Synergy in information use for mate finding: demonstration in a parasitoid wasp

Keywords: cue mating system parasitoid sex pheromone signal Venturia canescens wind tunnel In many animals, mating takes place after natal dispersal. Consequently, use of reliable information is required to increase the probability of encounters between the sexes. Most of the studies on mate finding in parasitoid insects have focused on the role of a single information source: a sex pheromone. Other sources have been mostly ignored. We studied the nature of olfactory information used for mate finding by the parasitoid Venturia canescens both at a distance and at host patch level, and investigated how this information is used. We tested which sex attracts the other and whether mate location is improved by combining different sources of information. We found that males simultaneously used two types of olfactory cues to find their mate: information directly related to females and an environmental cue provided by hosts. Male efficiency in locating virgin females was enhanced threefold by the association of females with hosts, whereas host patches, on their own, were unattractive to males. Our results also suggest that females emit a volatile pheromone. At the host patch level, males used chemical marks left by females foraging for hosts. These results led us to consider the distinction between signals and cues and we suggest that the volatile pheromone emitted by the females, always described as a signal, could rather be a cue. Although evidence for a volatile sex pheromone is pervasive in parasitoids, our study stresses the role of other cues in mate-finding strategies. Mating systems depend on the reproductive biology of both sexes, the intensity of intrasexual competition and the distribution of partners in time and space Mate finding is a crucial step in the mating system. Increasing both mating success and the probability of finding a mate requires the use of reliable information relative to the environmental noise. Although animals can use multiple cues for decision making (Fawcett & Johnstone 2003; Campbell & Borden 2009), studies of mate finding have primarily focused on a single information source: sex pheromones (Quicke 1997). A sex pheromone is a chemical signal that informs the other sex or alters the sexual behaviours of conspecifics. Females can release contact or close-range pheromones which arrest and attract nearby males and/or elicit male courtship behaviour (Danci et al. 2006; reviewed in Kainoh 1999; see also Ruther et al. 2000). Depending on the mating system, chemicals might have different roles …