Asymmetries affecting aggressive contests between solitary parasitoids: The effect of host species

In parasitic wasps, which are important biological control agents of many agricultural pests, contests between females determine which individual exploits hosts (which can be pests or non-pests) for offspring production. Previous studies on parasitic wasps rarely considered the role of ecological factors generating variation in characteristics that could influence the strength of asymmetries. Some parasitoid wasp species parasitize host species of various sizes, producing offspring that vary considerably in size and potentially fighting ability. In this study, we reared the a parasitic wasp on two host species (one pest, one non-pest) to measure the effect of body size on contest resolution and how it interacts with ownership and resource value asymmetries, and how it affects how many host eggs they kill. Our results showed that ownership status best predicts the final contest outcome when similar-sized wasps fight over hosts. The frequency and outcomes of individual fights structuring contests were better explained by the difference in the number of eggs laid in the hosts by each female at a given time. When contestants varied in body size, larger intruders frequently dislodged small owners regardless of ownership and resource value asymmetries. These results imply that body size is an important factor to consider in solitary parasitoid contests and that it can overshadow the effects of other asymmetries. Our study suggests that host community diversity could have a direct effect on parasitoid contests and that biotic communities, through their effects on animal phenotypes, may play an underrated role in contest resolution. Finally, our study shows that the body size of parasitic wasps and how it affects contest resolution can have consequences for biological control of insect pests that they attack.