Endophytes of fescue grasses enhance susceptibility of Popillia japonica larvae to an entomopathogenic nematode

We evaluated tritrophic level interactions among fungal endophytes (Acremonium spp.) of fescue grasses (Festuca spp.), the root-feeding Japanese beetle Popillia japonica Newman larvae, and the entomopathogenic nematode Heterorhabditis bacteriophora Poinar. Third-instar P. japonica larvae were introduced into pots containing endophyte-infected or endophyte-free plants of tall fescue Festuca arundinacea Schreber (cultivars Kentucky 31 and Georgia Jesup Improved) and the Chewings fescue Festuca rubra commutata Guad. (cultivars F-93 and Jamestown II). After two weeks, the surviving larvae were recovered, and their susceptibility to nematodes was evaluated in sand columns. Endophytes enhanced the rate of nematode-induced mortality in all cultivars except Georgia Jesup Improved, and increased the proportion of dead larvae with nematodes in all cultivars except Jamestown II. Endophytes in the cultivar Kentucky 31 were associated with improved nematode establishment in the larvae. No effect on nematode reproduction was found. Since endophytes produce biologically active alkaloids, we tested the effects of an ergot alkaloid, ergotamine tartrate, on the feeding behavior and weight of P. japonica larvae in agar medium. The alkaloid caused feeding deterrence, and reduced the consumption of medium by the larvae, resulting in weight loss. These larvae were more susceptible to H. bacteriophora than the untreated larvae. Unfed ‘starved’ larvae were more susceptible to nematodes than those fed on untreated agar. Our results support the hypothesis that endophyte-induced starvation of P. japonica would reduce larval vigor, and render them more susceptible to entomopathogenic nematodes.