Dichotomous table for gallers on Pyrus

by Hans Roskam

(Pyrus communis s. lat.; including cultivated pear, P. domestica, as well as P. communis subsp. achra and pyraster)

1a On above-ground parts => 4

1b On root, root collar or basal stem parts => 2

2a Malformation larger than 10 mm => 3

2b Root with nodular swellings. P. communis: Meloidogyne hapla

3a Roots, including the older ones, with cancer-like, and. buckled enlargements or rotund swellings. P. communis, nivalis: Eriosoma lanigerum

3b Root, root collar or also basal stem parts with hazelnut- to egg-size or even larger, tuberculate proliferations, which occasionally coalesce into voluminous complexes. P. communis: Agrobacterium tumefaciens

4a On flowers or fruits => 28

4b On vegetative organs => 5

5a On leaves or buds => 10

5b On lignified parts => 6

6a Predominantly on stem parts, occasionally on thicker branches => 7

6b On thicker branches, less frequent on stems, variously slightly spindle-shaped, swollen. From the galls develop: Viscum album

7a More or less open, rimmed cancer wounds on thicker branches => 9

7b Mainly closed cancers on shoot axis, especially on younger trees, or irregular depressions on bark of younger shoots => 8

7c Midge larvae cause woody, plurilocular galls on twigs. P. communis: Apiomyia bergenstammi

8a Bark of younger stems with irregular rimmed depressions, containing causer beneath a 1.2–1.6 (1.8) mm long, dirty-grey, rotund scale. P. amygdaliformis, communis and forms: Epidiaspis leperii

8b Occasionally also on Pyrus species in similar galls beneath a pear-shaped scale up to about 2.5 mm long: Chionaspis salicis

8c Local, according to the organ’s development, usually closed cancer-like proliferations, especially on stems of younger trees or on thinner branches. P. communis: Eriosoma lanigerum

9a Irregular, eventually open cancer wounds, developing from proliferations and thickenings of bark; sometimes containing several lepidopteran caterpillars eating bark and sapwood. P. communis: Enarmonia formosana

= The clear-wing moth Synanthedon myopaeformis, which lives mainly on apple is an occasional inhabitant of cancers, but do not cause them.

9b Expanded open cancer wounds caused by fungi: Neonectria ditissima

10a On leaves => 11

10b Buds transformed into a globular to conical, yellowish, multi-chambered, woody gall. If strongly infected, stunting of shoot and accumulation of galls into a larger, irregular clustering. Each chamber containing a single larva. P. communis, salicifolia, syraica: Apiomyia bergenstammi

11a Galls of indefinite shape. Leaf blade extended and variously disfigured; folded, ± irregular and without particular thickening, only loosely rolled inwards, variously bulging swollen or ± curled => 19

11b Gall constant, locally ± defined; narrow or tough marginal roll; callosity, pock, pustule, abnormal pubescence or local, strictly defined bulges => 12

12a Narrow, restricted to edge roll of margin or thick-walled upward roll of the complete leaf blade => 18

12b Gall formation on the leaf blade => 13

13a Bladder-like enlargement, bulges, pocks or pustules => 14

13b Felt-like, initially yellowish or reddish, later on brownish pubescence, mainly of leaf underside. Hairs long, cylindrical, blunt, bent. P. communis: Unidentified gall mite

14a Callosities, pucks or pustules => 15

14b Up to 10 mm broad, pale-, later on yellowish-green, soon blackening, upward arched bladders, single or in groups. At maturity of fungus densely covered with pink-coloured asci. Exceptionally also on floral parts. P. communis, especially cultivated-, less abundant on wild forms, also on P. amygdaliformis: Taphrina bullata

= Various archings of leaf might be caused by viruses.

15a Rotund to elongate spindle-shaped, yellowish to orange-red bulges, predominantly partially including the main venation. Rust fungi => 16

15b Initially yellowish, ± red tarnished, later on brownish to 5 mm broad, per leaf blade usually many, irregular pocks, protruding on both sides. Exit underside. The mites live in enlarged intercellular spaces of the swollen leaf parenchyma. Pyrus spp.: Eriophyes pyri

= Warts on the leaves, hollow on the underside are caused by the gall mite Eriophyes pseudoinsidiosus. They are the result of sucking damage to the leaf while still in the bud stage. P. communis

15c Translucent usually solitary pustules on the leaf blade or midrib, visible on both sides, vacated by eclosing larvae (procecidia: oviposition scars, not true galls): Pristiphora abbreviata

16a Swelling slightly arched. The cylindrical peridium of aecia developing from the bulge opens at apex and frays out. Telia on Juniperus communis etc. => 17

16b Swellings very distinct. Peridium of aecia egg- to cone-shaped. Unopened at apex, opening with longitudinal slits. Pyrus spp.: Gymnosporangium sabinae

