Investigating phenotypic and genomic cross-resistance in the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The Colorado potato beetle (Leptinotarsa decemlineata Say; CPB) is considered the most prominent insect pest of potatoes (Solanum tuberosum) worldwide, and is also a model organism for molecular research due to its propensity for rapid and repeated evolution of insecticide resistance. Cross-resistance, defined as the conferment of resistance among insecticides originating from different mode of action classes despite no prior exposure to one or more chemicals, is a complex molecular phenomenon. Though possible to arise through multiple genetic, metabolic or behavioral mechanisms, cross-resistance is most frequently observed between insecticide classifications that share a similar site of activity (target-site). One such receptor targeted by two frequently used insecticides against CPB, imidacloprid (Group 4A) and spinosad (Group 5), is the nicotinic acetylcholine receptor (nAChR). In this study, populations of CPB were collected from 10 different organically managed potato fields. The potential for resistance and cross-resistance was evaluated through phenotypic, dose-response assays, which supported a hypothesis of cross-resistance between the two insecticides. Further analysis through preliminary RNA sequencing compares the genetic patterns of expression between imidacloprid and spinosad in select populations, enhancing our understanding of the rapid evolutionary patterns observed in CPB. The implications drawn through connecting phenotypic and genetic assessments allow for tangible conclusions that are crucial to learning about the potential for cross resistance, as well as opening new avenues for conservation in organic agriculture.