Study On The Mechanism Of The Effect Of Selective Insecticides On The Reproduction Of Stripe Stem Borer, Chilo Suppressalis (Lepidoptera: Pyralidae)

This paper investigated that residues of imidacloprid in the rice plants, effect of selective pesticides on the fecundity of the stripe stem borer, Chilo suppressalis (Lepidoptera:Pyralidae), and effects of the pesticide on juvenile hormone (JH) and molting hormone (MH) in larvae and female adults of C. suppressalis. Main results were as follows:1. Residue dynamics of imidacloprid in rice plants.The residues of imidacloprid in the different positions and stages of rice after two application methods, foliar spray and water application, with 30 ppm imidacloprid were measured for rice (wujing15 and fengyouxiangzhan). Results showed that residues of imidacloprid at the tillering stage showed a significant difference between wujing15 and fengyouxiangzhan. The residue concentration of imidacloprid in wujing15 at 7 days after treatment (7DAT) was significantly higher than that in fengyouxiangzhan. Residue concentrations of imidacloprid in plant parts at 7 days after foliar spray at the tillering stage for two varieties were maximum value. Residue concentration in leaf and unexpanded leaf for fengyouxiangzhan significantly reduced compared with that in stem. Under water application, The change of maximum residue concentration was related to rice variety and plant parts. However, wujing 15 showed a different trend compared to fengyouxiangzhan.At the booting stage, the residue concentration in leaf after both foliar spray and water application for fengyouxiangzhan was higher that in stem. For different application methods, residue concentration of imidacloprid in the same plant parts showed a different dynamics trend. Residue concentration in stem under both foliar spray and water application reached a maximum value at 28 DAT, that in leaf, however, did the value at 14 and 28 DAT for foliar and water application, respectively. For fengyouxiangzhan, residue concentration in leaf at 14 and 21 DAT showed significant differences between two application methods of imidacloprid, the others did not show significant differences. 2. Effect of several insecticides on fecundity and hormones of C. suppressalisAlso, the paper investigated effect of insecticide-treated rice and coba on JH and MH in larvae and female adults and fecundity of female adults. Results demonstrated that there were significant differences on the weight of pupae developed from larvae fed on insecticide-treated rice plants among treatments, but there were no significant differences compared to control (fed on untreated rcie plants). The weight of pupa developed from 4th larvae fed on the rice plants treated by the 60ppm of imidacloprid was the smallest, and the weight of pupa developed from 1st larvae fed on treated plants was the greatest, with significant difference between them. But there were no significant differences compared to control. The fecundity of female adults developed from the larvae fed on wujing 15 treated by 30ppm of imidacloprid was lower than that of CK, decreasing by 40.43%, but there was not significantly difference between treatment and control. The fecundity of female adults developed from the larvae fed on fengyouxiangzhan treated by 15ppm of imidacloprid was significantly lower than that of CK, reducing by 37.82 % compared with that of control. The fecundity of female adults developed from the larvae fed on fengyouxiangzhan treated with 30ppm of imidacloprid was higher than that on wujing15. There was not significant difference in the fecundity of female adults developed from the larva fed on the coba treated by 15ppm and 10ppm of imidacloprid compared to control, but there were significant difference between 15ppm and 10ppm of imidacloprid.The effect of pesticides on changes of JH and MH in 4th larvae and JH in the female adult were studied on rice (wujing15 and fengyouxiangzhan) and coba. The results indicated that the concentration of JH in the larvae fed on the coba treated by pesticides showed a significant difference compared to control, but that of MH did not. JH/MH ratio showed a significant change, indicating that insecticides impacted hormone balance in larvae.Changes in JH in larvae were related to application methods of imidacloprid on rice. JH concentration in 4th larvae fed on fengyouxiangzhan treated with 30ppm of imidacloprid and 10ppm of triazoplos significantly increased compared with that on control plants. However, JH concentration in 4th larvae fed on wujing 15 treated with 30 ppm of imidacloprid did not show significant difference. For fengyouxiangzhan, there was not significant difference on MH level between the treatment and CK. But for wujing 15, MH level varied with insecticides, for example, MH level in larvae developed from larvae fed on wujing 15 plants treated with 30 ppm of imidacloprid showed a significant difference compared to control. JH level in the larvae fed on wujing 15 plants treated with water application with 30 ppm of imidcaloprid significantly decreased compared to control.Concentration of JH in female adult developed from larvae fed on fengyouxiangzhan plants treated with several doses of imidacloprid did not show significant differences compared with that on contro plants. Concentration of JH in female adult and application concentrations of imidacloprid showed a negative linear regression.