Managing resistance and cross resistance between imidacloprid and spinosad in Colorado potato beetle

Resistance to imidacloprid is widespread, though it still provides significant protection. On a regional scale resistance to imidacloprid and to spinosad are correlated, but it is not clear that resistance to the two compounds has a mechanistic basis, rather than resulting from frequent use of both treatments in some areas. I will test for genetic correlations between resistance to imidacloprid and to spinosad by combining a lab and field study. In the lab I will separately perform selection for imidacloprid and spinosad resistance on heterogenous populations and measure the correlated response, if any, in resistance to the unselected insecticide. In the field I will collaborate with growers to plant fields treated with Admire™ and Spintor™, Admire™ but not Spintor™, and Spintor™ but not Admire™, and measure any correlated shifts in resistance in response to the alternative treatments. We will estimate the economic consequences of planting spatial refuges from Admire™ and Spintor™. I will share these results in peer-reviewed and extension literature, and in informal and formal meetings with growers.

Objective I. I will perform selection on heterogeneous populations in the lab for resistance to imidacloprid and spinosad individually, and measure any correlated response in resistance to the unselected substance. Objective II. In collaboration with Wesnofske farm we will establish portions of fields treated with imidacloprid or spinosad alone, or both together, and measure CPB population size and resistance to imidacloprid and spinosad in the current year and the following year’s emergers. Objective III. We assess the costs in time and inputs for fields with mixed treatments containing some in-furrow imidacloprid and some untreated portions, compared with uniformly treated fields.