A key to larvae of Diamesa Meigen, 1835 (Diptera, Chironomidae), well known as adult males and pupae from Alps (Europe)

A key to species belonging to the genus Diamesa Meigen, 1835 (Diptera, Chironomidae) well known as adult males and pupal exuviae from European Alps, is presented; the characters useful in species identification are pictured. The key considers both qualitative and quantitative characters. Thirteen morpho-species are distinguished, probably more species have a very similar larva and can be separated only in the adult or pupal stage. The most discriminant quantitative characters are the length and thickness of anal setae, among qualitative characters the most discriminant ones are the head capsule colour and the split of setae anteriores of labrum. The shape of mental and mandibular teeth are good taxonomic characters, but can be rarely used because teeth are often worn out in samples collected in the field. Quantitative characters show variability within each species, differing according to the sampled site and season, and must be used with caution. The following species groups can be easily separated in the larval stage: i) dampfi, including D. dampfi and D. permacra; ii) latitarsis including D. modesta and D. latitarsis; iii) zernyi including D. zernyi and D. vaillanti. D. starmachi, D. steinboecki, D. goetghebueri, D. bertrami, D. aberrata, D. incallida, D. cinerella, D. tonsa and D. insignipes can be separated from all the other known species in larval stage, but some of them, D. cinerella and D. insignipes for example, have a very similar larva, so are better separated on the basis of their distribution and collection of adults and pupae are strongly recommended to support identifications. A new character bound to head capsule colour is proposed to separate D. insignipes, D. cinerella, D. tonsa and D. zernyi.