Dichotomous table for gallers on Salix

by Hans Roskam

A. Galls on roots, stems, branches or twigs

1a On above-ground parts => 2

1b Nodule-shaped galls on roots: Meloidogyne sp.

1c Small galls on root tips or root hairs: Jaraia salicis

2a The inducer lives inside the galls or cancerous malformations => 5

2b The inducer lives on the outside of the gall or is fruiting there with orange-coloured spores => 3

3a Malformations caused by mistletoes, or covered with fungal spores => 4

3b Bark of the younger shoots often with many, ± oval, embossed depressions with bulging rims: Chionaspis salicis

4a Older twigs and branches, more rarely also stems, with conspicuous spindle- or club-shaped swellings; from which sprouts: Viscum album

4b Witches’ broom-like malformations: Melampsora deformans

5a Malformations not cancer-like wounds => 6

5b Wound cancers on older stems and branches. The exposed large wood bodies bulge out and are surrounded by proliferations of the bark tissue: Neonectria ditissima

6a Axial parts of various older organs with swellings on one side or on all sides which possess one or several chambers, or bear pustule => 7

6b Woody major stems, usually on basal parts, rarely on higher parts, bursting conspicuously from the bark, massive proliferations: Agrobacterium tumefaciens

7a The galls develop at ± large distance below the shoot tips. Lateral buds not conspicuously crowded => 10

7b Terminal part of shoot stunted, swollen, ± club-shaped. Buds often crowded and enlarged => 8

8a Galls on broad-leaved willows => 9

8b Apical part of shoots of S. repens swollen, club-shaped, provided with crowded, pubescent, sometimes glabrous, buds. Buds containing a single red larva: Rabdophaga repenticola

8c Axis below the stunted tip swollen on all sides; galls bell/spindle-shaped, longer than 10 mm. S. repens, rosmarinifolia: Euura (Euura) weiffenbachiella

9a Tip of shoot severely stunted over about 15 mm and swollen, club-shaped, especially the terminal part densely occupied often with abnormally pubescent buds. Containing one red larva inside each bud. S. aurita, caprea, cinerea, myrsinifolia: Rabdophaga clavifex

9b Swelling ± egg-shaped, thin-walled, often heavily, almost felt-like pubescence. Lateral buds usually not accumulated and enlarged. In the greatly widened cavity in the pith several, remarkably large, red larvae. S. aurita, caprea, cinerea: Rabdophaga pierreana

10a Galls almost exclusively occurring close to solitary, sometimes also galled, buds => 37

10b Galls without particular association with buds, situated in or on the internode => 11

11a Axis usually evenly thickened on all sides => 19

11b Thickening predominantly one-sided. Solitary galls sometimes hardly arched. Gregarious galls appear sometimes on all sides, but in that case are irregularly bulged => 12

12a Galls contain larvae => 13

12b Young shoots with alternating double row of often 70‒80 egg capsules; “procecidia”, oviposition scars: Nematus miliaris

13a Galls usually conspicuous => 14

13b Young twigs often with only inconspicuous one-sided thickening. Containing a single orange-red larva. S. alba, probably als on broad-leaved willows: Rabdophaga albipennis

14a Larval chambers situated predominantly outside the woody parts or larvae protrude into the pith at maturity => 16

14b Already the early larval stages start development in the pith => 15

15a Gall on thinner twigs, predominantly emerging from the pith and woody parts; often clearly buckled, one-chambered, or often multi-chambered by coalescing of several galls, in that case 20‒30 mm long, 8‒15 mm broad. Contain several yellowish larvae. S. pentandra: Euura (Euura) amerinae

15b Similar, but smaller up to about 10 mm long and 3 mm thick, egg- to spindle-shaped galls on S. repens & subsp. rosmarinifolia: Euura (Euura) weiffenbachiella

16a Larvae lacking a distinct head capsule, but with mouthparts. Galls mainly developing by increasing of the bark tissue. Chambers predominantly longitudinally oriented in the sapwood. Each chamber containing a single fly maggot or puparium => 18

16b Larvae with conspicuous head capsule => 17

17a Larvae cream-coloured, with narrow, dark head. Gall one-sided; emerging from the bark, about 3 mm long, up to 2 mm wide, usually situated below a bud in the terminal part of the shoot: Melanapion minimum

17b Following Euura species have limited host ranges. They are distinct as follows:

a On S. alba, x fragilis, not on sallows or S. repens. Gall elongate spindle-shaped, mainly emerging on one side, 10‒15 x 5‒7 mm. Larvae solitary; initially white, bright green laterally, with wide, clearly contrasting brown head; initially between bark and sapwood, eventually feeding from pith: Euura (Euura) atra

b Similar, on S. aurita, cinerea & subsp. oleifolia, lapponum: Euura (Euura) auritae

c Similar, on S. elaeagnos: Euura (Euura) elaeagnos

d Similar, on S. myrtilloides: Euura (Euura) myrtilloides

e Similar, on S. purpurea and hybrids: Euura (Euura) salicispurpureae

18a Galls arching conspicuously from the bark, usually more or less bean-shaped, protruding distinctly, up to 10 mm long. Bark glabrous. Sometimes occurring with several on the same twig, but separated. S. aurita, caprea, cinerea, repens, viminalis and hybrids: Hexomyza cecidogena

18b Solitary galls spindle-shaped, gradually giving way to normal tissue. Often with several, mutually coalescing complexes, almost ± humped on all sides. S. caprea is main host plant, furthermore on S. aurita, cinerea, pedicellata, repens: Hexomyza simplicoides

19a Galls gradually giving way to the normal parts, ± spindle-shaped, a few mm to several cm long, or in other cases hidden from the outside in the invisibly swollen bark, almost like cryptocecidia => 26

19b Axis with conspicuous, often nodule- or egg- to barrel-shaped swellings. Galls distinctly tapered terminally => 20

20a Galls caused by gall midge larvae on one year old twigs => 23

20b Galls with a large central feeding cavity, encroaching into the pith of the uninfected stem parts. Larvae with a distinct head capsule => 21

21a Galls usually occurring on two year old to older branches => 22

21b Galls predominantly occurring on the nodes of previous year shoots, – oblong-oval, up to about 10‒15 x 6‒8 mm. The pith contains a pale to greenish-yellow caterpillar with a dark brown or black head: Cydia servillana

22a Two year old twigs with nodular swelling. Containing a single caterpillar. S. aurita, caprea, cinerea and hybrids: Synanthedon flaviventris

22b Nodular swellings, usually on finger-thick twigs. Containing a single caterpillar. Salix spp.: Paranthrene tabaniformis

23a Both ends of galls similarly abruptly tapering => 24

23b Galls pear-shaped; one end acutely, almost angularly constricted, the other end gradually tapering; up to about 10‒12 x 5‒8 mm. Bark not cracking. Several lemon-yellow midge larvae. S. aurita, caprea, cinerea, helvetica, repens, etc.: Rabdophaga dubiosa

24a Galls thick-walled, rotund to oblong, ± barrel-shaped, multi-chambered. Bark bursting later on => 25

