Larval antennal sensilla in water-living insects

An overview of larval antennal sensilla in hemimetabolous and holometabolou s water-living insects is given by updating current knowledge on the fine s tructure of these sensory systems. In the absence of successful electrophys iological studies, the possible function of sensilla is deduced from their architecture. Various kinds of sensilla are described in hemimetabolous ins ects, such as Ephemeroptera, Odonata, and Plecoptera, and holometabolous in sects, such as Diptera Nematocera (Culicidae, Simuliidae, Psychodidae, Chao boridae) and Trichoptera. Their possible function in responding to stimuli from the freshwater environment is illustrated and discussed. The importanc e of sensilla as taxonomic and phylogenetic traits is reported in Baetidae (Ephemeroptera) and in Diptera Nematocera. Some homologies outlined in Dipt era Nematocera give evidence of a Link between species, such as Chaoboridae and Psychodidae, whose antennae are highly modified, prehensile in the for mer and very reduced in the latter Particular features, such as cuticle wit hout pores in chemosensory sensilla and naked perikarya, are so far found e xclusively in some water-living arthropods, thus reflecting a possible adap tation to the aquatic habitat. The structure of sensilla and chloride cells , which have a similar external morphology, is presented and discussed in v arious insect groups, considering the possible derivation of the chloride c ells from sensilla. (C) 1999 Wiley-Liss, Inc.