Comparisons of stimulatory effects of a series of concentrations of four insecticides on reproduction in the rice brown planthopper Nilaparvata lugens Stal (Homoptera: Delphacidae)

The rice brown planthopper, Nilaparvata lugens (Stal) (Homoptera: Delphacidae), is the type of insect pest whose resurgence is induced by pesticides. Outbreaks of the pest frequently occur in Asia. We investigated the effects of series of concentrations of four insecticides, imidacloprid, buprofezin, deltamethrin and triazophos, on the durations of the preoviposition (DPP) and oviposition period (DOP), female longevity (LOF), realized fecundity (RFE) and egg hatchability of N. lugens on two rice varieties: TN1 and Xieyou 963. DPP, DOP, LOF, NLE and hatchability varied with insecticide type, concentration, number of applications, and rice variety. For imidacloprid and buprofezin, RFE and hatchability decreased, DPP increased, and DOP and LOF lessened significantly with increasing concentration. In contrast, for deltamethrin and triazophos, DPP and DOP shortened, and LOF, RFE and hatchability increased significantly with increasing concentration. Increase in the number of applications for the four insecticides amplified the effects on these life-history variables. For example, three successive sprays of deltamethrin significantly increased RFE compared to a single spray under the same concentrations and rice variety. Additionally, rice variety also showed a significant influence on the variables. For example, RFE on TN1 significantly increased compared to on Xieyou 963 under the same concentrations and spray times. There were significant correlations between each index and insecticide concentrations for four insecticides on both rice varieties except in the case of hatchability for a single spray of buprofezin on TN1 and for LOF for a single spray of deltamethrin on TN1. Our findings have important implications for the understanding of mechanisms of N. lugens resurgence, and for management of the pest in commercial rice production.