24b Galls globular to egg-shaped. Surface glabrous or, on pubescent hosts sometimes almost felt-like, not bursting. Wall thin; a large cavity inside with sometimes solitary or usually several to many large red larvae. S. aurita, caprea, cinerea, etc.: Rabdophaga pierreana

25a Galls about 10 mm long and 5‒12 mm thick, initially green, grey or dark brown later on. Often with several ± segmented swellings in a row and coalesced to 20‒50 mm long. On one year old twigs. The bark bursts soon and becomes ± detached. Chambers isolated, in pith, pith rays, rarely in bark. Each chamber containing a single larva. Salix spp.: Rabdophaga salicis

25b Galls usually slender barrel-or spindle-shaped, 10‒30 mm long, 5‒8 mm thick and gradually narrowing; glabrous; bark not bursting. Sometimes several, ± close galls per shoot in a row, which may also develop terminally on shoots. Inside are several, distinctly separated chambers each containing a single yellow-red larva. S. purpurea, daphnoides and related hybrids: Rabdophaga degeerii

26a Gall midge galls on one year old to perennial stems => 27

26b Swelling oblong spindle-shaped. Inside the gall is a large curved chamber, both sides encroaching in the pith of the ungalled stem parts. Larva with distinct head capsule. S. caprea, etc.: Saperda populnea

27a The larval chambers are situated outside of the woody stem part => 31

27b The larvae are situated in the pith. Galls mainly on one- or two year old twigs => 28

28a Larvae yellow- to orange-coloured => 30

28b Larvae red => 29

29a Swelling usually on two year old twigs, distinctly protruding, up to about 15 x 3‒5 mm wide, glabrous, often ± discoloured. A large cavity in pith. The shoot above the gall is conspicuously stunted and dies off prematurely. S. repens: Rabdophaga exsiccans

29b Swelling smaller, weak, solitary or with several together and then up to 10 mm long. Chambers in pith and in wood each contain a single larva. S. aurita, repens and narrow-leaved willows: Rabdophaga viminalis

30a Swellings weak, but usually distinct, about 10‒20 mm x 3‒4 mm, with glabrous, red-brown surface. Several orange-coloured larvae in an extended, thin-walled, cavity. S. repens: Rabdophaga dubiosa

30b Galls uniformly, spindle-shaped or cylindrical on all sides, up to about 8‒15 mm long and 3 mm thick. Larvae yellow or reddish, solitary in pith. Mainly on broad-leaved willows: Rabdophaga karschi

30c Orange-coloured midge larvae develop in slightly longitudinal swellings on twigs. Salix spp.: Rabdophaga nielsenii

30d Orange-coloured larvae develop in inconspicuous stem galls on S. aurita: Dasineura medullaris

30e Orange-red midge larvae develop in one-year shoot causing an indistinct swelling. S. pentandra: Rabdophaga lattkei

31a Galls on newly developed- or previous year twigs, difficult to find => 33

31b Older twigs to even arm-thick branches flattened and swollen on one side or, in cases of heavy infestation, on all sides. The gall complexes, often expanded predominantly by swelling of the outer sapwood, gradually narrowing into the uninfected parts. Larval chambers on the outside of the woody parts => 32

32a On S. alba, babylonica, caerulea, x fragilis. Chambers in the outer sapwood, spindle-shaped, many, running in the same direction along the longitudinal axis of the shoot or are somewhat inclined. The hardly thickened bark on the galls bursts soon, dies off and disintegrates, exposing large areas of irregularly shot hole-like perforated sapwood after emergence of the midges. Each chamber containing a single bright orange-yellow, sometimes ± reddish larva: Rabdophaga saliciperda

32b On S. aurita, cinerea, caprea. Similar galls, often hardly protruding. Bark not bursting. Chambers stand parallel to the longitudinal axis of the shoot. Each chamber containing a single larva: Rabdophaga pierrei

32c Together with the previous species, reared from similar galls: Rabdophaga schwangarti

32d A large spindle-shaped swelling on the branch containing a solitary larva. S. repens, very rare: Rabdophaga schicki

33a Galls on S. purpurea => 35

33b Galls on other Salix species => 34

34a On S. triandra. Galls on the base of annual shoots or coppice. From the outside sometimes hardly discernible in the beginning. Larvae, isolated, in often many oblong-oval, shallow chambers in the sapwood running along the longitudinal axis. Exuviae protruding from the galls after emergence of the adults, leaving dark “shot holes” in the ± disintegrating bark. Each containing a single larva: Rabdophaga triandraperda

34b On S. viminalis, similar galls, but in the upper part of the twig, which may be slightly twisted. Position of larval chambers as in the previous species. The exit holes are preformed as small windows. Usually the twig above the gall dies off prematurely: Rabdophaga viminalis

35a Malformation as on S. triandra: Rabdophaga purpureaperda

35b Galls hardly visible from the outside, only on young shoots, predominantly situated close to buds; chambers distinctly isolated. Larvae in a shallow, oblong-oval depression of the sapwood; galls with preformed exit hole, each containing a single larva. The damage appears as “shot holes”: Rabdophaga justini

36a Axis close to the bud of the usually inconspicuously shortened shoot, swollen on one side or on all sides. Larvae with distinct head capsule and legs => 38

36b Axis below the sometimes slightly enlarged, usually not opening buds swollen on one side or on all sides. Larvae without contrasting head capsule and legs => 37

37a Axis with several swellings, sometimes situated below a galled bud. Internodes sometimes stunted; occasionally ± arched or bent in- and outwards. Each gall containing a single pale red larva, usually at the bud base. S. aurita, caprea, cinerea, purpurea, silesiaca: Rabdophaga pulvini

37b Similar malformations on S. purpurea. The exit hole is always situated at the base of the bud pad: Rabdophaga insignis

38a Young shoots below the often hardly changed bud swollen on one side hemispherical to bulb-like. Containing a, whitish to yellowish, brown-headed caterpillar. S. viminalis: Euura (Euura) subgemma

38b Shoots swollen on all sides, ± oblong-oval, up to about 10–15 x 6–8 mm, usually on previous year shoots. In the pith a pale to greenish-yellow caterpillar with dark head capsule: Cydia servillana

B. Malformation of complete shoot systems or galls on shoots or on lateral buds

1a The malformations do not, or only to a limited extent, expand over different organs of ± extensive shoots => 2

1b The malformations, only a few mm long to very extensive, many cm long malformations on terminal and lateral shoots or catkins, often associated with excessive branching and leafiness; “wirrzöpfe” (witches’ brooms). Frequent on many narrow-leafed willows, rarer and usually less luxurious on many other willows: Many gall mite species

= Sometimes witches’ broom-like malformations are caused by fungi and bear fruiting bodies.

