Prey detection through olfaction by the soil-dwelling larvae of the carabid predator Pterostichus melanarius

Immunological and behavioural studies have shown that adult carabids such as Pterostichus melanarius (Illiger) are predators of slugs. However, little is known about the trophic interactions and spatial ecological of carabid larvae in the soil. Having demonstrated that the larvae will readily consume slugs in the laboratory and can reduce slug numbers in semi-field soil microcosms, experiments were designed to test the hypothesis that the larvae respond to chemical cues from their prey. Electroantennograms (EAG) showed that P. melanarius larvae were able to detect the presence of a range of volatiles using olfactory cues. There were significant EAG responses to both live and dead slugs (Derocerus reticulatum) and Diptera larvae (Calliphora sp.). Dead prey did not induce a response that was significantly different from that to live prey. Behavioural bioassays demonstrated attraction to odours from both live and dead slugs beneath the soil, but when offered a choice there was (after 6 h) a significantly greater attraction to live slugs. These results demonstrate for the first time that P. melanarius larvae appear to use olfactory cues to locate their subterranean prey.