| 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. In the present paper, toxicities of several newly-typed insecticides were evaluated and two kinds of molecular targets of these insecticides were cloned. These results were useful for proper choice of insecticides and integrated pest management.1. Toxicities of several newly-typed insecticides to 4th-instar larvae and adultsContact toxicities of cyhalothrin, chlorantraniliprole, fipronil, abamectin, spinosad and diflubenzuron to 4th-instar larvae and adults and stomach toxicities to 2nd-,3rd-, and 4th-instar larvae and adults were evaluated. It was found that fipronil, abamectin and spinosad may spray in potato fields to control both adults and larvae. Chlorantraniliprole may be suitable to control young larvae. The toxic effect of diflubenzuron was low in laboratory, further researches are necessary to evaluate its field effects.2. Susceptible differences of several newly-typed insecticides among seven field populations from northern XinjiangSusceptibilities of cyhalothrin, chlorantraniliprole, fipronil, abamectin, spinosad tebufenozide and diflubenzuron to 4th-instar larvae and adults from 7 counties (cities) in northern Xinjiang were assessed by a topical bioassay in 2009 and 2010. It was found that the susceptibilities of abamectin and tebufenozide in some field populations varied significantly between years, whereas the susceptible differences of chlorantraniliprole, fipronil, spinosad and diflubenzuron were less than 5-fold among the 7 field populations. Abamectin, spinosad and fipronil exhibited high toxic effects to both 4th-instar larvae and adults. Chlorantraniliprole, however, are more toxic to the larvae. Susceptible differences among field populations were not related with resistances of these populations to conventional insecticides. These results indicated that these newly-typed insecticides may be useful in the control of Colorado potato beetle and insecticide resistance management.3. Chlorantraniliprole detoxification enzymes and molecular cloning of target genesIn order to indentify detoxification enzymes to chlorantraniliprole by Colorado potato beetle, the inhibitory effects of piperonyl butoxide (PBO), triphenyl phosphate (TPP) and diethylmeleate (DEM) on the contact toxicities in the adults and the 4th instar larvae of L. decemlineata were evaluated. PBO significantly synerthized the toxicity in 4th-instar larvae of Nilka field population but had slight synergistic effect on Qapqal beetles. In contrast, TPP and DEM had no synergistic effects in Tekes, Nilka and Qapqal field populations. These results demonstrated that mixed-function oxidase played a role in detoxification of chlorantraniliprole. Moreover,20 ryanodine receptor fragments were cloned. This is useful for further researches.4. Cloning of the genes involved in juvenile hormone biosynthesis and metabolism and RNAi resultsSome gene fragments associated with juvenile hormone biosynthesis and metabolism were cloned. These fragments included acetoacetyl CoA thiolase, hydroxymethylglutaryl-CoA synthase,3-hydroxy-3-methylglutaryl CoA reductase, mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate decarboxylase, isopentenyl-diphosphate delta-isomerase, short-chain dehydrogenase, farnesoic acid O-methyltransferase, ATP citrate lyase, adenosylhomocysteinase, adenosine kinase, juvenile hormone esterase, juvenile hormone epoxide hydrolase, and juvenile hormone diol kinase. A dsRNA-produced vector was constructed and transferred to Escherichia coli HT115. The engineered bacterium was cultured, and a great amount of dsRNA derived from 3-hydroxy-3-methylglutaryl CoA reductase, mevalonate kinase, adenosylhomocysteinase, juvenile hormone esterase in L. decemlineata was obtained. The bacteria liquids contained adenosylhomocysteinase dsRNA showed lethal effect to the larvae when oral administrated to 2nd-instar larvae. |
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