Assessment of pyrethroid resistance and alternative insecticide efficacies in a fall armyworm population from central Kentucky

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) is a major agricultural pest that feeds on row crops, forages, and vegetables. Well known for its rapid spread and adaptability, this insect can quickly develop resistance to commonly used insecticides, occasionally leading to outbreaks that force farmers to take challenging management decisions. During a recent outbreak in a wheat field in Daviess County, central Kentucky, a farmer applied a generic formulation of ß-cyfluthrin. However, this pyrethroid failed to control this local fall armyworm population. A laboratory colony was established from specimens collected at the site. Once larvae reached the third instar, they were tested for resistance to several insecticides: ζ-cypermethrin, λ-cyhalothrin, ß-cyfluthrin, bifenthrin, chlorantraniliprole, and indoxacarb. Bioassays were conducted via topical application using a Hamilton micro-syringe. The results have shown that this FAW population developed resistance to most pyrethroids tested. In contrast, bifenthrin, chlorantraniliprole, and indoxacarb demonstrated effective control. These findings highlight the importance of continuous monitoring and integration of insecticides with new modes of action in fall armyworm management programs. Detailed results, including LD₅₀ values of ß-cyfluthrin for this resistant and a susceptible population, will be presented and implications for sustainable control strategies in the region will be discussed.