Response of sod webworm Chrysoteuchia topiaria Zeller (Lepidoptera: Crambidae) to endophyte infection and mycotoxin profiles of cool-season turfgrass species grown for seed in Oregon

The subterranean sod webworm, also known as cranberry girdler (Chrysoteuchia topiaria), is one of the most damaging insect pests in cool-season grass grown for seed crops in Oregon. Chemical control options are limited and require irrigation or rainfall for adequate insecticide incorporation to control C. topiaria larvae. Epichlo & euml; endophytes associated with cool-season turfgrass species and their mycotoxin profiles are well-documented in offering plant protection against invertebrates; these fungi may offer sustainable pest management tools. Our objectives were to characterize endophyte-mediated resistance to C. topiaria in 19 commercially available cultivars of tall fescue, perennial ryegrass, and fine fescue grown for seed in Oregon. Endophyte status (presence and viability) of fungal endophytes and their mycotoxin profiles were measured using polymerase chain reaction, and liquid chromatography-tandem mass spectrometry, respectively. No-choice assays were conducted in the laboratory to measure the impact of endophyte status on C. topiaria larvae in two separate no-choice experiments. Our results suggested that increased mortality of C. topiaria larvae (R-2 = 0.8526, Experiment 1; R-2 = 0.6628, Experiment 2) in tall fescue cultivars was most influenced by total peramine and ergot alkaloid, and total ergoline concentrations in Experiment 1 and 2, respectively. However, no significant effect on insect mortality was found in the perennial ryegrass and fine fescue cultivars included in this study. Overall, these findings suggest a viable grass-endophyte association can be utilized as a sustainable alternative to foliar insecticides for C. topiaria management in tall fescue seed crops. Plain Language Summary This is an applied research article. This study explored the endophyte status of 19 commercially available cultivars of three cool-season grass species. Two experiments were conducted in which insect response was measured regarding mortality after 7-10 days of feeding on each cultivar. We found that increased mortality occurred in endophyte-infected tall fescue cultivars. Furthermore, the insect resistance response was also found to be associated with the production of mycotoxins in these cultivars.