| The diamondback moth, Plutella xylostella L, is important pest of crucifer vegetables.Since 1758, Plutella xylostella was named by linnean, it was thought as the widely distributing insects of Lepidoptera. Before 1940s, Plutella xylostella. rose to major pests in many countries and regions. After 80s, Plutella xylostella extended to all cultivated cruciferous vegetables countries and regions,its caused to billions of dollars of economic losses every year. Because of using a great of pestcides long time, it that their resistance is increasing rapidly was become the best of prevented inscets. Thereore, with Plutella xylostella as the research object of this paper, On the basis of LC50 determination and the optimal ratio of two insecticides, which showed the synergistic effect,used method of CTC and proved controlled effect by field tests. The main research methods and results could be summarized as follows:1 The screening of optimum RatioThe toxicity of eight insecticides which are beta-cypermethrin, chlorfluazuron, tebufenozide, spinosad, chlorfenapyr, fipronil, diafenthiuron, indoxacarb were measured by dipping leaves method.The results showed that:the ratio of chlorfluazuron'and chlorfenapyr(13.20:1.72) was highly synergisticto in Plutella xylostella with 241 of co-toxicity coeffeciency (CTC). The other four strong synergism were also found in the mixture of chlorfluazuron and tebufenozide (13.2:74.80),chlorfluazuron and indoxacarb(2.20:3.60),spinosad and chlorfluazuron(8.80:0.84),indoxacarb and fipronil(18.82:1) in the pest with 181,142,198,189 of CTC respectively.2 Insectides trials of the best ratio of pesticide mixedThe experiment results showed that after a week, the average control effect of 2000 times chlorfluazuron and chlorfenapyr(13.20:1.72)reached to 84.24% which was better than the 3000 times and 4000 times. The average control effect of 3000 times chlorfluazuron and tebufenozide(13.2:74.80) reached to 79.41% which was better than the 4000 times and 5000 times and the average control effect of 2000 times chlorfluazuron and indoxacarb(2.20:3.60) reached to 85.08% which was better than the 3000 times and 4000 times.3 Influences of the mixture on metabolic enzymes in Plutella xylostellaThe activities of carboxylesterase, glutathione, glutathione-S-transferase enzyme, mix-function oxidas were treated by sublethal dose of insecticides. The results showed that:three mixtures with sublethal dose have different levels carboxyles terase of inhibition relative to Plutella xylostella strains susceptible and resistances, with the strongest inhibition by mixtures of chlorfluazuron and tebufenozide(13.2:74.80). The effect of the treatments on activities of glutathione-s-transgerase (GSTs) agreed with the effect on the quantitative of glutathione (GSH). But the insecticides of chlorfluazuron and chlorfenapyr (13.20:1.72) and chlorfluazuron and indoxacarb (2.20:3.60) showed inhibition to activities of GST, with the most obvious inhibition for the mixture. After treatment, activities of mixed function oxidase (MFO) in O-demethylation and aldrin epoxidation were suppressed in relative to R and S strain but the insecticides of chlorfluazuron and and tebufenozide (13.2:74.80) chlorfluazuron and indoxacarb (2.20:3.60) showed inhibition to activities of MFO in relative to S strain. |
