An illustrated key to the galls of the trembling aspen (Populus
tremuloides) in central Alberta.
Tomas Roslin
Metapopulation Research Group
Department of Ecology and Systematics
Division of Population Biology
PO Box 65 (Viikinkaari 1)
FIN-00014 University of Helsinki
Finland
Phone: +358 9 191 57741
FAX: +358 9 191 57694 e-mail: tomas.roslin@helsinki.fi
This web site provides a complete and illustrated key to twenty galling and leaf-mining taxa encountered by Tomas Roslin and Jens Roland in our sampling of 27 patches of aspen forest in the area between Calmar, Drayton
Valley and Rocky Mountain House in central Alberta, Canada (for more details, cf. Roslin, T. and Roland, J. 2003. Insect outbreaks structure phytophagous arthropod communities. Ecological Entomology, submitted.
Enter the key
1. Leaf mine: tunnel or pocket excavated by larva; fully inside leaf, between upper and lower epidermis ............................................................................................................................. 2
Gall: leaf morphology distorted by arthropod: leaf or petiole thickened, leaf-edge folded or generally distorted; blob, knob or bump on leaf or twig ....................................................... 6
2. Larva feeding externally, excavating the leaf through round orifice. Mine on lower surface of leaf. Larva protected by silken sack; moves frequently among leaves. Coleophora sp
(Lepidoptera: Coleophoriidae).
Mine closed; larva spends its entire development within one and the same leaf ............... 3
3. Frass forming black, continuous string within long, silvery tunnel right under epidermis of leaf: moth Phyllocnistis populiella (Lepidoptera: Gracillaridae)
Frass dispersed ................................................................................................................... 4
4. Leaf surface flat; mine visible only on lower side of leaf. Greenish, shallow excavation under lower epidermis of leaf; frass in rounded, reddish corns, dispersed throughout mine.
Diptera sp.
Leaf edge bent into tent-like structure or pocket-like mine visible on both surfaces of leaf....5
5. Blotchlike “pocket” inside leaf, equally conspicuous on both upper and lower leaf surface; frass spread-out in small, black corns: Eriocraniidae sp. (Lepidoptera)

Pale blotch mine on lower surface of leaf; leaf usually bent into small tent along longitudinal axis of mine, only large mines visible on both sides of leaf: Phyllonorycter sp. (Lepidoptera:
Gracillaridae)
6. Galls cauliflowerlike, woody in appearance, formed by bud proliferation on twig. Dark green in early summer, later brick-red. Aceria parapopuli (Acari: Eriophyoidea).
Galls different....7
7. Galls on petioles and (or) leaves ..................................................................................... 9
Greenish gall on apex of fresh twig, elongate or tapered: Cecidomyiidae sp. 6
9. Galls on petiole .............................................................................................................. 10
Galls on leaves .................................................................................................................. 12
10. Gall purse- or flask-like, with distinct opening ............................................................. 11
Gall closed, small. Ectoedemia sp. (Lepidoptera: Nepticuliidae)
11. Galls roundish or pyramidshaped, with relatively small, regular orifice: “Cecidomyiidae petiole”.
Galls keel-like, longer than wide, opening along full length of gall (the gall itself formed by two long “lips” extending from petiole, with single larva in between): Cecidomyiidae sp. 2.
12. Gall distinct structure affecting only part of the leaf .................................................... 13
Whole leaf distorted, thickened; several leaves at shoot tip curled. Vasates dispar (Acari:
Eriophyoidea).
13. Gall hard blister at leaf margin or formed by turned-in edge of leaf ............................ 14
Gall different ...................................................................................................................... 15
14. Gall swollen, hard and green; spindle-like blister; sometimes ridge-like hardening along underside of leaf. Cecidomyiidae sp. 7.
Folded part of leaf not significantly thickened, often red, with larva inside separate ”envelope” formed by W-like foldening of the leaf: Cecidomyiidae sp. 4.
15. Gall scale-like, semi-transparent structures along leaf-vein with single larva inside.
Cecisomyiidae sp. 14 (Diptera: Cecidomyiidae)
Galls on leaf blade, more or less globular in shape, sometimes with spine-like protrusion16
16. Gall more or less spherical, no sharp protrusions ....................................................... 17
Gall with sharp, spine-like protrusion on lower part of the leaf, ca 1/3 of gall protruding above upper leaf surface: “Cecidomyiidae pointed gall”.
17. Galls clearly protruding on both sides of the leaf ........................................................ 18

Galls clearly protruding on only one side of the leaf (usually the upper surface) .............. 20
18. Galls always by junction between leaf blade and petiole; large as full-grown. Single bulb or paired structure, protruding on both sides of leaf. Walls fleshy and juicy, full-grown gall woody; often dark red or reddish-green in color. Gall opening downwards, orifice roundish but irregular in shape, on full-grown gall surrounded by wart-like protrusions. Gall with no pronounced central cavity; several larvae per gall: Cecidomyiidae sp. 3.
Gall not by junction with petiole; inside leaf blade proper. Pronounced central cavity; single larva inside ......................................................................................................................... 19
19. Gall thick-walled, rounded, green to reddish in color. Under-side more or less halfspherical, surface with distinctly marbled pattern. Opening with thick “lips”; these lips clearly protruding above upper leaf surface even on young galls. Wall two-layered, with juicy outer layer and hard inner layer. Cecidomyiidae sp. 10.
Gall roundish to oval, about equally protruding both above and below leaf blade. Located on leaf vein, usually several galls on the same leaf. Orifice round, highly regular in shape, visible even on young galls. Wall relatively thick, fleshy: Cecidomyiidae sp. 12.
20. Gall small (ca 2.5 mm), rounded, broadly attached to upper side of leaf. Wall thin but hard and brittle, green to dark red in color. Opens with slit-like orifice on lower surface of leaf; orifice not visible on young galls. Often many galls on one and the same leaf. Harmandia globuli .
Gall larger (3-6 mm), rounded, very thinly attached to upper leaf surface. Wall thick, outer layer juicy, inner surface of gall fibrous, hard. Color green to (usually) dark red. Often many galls on one and the same leaf.
Harmandia tremulae .