Studies On Mechanism Of Insecticide Resistance Of The White-backed Planthopper,sogatella Furcifera(horvath)(homopteera:delphacidae):biological,physiological And Biochemical Bases For Changes In Insecticide Susceptibility

In this paper, biological, physiological and biochemical bases for changes in insecticide susceptibility of the white-backed planthopper (WBPH), Sogatella furcifera Horvath are studied. The results are shown as follows.1 Comparison of insecticide susceptibility, activities of resistance-related enzymes and their frequency distributions among different populationsThe susceptibility of 4 WBPH populations collected in Zhejiang, Guangxi, Yunnan and Hainan provinces, China, respectively, to 4 insecticides (malathion, methamidophos, isoprocarb and buprofezin) and the activity of 4 enzymes (esterase, carboxylesterase, glutathione S-transferase and acetylcholinesterase) related to resistance were determined. Compared to results of a similar study by Fukuda et al. in 1969, there were significant increases in LDso values: 16.2-137.2 times higher for malathion and 10.3-15.6 times higher for isopcocarb. Both populations from Yunnan and Hainan were less susceptible but more heterogeneous to insecticides than those from Zhejiang and Guangxi, and this was reflected in higher enzyme activities in female adults. The zymogram for esterase isozymes was similar among different populations, with 6 bands, of which Rf values were 0.012, 0.05, 0.08, 0.11, 0.14 and 0.18, respectively. The staining level of zymogram in populations was corresponding with the activities of esterase tested. According to geographical difference in all evaluated indexes among populations, it could be inferred that long-distance migration may perform as a selection factor on resistance level of WBPH.2 Impacts of rice varieties on insecticide susceptibility and activities of resistance-related enzymes of WBPHThe female adult developed from WBPH nymph fed on N22, a middle-resistant variety, was more susceptible to malathion, and inversely to isoprocarb, while the activity of carboxylesterase was obviously suppressed but the others enzymes such glutathione S-transferase, alkaline phosphatase and acid phosphatase with the increase activities. The susceptibility of WBPH adults to malathion increased as the period fed on N22 increased. The activity of carboxylesterase was induced highly after fed on N22 for one day, then it declined successively. The day changes of the susceptibility to isoprocarb showed an adverse tendency against it to malathion, which maybe due to the decrease of the activity of acetylcholinesterase correspondingly. The adult resistance level to insecticides and enzyme activities seemed to be heightened after feeding on ASD7, a variety143resistant to BPH. The total phenol content in rice leaf sheath was the highest in N22, and could be regarded as one of the factors, which caused changes in susceptibility of WBPH to insecticide after feeding different rice varieties. It was recommended that suitable insecticides and planthopper resistant varieties should be coordinately used in practice so that they contribute more effects respectively.3 Changes in insecticide susceptibility, activities of resistance-related enzymes and their frequency distributions among the generationsThe susceptibility to methamidophos of WBPH showed no change after 53 generations successively rearing in the laboratory without use of insecticide. The resistances to malathion and isoprocarb were unstable, which decreased from 40.4-fold to 9.6-fold and from 11.1-fold to 3.1-fold, respectively. The analysis of changes in the activities and their frequency distributions of resistance-related enzymes, i.e. esterase, carboxylesterase, glutathione S-transferase and acetylcholinesterase, among the generations indicated that the reversion of malathion resistance was positively related to decrease in the activity of carboxylesterase significantly.4 Impacts of developmental stages on the resistance-related enzyme activities and the effects of insecticides on themActivities of esterase, carboxylesterase and glutathione S-transferase gradually increased with the growth of WBPH nymph from lsl instar to 5n instar, conversely that of acetylcholinesterase decrease...