Antennal responses to volatile organic compounds in a stonefly

Notwithstanding their long antennae, especially in the adult stage, Plecoptera represent a poorly studied group as regards their sensory structures and their ability to perceive olfactory stimuli is so far totally unknown. A recent investigation on the antenna of Dinocras cephalotes revealed two kinds of putative olfactory sensilla (multiporous single walled sensilla and digitated double walled sensilla). The present electrophysiological study (electroantennography, EAG), in which male and female antennae of D. cephalotes (Plecoptera, Perlidae) have been stimulated with a set of generic odours belonging to different functional groups, shows that Plecoptera can perceive olfactory cues through their antennal sensilla. Indeed, although many chemicals did not elicit any response, high EAG activity has been recorded in response to pentanoic acid, propanal, butyric acid, propionic acid, isoamylamine and ammonia. The response was very similar in both sexes even if propanal elicited a response only in males. EAG dose-responses curves in both males and females showed that EAG responses were similar in males and females and generally increased in amplitude with increasing doses of the chemicals. Behavioural, neuroanatomical and molecular investigations on Plecoptera olfaction, could be particularly interesting not only to increase the knowledge of the adult stonefly behaviour but also to better understand the adaptation of the olfactory sensory system in aquatic insects moving from land to water.