Novel tri-trophic interactions: Exotic food plant effects on parasitic wasps

Novel tri-trophic interactions: exotic food plant effects on parasitic wasps Positive interactions between exotic herbivores and plants could enhance one another’s invasion; however, how this influences resistance by natural enemies gained less attention. Earlier work has shown that the performance of the E. postvittana, and exotic leaf roller in California, was better on invasive exotic host plants compared to native plants; however, whether the invasion of E. postvittana will maintain to be successful may depend on the origin of the food plants influencing their parasitoids. We investigated how the performances of three parasitoids are influenced by food plant origin (invasive or native) mediated through their host. We tested egg to adult development time, sex ratio and adult body size of the egg parasitoid Trichogramma fasciatum, the larval parasitoid Meteorus icteris and the pupal parasitoid Pediobius ni. The parasitoids were offered hosts with feeding histories on 3 plant species exotic to California and 3 native congeners. Plant origin did not always differentially affect parasitoid performance, but depended on the plant nutritional quality and host weight. Most obvious outcome was that the development times of the parasitoids were shorter on E. postvittana from exotic plants, irrespective host development time. Prior invasion of exotic plants could function as a catalyst for the subsequent invasion of an exotic insect herbivore, enhancing the expansion of its novel geographic range. However, our results on the parasitoid performance suggest that the advantage of positive interactions between invasive species can be hindered by natural enemies when their performance is also better with exotic plants.