Dichotomous table for gallers on Fagus

by Hans Roskam

1a On stems or branches => 2

1b On buds or leaves => 6

2a Witches’ broom-like malformations on branches and twigs => 3

2b Smaller nodules or larger cancer-like proliferations in the bark of stems and branches => 4

3a Smaller witches’ broom, about 4–5 cm across. F. sylvatica: Inducer unidentified

3b More frequently much larger witches’ brooms occur on beech; again
Inducer unidentified

= Viscum album is doubtful on beech; all records involve confusion with witches’ brooms

4a Extensive cancer formations caused by fungi, predominantly on older stems. F. sylvatica: Neonectria ditissima and/or Neonectria coccinea

4b Lenticular or pock-shaped nodules in the bark of young shoots, which may secondarily partially develop into cancer-like formations => 5

5a Young, already woody stems with swellings, up to 3 mm thick, partially arranged in rows, up to more than 10 cm long, predominantly on the underside of lateral shoots. The bark tears open later on in a lateral direction, developing a loose succulent wound callus or also dries out ± soon. Similarly on branches and stems. F. sylvatica: Lachnus pallipes

5b On the bark of younger axial parts somewhat lenticular, shallow- to nodular swellings, which rupture the cork layer later on and cause cancer-like proliferations. F. sylvatica: Cryptococcus fagisuga

6a On leaves => 8

6b On buds => 7

7a Buds not opening, up to 30 mm long and 12 mm wide, or developing into a short, stunted, shoot. All new parts of the unfolding bud severely stunted. Leaves folded, like the usually undulate venation, densely covered with silver-grey hairs. F. sylvatica, x taurica: Acalitus stenaspis

7b Similar malformation; between the sometimes slightly thickened leaves, which remain small and folded upwards, several whitish to grey-yellow jumping, glossy larvae. F. sylvatica: Contarinia fagi

= Inquiline non jumping dull larvae in galls of Contarinia fagi: Macrolabis fagicola

8a Galls on the leaf blade, not exclusively on the margin => 9

8b Narrow and tight leaf roll, shorter than or often as long as leaf blade; with short, stiff, acuminate hairs inside. F. sylvatica, x taurica: Acalitus stenaspis

9a Galls of a distinctive shape, on or in the leaf blades => 15

9b Leaf folds, -curls or erinea of various kinds on the leaf blad => 10

10a Leaf curls or flat erinea => 12

10b Malformations associated with leaf folds => 11

11a Leaf blade with single or several, yellow- to reddish discoloured, ± pod-like, thickened, glabrous folds along a ridge-like downwardly protruding lateral vein. Usually initiated on the midrib, on small leaves extending to the margin. Containing 2–3 reddish larvae. F. sylvatica: Phegomyia fagicola

11b Hypertrophied, yellowish to reddish, downward folds of the leaf blade. Gall as well as inducer relatively unknown, larvae gregarious. F. sylvatica: Mikiola cristata

11c Whole leaf blade or apical segment remaining folded. Sites of infestation markedly pubescent, ± thickened and sometimes reddened; in case of weak infestation curled later on. F. sylvatica: Acalitus plicans

12a Erinea => 14

12b Curls => 13

13a Spool- to tube-shaped malformation on the deflected leaf underside caused by many bluish-white aphids, covered with woolly wax exudations; malformation variously discoloured and curled. F. orientalis, sylvatica: Phyllaphis fagi

13b Curl associated with additional curling and arching of stunted leaves. F. sylvatica: Acalitus plicans

14a Linear elongated erineum along the side veins; hairs short club-shaped. F. sylvatica, x taurica: Aceria nervisequa

14b Erinea not associated with the veins, almost exclusively on underside of leaf and on several segments (between lateral veins). F. sylvatica, x taurica: Aceria nervisequa

= In the modern literature no distinction is made between the erinea that strictly follow the veins, and the more or less rounded erinea that are independent of the leaf venation. In the older literature the latter is named Aceria maculifer; possibly also an inquiline of galls made by Aceria nervisequa

15a Glabrous galls of mostly constant shape in or on the leaf blade => 17

15b Heavily pubescent galls on the leaf upperside => 16

16a Gall slender, obtuse-cylindrical or barrel-shaped, leathery-woody, up to 3 (4) mm long, densely covered with brownish hairs. Containing a single white larva. F. orientalis, sylvatica: Hartigiola annulipes

16b Gall situated close to the midrib, rotund, on the underside flat disc-shaped, on the upper side ± globular, about 1 mm (up to 1.5 mm) large. With red-brown hairs at the tip, soon deflected, with their ends contacting the leaf, hence enveloping the gall. Narrow opening on the underside, containing a single larva. F. sylvatica: Unidentified gall midge

17a Galls pouch- to pustule-shaped or groove-like => 19

17b Galls acuminated, egg-shaped or blunt cylindrical, always on the venation, often in a corner between two main veins => 18

18a Galls slim cylindrical, up to 4 (5) mm long and 1.5 mm wide, tough-walled, initially pale green, brown later on; underside slightly arched. Containing a single larva. F. orientalis, sylvatica: Hartigiola annulipes

18b Galls alongside the venation, often on the midrib, acuminated, egg-shaped, pale green or often ± reddened; underside slightly arched, thick-walled woody, with large larval chamber. Larva white, solitary. F. orientalis, sylvatica, x taurica: Mikiola fagi

18c On F. orientalis, resembles the gall of Mikiola fagi, but has a blunt tip . Larva orange, solitary: Mikiola orientalis

19a Pustule- or groove-shaped galls, various locations on the leaf blade => 20

19b Slightly bumpy, ± discoloured protrusions in the vein axils on the midrib, rarely also on the main side veins, with hair tufts on the underside. F. sylvatica: Monochetus sulcatus

20a Rotund centrally non-umbicular galls, with nodular protrusions, often hardly 1 mm long, predominantly on the underside; usually surrounded by a yellowish to reddish, sometimes marginally more intensively discoloured border, up to 3 (4) mm wide, later yellowing. Containing a single white larva. F. sylvatica: Unidentified gall midge

20b Furthermore on leaves of developing spring- and lammas shoots on indefinite places single or several, inconspicuous arched parenchyma galls, about 1.5–2 mm wide, similarly on both leaf sides containing a single white larva. F. sylvatica: Hartigiola annulipes

20c Rotund, about 0.5 mm wide grooves on the leaf underside, corresponding, initially with hardly discoloured, later on anaemic protrusions on the upperside, soon surrounded by a yellowing, later on pale browning border, up to 3 mm wide. F. sylvatica: Unidentified gall midge

mod 30.iii.2020