2a Galls on closed, slightly developed, ± disfigured vegetative, usually lateral buds; sometimes encroaching into the neighbouring stem tissue or into the base of the protective bud scales => 17

2b Malformations of distinctly opened buds; outer parts of complete galls often ± open; on shoot tips or lateral buds => 3

3a Galls usually only up to 10 mm long, often smaller, predominantly on the lateral buds, but also on terminal buds => 11

3b Malformations terminally on main- and lateral shoots, usually over 10 mm long or wide, often conspicuous => 4

4a Leaves densely clustered because of shortening of the shoot axis, usually sessile; also the outer ones ± shortened and broadened; rosette-, cone- or tuft-like arrangement; inner gall leaves scale-shaped elongated, “willow roses” => 6

4b Leaves on the tip of the shoots rolled-in forming slender, erect, spindle-shaped galls => 5

5a The leaves form a slender, cone-shaped spindle-like tapering tuft above, swollen below, leaf blades basally glabrous or indistinctly pubescent and remain curled, folded and crinkled. The growth of the shoot is stopped and side shoots develop. Several to many orange-red larvae. On many narrow-leaved willows: Rabdophaga terminalis

5b Occasionally similar, usually more compact, shorter galls with conspicuous pubescence, predominantly on broad-leaved willows: Rabdophaga iteobia

6a Galls cone- or tuft-like, outer leaves not unfolding, except for the very tip => 9

6b The outer rosette leaves enclose the inner part of the gall which is broad funnel- or plate-like => 7

7a Outer leaves flat, plate-like, splayed out. Galls usually conspicuous, often much larger than 15 mm; with only one gall chamber situated on the thickened shoot tip or several larvae outside the bud => 8

7b Outer rosette leaves ± abruptly splayed out. Galled buds are also present in the terminal bud, and in the axils of several neighbouring leaves. Petioles are severely stunted and swollen, as are the bases of the midrib and the axis. Parts of the affected bud change into elongated, pale, later on browned scales, which contain an elongated oval larval chamber in the middle with a single cream-coloured, later orange-yellow to red larva. S. aurita, cinerea, caprea, and hybrids: Rabdophaga clavifex

8a Rosette uniform, often dense, with many sessile leaves, strongly widened at their base, rapidly shortened towards the inside, externally normally pubescent. Centrally between the inner leaves are single, pale-, later on orange-red larvae. Salix spp.: Rabdophaga rosaria

8b Galls often distinctly biarticulate. An up to about 10 mm long, ± bud-like converging, loose, inner rosette is surrounded by3‒6 sessile expanded leaves, which are shortened and widened only in their basal half. All leaf blades heavily white pubescent at their base. Between the parts are several yellow, sometimes reddish tinged larvae. S. triandra: Rabdophaga heterobia

9a Galls ± densely tuft-like, about 10‒15 mm long => 10

9b Galls usually more clear-cut. The distinctly shortened and widened leaves form a blunt cone, about 20‒30 mm broad, resembling a larch cone. Containing a pale red larva. S. purpurea: Rabdophaga rosaria

10a Rosette ± cone- to spindle-shaped, about 10‒15 mm long and 4‒6 mm wide, often ± silver-white pubescent. Containing a single yellow-red larva. S. repens, aurita x repens and other close hybrids: Rabdophaga jaapi

10b Tuft about 10‒15 mm long, strongly pubescent, often only bud-like, compact, ± bulging, oblong, rarely rotund-oval. Tips of leaves occasionally bent outwards. Containing several orange-red larvae. S. aurita, caprea, cinerea, glauca, repens: Rabdophaga iteobia

11a Galls caused by mites; lacking central cavity => 15

11b Galls with central cavity, containing midge larvae => 12

12a Galls oblong. The free ends of the scale-like leaves are brownish => 14

12b Galls similar but greened, especially before overwintering, partially resembling opening buds, or tuft-like, sometimes almost rosettes => 13

12c Little rosette gall, 3‒5 mm across, in a leaf axil. The full grown larvae do not have a sternal spatula, which is very unusual within the genus Rabdophaga. S. aurita, cinerea: Rabdophaga rosariella

13a Several lateral buds on young twigs disfigured into cabbage-like rosettes up to about 10 mm long. Outer leaves conspicuously haired at base. Galls containing single or several orange-yellow larvae, which are free-living between the parts. S. triandra and possibly other willows: Rabdophaga heterobia

13b Similar galls on S. cinerea: Rabdophaga terminalis

13c Lateral buds disfigured into a short, up to 5 mm wide ± splayed green sparsely-leafed green rosette. Between the inner, converging, scale-like leaves is a single larva. S. aurita, caprea, cinerea: Rabdophaga pulvini

13d A few leaves of a severely stunted apical bud remain rolled together, forming a slender spindle-shaped erect gall usually smaller than 8 mm. Between the two relatively large inner leaves is a single red larva. S. aurita, caprea, purpurea, repens and probably other willows: Dasineura minoterminalis

14a On S. repens. Buds swollen, apical part elongated. Usually the galls are separated by the tips of several scale-like, sometimes slightly spreading, haired or glabrous leaves; the gall base may variously encroach into the neighbouring stem part. Inside is a single larva: Rabdophaga repentiperda

14b In analogous, but still insufficiently discriminated galls on S. aurita, caprea, cinerea the larvae of the following gall midges develop: Rabdophaga clavifex and/ or Rabdophaga pulvini

15a Malformations on ± unfolded buds, with conspicuous abnormal pubescence => 16

15b Buds transformed into rosettes up to 8 mm long, glabrous or ± normally pubescent. S. aegyptiaca, aurita, babylonica, caprea, elaeagnos: Aculus gemmarum

15c More or less bud-like apical rosette, not excessively pubescent, usually less than 10 mm long. Salix spp.: Stenacis triradiata

16a Terminal shoots and sometimes also the ± unfolded laterals with buds markedly stunted, densely covered with almost white-felt-like leaflets, screw-like crowded, but not in rosettes. S. aurita, caprea, cinerea, repens: Aculus gemmarum

16b Dense, rotund, up to 8 mm long, ± strongly pubescent, bud-like leaf-rosettes on the tip of ± unfolded shoots. From the leaf axils develop many, short pubescent, severely stunted leaflets, their bases widened, bladder-like arched upwards or ± hood-like disfigured. S. herbacea: Unidentified gall mite

17a Apart from the clearly or only slightly disfigured buds, the leaf pads or neighbouring parts may be swollen. Especially midge galls => 19

17b Gall formation mainly of the bud. Galls caused by larvae with legs and distinct head capsules. Vacated galls contain frass. Sawfly galls => 18

18a Buds elongated, up to 13 mm long, forming horny, reddish tubes tapering to the tip which is open when mature; containing orange larva at the base. S. repens: Rabdophaga repenticornua

18b Buds not opening; swollen up to twice the normal size, not otherwise disfigured. Drying after departure of the solitary, yellow-green, brown-headed caterpillars. Galls on osiers and sallows or on trees and large shrubs with narrow acuminate leaves. On S. aurita, caprea, cinerea: Euura (Euura) mucronata

18c Following sawflies are distinguished, among other characteristics, by very narrow host ranges. Galls and larvae similar.

a On S. daphnoides: Euura (Euura) daphnoidica

b On S. viminalis: Euura (Euura) laeta

18d Galls and larvae similar, but on arctic or alpine shrubs, with rounded or oblong leaves

a On S. foetida, waldsteiniana: Euura (Euura) gemmafoetidae

b On S. helvetica: Euura (Euura) gemmahelveticae

c On S. hastata: Euura (Euura) hastatae

d Galls on S. lapponum: Euura (Euura) lappo

e Galls on S. mielichhoferi, myrsinifolia, phylicifolia: Euura (Euura) myrsinifoliae

f From the outside hardly disfigured buds on S. glauca, lanata: Euura (Euura) lanatae

