Benzoylurea resistance in western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae): the presence of a point mutation in chitin synthase 1

We examined the susceptibility of field strains (BO-1, BO-2, TO-1, and YH-1) and one laboratory strain (H-1) of the western flower thrip, Frankliniella occidentalis, to benzoylureas. LC50 values of novaluron were determined as 0.64ppm against laboratory strain and 2.1-130 ppm against field strains. In the presence of piperonyl butoxide, a cytochrome P450 inhibitor, the insecticidal activity of novaluron tended to be enhanced. To examine whether point mutations in chitin synthase 1 (CHS1) discovered in an etoxazole-resistant strain of Tetranychus urticae and a benzoylurea-resistant strain of Plutella xylostella exist in F. occidentalis, the nucleotide sequence of CHS1 was analyzed. We found a nonsynonymous substitution that corresponded to the location of the mutations found in T urticae and P xylostella in the field strains of E occidentalis but not in the laboratory strain, indicating that this point mutation might be associated with the benzoylurea resistance exhibited by the field strains. (C) Pesticide Science Society of Japan