Incidence and Mechanisms of Insecticide Resistances to Organophosphates and Carbamates in Colorado Potato Beetle, Leptinotarsa Decemlineata (Say)
|School||Nanjing Agricultural College|
|Course||Agricultural Entomology and Pest Control|
|Keywords||Colorado potato beetle insecticide resistance monitoring Organophosphate carbamate metabolic resistant mechanism Acetylcholinesterase point mutation|
Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is the economically most important insect pest of potatoes throughout North America, Europe, and parts of Asia. The beetle invaded China in the 1990s from Kazakhstan. Since then, it has spread eastward, and currently distributed through most of northern Xinjiang.Defoliation by CPB is a serious threat to potato and eggplant crops in northern Xinjiang. Insecticide treatments are currently indispensable for and effective on CPB control. Unfortunately, this pest has remarkable ability to develop insecticide resistance to virtually every chemical that has ever been used against it. Therefore, it is urgent and essential to estimate insecticide resistance in CPB in northern Xinjiang for proper choice of insecticides. This study is carried out to test resistance levels to five organophosphates (azinphosmethyl, diazinon, isocarbophos, malathion and phoxim) and three carbamates (carbaryl, carbofuran, and carbosulfan), and to study possible resistance mechanisms.1. Determination of an insecticide susceptible reference strainThe susceptibilities of the adults and the 4th instar larvae of the Tekes local population these organophosphates and carbamates were evaluated using topical bioassays. The b and LD50 values were completely comparable to those to some susceptible strains. Therefore, we selected the Tekes local population as an insecticide susceptible reference strain.2. A survey of insecticide resistance by a discriminating dose bioassayThe resistant individual proportions were estimated in several field populations from QT, JMS, URMQ, CJ, TC, US, TKS, QPQL, GL, NLK by a discriminating dose bioassay. It was found that several field populations have developed detectable levels of resistances to isocarbophos, malathion, carbofuran and carbosulfan. All field populations were still susceptible to other tested organophosphates and carbayl.3. A survey of insecticide resistance by LD-P linesThe log dose-probit mortality lines of the five organophosphates and three carbamates for the adults from TKS, QPQL and CJ field populations, and for 4th instar larvae from TKS, NLK and CJ populations were obtained. Among tested populations, the QPQL adults showed moderate resistance against carbofuran, with resistance ratio of 18.7. The Nilka larvae were 10.1 and 90 times more resistant to carbofuran and carbosulfan respectively, and the Changji 4th instar larvae was 17.6 and 24.7 times more resistant to carbofuran and carbosulfan, respectively. Moreover, the CJ population has developed 7.0 times of resistance to azinphosmethyl.4. Effects of several synergists to azinphosmethyl and carbofuranThe synergisms of piperonyl butoxide (PBO), diethylmeleate (DEM) and triphenyl phosphate (TPP) on azinphosmethyl and carbofuran in the adults of Tekes, Changji and Qapqal populations, and in the 4th instar larvae of Tekes, Changji and NLK populations were tested. PBO and TPP exited some synergistic effects on carbofuran in the adults of Qapqal population. In the 4th instar larvae, PBO, TPP and DEM exhibited greater synergistic effects in the Changji population and showed some synergistic effects in the Nilka population. In contrast, three synergists showed little effects on azinphosmethyl in these populations. These results demonstrated that mixed-function oxidase, esterase and glutathione S-transferase mediated detoxification of carbofuran in the Changji population. 5. Confirmation of mutation S291G in acetylcholinesteraseThree specific point mutations, R30K, S291G, and I392T in acetylcholinesterase in CPB associated with organophosphate- and carbamate-resistance have been documented. Here we cloned a fragment of acetylcholinesterase and confirmed the mutation of S291G in CJ field population. 6. Detection of mutation frequency of S291G in acetylcholinesterase using Bi-PASABi-PASA technology was used to detect the point mutation S291G in acetylcholinesterase in CJ field population. A total of 180 adults were treated individually with 0.0835μg of carbofuran and 91 adults were killed, with a mortality of 50.5%. A total of 27 remained living adults were detected using Bi-PASA for the point mutation S291G, Among them,9 individuals were resistant homozytes,18 individuals were heterozytes, no susceptible homozyte was found. According to the data, the calculated point mutation frequency of S291G in acetylcholinesterase in CJ field population was 32.9%, and the proportition of resistant homozytes was 16.3%.