Resistance Risk And Mechanism Of Laodelphgax Striatellus (Fallén)to Buprofezin

In recent years, the small brown rice planthopper（Laodelphax striatellus Fallén）becameone of the major pests of rice and maize production in china. In order to understand thecurrent resistance of L. striatellus against commonly-used insecticides in Tai’an, theresistance risk of L. striatellus to buprofezin and the mechanism of the buprofezin to L.striatellus, the sensitivity of commomly-used insecticides to L. striatellus was detected, theresistance risk to buprofezin was analysized, the effect of buprofezin on phenoloxidase（PO）and trehalase activity of L. striatellus was determind. The results were summarized asfollows:（1）Relative toxicity index of5insecticides against the3rd-instar nymphs of L.striatellus were surveyed with rice stem-dipping method. The results indicated that thetoxicity order is thiamethoxam> chlorpyrifos> acetamiprid> imidacloprid> buprofezin.Tai’an population has the highest sensitivity to thiamethoxam and chlorpyrifos, medium levelresistance to imidacloprid and high level resistance to buprofezin.（2）L. striatellus was continuously selected in greenhouse though spray method forresistance to buprofezin until12generations. After12times of selection with buprofezinduring13continuous generations, the LC50values of field population and selected populationwere52.853and2957.316mg·L^-1and the selected population obtained55.95folds ofresistance. So we can infer from above results that L. striatellus have high capability todevelop resistance to buprofezin in relative short time. When realized heritability was0.225and killing rate was80%⁹0%, resistance of L. striatellus reached l0folds in just4to5generations.（3）To investigate the effects of buprofezin on phenoloxidase（PO）and trehalaseactivity in L. Striatellus nymphae，anthrone methods and enzyme kinetics methods were usedto determine the activities of phenoloxidase（PO）and trehalase in3th instar nymphae of L.striatellus which were continuously treated with buprofezin for different length of time. Theoptimum reaction conditions of trehalase were pH6.0and best working temperature40℃with trehalose as substrate, The trehalase activity in vitro increased when buprofezinconcentrations were below0.1mmol·L^-1, reached its highest level at0.05mmol·L^-1concentrations. After the3th instar nymphae were continuously treated with three sublethalconcentrations(1.5mg·L^-1，5mg·L^-1and12mg·L^-1)of buprofezin for different length of time, the trehalase activity that after treated with three sublethal concentrations of buprofezin weresignificantly higher in low concentrations than in high concentrations, but the trehalosecontents were on the contrary. And the resistant strain’s activities of trehalase and trehalosecontents in different instars significantly higher than those contrast. The trehalase activity inthe3th instar nymphae of was increased in the certain dose range of buprofezin and inhibitedwith the increased concentrations. The resistance to buprofezin may have a certainrelationship of enhancing the activity of trehalase.The optimum reaction conditions of PO were pH7.0and best working temperature40℃by using catechol as substrate. The PO activity in vitro increased when buprofezinconcentrations were below0.4mmol·L^-1，reached its highest level at0.05mmol·L^-1and wasinhibited above0.4mmol·L^-1. After the3th instar nymphae were continuously treated withthree sublethal concentrations(1.5mg·L^-1,5mg·L^-1and12mg·L^-1)of buprofezin for differenttime, the PO activity was significantly higher than that of the control at the same treatmenttime and the activation rates at high concentrations were higher than that at lowconcentrations. The PO activity in the3th instar nymphae increased with treatment time.Buprofezin can activate PO activity in L. Striatellus.