Monitoring Of Insecticide Resistance And Risk Assessment Of Resistance To Buprofezin And Imidacloprid In Sogatella Furcifera (Horvath)

The white-backed planthopper Sogatella furcifera (Horvath) is one of the migratory insect pests, and occur in all the rice-growing areas of China. It causes serious lost of rice product, especially this insect may transmit rice virus as vector. At present the management of white-backed phanthopper mainly depended on the use of chemical insecticides; however the resistance development of this insect species to insecticides used impacted the efficacy of chemical control seriously. In order to guide the scientific chemical control of S. furcifera in our country the resistance status of imidacloprid, thiamethoxam, chlorpyrifos, buprofezin and pymetrozine in field populations collected from20counties of9provinces during2010and2011were investigated. The detoxification enzyme activities of esterase, monooxygenase and glutathione-S-transferase in the populations of S. furcifera were also analyzed and correlation analyses were made for the enzymatic activities and insecticidal toxicities. The risk of resistant development of imidacloprid and buprefizin by this species were assessed through insecticide selection under laboratory condition.1. The toxicity baseline of imidacloprid, thiamethoxam, chlorpyrifos, buprofezin and pymetrozine to S. furciferaOne field population of S. furcifera collected from Nanning, Guangxi in2006were reared on rice plants with no insecticide contact under laboratory condition, which lead to the development of a laboratory strain (Lab-NN). The susceptibilities to imidacloprid, thiamethoxam, chlorpyrifos and buprofezin of Lab-NN strain were significantly increased compared with its initiative population assayed in2006, especially the susceptibility to chlorpyrifos of this lab strain was raised9.4fold.2.1,1.9and1.4fold increases in insecticidal susceptibilities were obtained for imidacloprid, thiamethoram and buprofezin respectively. The LC50values of Lab-NN strain to imidacloprid, thiamethoxam, chlorpyrifos, buprofezin and pymetrozine were0.109,0.096,0.044,0.236and0.479mg ai/L respectively, and the LC50values of Lab-NN for these insecticides were the lowest for corresponding insecticide among the tested populations. This strain raised in our laboratory could be used for the monitoring of insecticide resistance, and toxicity data could be regarded as the toxicity baseline of S. furcifera.2. The resistance of S. furcifera to imidacloprid, thiamethoxam, chlorpyrifos, buprofezin and pymetrozineThe toxicity response of imidacloprid, thiamethoxam, chlorpyrifos, buprofezin and pymetrozine in25field populations of S. furcifera collected in China were assayed by rice stem dipping method. Considerable differences of insecticidal susceptibility existed among the field populations.28%of the tested populations exhibited moderate resistance to imidacloprid, population with the highest resistance level (15fold) was collected from Qianshan, Anhui province.32%populations were lower level resistance; the remained44%populations were susceptible to imidacloprid. Widespread of buprofezin resistance was observed in S. furcifera, moderate level of resistance had been developed to buprofezin by most of the populations (84%), the highest resistance level (25.6fold) was discovered from Hejiang, Sichuan province, only the populations from Nanning, Guangxi remained susceptible to this chemical. Fortunately for us, no obvious resistance were observed for thiamethoxam, chlorpyrifos and pymetrozine in the assayed populations, only28%,32%and28%of the field populations showed lower level of resistance to thiamethoxam, chlorpyrifos and pymetrozine respectively, most of the field population remained susceptible to the three insecticides.3. The difference of detoxification enzymatic activities among populations of51. furciferaThe activities of detoxification enzyme esterase, monooxygenase P450and glutathione-S-transferase of11field populations and one laboratory strain (Lab-NN) were determined. The lowest activities of esterase and P450were found in Lab-NN among the tested populations, which were significant lower than that from field populations, moreover, there were obvious variation of esterase and P450activities among the field populations. However, there was no obvious difference in activities of glutathione S-transferase among the populations analyzed in this study, and the GST activity of Lab-NN was similar with that of field populations, which may imply GST does not involve the insecticide resistance of white-backed planthopper. There were significant positive correlation between esterase activities and imidacloprid toxicities among the assayed populations, which indicate imidacloprid resistance of S. furcifera be related with the raise of esterase activity. Also positive correlations were revealed for P450activities with the toxicities of buprofezin and thiamethoxam, which demonstrate the activity of P450affect the resistance level of buprofezin and thiamethoxam in S. furcifera.4. Risk assessment of buprofezin and imidacloprid resistance developed by S. furciferaContinuous selection with buprofezin and imidacloprid on S. furcifera population collected from Nanning in2006were made by rice stem dipping method under laboratory condition. The resistance levels were raised22.3-fold and21.3-fold for buprofezin and imidacloprid with realized heritability (h2) of0.1219and0.2453after24and14generations of selections respectively. The projected rate of resistance evolution indicated that, if80-90%of the population was killed at each generation, then a tenfold increase in LC50would be expected in7-9and3-6generations for buprofezin and imidaclorpid respectively. Imidacloprid had higher resistance risk than buprofezin for S. furcifera.