Sex-related response to organophosphorus and carbamate insecticides in adult Oriental fruit moth, Grapholita molesta

During the development of a resistance-monitoring bioassay that uses males as the life-stage tested, the relationship of adult female and male susceptibility of Grapholita molesta to different classes of insecticides was investigated. Preliminary results indicated that more males survived diagnostic doses of azinphos-methyl than females. Additional research revealed that, although the body mass of adult male G molesta was only 69% of that of female moths (5.67 and 8.20 mg, respectively), their LC50 values were 2.6, 4.1 and 10.3 times higher than those of females for azinphosmethyl, malathion and parathion-methyl, respectively. However, female G molesta moths were more tolerant to methomyl than were male moths. There was no indication that this sex-related response occurred in G molesta larvae. The results presented here raise concerns regarding the use of pheromone traps for determining whether insecticide treatments are required and as part of resistance monitoring programs.