Exploring the molecular mechanisms of pyrethroid resistance in Hypera postica (Coleoptera: Curculionidade) across the Western United States

Alfalfa weevil (Hypera postica Gyllenhal (Coleoptera: Curculionidae)), is an economically damaging insect pest of alfalfa (Medicago sativa L. (Fabales: Fabacae)) in the western United States. Native to Eurasia, alfalfa weevils were accidentally introduced to the United States in the early 20^th century. Chemical control is the primary control tactic to manage their populations. Pyrethroids have been extensively used due to their efficacy and cost-efficiency. However, the identification of resistance of alfalfa weevils to type II pyrethroids was first reported in 2021 in Montana and subsequently in five additional western states. However, the molecular mechanism(s) of resistance has yet to be identified. To address this, RNA were extracted from five insects per location, collected from three resistant locations and three susceptible locations and the sodium ion channel gene was sequenced through Oxford Nanopore long-read Technology. This analysis revealed an F926E mutation in domain II of the sodium ion channel, a mutation not previously reported in the literature. This mutation was found in over 90% of western strain-resistant individuals collected but was absent in the Egyptian strain individuals from La Paz and Yuma counties of Arizona. This discovery suggests a novel mutation associated with pyrethroid resistance, distinct from other reported kdr mutations. To validate the role of this mutation in resistance, techniques such as voltage clamp or RNAi could be used to confirm the impact of this mutation on resistance expression.