Effects of sublethal doses of imidacloprid on the fecundity of green leafhoppers, Nephotettix spp. (Hemiptera: Cicadellidae) and their natural enemies.

Abstract

Laboratory and field experiments were conducted to examine whether a sublethal dosage application of imidacloprid can induce physiological or ecological resurgence in the green leafhoppers Nephotettix virescens and Nephotettix cincticeps. Fecundity of N. virescens and N. cincticeps exposed to imidacloprid-treated rice seedlings was reduced to one-third and one-half, respectively, that of insects not exposed. Effect of imidacloprid on egg parasitoids of N. virescens was not detected because the percentage parasitism of N. virescens eggs was very low. The number of N. virescens adults consumed by a lycosid spider Pardosa pseudoannulata which was exposed to imidacloprid-treated rice seedlings for the last 24 h before experiment was significantly lower than that on untreated ones. However, the number consumed by a spider fed prey treated directly with imidacloprid was not significantly different from that of untreated prey. Survivorship of the mirid bug Cyrtorhinus lividipennis and the proportions of N. cincticeps eggs preyed on by bugs exposed to imidacloprid-treated seedlings or fed on eggs laid in the stems of treated seedlings were significantly lower than those of untreated ones. The results suggest that a sublethal dosage application of imidacloprid does not cause physiological resurgence in both green leafhopper species but it does induce ecological resurgence.