Influence of low-lethal concentrations of thiamethoxam on biological characteristics of Neoseiulus californicus (Acari: Phytoseiidae)

For successful implementation of integrated pest management (IPM) programs, having knowledge on lethal and low-lethal effects of pesticides on natural enemies is necessary. The present study evaluated the low-lethal effect of thiamethoxam on life table parameters of the subsequent generation of the predatory mite, Neoseiulus californicus McGregor (Acari: Phytoseiidae) fed on Tetranychus urticae Koch under laboratory conditions. The low-lethal concentrations LC۵, LC۱۰ and LC۲۰ were determined based on a dose-effect assay. The raw data were analyzed based on age-stage two sex life table analysis. Exposure to the low-lethal concentrations of thiamethoxam had no significant effects on developmental time of offspring of treated mites. Compared with control treatment, the oviposition period of treated mites with LC۵, LC۱۰ and LC۲۰ decreased significantly. The highest and lowest values of total fecundity were obtained at control (۳۵.۳ eggs/female/day) and LC۲۰ (۲۳.۶ eggs /female/day), respectively. The net reproductive rate (R۰) decreased with increasing dose from LC۵ (۲۲.۶ offspring) to LC۲۰ (۱۵.۰ offspring). The intrinsic rate of increase (r) and finite rate of increase (λ), were not affected by increasing concentrations. The mean generation time (T) decreased significantly at upper dose (LC۲۰ = ۱۳.۲ d), compared with control (۱۴.۷ d). In consequence, the low-lethal concentration influences of thiamethoxam in combination with N. californicus in order to design management programs of T. urticae are discussed.

Keywords:

predatory mite , LC۵۰ , Tetranychus urticae , toxicity , life-table