Simple Insecticide Bean-Dip Bioassay Shows Pyrethroid Susceptibility of Helicoverpa zea (Lepidoptera: Noctuidae) Populations in Virginia Varies across Locations and Years1

Abstract

Corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), is a major insect pest of many agricultural crops in Virginia. Pyrethroids have been the major insecticide class used to control the pest for decades; however, H. zea resistance to pyrethroids has been widely documented in the southeastern and midwestern United States. To assess the pyrethroid susceptibility of H. zea in Virginia, we collected larval populations from the same five locations in 2021 and 2022 and used a quick end user–friendly bioassay to assess survival of larvae after feeding on insecticide-dipped edamame [Glycine max (L.) Merrill] pods. Pyrethroid efficacy varied between years and locations, with some 2021 H. zea populations showing reduced pyrethroid susceptibility, but not in 2022. This variability is most likely influenced by factors such as overwintering survivability in Virginia. Thus, the need for continued annual monitoring is important to track efficacy trends and grower recommendations. The simple bean-dip bioassay could be used as an efficient monitoring tool in the future, with pyrethroid susceptibility determined in 48 h from field collection.