Sublethal effects of emamectin benzoate on development, reproduction, and vitellogenin and vitellogenin receptor gene expression in Thrips hawaiiensis (Thysanoptera: Thripidae).

Thrips hawaiiensis (Morgan) (Thysanoptera: Thripidae) is a sap-sucking pest that seriously damages several crops and reduces their economic value. Exposure to low concentrations of insecticides may have a sublethal effect on surviving insects. In order to provide a reference for the rational application of emamectin benzoate, its sublethal effects on the development and reproduction of T. hawaiiensis were evaluated. Pupal development time was significantly shorter in T. hawaiiensis treated with sublethal concentrations of emamectin benzoate (LC10 and LC20) than in control. Female adult longevity and female total longevity were significantly longer following LC20 treatment than in the control and LC10 treatment groups. Nevertheless, male adult longevity and male total longevity were significantly shorter in the LC10 treatment group than in the control and LC20 treatment groups. The sublethal concentration of emamectin benzoate (LC20) significantly shortened the preadult stages and the mean generation. Meanwhile, it significantly increased the finite rate of increase, intrinsic rate of increase, and net reproductive rate. The fecundity was significantly higher after LC20 treatment than after LC10 and control treatments. Compared with the control group, the LC10 and LC20 groups of T. hawaiiensis adults showed a significantly higher expression of the vitellogenin (Vg) and vitellogenin receptor (VgR) genes, which played a key role in increasing their fecundity. These findings suggest that short-term exposure to sublethal concentrations of emamectin benzoate may lead to a resurgence and secondary outbreak of T. hawaiiensis infestation. The results have practical applications for the management of this important and noxious pest.

Effects of spirodiclofen on life history traits and population growth of a spider mite predator Oligota flavicornis (Coleoptera: Staphyllinidae) based on the age-stage two-sex life table theory.

BACKGROUND: Knowledge of the compatibility between spirodiclofen and the predator Oligota flavicornis is an important aspect for the management of spider mites. RESULTS: We used the age-stage, two-sex life table to assess the effects of spirodiclofen on the life history traits and population growth of O. flavicornis. At the maximum recommended concentration (60 mg a.i. L-1 ) and also at twice the maximum recommended dosage (120 mg a.i. L-1 ), the preadult stages of O. flavicornis were significantly lengthened, while the adult longevity and fecundity decreased significantly. The finite rate (λ), intrinsic rate of increase (r), and net reproduction rate (R0 ) decreased, while the mean generation time (T) was longer after both the 60 and 120 mg a.i. L-1 treatments than it was in the control and 30 mg a.i. L-1 treatments. Life expectancy and reproductive value were higher in the control and 30 mg a.i. L-1 treatment than in the 60 and 120 mg a.i. L-1 treatments; the two higher concentrations were detrimental to the development of O. flavicornis. CONCLUSION: A proper combination of the O. flavicornis and spirodiclofen to control the spider mite, while avoiding the side effect of spirodiclofen, could be achieved based on the knowledge of life tables. © 2018 Society of Chemical Industry.