19a Gall formation includes the neighbouring stem parts and/or leaf pads as well as the ± disfigured bud => 23

19b Gall formation involves only the bud => 20

20a Buds usually distinctly enlarged => 21

20b Buds brownish, slightly thickened; often also ± stunted. Containing a single yellow-red larva. S. aurita, caprea, cinerea: Rabdophaga gemmicola

20c Slender, pod-like gall, 4–5 mm long, at base 2–2.5 mm wide, developed from elongated bud scale, tip rounded and deflected from twig axis; larval chamber may reach the woody part of twig. S. aurita, caprea: Rabdophaga palliumparens

20d Inconspicuous bud gall, without involvement of sapwood. Bud scale covers incompletely the small elongated and slightly deflected, distinctly reduced developing young leaves. The pupa emerges via the tip of the bud, leaving its pupal case attached for a while. S. purpurea: Rabdophaga lindhardti

20e Similar lateral bud gall, leaf pad slightly thickened, if several buds are infected, the internodes may be shortened and slightly distorted. S. viminalis: Rabdophaga vigemmae

21a Galled buds without abnormal pubescence => 22

21b S. repens incl. subsp. rosmarinifolia. Infected leaf buds slightly enlarged, often densely pubescent. Containing a single orange larva. Rabdophaga repenticola

22a Bud greenish, sometimes conspicuously elongated and/or strongly thickened, up to 8 mm long, however, usually slender spindle-shaped. Containing a single red larva. S. aurita, caprea, cinerea: Rabdophaga gemmicola

22b Bud slightly elongated, narrowed-egg-shaped, consisting of scale-like brownish leaves often with free apical part. Containing a single larva in the central or even upper part of the bud. S. aurita, caprea, cinerea, triandra: Rabdophaga pulvini

23a Apart from the ± disfigured bud, the shoot axis is often clearly swollen and sometimes also the leaf bases are thickened => 25

23b The often inconspicuous gall formation includes the bud and the only weakly thickened leaf pad => 24

24a Buds rather short, rotund, thick; the shortened bud scales are dull. Bud pad weakly thickened. Containing a pale yellow larva. S. aurita: Unidentified gall midge

24b Buds about 2‒3 times as long as normal, cone-shaped; leaf-, bud pad markedly thickened. Containing a single larva. S. aurita: Rabdophaga sp.

25a Galls caused by midge larvae which lack a distinct head capsule or mandibles => 26

25b Gall often strongly swollen below the ± thickened bud. Larva up to 7 mm long, whitish or yellowish, with brown head capsule. Solitary, feeding below and into the bud. S. viminalis: Euura (Euura) subgemma

26a Disfigured buds lack conspicuous pubescence => 27

26b One or usually several, abnormal pubescent buds, slightly swollen like the shoot tip to which they belong. Each bud containing a single red larva. S. aurita, caprea, cinerea, myrsinifolia: Rabdophaga clavifex

27a Leaf pads and the often bent or stunted axis clearly swollen => 28

27b Bud shortened, ± cone-shaped swollen. Bud base often slightly thickened. Axis, especially below the bud dying, ± swollen over a length of about 10 mm. Containing a single yellow-red larva. S. aurita, ? repens: Rabdophaga karschi

28a Shoot axis usually not distinctly shortened, sometimes bent => 29

28b Shoot axis locally often distinctly shortened. Buds weakly thickened. Base swollen. Containing a single larva. S. alba, caprea, lapponum, purpurea: Unidentified gall midge(s)

29a Shoot axis close to the bud as well as leaf pad distinctly swollen. Bud often slightly shortened, ± greened, conical. Sometimes several galls on the occasionally ± bent shoot. A pale red larva inside the bud. The midge emerges from the gall by passing through the bud. S. aurita, caprea, cinerea, ? purpurea, silesiaca: Rabdophaga pulvini

29b In similar, up to now insufficiently distinct galls, on S. purpurea: Rabdophaga insignis

29c On S. aurita and occasionally other willows: Rabdophaga viminalis

29d Galls from the outside ± similar, below the bud a conspicuous, one-sided oval to elongate club-shaped large-chambered swelling; leaf pad usually distinctly thickened. Containing a yellow larva in the stem part. Before emerging the pupa perforates the bark of the swelling. S. alba, x fragilis, viminalis: Rabdophaga albipennis

29e Yellow midge larvae live in stunted leaf buds. S. alba, viminalis: Rabdophaga deletrix

C. Galls on leaf blades, veins or petioles of one or more leaves

1a Malformations caused by animals, or by fungi which sporulate inside the galls => 3

1b Malformations caused by fungi which sporulate on all green parts. The sori are numerous usually, and arranged in small groups of yellowish to violet-margined rotund sori, predominantly on the underside => 2

= The sac fungus Rhytisma salicinum develops in expanded deep black crusts on the leaf upperside of sallows and occasionally on narrow-leafed willows. These are not true galls

2a Fungus develops all spore forms on the same host. Aecia, unlike uredinia, lacking paraphyses. S. triandra, pentandra and related hybrids: Melampsora amygdalinae

2b Fungus host-alternating or occasionally facultatively without alternation of host; perennially developing uredomycelium on willows. This mycelium develops initially in spring in gall-like malformations, which sometimes are strewn with orange-coloured uredinia possessing paraphyses. Salix spp.: Melampsora salicina

= Mycetophagous very frequent gall midge: Mycodiplosis melampsorae

2c Subsequently reported fungi and host combinations have been recorded on important host species and forms.The records are mainly based on experimental studies. The fungi mainly belong to the Melampsora epitea species complex

3a Malformations of various shape, involving entire leaf blades of several terminal leaves and caused by aphids, psyllids, froghoppers or thrips => 50

3b Galls distinctly defined; with relatively constant shape => 4

4a Galls on petiole or on the main leaf venation => 39

4b Galls on the leaf blades => 5

5a Malformations of the leaf margin => 27

5b Galls on other parts of the leaf blade => 6

6a Galls of various shape; developing on all sides, closed or with narrow opening, opening to a large extent closed by hairs => 10

6b Galls not closed on all sides, fold-, groove- or pouch-like => 7

7a Leaf blade often with several open groove- or pouch-like protrusions on underside => 9

7b Leaf blade folded upwards over the curved midrib => 8

8a Midrib of single or of several terminal leaves ± bent sickle-shaped downwards at the base of the leaf blade. Neighbouring parts of the leaf blade almost pod- or mussel-like, folded upwards, swollen, usually pale green. The cavities contain several reddish larvae. On several narrow-leafed willows: Rabdophaga terminalis

8b Leaf blade folded upwards over the ± screw-like twisted midrib, abnormally pubescent. Venation ± swollen at the place of infestation. Larvae free living at the base of the fold. S. caprea: Rabdophaga iteobia

9a Protrusions small, groove-shaped, glabrous. Contain a flat wax-margined froth-covered nymph. S. alba: Bactericera albiventris

= It is not sufficiently elucidated whether other psyllids occurring on willows cause similar, or differently shaped, gall-like deformations.

