Sublethal effects of spinosad on Plutella xylostella (Lepidoptera: Yponomeutidae)

The effects of sublethal concentrations of spinosad applied for 48 h at LC25 (0.12 mg L-1) and LC50 (0.28 mg L-1) on the biological characteristics of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae), were investigated. The characteristics studied including development time, pupation rate, pupal weight, fecundity, fertility, larval weight and survival rate in the parent and offspring. The pupation rate and Papal weight were significantly lower in treated groups in which the third instars were treated with spinosad at LC25 or LC50 than in the control group. The fecundity, egg size and reproductive effort (fecundity x egg size) were strongly reduced, and the hatchability of smaller eggs tended to be lower in treated groups. The survival rate of the offspring at immature stages was lower in the LC25 and LC50 treatment groups than in the control group, and the development time tended to be prolonged in the treatment groups. The mean values of the intrinsic rate of increase (r(m)), finite rate of increase (lambda), gross reproductive rate (GRR) and net reproductive rate (R-0) were significantly lower in the treatment groups than in the untreated group. Generally, the effects on biological characteristics were greater in the LC50 treatment group, and the effects on the offspring were much smaller than those on the parent generation. Our results suggest that sublethal concentrations of spinosad may reduce population growth of P xylostella by affecting its survival, development and reproduction. (C) 2008 Elsevier Ltd. All rights reserved.