CHARACTERIZING THE POTENTIAL FOR INSECTICIDE CROSS-RESISTANCE AMONG SELECTED POPULATIONS OF COLORADO POTATO BEETLE USING PHENOTYPIC AND DIFFERENTIAL GENE EXPRESSION ANALYSIS

Abstract

Insect pest control through the use of insecticides is an important issue for food security, sustainable agricultural practices, and on-farm economics. The evolution of metabolic resistance is problematic, considering the destructive capabilities of the most prominent commercial potato pest, the Colorado potato beetle, Leptinotarsa decemlineata (CPB). This beetle can be a devastating pest and is well known for its rapid adaptive evolution to resist entire classes of insecticides, through various phenotypic and genetic changes. In this project, dose-response bioassays were used to characterize the extent of cross-resistance to a novel insecticide, and genetic testing was used to examine the molecular response. Populations were exposed to serial doses of the neonicotinoid, imidacloprid (AdmirePro), as well as a novel and currently unregistered compound, isocycloseram (Plinazolin). Both compounds act on specific nervous system sites, however, isocycloseram represents a new mode of action (IRAC Group 30) and an associated target site to which most, if not all L. decemlineata populations are expected to be highly susceptible. Further examination of the underlying genetic mechanisms of L. decemlineata resistance through amplicon sequencing of RNA compared the differential expression of target site and metabolic detoxification genes between the different active ingredients, each of which were tested across a diverse set of L. decemlineata populations. This project shows that expression of gene families involved in metabolic detoxification may be acting upon both active ingredients, underpinning potential cross-resistance to the novel insecticide.