Effect of a Fungal Endophyte on the Growth and Survival of Two Euplectrus parasitoids

Abstract

Presence of the endophytic fungus, Acremonium coenophialum, within tall fescue (Festuca arundinacea) deters many vertebrate and invertebrate herbivores, apparently because of alkaloids produced by the grass-fungus symbiotum. In one set of experiments we tested if A. coenophialum alters the growth and survival of two parasitoids of an insect herbivore feeding on tall fescue. We fed fall armyworm [Spodoptera fruigiperda (Lepidoptera: Noctuidae)] larvae tall fescue either infected or lacking its endophytic fungus and then allowed the parasitoids, Euplectrus comstockii and Euplectrus plathypenae (Hymenoptera: Eulophidae), to parasitize larvae. We found the presence of endophyte-infected plants in the diet of fall armyworm had a negative impact on the pupal mass of parasitoids. In contrast, developmental rate of the parasitoids was generally not affected by the fungal endophyte. Survival of neither parasitoid to the adult stage was reduced by the presence of endophyte-infected grass in the diet of fall armyworm. We also tested if effects of the fungus on E. comstockii were due to the specific alkaloids, N-acetyl and N-formyl loline, that are produced by the grass-fungus symbiotum. When added to artificial diets of fall armyworm, both lolines resulted in reduced survival of parasitoids. Overall, we found the fungus had a moderate negative impact on two natural enemies that mirrors some of the effects the fungus has on insect herbivores and that may be mediated, at least in part, by alkaloids associated with the fungus. We discuss implications of our work for the hypothesis that endophytes defend their host grasses from herbivores.