Insecticide resistance status of Colorado potato beetle in northern Xinjiang Uygur Autonomous Region

Colorado potato beetle, Leptinotarsa decemlineata (Say), has become the economically most important insect defoliator of potatoes in northern Xinjiang Uygur autonomous region in China. We have conducted resistance tests for nearly 20 insecticides against the local populations using topical bioassay. The results showed that local populations exhibited moderate to extremely high levels of resistance to carbofuran, carbosuflan, deltamethrin and cyhalothrin, and low to moderate levels of resistance against thiamethoxam. Synergism studies revealed that Triphenyl phosphate (TPP), diethylmeleate, and piperonyl butoxide (PBO) had different synergized effects in adult and larva populations. The three synergists had little synergism to cyhalothrin in adult populations, whereas PBO had significant synergism in larva sample. DEM had a little synergistic effect to carbofuran in the Changji adult population, and PBO, TPP and DEM exhibited significant synergism in the 4^th instar larva sample. Therefore, enzymatic detoxification may be one of the resistance mechanisms to cyhalothrin and carbofuran for local populations in Xinjiang, there are probably additional resistant mechanisms involved,such as target site insensitivity. A modified bi-PASA was developed to simultaneously detect point mutations of S291G in the AChE and L1014F in the LdVssc1 genes, resulting in the resistance to carbamates and to pyrethroids respectively. The results of molecular tests showed that correlation was positive between the incidences of individuals with resistance alleles and the resistance ratios to cyhalothrin and deltamethrin, carbosulfan and carbofuranin in the five field populations. These results demonstrated that point mutations of S291G in the AChE and L1014F in the LdVscc1 are responsible for, at least partially, the resistance to carbamates and pyrethroids in L. decemlineatain some field populations in northern Xinjiang.

Key words:  Leptinotarsa decemlineata, insecticide resistance, topical bioassay, synergist, target insensitivity