Assessing population structure among Colorado potato beetles (Leptinotarsa decemlineata) in the Midwest with Genotyping-by-Sequencing

Adaptation of agricultural pests to insecticides continues to present a serious challenge to growers and pest managers. Knowledge of population structure and gene flow among pest populations could aid in understanding the spatial heterogeneity of resistance and potential for spread of adaptive variation. We aim to characterize population structure and gene flow among Colorado potato beetles (Leptinotarsa decemlineata Say) in Wisconsin and the Midwest as part of an effort to understand the evolution of neonicotinoid resistance. Using a genotyping-by-sequencing (Elshire et al. 2011) approach, we genotyped 144 Colorado potato beetles, representing field populations from IN, KY, MI, NE, and WI, at several thousand single nucleotide polymorphism loci. Preliminary analyses with PCA and STRUCTURE suggest there is no population structure among populations in WI, but some structure on the larger scale of the Midwest. Little or no population structure could reflect high gene flow among populations, or too recent of common ancestry for populations to have become genetically differentiated, possibilities we explore with simulated data. Measuring gene flow in this system could be complicated by recent divergence times, and large effective population sizes. Moving forward, we plan to increase sequencing effort to obtain more loci and increase confidence in our genetic inferences.