A key to species belonging to the genus Diamesa Meigen, 1835 (Diptera, Chironomidae) from the Alps and Apennines (Italy) is presented using characters observable in the fourth-instar larva. The larvae are separated on the basis of qualitative and quantitative characters. At present fifteen species from the Italian Alps are described in all three life stages, but only twelve species groups can be separated as larvae. The separation is based on the length and thickness of anal setae, antennal ratio, head capsule color and few other characters of the labrum and mentum. The shape of mental and mandibular teeth is still a valid taxonomic character, but unfortunately these characters can be rarely used because teeth are often excessively worn in samples collected in the field. Quantitative characters show variability within each species, differing according to the duration of larval development and must be used with caution. The species groups which can be separated in the larval stage are: the dampfi group, which includes D. dampfi and D. permacra, the latitarsis group including D. modesta and D. latitarsis, the zernyi group including D. zernyi and D. vaillanti. The species within each of these groups at present cannot be separated. 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.Keywords: Chironomidae, Diamesa, dicothomic key, larvae, Italian fauna
IntroductionThe species belonging to the genus Diamesa Meigen, 1835 were described as adult males (Pagast 1947), some also described as females (Willassen and Cranston 1986;Willassen 2005) and as pupal exuviae (Pagast 1947;Langton 1991;Langton and Visser 2003), but few species were described in the larval stage (Schmid 1993;Janecek 1998;Casas and Langton 2001; Lencioni et al. 2007). Unfortunately only larval samples are often collected in hydrobiological studies and the lack of recent keys identifying larvae hinders taking the full advantage of information given by presence or absence of different species in different habitats (Rossaro et al. 2006). Much of the present knowledge about the ecology and distribution of Diamesinae is largely based on the collection of adult and pupal exuviae (Serra-Tosio 1973) or on old even if still valid contributions (Thienemann 1954), so a comprehensive knowledge of the ecological niche of each species is lacking (Lencioni and Rossaro 2005).The aim of the present paper is to give a description and a key to larvae of the species known in all life stages collected in Italian Alps and Apennines though some material from other European countries (Switzerland, Serbia, Iceland) was also examined. Short notes about the ecology of those described species is given here, while more detailed autoecological notes will be matter of future contributions.
Material and MethodsLarvae were fixed in 70% ethylalcohol or in 4% formalin, transferred in acetic acid and in a mixture of phenol : xylol 3 : 1 (W...