Effects of neem-based insecticides on beet armyworm （Lepidoptera： Noctuidae）

Abstract Three commercial neem [ Azadirachta indica A. Juss (Meliaceae)]-based insecticides, Agroneem, Ecozin, and Neemix, and a non-commercial neem leaf powder, were evaluated for oviposition deterrence, antifeedant effect on larvae, and toxicity to eggs and larvae of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), on cotton leaves in the laboratory. Oviposition deterrence in no-choice, and two- and fivechoice assays, was observed for the neem-based insecticide treatments when compared with a non-treated control. Neem-based insecticides also deterred feeding by beet armyworm larvae. Direct contact with neem-based insecticides decreased the survival of beet armyworm eggs. Survival of beet armyworm larvae fed for 7 days on leaves treated with neembased insecticides was reduced to 27, 33, 60, and 61% for neem leaf powder, Ecozin, Agroneem, and Neemix, respectively. Possibilities for adoption of neem-based insecticides in commercial cotton for beet armyworm control are discussed.     

甜菜夜蛾对甲氧虫酰肼抗药性选育及其抗性生化机理初探

在室内用甲氧虫酰肼对甜菜夜蛾Spodoptera exigua(Hübner)幼虫进行抗药性选育,经过13代汰选,甜菜夜蛾抗性种群(Met-R)对甲氧虫酰肼的抗性倍数为4.19倍;交互抗性测定发现,Met-R甜菜夜蛾对毒死蜱、高效氯氰菊酯、虫螨腈、虫酰肼、甲胺基阿维菌素苯甲酸盐等药剂的交互抗性比值在1.05～2.07之间,不存在交互抗性。离体酶活性测定结果表明,Met-R甜菜夜蛾5龄幼虫中肠谷胱甘肽S-转移酶比活力是相对敏感种群(SS)甜菜夜蛾的2.44倍,存在显著性差异,说明谷胱甘肽S-转移酶活性增强可能与甜菜夜蛾对甲氧虫酰肼产生抗药性有关;但Met-R甜菜夜蛾全酯酶催化活性与SS的无显著性差异,说明其抗药性可能与酯酶无关。     

Effects of photoperiod and temperature on diapause induction in Conogethes punctiferalis （Lepidoptera： Pyralidae）

The yellow peach moth, Conogethes punctiferalis （Guenee）, a multivoltine species that overwinters as diapausing larvae, is one of the most serious insect pests on maize in China. Effect of photoperiod and temperature on larval diapause was examined under empirical laboratory conditions. Short-day treatments caused larval diapause at 25℃, and the critical photoperiod was between 12 and 13 h （or 12 h 51 min） light per day. No sensitive instar was identified for diapause induction under alternated short- （L ： D 11 ： 13 h） and long-day （L ： D 14 ： 10 h） treatments at different larval stages. However, accumulative treatment of three instars and 10 d under short-day treatment was required for the induction of 50% larval diapause. All larvae entered diapause at 20℃, whereas less than 3% did so at 30℃, irrespective of the long- or short-day treatment. Furthermore, under the short-day treatment, more than 90% of larvae went into diapause with temperatures ≤ 25℃, but less than 17% did so at 28℃. In contrast, under the long-day treatment, less than 19% of larvae went into diapause with temperatures ≥23 ℃. The forward shift （5℃） of critical temperature under the long-day regime demonstrated the compensatory effect of temperature and photoperiod on diapause induction. In conclusion, C. punctiferalis had a temperature-dependent type Ⅰ photoperiodic diapause response; there was no sensitive instar for diapause determination, but the photoperiodic accumulation time countermeasures both of the short-day cycles and the number ofinstars exposed, and the photoperiodic diapause response, was a temperature-compensated phenomenon.