Perennial ryegrass infected by the symbiotic fungus Neotyphodium lolii receives several competitive benefits including increased drought tolerance and decreased susceptibility to diseases and herbivory. The fungus produces a variety of alkaloids that are toxic to vertebrate and invertebrate herbivores. Two lepidopterans from the family Noctuidae, Spodoptera frugiperda and Agrotis ipsilon, are generalist herbivores that can feed on endophyte-infected perennial ryegrass and complete development. We exposed them to Steinernema carpocapsae (All), an entomopathogenic nematode that is used for biological control of these insects. In the presence of S. carpocapsae, the noctuids fed on infected grass lived significantly longer than those fed on uninfected grass. Although fall armyworm larvae fed on endophyte-infected perennial ryegrass had significantly less biomass than those fed on uninfected perennial ryegrass, the size differences did not explain differences in susceptibility to S. carpocapsae. Additionally, older A. ipsilon larvae (4th instar) fed on plants with high (>90%) incidence of endophyte are less susceptible to entomopathogenic nematodes than larvae fed uninfected grass, whereas younger larvae (2nd instar) were equally susceptible to nematode attack. Some lepidopterans are capable of utilizing host plant secondary compounds for defense against natural enemies. Literature demonstrates that some secondary compounds affect entomopathogens and parasitoids. Therefore, we have examined the direct effects of alkaloids on S. carpocapsae and its symbiotic bacteria, Xenorhabdus nematophilus. The potential mechanisms for the decreased susceptibility exhibited by these noctuids will be addressed.
Species 1: Lepidoptera Noctuidae Agrotis ipsilon (black cutworm)
Species 2: Lepidoptera Noctuidae Spodoptera frugiperda (fall armyworm)
Keywords: biological control, perennial ryegrass
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