9b Protrusions several mm long, the inside abnormally pubescent. S. daphnoides: Aceria effusa

= Mite galls also occur occasionally on other willows, e.g., S. aurita, pentandra, purpurea, which cause flat, bulging upward protrusions in the leaf blades, rotund, the inside with bumps and ± pubescent, sometimes in various ways coalescing and arching

10a Galls in mature stage over 5 mm long; completely closed on all sides. Sawfly galls => 14

10b Galls wart-, nodule-shaped or globular, about 0.5–3 mm across, with narrow opening => 11

11a Gall distinctly protruding on both sides of leaf => 13

11b Gall predominantly on only one side of leaf => 12

12a Galls wart-like, closed, hardly 1 mm across, yellowish translucent; only on basal stem parts or underside of leaves. S. caprea, purpurea: Synchytrium aureum

12b Similar but orange-red small warts on S. repens: Cause unknown – ? fungus, ? alga

12c Galls nodule-shaped, about 0.5–2 (4) mm high, greenish or reddish coloured, one-sided, usually protruding upwards, often many per leaf blade; polymorph. The outside glabrous or pubescent; inner wall glabrous, ± pubescent or provided with variously shaped protrusions. Opening on leaf underside mostly closed by hairs. Salix spp.: different species of gall mites:

a Aculus tetanothrix s. lat. Predominantly on narrow-leafed willows but also on sallows

b Aculus laevis. Gall mite predominantly living on S. aurita, caprea, cinerea and hybrids.

c Aceria iteina s. lat. Galls usually conspicuous, up to 3 mm across. Inner wall with many multicellular proliferations; predominantly on S. aurita, caprea, cinerea and relatives.

d Aculus truncatus. Mainly in nodular galls on S. purpurea, but also in several other willows, e.g., S. alba, caprea. Furthermore in rolls of the leaf margin.

e Aculus myrsinites. Recorded on S. alba, myrsinites, phylicifolia, polaris, reticulata from Fennoscandia.

13a Outgrowths with tough, woody wall. Galls rotund, 1.5–2 mm or more across, ± equally protruding on both leaf sides; initially greenish-yellow, yellow later on; occasionally violet-tinged on top; one-chambered; the underside with narrow, round exit hole. Usually many on leaves and often coalescing. Each gall containing a single, initially white, later orange and eventually red larva. Predominantly on sallows and several Nordic-alpine species, also recorded on S. myrsinifolia, viminalis, etc.: Iteomyia capreae

13b Larvae develop in parenchyma under the epidermis. S. aurita; not true galls: Dasineura pseudococcus

13c Nodular, not woody, about 0.5–2 mm across, sometimes reddened galls, often many and protruding ± equally on both leaf sides. Depending on the host, glabrous on the outside or especially on the underside ± strongly pubescent. Wall inside glabrous, haired, or provided with variously shaped outgrowths. Salix spp.: various species of gall mites

14a Galls ± globular, more rarely pear- to barrel-shaped, higher than wide in the latter case. Spongy when young, thick-walled. Predominantly on one side of the leaf, often the underside, the opposite side shows a flat arched disc => 20

14b Galls approximately emerging to the same extent on both sides of leaf => 15

15a Galls initially thick-walled, irregular, rotund or elliptical => 17

15b Galls oblong bulging or bladder-shaped and thin-walled => 16

16a Galls elongated bulging or cylindrically grooved; often situated in both leaf halves in pairs parallel to midrib; strongly protruding on the upperside -, not so on the underside; initially dark green, paler later on to brownish or reddish, the underside yellowish. Containing a single larva. Galls on S. purpurea, viminalis x purpurea: Euura (Pontania) virilis

= Further identification of sawflies according to host plant associations:

a Galls on S. lapponum: Euura (Pontania) dolichura

b Galls on S. elaeagnos: Euura (Pontania) elaeagnocola

c Galls on S. glauca: Euura (Pontania) glaucae

d Galls on S. helvetica: Euura (Pontania) helveticae

e Galls on S. mielichhoferi, myrsinifolia: Euura (Pontania) nigricantis

16b Gall ± bean-shaped, relatively thin-walled; pale to yellow-green, up to 20 mm long and 15 mm wide; galls transected horizontally by the leaf blade, often taking up half the width of the leaf and extending conspicuously. Containing a single dull yellow-green larva with glossy, partially yellow-, partially red-brown head capsule. S. purpurea: Euura (Pontania) vesicator

= In similar galls on S. phylicifolia develop the grey-green, brown-headed larvae of Euura (Pontania) pustulator

17a Galls broad elliptical or kidney-shaped, 7–10 mm long and 4–5 mm wide. Wall initially succulent, up to a thin outer wall excavated laterally. Solitary or with several between midrib and leaf margin => 18

17b Galls ± globular, thick-walled initially, about 7–10 mm long, green or ± reddened. Protruding on upper side on up to half or a third of the leaf blade. Galls recorded from various Salix spp. (arbuscula, breviserrata, foetida, helvetica, herbacea, lapponum, polaris, retusa, waldsteiniana), belonging to different host plant-specific species of Euura (Pontania). Larvae of most species with many small black or fuscous-black dots, arranged in rows. Containing a single greenish- to grey-brown larva with lateral rows of black dots: Euura arbusculae

= Further identification of sawflies according to host plant associations:

a In similar galls on S. breviserrata: Euura (Pontania) breviserratae

b In similar galls on S. foetida, waldsteiniana: Euura (Pontania) foetidae

c In similar galls on S. herbacea, polaris: Euura (Pontania) herbaceae

d Larvae missing small black or fuscous-black dots, also in similar galls on S. herbacea, polaris and hybrids: Euura (Pontania) aquilonis

e In similar galls on S. lapponum: Euura (Pontania) crassipes

f In similar galls on S. helvetica: Euura (Pontania) maculosa

g In similar galls on S. retusa: Euura (Pontania) retusae

18a Galls on narrow-leafed willows, often several arranged in rows per leaf blade => 19

18b Galls on S. appendiculata, aurita, caprea, cinerea, foetida, waldsteiniana and related forms, and hybrids. Containing a single sawfly larva: Euura (Pontania) bridgmanii

19a On S. triandra and forms; galls predominantly solitary on both sides of the midrib. Each containing a single larva: Euura (Pontania) triandrae

19b On S. alba, x fragilis and their hybrids. Galls usually in rows on both sides of the midrib, with though, thick wall, up to 8 mm long. Containing a single yellow-green larva with black-brown head capsule: Euura (Pontania) proxima

20a Galls about (5) 6–12 mm size => 21

20b Galls about 4–6 mm long, rotund- pea-shape, glabrous, often strongly reddened, sometimes irregular; sometimes occupying the whole leaf blade; on the upper side recognizable as a hardly arched disc. Contain a dirty grey-green larva. S. reticulata: Euura (Pontania) reticulatae

20c Globular pea-sized leaf gall, equally protruding at either side. S. alpina: Euura (Pontania) alpinae

