Combined Toxicity Of4Insecticides Against Mythimna Separata And Evaluation Of Field Control Efficacy

As a means of chemical control, the use of pesticides is irreplaceable in the process ofcontrolling crop pests, because of it’s low cost, simple to use, less medication, fast-effective.The pesticide mixture not only can produce significant synergistic effect for pest control butalso observably delay the development of pest resistance to insectide. Therefore, the complexformulation of pesticides have great significance for inhibiting the development of pestresistance, protecting our environment and extending the life of the pesticide.This paper, by using leaf dipping method, evaluated the toxicity of4insecticides andjoint-toxicity of6combination of these4insecticides against3rd instar larvae of Mythimnaseparata. A synergism combination and it’s optimum ratio were determined. Field efficacytrials of this synergism combination also be evaluated. This results could provide a theoreticalbasis for resistance management and controlling Mythimna separata. The main results are asfollows:(1) Toxicity of4insecticides against3rd instar larvae of Mythimna separata wereevaluated using the methods.Bioassay showed that1%emamectin benzoate EC>2.5%lambda-cyhalothrin EC>5%acetamiprid EC>40%chlorpyrifos EC. And the LC50values ofthe4insecticides were2.554mg/L,6.513mg/L,14.558mg/L and254.338mg/L,respectively.(2) By joint-toxicity trail of these4insecticides, We found the synergism combination is1%emamectin benzoate EC and5%acetamiprid EC in7:3(active ingredient ratio is2.14:1).And it’s co-toxicity coefficient (CTC) is207.90, that means that this combination wassignificantly synergistic.(3) The500times,1000times and1500times dilution of synergism combination weredetermined for controlling Mythimna separata in field. The result of field efficacy trialsshowed that these3treats of synergistic combination were all significantly better effectivethan other two single-dose insecticides at the95%confidence level. The synergismcombination had both quick effect and longer duration. The results of this study have apositive significance on the control of Mythimna separata and the registration of relatedpesticides in the future.