Susceptibilities To Four Neonicotinoids And Related Tolerant Mechanisms In Colorado Potato Beetles (Leptinotarsa Decemlineata)

Colorado potato beetle, Leptinotarsa decemlineata (Say), native to the southwestern United States and Mexico, has become the most important insect defoliator of potatoes throughout North America, Europe, and parts of Asia. The beetle is currently known to be widely distributed through most of northern Xinjiang, including Urumqi city, Qitai, Jimsar and Mori Kazak autonomous counties.CPB causes significant damage to potato and eggplant. Chemical control is widely practiced. This may result in the development of insecticide resistance. Therefore, it is urgent and essential to estimate resistance to neonicotinoids in CPB in northern Xinjiang Uygur autonomous region for proper choice of insecticides and integrated pest management.Susceptibilities of nine field populations of Leptinotarsa decemlineata adults from northern Xinjiang Uygur autonomous region to 4 neonicotinoid, including imidacloprid, acetamiprid, thiamethoxam and thiacloprid, were evaluated by a topical bioassay in 2009 and 2010. The sensitivity of the pest to imidacloprid and thiamethoxam was reduced yearly. Half of the 6 tested field populations developed low levels of resistance to acetamiprid and thiamethoxam in 2009. All the 6 tested field populations, exhibited resistance to thiamethoxam in 2010, among them 3 populations showed low level and the other 3 populations showed moderate level of resistance to thiamethoxam. There was cross-resistance between thiamethoxam and cyhalothrin in the pest. In contrast, the 4th instar larvae are still susceptible to the 4 neonicotinoids. Moreover, no cross-resistance between conventional insecticides and the 4 neonicotinoids was found in the 4th instar larvae.The inhibitory effects of piperonyl butoxide (PBO), triphenyl phosphate (TPP) and diethylmeleate (DEM) on the contact toxicities of neonicotinoids in the dults and the 4th instar larvae of L. decemlineata were evaluated. For the 4th instar larvae. PBO, TPP and DEM showed great synergistic effect on imidacloprid in Nilka, Urumqi and Qitai field populations. In contrast, these three synergists had no synergistic effects on thiamethoxam in Nilka, Urumqi and Qitai beetles. For the adult, PBO significantly synerthized the toxicity of imidacloprid in Qapqal beetles, and TPP and DEM greatly enhanced the toxicity of thiamethoxam in Qitai field population. These results demonstrated that mixed-function oxidase, esterase and glutathione S-transferase played a role in detoxification of neonicotinoids, with various detoxificative effects dependent upon insect developing stage and resistant levels.Based on a transcriptome from L. Decemlineata,34 cytochrome P450 fragments were cloned and sequenced and 32 Cyp genes were identified. This will facilitate the future research on this topic.Ten fragments of a subunits of nicotinic acetylcholine receptors (nAChRs) were cloned and sequenced. These fragments are members of nAchRa3,4,5,7,9 or/and 10 subunits by running a NCBI blast. A putative nAchRa10 with the length of 1378bp was obtained by RACE technology. The full-length reading frame (ORF) was 1344 bp and had 448 deduced amino acids.