Sublethal effects of imidacloprid on the performance of the bird cherry-oat aphid Rhopalosiphum padi

The bird cherry-oat aphid, Rhopalosiphum padi (L.), is a major insect pest of cereal crops in many countries. Imidacloprid has been widely used for controlling piercing-sucking insect pests worldwide, but its sublethal effects on R. padi have not been well addressed. In this study, we investigated the sublethal effects of imidacloprid on biological parameters and five enzyme activities of R. padi. The LC(10), LC(20), and LC(25) of imidacloprid to adult aphids were 0.0053, 0.0329 and 0.0659 mg L(-1), respectively. These concentrations significantly decreased pre-adult survival rate, but prolonged the development duration of 1(st) instar nymphs, pre-oviposition period, and adult longevity. Adult oviposition period was also extended by LC(20). The intrinsic rate of increase (r), net reproductive rate (R(0)), and finite rate (λ) decreased at all three concentrations, whereas mean generation time (T) increased. Moreover, LC(20) and LC(25) significantly inhibited superoxide dismutase (SOD) activity, but increased catalase (CAT) activity. Acetylcholinesterase (AChE) activity also increased at LC(20). However, cytochrome P450 enzyme and peroxidase (POD) activity did not differ between imidacloprid treatments and the control. In conclusion, the imidacloprid concentrations tested here have negative impacts on the performance of R. padi by reducing its nymphal survival, extending the development duration of some stages, decreasing the rate of population growth, and altering enzyme activities.