Resistance to pyrethroid insecticides in cabbage stem flea beetle (Psylliodes chrysocephala) and rape winter stem weevil (Ceutorhynchus picitarsis) populations in France

Abstract: Cabbage stem flea beetle (Psylliodes chrysocephala) and rape winter stem weevil (Ceutorhynchus picitarsis) management in oilseed rape has become difficult for some years. Available data collected since 2013 show the presence of cabbage stem flea beetle and rape winter stem weevil populations resistant to pyrethroids over the whole oilseed rape growing areas of France. This is probably not a new phenomenon considering the diversity of involved mechanisms.For cabbage stem flea beetle, a mutation in the sodium channel gene is known to be linked to the knock-down resistance (kdr) phenotype was discovered. This mutation is well spread in the French territory. Moreover, another mutation known as super-knock down resistance (skdr) was also detected. It is present in the East of France, mainly in the Yonne region. For rape winter stem weevil, the kdr mutation was found in the Centre and in the East of France, but not skdr. Resistance by detoxification is suspected to be combined with these mutations in the two species.The first results of this work show that kdr mutations would confer a low resistance level to cabbage stem flea beetle. However, there is a good correlation between mortality rate in laboratory and the proportion of individuals with skdr mutations.