felt-like cover => 34

28b Leaf galls of roughly defined shape, usually not excessively pubescent => 29

29a Galls wart-, nodule- or ± pouch-like, under 2 mm wide => 31

29b Parenchyma galls; rotund, weakly protruding on both leaf surfaces, about 3–4 mm wide; yellowish, usually red-rimmed. Often several per leaf => 30

30a On B. pendula, pubescens. Each gall contains an initially white, eventually sulfur-yellow larva. Galls usually several per young leaf. Anisostephus betulinus

30b On B. pendula, pubescens. Older leaf blades with solitary or only a few, very flat, concolorous, hardly protruding parenchyma galls. Containing a single pale to lemon-yellow larva. Massalongia betulifolia

30c On B. nana. Similar thick-walled parenchyma galls, strongly arched on the underside. Each gall contains a single orange-reddish larva. Massalongia bachmaieri

31a Galls larger than 1 mm => 32

31b Galls wart-shaped, smaller than 1 mm, golden-yellow translucent, often many on the basal leaves or stems. B. nana, pendula, pubescens: Synchytrium aureum

32a Galls persistent, tough-walled => 33

32b Leaf tips with irregularly distributed egg capsules on the underside which rapidly collapse after the larvae have hatched. “Procecidium” (oviposition scars, not true galls). Betula spp.: Nematus cadderensis

33a Leaf blade with, scattered glabrous nodules, about 1–1.5 mm long, ± reddish, later on browned, protruding strongly on the underside and with an exit hole closed by a rim of rigid hairs; wall of the cavity glabrous. B. pendula, pubescens: Eriophyes leionotus

33b otund, up to 3 mm high, ± pubescent pouch-like protrusions on the leaf upper side, predominantly close to the margin, rarer in the vein axils; wall of the cavity provided with yellowish-white, ± cylindrical, rigid hairs. B. pendula, pubescens: Acalitus longisetosus

34a Hairs cylindrical => 36

34b Hairs club- to toadstool-shaped => 35

35a Erinea dense, ± irregularly margined, initially often intensely red, eventually ± browned, predominantly on upper side, occasionally also on the underside. Hairs irregular head-shaped or ± toadstool-like. Betula spp.: Acalitus longisetosus

35b Dense wine-red coloured erinea with irregular head-shaped hairs; predominantly at the leaf base or along the veins. B. nana: Aceria vinosa

35c Erinea usually on leaf underside, sometimes on both sides, rarely on upper side; initially whitish, later on yellowish, eventually rust-coloured or brownish. Hairs head-shaped, usually longer stalked than those of the previous species. B. humilis, nana, pendula, pubescens, etc.: Acalitus rudis

36a Erinea on the leaf underside, in arched protrusions, predominantly in vein axils => 39

36 Erinea on the leaf underside, also in arched protrusions, but free in the leaf blade or near the margin, or erinea predominantly on petioles or leaf veins => 37

37a Erinea mainly in areas on the leaf blade => 38

37b White, also reddened erinea predominantly on the petioles and on the venation of the leaf base or extending from the stalks into the leaf base venation. B. pendula, pubescens, pubescens var. glabrata, etc.: Eriophyes leionotus

38a Leaf blades of B. nana predominantly close to the margin with ± discoloured archings on the upper side, which contain purple-red to almost whitish felt masses with cylindrical hairs. Aceria fennica

38b Leaves of B. pubescens with upward archings predominantly on the leaf blade, more rarely in the vein axils, which display on the underside ± dense, cylindrical, rigid, whitish-yellow hairs. Acalitus notolius

39a On the upper side arched, glabrous or more rarely weakly pubescent protrusions in the vein axils containing on the underside cylindrical, soon browned, densely packed, not spiralling hairs. B. pendula, pubescens: Acalitus longisetosus

39b Erinea relatively loose, with cylindrical, pointed contorted hairs; usually on the underside in rotund to oval, ± heavily pubescent pale green bladders, situated predominantly in the vein axils at the base of the midrib, more rarely close to the margin or on the leaf blade. B. pubescens & var. pumila, x intermedia: Eriophyes lissonotus

39c In similar galls, but containing beads or short finger-shaped blunt hairs. B. pubescens & var. pumila, x intermedia: Eriophyes leionotus

40a Galls caused by aphids or mites => 44

40b Malformations caused by fungi which fruit on the gall surface => 41

41a Malformations often only locally; on single or several leaves of a shoot => 43

41b Leaves on the infected, systemically attacked shoots often hardly disfigured, although completely or substantially attacked. Leaf blades usually paler, ± slightly enlarged and slightly arched upwards, without conspicuous thickening => 42

42a Fungus frequent or with only boreal-alpine distribution. Initially infections of fungi which occur on the same plant or in the same host population in conspicuous witches’ brooms. Asci with stalk cells

a Leaf blades of young shoots pale green, sometimes slightly enlarged. Axial parts ranging from not disfigured to witches’ broom-like malformations. Betula spp.: Taphrina betulina

b Similar malformations. Betula spp.: Taphrina nana

42b Usually witches’ broom-like malformations develop without simultaneous malformations of shoots and leaves

a Asci with stalk cells. Malformations rarely on axial parts, usually minor on leaves. Betula spp.: Taphrina splendens

b Asci lacking stalk cells. Leaves of the infected shoots often yellowing, sometimes with slightly enlarged leaf blades. Betula spp.: Taphrina bacteriosperma