21a Mature galls glabrous or ± loosely to densely short-haired => 23

21b Mature galls with long or short dense, felt-like pubescence => 22

22a Galls densely felt-like, white to grey pubescent; ± globular or slightly irregularly shaped, attached with broadened base which is recognizable on the upper side as a flat disc; up to 6 (8) mm long, green, yellow or whitish. Containing a single pale yellow larva with a pale brown head. S. elaeagnos: Euura (Pontania) kriechbaumeri

22b Galls more or less long white pubescent; about 6–8 mm long, globular, often whitish or yellow-green, sometimes red marbled, succulent; ± point-shaped attachment. Containing a single greyish larva with a brown head. S. myrsinifolia, including the synonymous forms/subspecies borealis and alpicola: Euura (Pontania) saliciscinereae

22c In felt-like haired galls on S. lapponum, lapponum × phylicifolia: Euura (Pontania) samolad

23a Galls predominantly on narrow-leafed willows or on mostly glabrous broad-leafed willows => 24

23b Galls on S. caprea, cinerea, their forms and close hybrids; depending on locality with a loose or a dense short pubescence, especially during the immature stage; globular or sometimes ± rotund-oval; up to about 6 mm long; greenish to yellow, often reddish tinged, on the upper side of the leaf visible as a flat disc. Containing a single yellowish larva with a yellowish to vitreous pale green head capsule. Euura (Pontania) pedunculi

24a Galls mainly globular, sometimes compact pear-shaped. Usually attached besides the midrib. On the upper side visible as a yellowish or reddish discoloured small disc => 26

24b Galls predominantly egg- or kidney-shaped, glabrous. Top half sometimes subdivided into 2‒3 (4) conical outgrowths => 25

25a Galls egg- to pear-shaped. Containing a single larva. S. phylicifolia, lapponum × phylicifolia: Euura (Pontania) arcticornis

25b Galls broad egg- to pear-shaped, sometimes ending with conical papillae. Containing a single larva. S. purpurea: Euura (Pontania) viminalis

26a On S. repens, rosmarinifolia, incl. subspecies, forms and hybrids. Galls up to about 7 mm long; glabrous to slightly tuberculate; yellowish or sometimes partially to completely pale to dark red. Containing a single whitish-green to pale yellow larva. Head capsule uniformly coloured or slightly brownish, with glossy black eyespots: Euura (Pontania) collactanea

26b On S. lanata. Galls conspicuous, felt-like pubescent, attached on the midrib of the leaf underside; on the upper side visible as distinct, usually reddened small discs. Containing a single larva: Euura glabrifrons

26c On S. acutifolia, daphnoides. Galls rotund, up to 12 mm long. Glabrous on the majority of willows, slightly pubescent on others. Sometimes warty-tuberculate, greenish-yellow to conspicuously reddened, attached on the midrib of the leaf underside; on the upper side visible as distinct, usually reddened small discs. Containing a single pale to yellowish-green with brown head capsule and black eyespots: Euura (Pontania) acutifoliae

26d Galls glabrous, often conspicuously reddened, hardly warty-tuberculate, on S. hastata: Euura (Pontania) hastatavora

26e Galls glabrous, mostly yellowish, hardly warty-tuberculate, on S. ? alpina, foetida, waldsteiniana: Euura (Pontania) foetidatumida

26f Galls glabrous, often conspicuously reddened, normally not warty-tuberculate, on S. myrtilloides: Euura (Pontania) myrtilloidica

26g Galls glabrous, protruding on upperside on up to half or a third of the leaf blade, often conspicuously reddened, normally not warty-tuberculate, on S. myrsinites: Euura (Pontania) myrsiniticola

26h Galls slightly pubescent, yellowish, not warty-tuberculate, on S. glauca, glaucosericea: Euura (Pontania) nivalis

27a Leaf margin folded or loosely to narrowly rolled. Leaf blades sometimes curled and curved => 29

27b Leaf margin serrate, especially with teeth from the side onwards; the separately situated capsules contain eggs. “Procecidia” (oviposition scars, not true galls). The free-living larva feeds on the leaf blade => 28

28a On S. aurita, caprea. Mature larvae green with white side stripes, three transverse rows of black dots per segment. Head greenish-light brown: Arge ustulata

28b On S. pentandra, x fragilis, alba and other narrow-leafed willows: Pristiphora conjugata

28cOn glabrous- or narrow-leafed willows, on indentations of the leaves, usually solitary egg capsules of Pristiphora melanocarpa, P. micronematica and/or Arge enodis

29a Leaf blade deflected downwards, or, without thickening, rolled, sometimes heavily curved and curled. Containing a single larva with a distinct head capsule. The older larvae desert the variously excavated galls and feed, especially at night, on the free leaf margins. Sawfly galls, which are already completely developed before the wasps emerge => 34

29b Leaf margin locally, or over a larger part narrowly, compactly or loosely upwardly- or downwardly rolled, at least locally distinctly thickened. Inside without distinct feeding marks. Galls caused by gall mites or gall midges => 30

30a Leaf rolls down- or upwards, narrow, compact or expanded cylindrical to bulge-like, sometimes strongly curved in and out. Mite galls => 33

30b Loose downward leaf rolls, of various expansion, at least locally with cartilaginous thickening. Midge larvae develop inside the rolls => 31

31a Walls of the irregular leaf rolls strongly thickened, almost brittle => 32

31b Very narrow marginal roll, usually upwards and glabrous, cylindrical, up to 8 mm long, in the middle slightly thickened, narrowing towards the ends, occasionally, slightly bent, often yellowish spotted or discoloured; sometimes several galls coalescing. Each containing a single larva. S. alba, babylonica, triandra, etc.: Aculus magnirostris

32a Leaf margin over large area, often over both leaf halves, rolled downwards. Roll over 20 mm long and composed of several, oblong-cylindical single galls, centrally more strongly thickened, narrow, both ends narrowed, against each other ± distinctly bordered. Only one single yellowish-red larva in each of these pale green, ± yellow or red-spotted swellings. S. viminalis, elaeagnos and close hybrids: Rabdophaga marginemtorquens

32b Shorter galls, 9–12 mm long, the wall usually conspicuously rugose; solitary or occasionally with several coalescing, and ± twisting the leaf blade. Each gall containing a single yellowish larva. Sallows: S. aurita, caprea, cinerea and hybrids: Dasineura auritae

32c Similar galls on S. viminalis: Rabdophaga roskami

33a Narrow, hardly 1 mm wide, narrow, compact, weakly thickened and weakly rugose marginal roll of usually only a smaller part of the leaf, both upwards and downwards. Galls often many on both leaf margins, variously coalescing. On many willows, particularly narrow-leafed ones: Aculus magnirostris

33b Also the causer of nodular galls on many willows has been recorded as a causer of leaf rolls: Aculus tetanothrix

