Evaluation Of Effectiveness Of Several Insecticides On Bemisia Tabaci(Gennadius) And Application Study Of Nitenpyra

Bemisia tabaci(Gennadius) is one of the most important pests of greenhouse vegetables.Control effects of several insecticides on B.tabaci were studied.Action mode and mechanism of nitenpyram,as well as its application techniques in field and resistance risk assessment in B.tabaci were investigated in this paper.The major results are as follows:1.Biological activities and control effects of several insecticides on B.tabaci were studied.The results of bioassay indicated that the toxicity of abamectin was the highest (LC₅₀:2.286 mg/L) to adult B.tabaci,followed by thiamethoxam,nitenpyram,imidacloprid,pymertrozine(LC₅₀:6.411mg/L,13.826 mg/L,36.814 mg/L,73.621 mg/L,respectively).Buprofezin was most toxin(LC₅₀:77.147mg/L) to eggs of B.tabaci, while abamectin had the highest toxicity to both low and high instar nymph(LC₅₀:2.588 mg/L,4.440 mg/L,respectively).The LC₅₀ of nitenpyram,thiamethoxam,imidacloprid,pymertrozine to low instar nymph were 6.373 mg/L,10.744 mg/L,25.311 mg/L,35.852 mg/L,respectively,while the values to high instar nymph were 9.541 mg/L,12.800 mg/L,62.122 mg/L,87.667mg/L,respectively.The LC₅₀ of Beta-cypermethrin,chlorpyrifos,cyhalothrin,buprofezin to both low and high instar nymph of B.tabaci were more than 115.310 mg/L.The results of field experiments showed that control efficacy of 1.8%abamectin EC,10%nitenpyram AS,25% thiamethoxam WG,25%pymertrozine WP after 9 days treatment with 2000x were the highest,with the value being more than 78.26%,followed by 10%imidacloprid WP, with the value being 66.61%,and 5%Beta-cypermethrin EC,40%chlorpyrifos EC,2.5%cyhalothrin WP,25%buprofezin WP had the lowest efficacy,with the value being less than 61.58%after 9 days treatment with 1000x.2.Different action modes of nitenpyram were tested.The results showed that nitenpyram had several kinds of action mode,including contact toxicity,stomach toxicity and intake transportation activity.The efficacy order of different action modes was intake transportation activity＞contact toxicity＞stomach toxicity.3.The effects of nitenpyram on activity of several enzymes in B.tabaci were tested. The results indicated that there was reversible inhibition of nitenpyram with LC₅₀ concentration on activity of carboxylesterases in B.tabaci.At 12h after nitenpyram treatment the specific activity of carboxylesterases was 0.6699 which increased with the time,and it reached 1.3510 at 48h after nitenpyram treatment.The activity of acetylcholinesterase was inhibited by nitenpyram,and the effect decreased with the time. The specific activity of acetylcholinesterase was 0.9386 at 12h after nitenpyram treatment,which decreased to 0.8041 at 48h after nitenpyram treatment.4.There were significant influences of environmental temperature on application effect of nitenpyram.The results showed that the toxicity of nitenpyram at 32℃was 12.67 times higher than that at 19℃.The corrected mortality of nitenpyram to adult B. tabaci was 92.13%-80.18%within 15 days after treatment,which decreased with the time.5.Different treatment methods had different results on effect of nitenpyram.The effects of nitenpyram treated by spraying and irrigating to the root were better than that treated by single leaf treatment and painting stem.Spraying was best on quick,and irrigating to the root was best on validity.6.Nitenpyram resistance was selected in laboratory with B.tabaci.After six selections with nitenpyram during eight generations,the resistance was 2.653-fold higher than before.The realized heritability(h²) of resistance was estimated as 0.1025, indicating a risk for B.tabaci to develop resistance to nitenpyram.