Multiple evolutionary origins of knockdown resistance (kdr) in pyrethroid-resistant Colorado potato beetle, Leptinotarsa decemlineata

Abstract

The Colorado potato beetle (CPB), Leptinotarsa decemlineata, is a serious agricultural pest that is difficult to control due to its rapid evolution of resistance to most insecticides. Knockdown resistance (kdr) has been identified as the chief mechanism of resistance against pyrethroid insecticides in CPB and is due to a single nucleotide polymorphism, L1014F, of the voltage-sensitive sodium channel gene, LdVssc1. In order to determine whether kdr had a single or multiple evolutionary origins in CPB, 96 larvae from 10 locations (nine from across the United States and one in Bulgaria) were collected, and partial genomic sequences for LdVssc1 were obtained for each individual. The associated intron, three base pairs downstream from the mutation site, was used in the identification of novel resistant (F1014) and susceptible (L1014) alleles. In addition, genotyping was performed to investigate the presence of the super-kdr allele (L1014F+M918T). In total, 8 resistant haplotypes (all kdr) and 21 susceptible haplotypes were identified. While no M918T was found, a T929I mutation, which is also associated with pyrethroid resistance in other species, was present in 16 larvae from Bulgaria. A novel T929N mutation was found in conjunction with L1014F. Within the United States, collections with only susceptible haplotypes exhibited higher allelic diversity than collections with primarily resistant haplotypes. Phylogenetic analysis suggests 2–3 independent origins of kdr.