Sublethal concentrations of thiamethoxam adversely affect life table parameters of the aphid predator, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae)

Abstract

Demographic approaches give a better understanding of the side effects of pesticides on beneficial organisms. In this study the effect of sublethal (LC10 and LC30) concentrations of thiamethoxam on the demographic parameters of Hippodamia variegata were assessed and the data analyzed using the age-stage, two-sex life table procedure. Results showed that thiamethoxam didn't have any significant effects on the developmental time of third instars, adult longevity and fecundity. However, the developmental time of fourth instars, pupae, the total preoviposition period (TPOP) and the adult preoviposition period (APOP) were affected significantly. Three main population parameters (r, λ and R0) were affected by the sublethal treatments. The intrinsic rate of increase (r) was 0.18 day−1 in the control but in LC10 and LC30 thiamethoxam treated insects this parameter declined to 0.15 and 0.13 day−1, respectively. The finite rate of increase (λ) in controls was about 1.20 whilst it was 1.16 for LC10 and 1.14 day−1 for LC30 treated insects. The net reproductive rate (R0) in control, LC10 and LC30 treated insects were 232.5, 114.6 and 68.5 offspring/individual, respectively. Therefore, the results achieved in this study showed that thiamethoxam at sublethal concentrations have potential to affect the predatory lady bird adversely. Thus more care should be taken when this insecticide is used in IPM programmes.