Bulk segregant analysis reveals genomic regions associated with imidacloprid resistance in the Colorado potato beetle

Given the increased accessibility of genomic techniques, the speed of evolution of resistance, and the large number of genes involved in resistance, investigations into the genetic basis of resistance in more species are pertinent. Despite being an important agricultural pest, only a limited number of genetic mapping studies based on crossed populations have been performed to identify genes involved in resistance in the Colorado potato beetle ( Leptinotarsa decemlineata , CPB). Here, we performed bulk segregant analysis on a mapping population generated by creating advanced intercross lines from five European strains of CPB. We identified eight peaks across chromosomes 1,8,10, and 16 involved in resistance against the neonicotinoid, imidacloprid. We identified 337 genes within these peaks and shortlisted three candidates based on gene expression and functional annotation. Among the three candidates thus identified, we found that an ABC transporter and a galactosyl transferase are expressed in relatively higher amounts in a relatively more susceptible strain than in a resistant strain. We attempted to validate the role of these two genes in insecticide resistance by knocking them down in a resistant strain using RNA interference (RNAi) and performing toxicity experiments. Surprisingly, our results showed that the activation of RNAi machinery reduced imidacloprid resistance and the effect is not specific to the tested candidate genes, which raised a concern on the suitability of using RNAi for validating insecticide resistance mechanisms in CPB.