Neonicotinoid resistance in the Colorado potato beetle

The Colorado potato beetle (Leptinotarsa decemlineata) is a significant pest of potato in most potato-growing areas of the world. Left unmanaged, the beetle can completely defoliating potato plants and reduce the yield by up to fifty percent. Currently, the management of L. decemlineata relies on use of insecticides, neonicotinoids in particular. However, emergence of insecticide resistance is a major concern. In insects, the most common cause of insecticide resistance is elevated detoxification of insecticide molecules, caused by quantitative changes in protein levels of detoxifying enzymes such as cytochrome P450s, uridine 5'-diphospho-glucuronosyl transferases (UDP-GTs), esterases, glutathione S-transferases (GSTs), and ATP-binding cassette (ABC) transporters. Therefore, we postulated that overexpression of these proteins contributes to neonicotinoid resistance in L. decemlineata. Using RNA sequencing and qPCR analyses, we identified multiple detoxifying enzyme and ABC transporters genes which are transcriptionally upregulated in a neonicotinoid resistant strain of L. decemlineata compared to a sensitive strain. To reveal their potential role in neonicotinoid resistance, we used RNA interference (RNAi) to knock-down the transcript levels of several of these genes in the resistant insects. We demonstrated that RNAi knock-down of transcription for a cytochrome P450 and a UDP-GT enzyme gene results in a significant increase in susceptibility of resistant insects to imidacloprid (a neonicotinoid insecticide), indicating contribution of these genes to resistance. Together, our results suggest that RNAi knock-down of resistance-related genes, in combination with chemical insecticides, can offer a novel control strategy for economically important pests, including L. decemlineata.