Dichotomous table for gallers on Erigeron

(incl. Chiliodenus, Conyza)

by Hans Roskam

1a Malformations locally => 2

1b Whole plant stunted in development, bushy, terminal part of stems stunted; leaves clustered, white-spotted, sometimes ± curved. Erigeron spp.:
Brachycaudus helichrysi

2a In capitula and fruits => 12

2b On vegetative parts => 3

3a Swellings of the stem, not in the terminal parts => 11

3b Galls in basal rosettes, in buds, growing points or leaves => 4

4a On shoot tips or leaves => 6

4b Galls of various kinds in stunted or on stunted rosettes or lateral buds; tuft of leaves variously developed or even missing => 5

5a Galls ± onion-like, swellings succulent, predominantly, at least in the rosettes, with tuft of leaves and sometimes lateral shoot. E. acris, uniflorus: Rhopalomyia ruebsaameni

5b Inner rosette leaves converted into a rotund or long-oval, up to 10 mm long, spongy gall. E. acris, uniflorus: Rhopalomyia ruebsaameni

6a Leaves with localised galls or occurring over larger areas with several galls, malformed predominantly in the terminal part of the shoot => 7

6b Leaves accumulated on the shoot tips tuft-like, at the base ± shell-like broadened, pale, the outer ones often reddened, their terminal parts ± stunted, but not conspicuously deformed or discoloured. E. acris: Dasineura erigerontis

7a Leaf blade over large parts rolled, curved or curled => 9

7b Leaves with restricted, wart- or bulge-shaped swellings => 8

8a Galls often many, less than 1 mm long, yellowish, sometimes coalescing. E. canadensis: Synchytrium aureum

8b Leaf veins and stems with black-brown dusty sori on weakly swollen bulges. Erigeron spp.: Puccinia dovrensis

9a Leaf blade loosely rolled inwards and curled; by aphids => 10

9b Top and margin of the leaf blades of the larger basal leaves bent together; stem leaves with several correspondingly deformed and often nest-like clusters on the locally stunted and ± curved stem. Close to the froth-covered nymph curled and dark green. Erigeron spp.: Philaenus spumarius

10a Margin of leaf blade rolled, slightly curled, with minor paler, upward bulges. E. acris, annuus, canadensis: Brachycaudus helichrysi

10b Similar, slight curling of leaves. Erigeron spp.: Aulacorthum solani

10c Leaves swollen and curled. E. acris: Acuticauda erigerontis

11a Development of young stems severely stunted; basal internodes on all sides with perforating shoots ± one-sided spongy, swollen and bent. Inserted leaves at the sites of infestation deformed to various extents. E. canadensis: Ditylenchus dipsaci

11b Basal shoot stem with rugose embossments; one larva inside. E. acris: Cause unknown – ? beetle

12a Malformations of single or several capitula => 13

12b Fruit aborted, larva bright yellow. E. acris: Cause unknown – ? gall midge

13a Malformation of single capitula by gall midge larvae => 15

13b Malformation of inflorescence extended over several capitula => 14

14a Capitula deformed, ± sprouting and abnormally pubescent. E. annuus: Cause unknown – ? gall mite

14b Capitula stunted, small, only opening a little. Flowers ± withered, ovaries malformed, styles often elongated and discoloured violet. E. acris, uniflorus: Aceria puculosa

15a Galls caused by gall midges => 16

15b Receptacles swollen, tephritid inducers. Chiliadenus glutinosus: Myopites jasoniae

16a Terminal capitula basally slightly swollen, often remaining closed. Larvae red, non-jumping. E. acris: Dasineura socialis

16b Similar malformations. Heads on shortened stalks, shrivelled, hardened and dying off prematurely. Larvae yellow, jumping. E. acris: Contarinia erigeronis

mod 25.iii.2020