Biochemical and physiological characteristics in chlorfluazuron resistant diamondback moth

Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) showed a high resistance to chlorfluazuron by laboratory selection. However, this resistance was not stable under the laboratory condition without chlorfluazuron selection. When in vivo metabolism of 14C-chlorfluazuron was studied, higher metabolic activities were observed in the chlorfluazuron resistant strain than in the susceptible one. From the metabolites which were obtained by carboxyamide cleavage, it was considered that higher carboxyamidase activity in the resistant diamondback moth was involved as one of important causes of resistance. Assay of carboxyamidase activity in vitro showed that the enzyme activity was higher in the resistant strains than in the susceptible ones. The sensitivity of male adults of diamondback moth to synthetic sex pheromone was compared between two strains by a bioassay method in the laboratory. The results indicated that chlorfluazuron resistant strains responded to a wider range of synthetic sex pheromone concentration than that of the susceptible ones. The results obtained here require further studies, however, they showed interesting points to understand the mechanism of chlorfluazuron resistance and control by mating disruption method in the diamondback moth.