17a Minor swellings. Aecia often hardly developed. Spores 19–26 x 19–22 μm. Gymnosporangium confusum

17b Swellings and aecia usually distinct. Spores 22–30 x 18–26 μm. Pyrus spp.: Gymnosporangium clavariiforme

18a Usually both leaf halves, tip excepted, from margin often to midrib rolled upwards. The rolled part arched, thickened, ± yellowed or reddened, soon browned. Galls predominantly on terminal leaves of suckers or young trees. Larvae often many, white or reddish. Pyrus spp.: Dasineura pyri

18b Similar galls on Pyrus salicifolia. Only one cream coloured larva develops in a gall. It is not clear if it is a gall causer or inquiline in galls caused by Dasineura pyri: Macrolabis pyricola

18c Leaf blades of extending leaves remain unrolled up to midrib. Containing a yellow black-headed larva. Pyrus spp.: Anthonomus spilotus

18d Upward roll narrow, compact, hardly thickened. Leaf blade sometimes darker discoloured. Pyrus spp.: Epitrimerus marginemtorquens

19a Malformations caused by aphids => 20

19b Malformations caused by psyllids or gall mites => 21

20a Leaf blade more or less stunted and browned, weakly rolled. Usually many leaves are infected on the ± stunted shoot tips. Pyrus spp.: Epitrimerus pyri

= Similar malformations are caused by thrips. Taeniothrips inconsequens lives on Pyrus and also in a similar way on other hardwoods

20b Leaves variously slightly to spirally deflected, curled and discoloured. Pyrus spp.:

a Cacopsylla pyrisuga ‒ The only psyllid harmful on pears.

b Cacopsylla pyricola – Galls similar, but facultative.

c Cacopsylla pyri – Gall-like malformations exceptional, only on young plant parts; infestation of older leaf blades results in spotting and browning of prematurely dropping leaves.

21a The disfigured leaves are ± uniformly distributed on the stunted shoot tip => 25

21b Infected leaves usually ± clustered at the shoot tip => 22

22a Aphids pale to dark-green or reddish-brown to brown. Apterous aphids powdered or dull; dorsal side at most with some pigmented spots => 23

22b Aphid black-brown with pale legs; apterous adults with dark pigmented glossy backs, grey powdered as froth-covered nymphs. Leaf roll very variable, in spring; midrib often circular-, spirally- or screw-like rolled. Leaf blades variously stunted, ± yellow marbled or discoloured. P. communis: Melanaphis pyraria

23a Aphids reddish-brown to brown, covered with wax powder => 24

23b Aphid leaf-green, lacking wax powder, with rather long dark siphunculi; on leaf underside and on shoots. P. communis: Aphis pomi

23c Occasionally observed as causer is: Rhopalosiphum oxyacanthae

24a Leaves loosely or strongly deflected; midrib contorted in loose spiral. Leaf- cluster loose; at latest vacated by end 5. Aphid yellowish-green, with dark-green, segmentally striated pattern on back, weakly grey-powdered. Producing red juice when crushed. Pyrus spp.: Dysaphis pyri

24b A very close aphid lives in similar ± triangular bag-like rolled malformations. Galls still inhabited in 7, 8; locally serious pest: Dysaphis reaumuri

25a Aphids green or brown. Leaves yellow; along the midrib almost bag-shaped, more rarely rolled-folded, ± marbled => 26

25b Aphids black. Leaves on the usually slightly stunted shoot tip spoon-shaped deflected and more strongly rolled at margin. On the shoot tips of seedlings or coppice. Aphis fabae

26a Immature alates produced by brown fundatrices => 27

26b Immature alates produced by green fundatrices, with a double row of dark green spots: Anuraphis farfarae

27a Galls indistinguishable from previous species: Anuraphis subterranea

27b In galls indistinguishable from previous species lives the presumably inquiline Anuraphis catonii

28a On fruits => 29

28b Flowers severely stunted. Corolla unopened covering the eaten inner parts. Containing a single larva. P. communis, amygdaliformis: Anthonomus pomorum

= Anthonomus piri deposits its eggs already in late autumn in flower bud primordia, larvae develop in early spring, destroying many flower primordia, however, without causing galls.

29a Infected fruits swollen calabash-like; initially significantly faster growing than normal ones; up to hazelnut size; hence distinguishable from the only half as large healthy ones. Often ± buckled, soon black-spotted, inside spongy, later hollow, then dropping. Containing gregarious larvae, white to pale yellow, jumping. P. communis, salicifolia: Contarinia pyrivora

29b Younger or older immature fruits with wart-shaped soft swellings, usually less than 5 mm across, occasionally coalescing, pale-green. P. communis: Eriophyes pyri

= Conspicuous, bump-shaped, hard fleshy swellings on the ± deformed fruits are caused by punctures of the bug Closterotomus fulvomaculatus

mod 15.ii.2020