33c Leaf margin about 1‒2 mm wide, narrowly rolled upward or downward, with cartilaginous thickening. Rolls short, nodule-like or elongate and bulging, variously coalescing, or sometimes irregularly curled, bent or variously with nodule-shaped or oblong oval, ± pouch-shaped outgrowths. Often many on both leaf margins; in cases of heavy infestation sometimes simultaneously protruding from both sides of the leaf blades as irregular nodule-, pouch- or bulge-like galls. Several species of gall mites; The following have, been reported:

a Aculus craspedobius

b Aculus tetanothrix

c Aculus truncatus

d Aceria craspedophyes

e Acaphyllisa salicobia

f Aculus myrsinites

34a Larvae living in leaf folds or rolls, usually only one edge of the leaf folded, creating a flat or vaulted cavity for the larva, not distinctly twisted. Leaf folds are induced by multiple ovipositor insertions of the female, restricted to only one half of the leaf blade => 36

34b Larvae living in leaf rolls, usually both edges of the leaf blade rolled downwards, normally distinctly twisted or curled along the longitudinal axis. Leaf rolls are induced by multiple ovipositor insertions of the female, extending on both halves of the leaf blade => 35

35a Leaf blade distinctly twisted along the longitudinal axis. Galls on sallows and montane Salix spp. (S. appendiculata, aurita, caprea, cinerea, helvetica, lapponum, silesiaca), belonging to different host plant-specific species of Euura [previously Phyllocolpa]. Containing a single larva:

a On S. appendiculata: Euura (Phyllocolpa) spirappendiculata

b On S. aurita, cinerea, silesiaca: Euura (Phyllocolpa) leucapsis

c On S. helvetica: Euura (Phyllocolpa) spirhelvetica

d On S. lapponum, ? glauca: Euura (Phyllocolpa) acutiserra

35b Leaf roll, normally both edges of a leaf rolled downwards and forming a curled spiral along the longitudinal axis, creating a very small cavity for the larva. Galls on S. purpurea or phylicifolia. Containing a pale green, dark-headed larva:

a On S. purpurea, mostly apical leaves are rolled down and the whole leaf is curled: Euura (Phyllocolpa) purpureae

b On S. caprea: Euura (Phyllocolpa) cyrnea

c On S. phylicifolia. Older larvae feed on the leaf edge at the top of the gall: Euura (Phyllocolpa) nudipectus

36a Galls predominantly on narrow-leafed willows => 38

36b Galls usually on sallows with strict host association => 37

37a Leaf margin over large distance loosely folded or rolled downwards, creating a vaulted cavity for the larva. Leaf blade sometimes bent but not twisted. Containing a single larva. Mature larvae about 8 (11) mm long, bluish-green to yellowish-brown, with darker dorsal side and glossy deep-yellow to brown head capsule:

a On S. cinerea, ? caprea: Euura (Phyllocolpa)prussica

b On S. aurita, caprea: Euura (Phyllocolpa) leucosticta

c On S. appendiculata: Euura (Phyllocolpa) hubertpschornwalcheri

37b Small fold at the outermost margin of the leaf, creating a very small, flat cavity for the larva, sometimes up to three galls per leaf. Older larvae leave their gall and feed on the leaf edge, leaving behind arch-shaped feeding marks. Containing a single larva. On S. caprea, hastata: Euura (Phyllocolpa) anomaloptera

38a Leaf margin over large distance flatly folded downwards, often sickle-shaped, not thickened and discoloured. Containing a single larva. Galls especially on narrow-leafed Salix spp. (S. alba, daphnoides, x fragilis, glauca, glaucosericea, lapponum, mielichhoferi, myrsinifolia, pentandra, phylicifolia, purpurea), belonging to different host plant-specific species of Euura [= Phyllocolpa]

a Galls on S. alba, babylonica, × fragilis, × rubens, triandra, vitellina: Euura (Phyllocolpa) oblita

b Galls on S. daphnoides, ? acutifolia: Euura (Phyllocolpa) plicadaphnoides

c Galls on S. glauca, glaucosericea, pentandra, phylicifolia. S. myrtilloides, lapponum are additional hosts: Euura (Phyllocolpa) destricta

d Galls on S. lapponum: Euura (Phyllocolpa) plicalapponum

e Galls on S. mielichhoferi, myrsinifolia: Euura (Phyllocolpa) ischnocera

f Galls on S. phylicifolia: Euura (Phyllocolpa) plicaphylicifolia

g Galls on S. purpurea, purpurea × silesiaca: Euura (Phyllocolpa) polita

h Reported from W-Alps and C-Eu, probably on S. retusa, reticulata: Euura (Phyllocolpa) kopelkei

38b Nearly a complete half or often both halves of the leaf blade rolled or folded downwards along the midrib. Larvae up to 10 mm long, pale green. Head-capsule black in immature larvae, pale brown in older larvae, with black fields surrounding the ocelli. Gall containing a single pale-green larva with first black and later pale brown head capsule with black spots around the ocelli. On S. dasyclados, viminalis: Euura (Phyllocolpa) anglica

39a Galls on the midrib or the main side veins; occasionally also on the petioles => 45

39b Galls on the petiole, sometimes encroaching into the midrib or occurring on it => 40

40a Galls usually conspicuous, several mm long, caused by insect larvae => 41

40b On the petiole of S. caprea, arranged in two rows, egg capsules ‘procecidia’ (oviposition scars, not true galls); petiole bulged later on because of regeneration of the tissue: Cladius grandis

41a Galls of the axis with ± broadened base, narrowed towards the leaf blade => 42

41b Galls strongly narrowed towards both ends, ± spindle-shaped, up to 10 mm long and 5 mm broad; occurring at different positions on the petiole above the leaf base, sometimes on the midrib, or, close to it, on the leaf blade. Large central larval chamber. Containing each a single larva. S. alba, babylonica, × blanda as elegantissima × fragilis, x rubens, triandra: Euura (Euura) testaceipes

42a Galls of approximately defined shape, with large central larval chamber. Containing a single larva with distinct head capsule, which excavates the initially thick succulent gall and leaving a crumbled frass => 43

42b Galls varying in size; sometimes with only one, often with several, larval chambers which are always devoid of frass. Containing each a single midge larva, which is initially white, yellow-red later on. Midge living on several willows; of this shape especially on S. aurita, cinerea, elaeagnos: Rabdophaga salicis

43a The galls contain larvae with legs and head capsules which are about as broad as the body => 44

43b Larvae lacking legs; the head-capsule is distinctly smaller than the body width. Galls usually broadest at the base of the petiole, often inconspicuous but provided with slightly conical protrusion. Containing a single larva. Melanapion minimum

44a Base of petiole strongly broadened and enlarged; enveloping the ± swollen and elongated bud; gall gradually narrowed towards the top. Containing a single larva. S. viminalis: Euura (Euura) subgemma

44b Petiole often swollen over all its length. Galls broadest in the basal part, narrowed towards the leaf blade, on short-stalked leaves additionally encroaching into the midrib; with ± notched base mounted on the shoot, about (7) 8‒10 (15) mm long. at base 2‒3 (5) mm wide. A large central larval chamber, sometimes situated more laterally, containing a single whitish-green, brown-headed larva. S. aurita, caprea, lapponum, silesiaca, rarely S. cinerea, atrocinerea: Euura (Euura) venusta

