RELATIONSHIPS BETWEEN LABRAL FAN MORPHOLOGY, BODY-SIZE AND HABITAT INNORTH SWEDISH BLACKFLY LARVAE (DIPTERA, SIMULIIDAE)

A comparison was made of the labral fan morphology of 29 populations b elonging to at least 21 different simuliid species present as mature l arvae in spring-early summer in North Swedish streams and rivers. The study revealed that there are both adaptive, morphological and phyloge netic traits evident in the material. Two basically different particle capture techniques can be deduced from morphology, where two prosimul iids, Cnephia pallipes and Metacnephia trigonia, represent species whi ch mainly rely on a sieving technique, whereas all other species inves tigated capture particles by some other process, such as diffusional d eposition. Within tribe Simuliini there are significant relationships between several fan traits and habitat. Thus, fast rivers are inhabite d by species with small fans, having short and stout rays, whereas sma ll, slow streams harbour species with large fans consisting of elongat ed, delicate rays. The finer morphology of the fan rays in terms of se condary structures, the microtrichia, appears to be more related to ph ylogeny than habitat. Since a phylogeny of blackfly species still is l acking, this conclusion cannot be tested. In two subgenera, however, w hich are particularly well represented in the present material (Simuli um s. str. and Nevermannia), and whose taxonomy is based on criteria o ther than fan morphology, there is consistent support for the conclusi ons about habitat-morphology relations. (C) 1996 The Linnean Society o f London