| Corn borer is a worldwide corn pest including European corn borer(Ostrinia nubilalis)and Asian corn borer(Ostrinia furnacalis).Asian corn borer is dorminant in China.Xinjiang is the main corn production area in China.As one of the most serious and most harmful pests in corn production in Xinjiang,a severe currence of O.furnacalis could cause more than 50 percent of corn crop loss,which seriously affected the yield and quality of corn.At present,insecticide treatments are still the effect measure to control Asian corn borers,but the unreasonable use will inevitably lead to the development of resistance.Following the field application insecticides degrade over time by biological and environmental factors to become sublethal concetration.Low dose of insecticides has different effects on insects,which is one of the reasons why insects develop resistance to insecticides.As a new generation of high-efficiency insecticide,chlorantraniliprole has been widely used since its introduction.However,many studies at home and abroad reported that lepidopteran pests had developed different level resistance to chlorantraniliprole.The sensitivity dynamics of Asian corn borer to commonly used insecticides have not been reported.In this study,it was monitored for the resistance to commonly used insecticides including chlorantraniliprole against Asian corn borer in Xinjiang,and the local populations were initially found to be reduced sensitive to chlorantraniliprole.To further study the metabolic mechanism of resitance to chlorantraniliprole of O.furnacalis,the resistant strain was selected by chlorantraniliprole in labatory.Furthermore,it was detected for expression and the resistance mutations of ryanodine receptor in the field populations.The results of the study are as follows:1.Monitoring on resistance to commonly used insecticides of Ostrinia furnacalis in XinjiangThe topical application and artificial diet dipping method were used to determine the sensitivities of chlorantraniliprole,lambda-cypermethrin,thiamethoxam,cyantraniliprole and alica(thiamethoxam·lambda-cyhalothrin)and liangtai(avermectins· chlorantraniliprole)in four populations of Asian corn borers from Urumqi,Yining,Shule and Zepu in Xinjiang.The results showed that Shule and Zepu populations had reduced sensitivity to chlorantraniliprole with resistance ratios(RR)were 4.00 and 4.20-fold compared to Urumqi population as being a relatively sensitive population,respectively;Yining population developed moderate resistance to cyantraniliprole and alica,with RR being 15.26 and 14.10-fold respectively,and low-level resistance to thiamethoxam with RR of 5.40-fold;Shule population reached moderate levels of resistance to alica with RR of 20.17-fold;Zepu population had a moderate level of resistance to alica and liangtai with RR of 10.97 and 13.48-fold,respectively.The above results provide a basis for guiding the rational use of insecticides for controlling O.furnacalis in the field.2.Effect of sublethal dose of chlorantraniliprole on growth and reproduction of Ostrinia furnacalisIn this paper,the effects of the short-term and long-term treatment with sublethal dose of chlorantraniliprole on the growth and development of O.furnacalis was studied.The results showed that the pupal weight and fecundity were significantly lower than those in the control by 9.2 and 30%respectively after exposed to chlorantraniliprole LD20 for 72 h;While continuously selected with chlorantraniliprole LD50 for nine generations(CAP-Sel),the all larval duration of CAP-Sel F10 were prolonged,of which the larval stages of 1st and 3rd instars were significantly increased compared with sensitive strain(S);The number of egg laying by single female and the hatching rate were significantly reduced by 15%and 6%less than the control.The net proliferation rate and intrinsic growth rate of CAP-Sel decreased significantly.The results showed that the sublethal dose of chlorantraniliprole had a significant inhibitory effect on the growth and development of Asian corn borer.3.Metabolic mechanism of resistance to chlorantraniliprole against Ostrinia furnacalisIn this paper,the biochemical mechanism of resistance to chlorantraniliprole against Asian corn borer was analyzed by measuring the activities of cytochrome P450,glutathione S-transferase(GST)and esterase(Est)in field populations and strain of Asian corn borer selected by chlorantraniliprole in laboratory.The enzyme activity analysis results in field populations showed that Yining population had the highest P450 enzyme activity with 3.16-fold as high as that of Shule population,and Shule population had the highest enzyme activity of GST(DCNB as substrate),which was 2.55-fold as high as Yining population in 2018;The enzyme activities of P450 and GST(with CDNB as substrate)in Changji population in 2019 were 2.79 and 2.18 times higher than those in sensitive population,respectively.The activities of P450 and GST(with CDNB as substrate)in Urumqi population were also significantly higher than those in the sensitive population(1.82 and 3.86-fold respectively).The treatment with chlorantraniliprole at doses of LD20 and LD50 for 72 h caused significant increase of GST activity(with DCNB as substrate)(46%and 86%respectively)in Asian corn borer;The activities of P450 and GST(CDNB as the substrate)in the 5th(F5)and 8th(F8)generation of CAP-Sel were significantly improved 4.25,5.06 and 1.27,1.33 times as high as that of the sensitive population,respectively.The GST(DCNB as the substrate)activity of the selected strain F8 was significantly increased by 36%compared with the sensitive population.The results showed that the increase of P450 and GST activities may be related to the resistance of O.furnacalis to chlorantraniliprole.4.Molecular detection of target resistance to diamide insecticides in field populations of Ostrinia furnacalis in XinjiangThe action target of diamide insecticides is the ryanodine receptor(RyR),and the resistance monitoring results show that the the field populations of O.furnacalis in Xinjiang had different levels of resistance to the diamide insecticides.In this paper,we determined the molecular mechanisms of resistance to diamide insecticides against O.furnacalis through analysing and detecting the expression changes and mutation of ryanodine receptors in field populations from Xinjiang in 2018 and 2019.The results showed that there was no significant difference in the expression of ryanodine receptors among different field populations in Xinjiang collected in 2018,while the expression of ryanodine receptors in Changji and Yining populations increased significantly by 4.04 and 3.86 times compared with sensitive strains collected in 2019;The gene mutation test results show that it was detected for a mutation in the ryanodine receptor of Changji population in 2019,in which glutamic acid(E)was replaced with aspartic acid(D)at position 1424(E1424D)with 30%of the mutation frequency.The above results may indicate that the resistance of Asian corn borer to diamide insecticides is related to the expression level and mutation of the ryanodine receptor. |
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