Alfalfa Weevil: A Challenging Insect Pest of Forage Alfalfa in the Western United States

Abstract

Alfalfa weevil, Hypera postica Gyllenhal, native to Eurasia, is an invasive insect pest of alfalfa in North America. Alfalfa weevil causes economic damage in the central and western regions of the United States and is a minor pest of alfalfa in the north-eastern region of the country. This pest species is currently managed through biological (e.g., introduced parasitoid wasps), mechanical (e.g., harvesting one week early), cultural (e.g., maintaining a healthy alfalfa stand), and chemical (e.g., insecticide applications) control tactics. However, over the last half-century, there has been an overreliance on chemical control tactics, primarily pyrethroids (Mode of Action group (MoA) 3A), resulting in resistance developing within localized populations. Pyrethroid resistance can be addressed by following well-established integrated resistance management (IRM) and integrated pest management (IPM) strategies, that could lead to long-term sustainable management of this pest species. This case study provides diverse recommendations that can be utilized to help reduce reliance on chemical control tactics. Furthermore, new research endeavors that may provide improved IRM and IPM recommendations for this pest species are presented. © The Authors 2023