43a eaves often with conspicuous yellowish or reddish discoloured, thickened, bladder-like swellings. Asci lacking stalk cells. Betula spp.: Taphrina carnea

43b Minor swellings, sometimes several per leaf on early infected young leaves. Infection sites about 2–10 (15) mm across, rotund, ± discoloured. Asci with stalk cells. Betula spp.: Taphrina betulae

43c On leaves, probably non-cecidogenic. Betula spp.: Melampsoridium betulinum

44a Malformations caused by aphids => 45

44b Leaves ± spoon-shaped bent downwards. Leaf blades soon yellowish to brownish discoloured; on the underside with free-living mites. Betula spp.: Epitrimerus subacromius

45a Leaves to various extents folded or curled => 46

45b Leaves with irregular, conspicuous bladder-like swellings, up to 10 mm high, upwardly directed, which occupy a major part of the leaf blade. Aphid egg-shaped, dark purple-red, covered with wax. B. x alpestris, pendula, pubescens: Hamamelistes betulinus

46a Aphids in various shades of yellow or green, or (because of its banded pattern) almost black => 47

46b Aphid dull brown, 2.5–3.5 mm long with brownish transverse stripes; on the underside of irregular undulate leaves. B. pendula, pubescens: Symydobius oblongus

47a Antennae shorter than body => 48

47b Antennae longer than body. Aphid about 2.5 mm long, pale yellowish or –greenish, with yellowish or greenish spots. Younger leaves curled, in cases of heavy infestation upwardly arched. B. pendula, pubescens: Calaphis betulicola and/or Calaphis flava

48a Aphids with dark coloured or margined short siphunculi => 49

48b Aphid about 1.3–2 mm long, greenish-white to pale yellowish-green. Siphunculi very short, yellowish-white, like the also equally short wart-shaped cauda. Antennae reaching beyond the middle of the body. Infected leaves ± distinctly upwardly arched, often withering prematurely; on the underside with considerable colonies. B. humilis, pendula, pubescens: Betulaphis quadrituberculata

49a Aphids more than 2 mm long; siphunculi black or black-green; antennae half the body length => 59

49b phid 1.5–2 mm long, almost egg-shaped, pale or yellowish-green, with broad, dark-green to brown, medially interrupted transverse bands. Antennae often shorter than half the body length. Internodes of young shoots ± stunted. Leaves curled or, in case of heavy infestation, upwardly arched. B. pendula, pubescens: Glyphina betulae

50a Aphid about 2.5 mm long, usually yellowish or greenish, deep to almost black-grey coloured by lighter or darker blackish transverse bands. Siphunculi very short, black; cauda only wart-shaped, green. Leaf margins ± downwardly bent and folded. B. pendula: Callipterinella calliptera

50b Similar malformations. Aphid about 2 mm long, pale yellow, abdomen near thorax with a wide brown-red transverse band, a large greenish-black spot behind, caudal margin brown-red. Siphunculi black-green, cauda pale yellow. B. pendula: Callipterinella tuberculata

51a Malformations visible on outside of catkins => 54

51b Malformations only visible after crumbling the female catkins => 52

52a Gall restricted to fruits, which are enlarged and paler than the healthy ones => 53

52b Galls restricted to the somewhat thickened base of the fruit scales, which are firmly connected to the spindle of the catkin. Containing a single bright orange-red larva. Betula spp.: Semudobia skuhravae

53a Fruit more or less egg-shaped, swollen, dull, more or less pubescent, wings smaller than those of healthy fruits, but distinctly developed. Exit circular, distinct. Contains a single bright orange larva. Betula spp.: Semudobia betulae

53b Fruit almost globular, swollen, glossy, glabrous, wings almost completely reduced, exit indistinctly translucent. Contains a single bright orange-red larva. Betula spp.: Semudobia tarda

= A frequent inquiline is the gall midge Dasineura interbracta, whose pink larvae adhere to the outside of the galls and feed on these galls at the expense of Semudobia betulae as well as S. tarda, larvae of which eventually die

= A less frequent inquiline gall midge: Dasineura fastidiosa, whose pale yellowish larvae adhere to the outside of the galls and feed on these galls at the expense of mainly Semudobia betulae, larvae of which eventually die

54a Caterpillars with distinct thoracic legs => 55

54b Larvae with distinct head capsules, lacking distinct thoracic legs; inside the variously stunted fruit catkins. They tunnel along the spindle of the catkin and feed both on plant tissues and on midge larvae and their galls. B. pendula, pubescens: Betulapion simile

54c Catkin enlarged, caused by gall midges. B. pendula: Unidentified gall midge

= Furthermore the aphid Callipterinella minutissima has been recorded from birch catkins.

55a Catkins shortened, appearing ± thickened, often twisted screw-like and not reaching maturity. B. pendula, pubescens: Cochylis nana

55b atkins similarly stunted. B. pendula, pubescens: Epinotia bilunana

55c Further facultative deformations are occasionally caused by the caterpillar of Epinotia tenerana

Last modified 27.vii.2020