Target-site and metabolic resistance against λ-cyhalothrin in cabbage stem flea beetles in Denmark

The cabbage stem flea beetle, Psylliodes chrysocephala (L.) (Coleoptera Chrysomelidae) is a major pest of oilseed rape throughout Europe. Pyrethroids has been widely used for control of P. chrysocephala, but in recent years control failure has occurred, possibly due to resistance. Thirteen out of 15 populations collected in Denmark were susceptible to λ-cyhalothrin. Just two populations, both from the south of Denmark had decreased susceptibility. The target site resistance allele, kdr, was found in a frequency from 0.00 to 0.76. There seemed to be a good relationship of the frequency of the target site mutation and resistance levels with some regional differences. Based on the data presented here target site mutation is a good indicator of decreased λ-cyhalothrin susceptibility. However, it is not the sole contributor to pyrethroid resistance in Danish P. chrysocephala, and the potential involvement of metabolic resistance should be investigated.