1a mine ends in a circular excision: Tachyerges decoratus

1b lower-surface tentiform mine => 2

1c corridor, not appreciably widened towards the end => 8

1d blotch, may be preceded by a corridor => 18

2a mine begins with a usually lower-surface, long, epidermal corridor that terminates in a silvery tentiform mine of ca. 1 cm; larva later lives free in a folded leaf margin: Caloptilia stigmatella

2b initial corridor very short, more often invisible; the mine not silvery, > 13 mm => 3

3a lower epidermis of the mine with 1 or 2 sharp folds => 4

3b mine without sharp folds => 6

4a pupa in a flimsy cocoon; pupa: cremaster longer than wide; hooks tiny or missing: Phyllonorycter pastorella

4b pupa in a well developed cocoon => 5

5a frass in a clump in a corner of the mine; cocoon white, free from frass: Phyllonorycter apparella

5b frass incrustrated in the cocon, when lighted from behind visible as two dark lines: Phyllonorycter connexella

6a pupa in a well-developed cocoon: Phyllonorycter populifoliella

6b cocon flimsy, cobweb-like => 7

7a on Populus tremula: Phyllonorycter sagittella

7b on other poplars: Phyllonorycter comparella

8a long, upper-surface epidermal corridor, resembling a snail’s trail; mine ends upon a a small piece of upturned leaf margin; there pupation takes place => 9

8b corridor not epidermal over its entire length => 11

9a frass line narrow and well defined, brownish black: Phyllocnistis labyrinthella

9b frass line broader, vague, greenish => 10

10a on P. alba, canescens, tremula: Phyllocnistis xenia

10b on other Poplar species, in particular P. nigra and x canadensis: Phyllocnistis unipunctella

11a at the start of the mine a globular, shining-black egg shell => 12

11b no egg shell at the beginning => 13

12a on Populus tremula, rarely alba or canescens; initial corridor contorted: Stigmella assimilella

12b on Populus nigra, canadensis-hybriden, alba or canescens; initial corridor not contorted: Stigmella trimaculella

13a corridor upper- or lower-surface; larva a maggot => 14

13b corridor full depth; larva with chitinised head => 16

14a puparium in the mine: Aulagromyza populi

14b pupation outside the mine => 15

15a corridor (in fact an elongated blotch) upper-surface: Aulagromyza populicola

15b corridor lower-surface: Aulagromyza tremulae

16a corridor very short, along the midrib, continued into a frass-covered silken tube: Gypsonoma oppressana

16b corridor much longer, different => 17

17a corridor descends from the leaf tip along the leaf margin: Tachyerges decoratus

17b corridor begins on the midrib and winds through the blade at some distance from the leaf margin: Anoplus plantaris

18a triangular, full depth blotch extending from a vein axil in the leaf base => 19

18b mine not developing from the leaf base => 20

19a on Populus nigra or P. x canadensis: Ectoedemia hannoverella

19b on Populus tremula: Ectoedemia argyropeza

19c on Populus alba or P. canescens: Ectoedemia turbidella

20a large primary blotch, upper-surface, opaque, black or dark brown, without an indication of a preceding corridor => 21

20b mine without this combination of characters => 25

21a upper surface of the mine with a group of flat, glistening egg shells; larvae white: Leucoptera sinuella

21b no egg shells visible; larvae amber => 22

22a frass in discrete grains; mine greenish at first, quickly turning dark brown; larvae are maggots; oviposition spot not discernable: Agromyza albitarsis

22b frass as a black layer flooring the mine; larvae with chitinised heads; ovipisition spots recognisable as somewhat transparent points (genus Zeugophora) => 22

23a epipharynx with 6 specialised setae; mala with 5 setae: Zeugophora scutellaris

23b epipharynx with 7 specialised setae; mala with 6 setae => 24

24a pronotum with 9 pairs of setae: Zeugophora subspinosa

24b pronotum with 6 pairs of setae: Zeugophora flavicollis

25a mine begins with a mostly lower-surface, long, epidermal corridor, ending in a silvery blotch of about 1 cm; larva later lives free in an folded leaf margin: Caloptilia stigmatella

25b mine not epidermal => 26

26a larva with thoracic feet => 27

26b larva without feet => 29

27a larva: feet short, ending bluntly; pupa in a discoid cocoon in the mine: Heterarthrus ochropoda

27b feet more slender, ending in an acute tip; pupation outside the mine => 28

28a on Populus x canadensis, nigra; larva: last pair of prolegs (‘anal feet’) surrounded by a broad, dark zone: Fenusella hortulana

28b on Populus tremula; anal prolegs surrounded by a narrower, less darkened zone: Fenusella glaucopis

29a mine mostly small, elongate-pear shaped, with much frass; elliptic larva always present in the mine (no pupa): Rhamphus pulicarius

29b mine larger => 30

30a larva a maggot; puation outside the mine => 31

30b larva with chitinised head; pupation in the mine => 32

31a mine associated with the leaf margin, rather transparent; Mediterranean species; larva: cephalic skeleton of Agromyzinae type: Japanagromyza salicifolii

31b mine not associated with the leaf margin, rather opaque; western and central European species; cephalic skeleton of Phytomyzinae type: Aulagromyza populicola

32a pupation not in a cocoon; mine round or oval, brown-black: Isochnus sequensi

32b pupation in a globular cocoon => 33

33a large blotch in the apical half of the leaf; the leaf here strongly disfigured: Tachyerges salicis

33b leaf tip not disfigured => 34

34a corridor, beginning at an oviposition scar in the midrib, widening into a blotch: Tachyerges stigma

34b oviposition not in the midrib; blotch, often oriented on the leaf venation: Tachyerges rufitarsis