Evaluation of endophyte-mediated resistance against Noctua pronuba (Lepidoptera: Noctuidae) in cool-season grasses in Oregon

Abstract Epichloë spp. grow symbiotically within cool-season grasses and can provide crop protection against pests and drought stress. Winter cutworm (Noctua pronuba L.) is a serious insect pest of cool-season turfgrass and grass seed crops in Oregon (United States). In 2023, we conducted 2 greenhouse experiments to measure the effect of Epichloë infection in 8 cultivars of tall fescue (Schedonorus arundinaceus (Schreb.) Dumort) and perennial ryegrass (Lolium perenne L.) on N. pronuba mortality, weight gain, grass biomass, and feeding damage at 3 time points. Epichloë infection in grass plants was molecularly validated postexperiment. We did not observe an effect of Epichloë infection level or grass cultivar on N. pronuba, regardless of grass species in trial 1. In trial 2, Epichloë infection level effects remained minimal, while cultivar affected feeding damage at 3 and 12 d in both grass species. Feeding damage at 15 d did not vary among cultivars in both tall fescue and perennial ryegrass due to continuous and severe defoliation by N. pronuba. Insect mortality and weight gain were different among tall fescue cultivars. However, some cultivars were forage type, which was selected to be palatable to grazing animals, and could be preferred by the larvae. The perennial ryegrass cultivars were all turf-type and showed no variability in insect responses. The observed feeding damage variations were likely associated with cultivar-specific traits rather than Epichloë infection levels. Understanding the role of grass genotype in grass–Epichloë symbioses is critical to develop practical management for N. pronuba, and other cutworm species.