Molecular mechanisms of imidacloprid resistance in Colorado potato beetles (Leptinotarsa decemlineata) in the Central Sands region of Wisconsin

The Colorado potato beetle (CPB: Leptinotarsa decemlineata) is a key agricultural pest of potato  crops in the Central Sands region of Wisconsin.  CPBs can consume vast amounts of potato foliage if not controlled with the correct measures, leading to loss of revenue for local farmers.  In 1995 the neonicotinoid insecticide, imidacloprid, was introduced into the arsenal of controls to fight populations of CPB which had already acquired organophosphate, carbamate, and pyrethroid resistance.  Since its introduction, beetles have now developed localized, high levels of resistance to imidacloprid, and there is an increasing need for improved understanding of resistance mechanisms in these populations.  Resistance levels of selected CPB populations in the Central Sands region was examined by determining the LD₅₀ values among 5 different field populations, of which four populations had previously experienced some level of field failure (e.g. resistant) and another population was deemed as susceptible.  A transcriptome was assembled from the RNA isolated from resistant and susceptible CPB populations to examine the genetic differences and gene regulation after exposure to imidacloprid.  The transcriptomic data suggests that gene regulation between susceptible and resistant populations varies substantially.  Genes that were upregulated in the resistant populations included cuticular proteins and Cytochrome P450s, a class of monooxygenases which are known for their ability to catalyze xenobiotic compounds.  Mining the transcriptomic data provides insight into the modes of imidacloprid resistance in these selected CPB populations and identifies possible genetic targets to further reduce resistance for future management.