Effects of Host Novelty and Social Cues on Oviposition Behavior in Callosobruchus Maculatus

Rachel Mestel, Vassar College '11 and Prof. Jeremy M. Davis

In holometabolous insects, such as beetles, larva can only consume the resources available in the host that their mother chooses for them, and therefore, their fitness relies entirely on the mother’s oviposition decisions. Maternal preferences for high quality hosts should therefore evolve over time through natural selection, but the emergence of unfamiliar environments requires mothers to pay attention to other sources of information in order to make adaptive decisions. Theory predicts that mother insects will utilize information from sources outside of their genome when those sources of information reliably indicate host quality and when hosts are novel. We tested these predictions in the bruchid beetle, Callosobruchus maculatus, a pest that feeds on dried beans in Asia and Africa.

Through a series of behavioral experiments we tested how previous experience with novel and familiar beans with and without previously laid eggs affected the egg-laying rate and preferences of female beetles. We found that the presence of eggs tended to increase the overall rate of egg-laying. We additionally discovered that previous experience with a bean increased a beetle’s preference for that bean. Finally, we found that while eggs on a familiar host caused beetles to seek out other uninfested familiar hosts, eggs on a novel host caused beetles to lay more eggs on that particular host. We hypothesize that because beetles are uncertain about the quality of novel hosts, eggs on these hosts are used as indicators of quality. Conversely, because there is little uncertainty about the quality of familiar hosts, eggs on these hosts indicate only competition. Further research is needed to determine if these behavioral patterns will influence host choice in natural populations of beetles.