Resistance to cypermethrin in melon thrips, Thrips palmi (Thysanoptera: Thripidae), is conferred by reduced sensitivity of the sodium channel and CYP450-mediated detoxification

Melon thrips, Thrips palmi Karny, is among the most destructive pests of vegetables in western Japan because of its development of insecticide resistance. To examine its resistance mechanisms against cypermethrin, a pyrethroid, we determined partial nucleotide sequences of the sodium channel gene and compared the deduced amino acid sequences of two strains (the KC and OK strains) of T. palmi. The KC and OK strains showed LC₅₀ values of 3922.9 and 72.1 ppm, respectively. The LC₅₀ values were thus above the agriculturally recommended concentration (60 ppm). Both strains had a resistant amino acid, Ile, at amino acid position 929. The synergist piperonyl butoxide caused 14.1- and 3.0-fold decreases in the resistance ratios of the KC and OK strains, respectively. These results suggest that the basal and differential resistance levels of both strains are conferred by reduced sensitivity of the sodium channel and cytochrome P450-mediated detoxification, respectively.