Frequency and spatial distribution of knock-down resistance (kdr) to pyrethroids in multiple oilseed rape pest species of the genus Ceutorhynchus.

BACKGROUND: The protection of European oilseed rape (OSR) from damaging insects relies on pyrethroid insecticides, but the development of resistance in key coleopteran pests such as the pollen beetle (Brassicogethes aeneus) and the cabbage stem flea beetle (Psylliodes chrysocephala) has resulted in reduced effectiveness of these insecticides. The sodium channel gene mutation L1014F knock-down resistance (kdr) is a contributing factor in resistance to pyrethroids in B. aeneus and P. chrysocephala, but little is known about the status of resistance in weevils of the genus Ceutorhynchus (Coleoptera: Curculonidae). Therefore, the present study investigated pyrethroid susceptibility and the presence of the kdr mutation in four Ceutorhynchus species. RESULTS: The kdr mutation in either its heterozygous or homozygous form was found in all investigated Ceutorhynchus species (C. picitarsis, C. pallidactylus, C. napi and C. obstrictus). Samples where pyrethroids in bioassays still provided control at 100% field rate or below contained kdr at frequencies of ≤12.5%, whilst bioassays using 100% field rate that did not control Ceutorhynchus populations contained homozygous resistant individuals at frequencies of greater than 55%. Field sampling demonstrated that kdr frequencies in populations of C. picitarsis and C. obstrictus collected from across France and Germany ranged from 0 to 100%. CONCLUSION: The present study demonstrated the potential of all four Ceutorhynchus species tested to develop pyrethroid resistance via the L1014F (kdr) mutation. Although kdr frequency varies among species and geographic locations, the risk of loss of pyrethroid insecticide effectiveness is high. Integration of other control tools for resistance management is therefore needed. © 2023 Society of Chemical Industry.

Overexpression of the UDP-glycosyltransferase UGT34A23 confers resistance to the diamide insecticide chlorantraniliprole in the tomato leafminer, Tuta absoluta.

The tomato leafminer, Tuta absoluta, is an invasive crop pest that has evolved resistance to many of the insecticides used for its control. To facilitate the investigation of the underpinning mechanisms of resistance in this species we generated a contiguous genome assembly using long-read sequencing data. We leveraged this genomic resource to investigate the genetic basis of resistance to the diamide insecticide chlorantraniliprole in Spanish strains of T. absoluta that exhibit high levels of resistance to this insecticide. Transcriptomic analyses revealed that, in these strains, resistance is not associated with previously reported target-site mutations in the diamide target-site, the ryanodine receptor, but rather is associated with the marked overexpression (20- to >100-fold) of a gene encoding a UDP-glycosyltransferase (UGT). Functional expression of this UGT, UGT34A23, via ectopic expression in Drosophila melanogaster demonstrated that it confers strong and significant resistance in vivo. The genomic resources generated in this study provide a powerful resource for further research on T. absoluta. Our findings on the mechanisms underpinning resistance to chlorantraniliprole will inform the development of sustainable management strategies for this important pest.

A single point mutation in the Bemisia tabaci cytochrome-P450 CYP6CM1 causes enhanced resistance to neonicotinoids.

The tobacco whitefly, Bemisia tabaci, is a polyphagous crop pest which causes high levels of economic damage across the globe. Insecticides are often required for the effective control of this species, among which the neonicotinoid class have been particularly widely used. Deciphering the mechanisms responsible for resistance to these chemicals is therefore critical to maintain control of B. tabaci and limit the damage it causes. An important mechanism of resistance to neonicotinoids in B. tabaci is the overexpression of the cytochrome P450 gene CYP6CM1 which leads to the enhanced detoxification of several neonicotinoids. In this study we show that qualitative changes in this P450 dramatically alter its metabolic capacity to detoxify neonicotinoids. CYP6CM1 was significantly over-expressed in two strains of B. tabaci which displayed differing levels of resistance to the neonicotinoids imidacloprid and thiamethoxam. Sequencing of the CYP6CM1 coding sequence from these strains revealed four different alleles encoding isoforms carrying several amino acid changes. Expression of these alleles in vitro and in vivo provided compelling evidence that a mutation (A387G), present in two of the CYP6CM1 alleles, results in enhanced resistance to several neonicotinoids. These data demonstrate the importance of both qualitative and quantitative changes in genes encoding detoxification enzymes in the evolution of insecticide resistance and have applied implications for resistance monitoring programs.