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.