| Colorado potato beetle (CPB), 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 insecticide resistance in CPB in northern Xinjiang Uygur autonomous region for proper choice of insecticides and integrated pest management.1. Determination of an insecticide susceptible reference strain.The susceptibilities of 4th-instar larvae of the Tekes local population to insecticides were evaluated by a topical bioassy. The b and LD50 values of 4th instar larvae to endosulfan, imidacloprid and abamectin was 1.89 and 0.1267μg/larva,1.54 and 0.0030μg/larva, and 1.60 and 0.0012μg/larva. The b and LD50 values of adult to imidacloprid and abamectin was 2.47 and 0.0127μg/adult, and 1.09 and 0.0164μg/adult, 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 to endosulfan and pyrethroids by a discriminating dose bioassayBased on diagnostic doses of bifenthrin,α-cypermethrin, cyhalothrin, deltamethrin, permethrin and endosulfan obtained from the Tekes field strain, the percentage of resistant individual of 15 field populations originating from Qitai (QT), Fukang (FK), Urumqi (URMQ), Changji (CJ), Usu (US), Tekes (TKS), Nilka (NLK), Qapqal (QPQL), Xinyuan (XY), Jimusaer (JMS), Hucheng (HC), Yining (YN), Gonglou (GL), Tacheng (TC) and Altay (ALT) to these insecticides were tested by a discriminating dose bioassay.Among these field populations, US, CJ, NLK, TC and HC adults populations had 92%,30%,30%,58% and 27.7% resistant individuals to cyhalothrin, and CJ adults population contained 34.8% individuals resistant toα-cypermethrin and 52.2% to deltamethrin. Similarly,60% individuals in URMQ population showed resistance to endosulfan.For 4th instar larvae,52.8%,34.3% and 65.7% individuals in URMQ, CJ and NLK populations were found to be resistant to cyhalothrin; and25% individuals in US population were resistant toα-cypermethrin. These results demonstrated that some field populations in Xinjiang Uygur autonomous region had developed detectable levels of resistances to several pyrethroids and endosulfan.3. A survey of insecticide resistance to endosulfan and pyrethroids by LD-P linesThe log dose-probit mortality lines of bifenthrin,α-cypermethrin, cyhalothrin, deltamethrin, permethrin and endosulfan for the adults and 4th instar larvae from several field populations were obtained.For the adults, CJ field population showed 41.1 times more resistant toα-cypermethrin. CJ and QPQL field populations were 2325.1 and 14.9 times more resistant to deltamethrin. CJ, TC, QPQL, NLK and GL field strains exhibited 403.3,617.6,14.3,37.3 and 12829.3 times more resistant to cyhalothrin. Moreover, Urumqi strain showed a moderate resistance to endosulfan, with a resistance ratio of 31.6.For the 4th instar larvae, CJ and NLK field populations were found 108.8 and 29.4 times more resistant to cyhalothrin, and 30.0 and 42.5 times more resistant to deltamethrin. Moreover, CJ and FK field strains have developed 8.9 and 13.0 times more resistance toα-cypermethrin.4. Effects of several synergists to cyhalothrinThe synergisms of PBO, TPP and DEM on cyhalothrin in the Tekes, Changji and Nilka populations were tested. For the 4th instar larvae, PBO showed great synergistic effect on the Nilka population. However, these three synergists only had slight or no synergistic effects in the Changji beetles. For the adult, these three synergists only had slight or no synergistic effects in the Changji and Qapqal beetles. These results demonstrated that mixed-function oxidase, esterase and glutathione S-transferase played little role in detoxification of cyhalothrin.5. Inheritance of resistance to cyhalothrinThe resistant ratios of 4th instar larvae of Tekes susceptible population, CJ resistant population, F1 progenys from cross of R female and S male and from cross of S female and R male were 1,403,17.3 and 1 time(s), respectively. The resistant ratio of F1 progeny from cross of R female and S male was significanyly greater than that of F1 progeny from cross of S female and R male, indicating maternal inheritance. The degree of dominance of the resistance was -0.2053 and -1, respectively, based on pooled F1 results, indicating incompletely recessive inheritance. Our results were similar to those of PE-R strain, which showed high resistance to permethrin, resulting partially from a single base pair mutation (C to T), and consequently an amino acid change (leucine to phenylalanine, L1014F) inα-subunit LdVssc1 of the sodium channel.6. Detection of mutation frequency of the a-subunit of the sodium channelBi-PASA technology was used to detect the point mutation of theα-subunit of the sodium channel in CJ field population. A total of 750 adults were treated individually with 0.6452μg of cyhathrin and 367 adults were killed, with a mortality of 48.9%. A total of 43 remained living adults were detected using Bi-PASA for the point mutation of L1014F, among them,35 individuals were heterozytes, and 8 adults were susceptible homozyte. According to the data, the calculated point mutation frequency of L1014F in sodium channel in CJ field population was 20.8%. These demonstrated that the mutation of L1014F inα-subunit of the sodium channel was, at least partially, responsible for the resistance of cyhalothrin in CJ field population.7. Detection of the best ratio of the mixture of endosulfan and cypermethrin or carbosulfanA mixture of endosulfan and cypermethrin with the ratio of 1 to 12, or 1 to 6, was significantly more toxic than either insecticide tested alone. The co-toxicity coefficient of the mixture with the ratio of 1 to 12 was 350, and that with the ratio of 1 to 6 was 158. The CTCs of the mixtures with the ratio of 1 to 3,4 to 3, and 2 to 3, were less then 100, which showed antagonistic effects.The co-toxicity coefficient values of the mixture of endosulfan and carbosulfan were with different ratios were compared. The value of CTC2:1 is 346, which exhibited synergistic interaction. The values of CTC4:1 and CTC1:4 were 108 and 99, respectively, which exhibited additive effects. The values of CTC1:1, and CTC1:2, were less then 100, which showed antagonistic effects. |
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