| Phyllotreta striolata(Coleoptera: Chrysomelidae) is a pest which feed on Cruciferous vegetables. P. striolata had developed varying degrees of resistance to organophosphates, carbamates, and pyrethroids pesticides on account of frequent, single and excessive use of the pesticides in south China, so the substitute insecticides were needed in the agricultural production. In this study, the toxicity of seven insecticides including clothianidin, thiamethoxam, dinotefuran, lambda-cyhalothrin, butene-fipronil, monosultap and pyridaben were measured by leaf-dipping method, comparing the changes between different years. In addition, the synergistic effect of three enzyme inhibitors and the specific activities of Car E and GST were measured, in the meantime, the synergistic effects of the mixtures of insecticides and pesticide adjuvants were also tested aiming at understanding the resistance development, exploring the initial biochemical mechanism and efficient methods of resistance management strategies, which would provide important theoretical references to delay the development of resistance and prolong the service life of insecticides. The results were as follows:1.The toxicity of seven insecticides to P. striolataThe toxicity of seven insecticides to P. striolata were tested by leaf-dipping method.The results in 2013 indicates, among the five insecticides, the toxicity of clothianidin was the highest with the LC50 value 153.8 mg/L, and the toxicity ratio was 6.39-fold higher than that of pyridaben. The LC50 values of lambda-cyhalothrin, monosultap and dinotefuran were259.0, 565.9 and 807.5 mg/L, respectively. And the toxicity ratios were 3.79-fold, 1.74-fold and 1.22-fold, respectively. Pyridaben had the lowest toxicity with LC50 value 983.4 mg/L.The results in 2014 indicates, among the seven insecticides, the toxicity of clothianidin was the highest with the LC50 value 315.1 mg/L, and the toxicity ratio was 5.56-fold higher than that of pyridaben. The LC50 values of thiamethoxam, lambda-cyhalothrin, butene-fipronil,monosultap and dinotefuran were 473.1, 543.1, 832.2, 912.7 and 1018.9 mg/L, respectively.And the toxicity ratio were 3.70-fold, 3.23-fold, 2.11-fold, 1.92-fold and 1.72-fold,respectively. Pyridaben had the lowest toxicity with LC50 value 1751.9 mg/L.2. The resistance development of P. striolataThe LC50 values of pyridaben were 132.7 and 1751.9 mg/L in 2004 and 2014,respectively. The resistance of pyridaben showed rapid growth with 13.20-fold in ten years.The LC50 values of thiamethoxam, lambda-cyhalothrin and monosultap were 153.2, 1324.7and 1012.3 mg/L in 2004, and 473.1, 543.1 and 912.7 mg/L in 2014. The resistance showed a gentle increase or decline with 3.09-fold, 0.41-fold and 0.90-fold, respectively. The LC50 values of clothianidin, dinotefuran, lambda-cyhalothrin, monosultap and pyridaben were153.8, 807.5, 259.0, 565.9 and 983.4 mg/L, and 315.1, 1018.9, 543.1, 912.7 and 1751.9 mg/L in 2014. The resistance showed a gentle increase with 2.05-fold, 1.26-fold, 2.10-fold,1.61-fold and 1.78-fold, respectively.3. Studies on the mechanism of P. Striolata in the field populationThe effect of mixed function oxidase(MFO) inhibitor PBO, carboxylesterase(Car E)inhibitor TPP and glutathione-S-transferase(GST) inhibitor DEM to clothianidin showed obvious synergis. The synergistic ratios of PBO, TPP and DEM mixed with clothianidin at the ratio of 0.5∶1and 1∶1 were 1.94-fold and 2.45-fold, 1.81 and 2.02-fold, 1.56-fold and1.98-fold, respectively. The adults were treated with clothianidin, lambda-cyhalothrin and pridaben at 100 mg/L by immersing the insect body. The inhibitions of clothianidin,lambda-cyhalothrin and pridaben were 71.79%, 7.80% and-74.47% on Car E, and 29.63%,9.26% and-38.89% on GST. Only clothianidin and lambda-cyhalothrin showed inhibitions4. The screening of synergistic formulationsAll the mixtures of clothianidin and lambda-cyhalothrin showed synergistic effects on P.striolata, among which the 2∶8 and 1∶9 group showed the highest synergism, with co-toxicity coefficient of 203.9 and 210.5 respectively. Most groups of clothianidin and butene-fipronil showed synergism against P. striolata except that of 5∶5, and the 1∶9 group showed the highest synergistic effect, with co-toxicity coefficient of 182.1. Among the mixtures of clothianidin and monosultap, the 3∶7 group showed synergism effect, withco-toxicity coefficient of 127.9.The mixtures that clothianidin combined with penetrant T, jiabeisha, Silwet 618 showed obvious synergism with 1.59-fold, 1.43-fold and 1.85 fold, respectively. The synergistic ratio of the mixture of clothianidin and PBO was 1.19-fold, then the mixture mixed with penetrant T, jiabeisha and Silwet 618 showed obvious synergism with 4.48-fold, 3.59-fold and4.84-fold, respectively. It will be of great value on controlling P. striolata. |
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