45a Galls ± spindle-shaped, one-chambered => 46

45b Separate galls rotund (1.5) 2‒4 (5) mm across; with tough, woody wall; on both sides of the leaf blade, usually more prominent on the underside, there with small, rotund, central exit hole. Usually several galls coalesce into irregularly margined clusters. The galls are initially discoloured yellow-green, soon brownish-yellow, on the upper side often discoloured reddish. Often on midrib, or the main lateral veins. Each chamber containing an initially white, later on orange-coloured, eventually red larva: Iteomyia major

45c On S. pedicellata, Algeria. On the underside of the leaf, often many subglobular swellings, 2–3 mm across, provided with lateral appendages about 1 mm long, straight or twisted, forming a sort of rosette. Larval chamber large, connected with a central exit hole in the centre of the rosette. At the upper side the gall is visible as a slight depression. Containing a single yellow, partially red larva; North African species. Iteomyia peyerimhoffi

46a Galls smooth-walled; containing larvae without legs or head capsule, midge galls => 47

46b Galls spindle-shaped up to 10 mm long and 5 mm thick; wall sometimes with little protuberances. Usually more strongly developed on the underside; leaf blade sometimes curved longitudinally. Containing a single larva. S. alba, babylonica, × blanda as elegantissima × fragilis, x rubens, triandra: Euura (Euura) testaceipes

47 Galls situated on the midrib, especially on the underside, distinctly protruding, up to 5 (7) mm long and 2‒3 (4) mm broad => 49

47b Galls inconspicuous, about (2) 3 mm long and 1 mm broad, on the underside => 48

48a Basal third part of midrib of the otherwise normal leaf blade with slender spindle-shaped swelling, about 4 mm long and 1.5 mm broad, which is only developed on the underside of the leaf blade and on one side of the midrib. Containing a single larva. S. cinerea: Rabdophaga sp.

48b Similar gall in the midrib of otherwise normally developed leaves of S. purpurea. Containing a single larva: Rabdophaga justini

49a Galls slender; especially distinctly protruding on the underside; one-chambered; 3‒5 (7) mm long and 2‒3 mm wide. On the midrib and sometimes on the main lateral veins, as well as usually only simultaneously also on the petioles. The neighbouring leaf blade may be locally bulged or otherwise disfigured. Sometimes several, clearly separated galls per leaf. Each gall containing a single reddish-yellow larva. Especially on S. alba, babylonica, elaeagnos, x fragilis, grandifolia, nigra, pentandra, phylicifolia, purpurea, sometimes on sallows, etc.: Rabdophaga nervorum

49b Galls up to 3 mm long, broad acuminated, egg-shaped, thick-walled, yellowish, glabrous. Containing a single whitish, later on orange-red larva. S. aurita, cinerea, elaeagnos: Rabdophaga salicis

50a Leaf margins rolled or folded downwards; leaf blade ± arched; usually several terminal leaves disfigured in a similar way. Galls caused by aphids, froghoppers or psylli => 51

50b Young leaves ± stunted; the margins slightly bent downwards; curled and discoloured. On S. alba, aurita, babylonica, repens, x rubra and relatives. Mycterothrips salicis

50c Similar malformations on S. x fragilis and other willows might be caused by Thrips viminalis

51a Malformations caused by aphids or spittlebugs => 52

51b Younger leaves distinctly rolled, ± curved. On the undersides of the leaves and in the leaf rolls are many flat larvae. S. aurita, etc.: Cacopsylla nigrita

51c Malformations of leaves of S. aurita, caprea, elaeagnos: Cacopsylla ambigua

51d Similar malformations, also on leaves of S. aurita, caprea: Cacopsylla saliceti

52a Malformations caused by aphids => 53

52b Curling of leaves and stunting of shoots caused by froth-covered nymphs of the polyphagous Philaenus spumarius

53a Aphids with long siphunculi => 54

53b Siphunculi very short; shorter than the width of the base. Leaf blade deflected downwards; the margin touching the underside. S. caprea: Chaitophorus salicti

54a Aphid 2 mm across; green marbled; with very long, slender, pale green siphunculi with brown tips. Antennae a little longer than half the body length. Already in 6‒7 fox red males appear in the colonies. Shoots often distinctly stunted; leaves arched and rolled or folded. On many narrow- and broad-leafed willows. Aphis farinosa

54b Aphid 2 mm long, bright green; the siphunculi of the same colour, rather long, slightly swollen. With a tongue-shaped bump over the cauda. Antennae shorter than half the body length. Young shoots disfigured. Leaves rolled. S. aurita, caprea, etc.: Cavariella pastinacae

D. Malformations on flowers (catkins)

0a Malformations on all parts of catkins, or predominantly on spindle => 3

0b Ovaries or stamens of the catkins often conspicuously elongated; other organs, without particularly distinct involvement of the midrib, disfigured to a ± substantial extent => 2

2a Stamens of flowers lengthened and thickened; usually in the lower, major, part densely woolly pubescent; partially over-topped by ± stalked, reduced anthers. Diameter of catkin in the infected, usually apical, part conspicuously enlarged. Larvae orange-red. Apparently occurring only on S. triandra and close relatives and hybrids: Rabdophaga heterobia

2b Up to 3.5 mm enlarged. densely crowded, basally thickened, ± disfigured, compact and ± reddened ovaria in stunted female catkins. S. lapponum, purpurea, reticulata: Rabdophaga cf. amenticola

3a Malformation primarily of the rachis of the catkin, with an expanded tunnel inside. Usually stunted, not a true gall => 6

3b Midrib lacking a cavity => 4

4a Malformations with conspicuous fungal sori => 5

4b Malformations caused by gall midges. Catkins partially disfigured, to varied extent. Stamens lengthened and thickened, with dense, white, woolly pubescence. Galled part of catkins, usually apically, appearing strongly thickened. Containing several orange-red larvae. S. triandra: Rabdophaga heterobia

5a Sori orange-coloured. Infected rachis ± swollen and convex if infected on one side. Infected bracts ± swollen, disfigured, persisting => 6

5b Sori almost only on the female catkins; pale or dark flesh red. Midrib and fruit stalk infected over all their length. Conidia ± compact during dry weather, gelatinous under damp conditions and swollen in that case up to twice its dry size. Salix spp.: different species of Fusamen, recorded are F. amentorum, fructigenum, lapponum

5c Similar infection of the female catkins (axis of the catkin and pedicels), producing a red spore mass that swells in humid weather and then is gelatinous. Salix spp.: different species of Gloeosporium, recorded are G. deformans, oelandicum

6a On catkins of S. triandra in early spring. Infected catkins remain attached longer. Aecia without paraphyses: Melampsora amygdalinae

6b On catkins of S. pentandra, triandra, and forms and late flowering hybrids, during summer. Uredinia with paraphyses: Melampsora amygdalinae

7a Larvae smaller than 1 cm. In female, more rarely in male catkins. Midrib stunted, bent, occasionally appearing thickened. Development of flowers ± stunted; according to some observations sometimes partially greened. Contain a larva with a small head. S. alba, aurita, caprea, cinerea, purpurea, etc.: Dorytomus taeniatus

7b Damage ± similar to the previous one. Larvae growing larger than 1 cm; with distinct broad head. Usually on S. caprea, occasionally on other willows: Unidentified lepidopteran

mod 9.xi.2019