Environmental and genetic determinants of ovicide in the parasitic wasp Bracon hebetor

Superparasitism occurs when a parasitoid lays a second clutch of eggs on a host previously parasitized by herself or a conspecific. Ovicide refers to a parasitoid destroying an existing clutch of eggs on a parasitized host before laying a second clutch. We investigated environmental and genetic determinants of ovicide in the parasitic wasp Bracon hebetor. Characterization of egg-laying behavior revealed that B. hebetor commits ovicide during the host examination phase of oviposition. The temporal costs of ovicide were found to be relatively small for females that experienced low rates of host encounter, whereas the costs of ovicide increased for females that experienced a high rate of host encounter. Individual wasps committed ovicide on conspecifically parasitized hosts more frequently than on self-parasitized hosts. Manipulation experiments suggested that B. hebetor females learn about their environment while foraging and commit ovicide on the basis of the travel time between successive hosts. Significant differences were also found in ovicidal behavior among laboratory and field populations of B. hebetor. The implications of our results for clutch size theory and the evolution of ovicide are discussed.