Alyokhin, A., G. Dively, M. Patterson, C. Castaldo, D. Rogers, M. Mahoney, and J. Wollam. 2007. Resistance and cross-resistance to imidacloprid and thiamethoxam in the Colorado potato beetle. Pest Management Science 63: 32-41.

One of the major challenges in managing the Colorado potato beetle, Leptinotarsa decemlineata (Say) is its remarkable ability to develop insecticide resistance to virtually every chemical that has ever been used against it. Resistance is particularly common throughout northeastern U.S. as far north as Maine. The first instances of resistance to imidacloprid have been already reported from several locations in New York, Delaware, and southern Maine. Rotating insecticides with different modes of action may delay insecticide resistance, but successful implementation of this technique depends on a good understanding of resistance and cross-resistance patterns in populations of target pests. We measured LC50 values for imidacloprid and thiamethoxam in Colorado potato beetle populations from a variety of locations in the U.S. and Canada using diet incorporation bioassays. We also evaluated field performance of imidacloprid, thiamethoxam, and clothianidin against imidacloprid-resistant beetles on a commercial potato farm in southern Maine. Correlation between LC50 values for imidacloprid and thiamethoxam was highly significant, even when populations previously exposed to thiamethoxam were excluded from the analysis. There was no statistically detectable difference in the LC50 values between populations exposed to both chemicals and to imidacloprid alone. Applications of neonicotinoid insecticides at planting delayed build-up of imidacloprid-resistant beetle populations on field plots by 1-2 weeks, but failed to provide adequate crop protection. Consistently with bioassay results, there was also substantial cross-resistance among the three tested neonicotinoid insecticides. Results of the present study support the recommendation to avoid rotating imidacloprid with thiamethoxam as a part of resistance management plan.