Insecticide Resistance And Biochemical Mechanism Of The Melanism Mutant Strain Of Spodoptera Exigua

Beet armyworm, Spodoptera exigua (Hiibner), is a worldwide distributed polyphagous pest on various cultivated crops, including vegetables, cotton, fruit trees, ornamentals, and so on. In past two decades, S. exigua has emerged as a serious pest in many countries and it has been noticed that some population of S. exigua has became resistant to many insecticides including Pyrethroids, which result in many insecticide failed to control the pests. So far many scientists have done some research in the resistance field, such as resistance monitoring, biochemical mechanisms for resistance, resistance evaluation, and resistance inheritance et al. But the study encountered the difficult to the further stage for the absence of remarkable genetic strain.In this study, the improvement of artificial diet of S. exigua was conducted, and find out that feed made of bean, barly, yeast extract with addition of vitamin C, agar, sodium benzoate, benzoic acid, honey and acetic acid is able to satisfy the need of normal growth for S. exigua. Sixteen generations of S. exigua were carried out with the improved feed. The degeneration of hatching rate was90% , larvae survival rate was80% , pupal period, weight of pupall5-130mg, pupation rate was 80% and emergence rate was 90% were not observed. This established a foundation of the providing of a large number of standard test pest which is inevitable in following research work.We primarily researched the change of sensitivity against conventional pesticides of two lines of S. exigua (the melanism mutant strain SEM and the wild strain SEW) feeded by different plant, which provided a theory basis for the developing progress of insecticide resistance and for the timely, economically insecticide application as well. The resulte of this experiment showed that different host plant significantly affected the sensitivity against pesticide of 5. exigua. Feeded by different host plant, both strains of S. exigua showed some different change in the sensitivity against deltametherin, chlorpyrifos, chlorfenapyr, tebufenozide, while the resistance of black strain is always higher than the normal strain. The sensitivity against deltametherin changed relatively higher in both strains with the 13.36 and 12.30 times higher of LD₅₀ respectively. However, the significant sensitivity change against tebufenozide was not found in both strains with the LD₅₀ 2.54 and 2.23 times higher respectively.Research on the biochemical resistant mechanism of S. exigua was also carried out in this study. We tested the change of detoxifying enzymes in both strains feeded by different host plants, the result of which showed a higher enzyme activity in mutant strain. Further more, the variation of enzyme activity of S. exigua was observed, in which the esterase and mixed function Oxidase showed significant difference while glutathione-s-transferase did not. Different host plant can induce the change of the activity of carboxylesterase, which is probably the main reason for the different sensitivity against pesticide observed in pests.