gallers on Corylus

1a On above-ground parts => 2

1b Nodules on roots. Corylus spp.: Subanguina radicicola

2a On catkins or fruits => 13

2b On vegetative organs => 3

3a On leaves => 9

3b On buds, young shoots or older branches => 4

4a On buds and young shoots => 7

4b On woody parts => 5

5a Cancers or witches’ brooms => 6

5b Thicker branches or stems with ± distinct nodular to club-shaped swellings. Corylus cornuta: Viscum album

6a Bark of woody parts with cancer-like proliferations. C. avellana: Neonectria ditissima

6b Small witches’ broom-like malformations. C. avellana: Cause unknown – ? gall mite

7a On young shoots => 8

7b Buds swollen, rotund, up to 10 mm long. Scales enlarged, thickened like the outer leaf primordia and inside with tubercular proliferations. C. americana, avellana, colurna, maxima: Phytoptus avellanae

7c Enlarged globular bud. Contains caterpillar in a large central cavity. C. avellana: Unidentified lepidopteran

8a Young shoots stunted. Usually leaves of several buds per twig are disfigured; their leaf blades curled, folded, partially rolled and more densely pubescent. C. avellana: Cecidophyopsis vermiformis

8b Young shoot with local, pustule-shaped swellings; apical part of shoot ring-barked, withering and soon breaking off. C. avellana, colurna: Oberea linearis

9a Leaves folded or curled => 11

9b Leaf blades with flat, rotund archings => 10

10a Flat upward proliferations, surrounded by a 6 mm long, slightly discoloured and thickened area; the underside cavity contains a single vitreous to whitish larva. C. avellana, maxima: Mikomya coryli

10b Leaf blade with parenchyma galls about 3–5 mm wide, weakly protruding on both sides, initially hardly discoloured. Containing a single larva. C. avellana, colurna, maxima: ? Arnoldiola tympanifex

11a Leaf blade curled => 12

11b Leaf blade folded and crumpled; at base, with white, jumping larvae. C. avellana: Contarinia cybelae

12a Younger leaves, if heavily infected, folded and curled. With green, rarely reddish, ca. 2.5 mm long aphids on the underside. C. avellana, colurna, maxima: Corylobium avellanae

12b Younger leaves, if heavily infested, with discoloured bulges. With pale yellow to yellowish-white, ± 2 mm long aphids on underside. C. avellana, colurna, heterophylla, maxima: Myzocallis coryli

12c Leaf blades loosely contracted together, curled. C. avellana: Philaenus spumarius

13a Malformations of the catkins => 14

13b Gall-like malformations in the developing fruits, from the outside inconspicuously changed. C. avellana: Curculio nucum

14a Catkins completely or only partially swollen => 15

14b Catkins sprouting. C. avellana: Unidentified gall mite

15a Catkins locally or completely pear- or barrel-shaped, swollen. Scales enlarged, glabrous; stamens ± stunted, larvae white, glossy, jumping. C. avellana, maxima Contarinia coryli

15b In similar galls. Larvae white, dull, non-jumping. Inquilines of the previous species: Dasineura corylina

15c Catkins locally swollen, often at their base. Scales ± irregular, sometimes elongated, lacerate, ± pubescent, slightly thickened, spreading at top. Stamens enlarged. C. avellana: Phyllocoptruta coryli

15d Male catkins distorted, often twisted screw-like. Containing one to several caterpillars. C. avellana, ? colurna: Unidentified lepidopteran