Incidence of resistance to neonicotinoid insecticides in Bactericera cockerelli across Southwest U.S.

Abstract

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae) is a vector of the pathogen (Candidatus Liberibacter solanacearum) that causes zebra chip in potato. The insect and the disease are managed solely through insecticide applications. One of the primary insecticide chemistries used to suppress the psyllid includes various formulations of neonicotinoid (group 4A) insecticides and their frequent use across Southwest U.S., where potato psyllids and zebra chip are prevalent, has raised concerns of widespread insecticide resistance. Potato psyllids collected from California and the Lower Rio Grande Valley (LRGV) of Texas have been previously shown to be resistant to these insecticides, but the psyllid susceptibility to neonicotinoid insecticides across Southwest U.S. has not been established. To test the extent of neonicotinoid resistance, we collected potato psyllids from Colorado, New Mexico, and from two major potato-producing regions of Texas. We exposed immature progeny of these field-collected potato psyllids to several doses of two neonicotinoids, imidacloprid and thiamethoxam. Survival of the psyllids was compared to a control colony of B. cockerelli, which was collected prior to widespread use of neonicotinoid insecticides and was known to be susceptible to them. Our results indicated that the psyllids were resistant to both insecticides. The degree of resistance depended on the geographic location of each psyllid population and on the insecticide, with imidacloprid resistance most prominent in psyllids from LRGV. These outcomes emphasize the need to diversify and integrate tactics used to suppress the psyllids and lessen dependence on insecticides to manage the insect and the disease.