Lipids as currency in parasitoid competition: Interactions between two lipid-scavenging species

Lipid scavengers are organisms that rely on exogenous lipid acquisition as they lack the ability to synthesize fatty acids de novo or in sufficient quantity. Most parasitoid wasps are lipid scavengers and obtain required lipids by feeding on their hosts as larvae. Here, we studied the nutritional ecology of competitive interactions and the possibility of trophic flexibility between a native species, the pupal ectoparasitoid Nasonia vitripennis and an exotic species, the larval-pupal endoparasitoid, Tachinaephagus zealandicus. While the former species has been shown to alter host lipid content to their own benefit, we show that T. zealandicus also relies on host lipids. Competitive interactions between the two species were studied using non-choice tests, in which oviposition of T. zealandicus on a host was followed by multiparasitism by N. vitripennis. The outcome of competition was determined by the duration of the time lag between oviposition events. N. vitripennis prevailed when arriving three days after oviposition by T. zealandicus. In contrast, nine days after oviposition by T. zealandicus, no N. vitripennis offspring survived. Only when N. vitripennis laid eggs fifteen days after T. zealandicus did both species emerge from the same host. This suggests that successful emergence of N. vitripennis in this treatment was achieved through hyperparasitism. Choice experiments with hosts at different time intervals after T. zealandicus oviposition revealed a partial mismatch in N. vitripennis females between competition avoidance and offspring performance, which may be linked to the limited co-evolutionary time interval between the native and introduced species. We discuss the role of lipids in the context of interspecific competition in parasitoids.