Sublethal Effects of Imidacloprid on Fecundity, Apoptosis and Virus Transmission in the Small Brown Planthopper Laodelphax striatellus

SIMPLE SUMMARY: The small brown planthopper (SBPH) Laodelphax striatellus is an economically important pest in Asia, especially in China. Imidacloprid, a neonicotinoid insecticide, is commonly applied in rice fields to control the planthoppers. However, the widespread application of imidacloprid also has led to the development of resistance and to other potentially negative effects on crop protection. The sublethal effects of imidacloprid have been reported in many insects. Here, we investigated the potential effects of different sublethal concentrations of imidacloprid on SBPH and found that imidacloprid could affect the fecundity, apoptosis and virus transmission in the viruliferous SBPH. The results indicated that sublethal concentrations of imidacloprid may increase the fecundity of SBPH and the impact of insecticides on the transmission of plant viruses by insects should be considered when insecticides are applied to manage insect pests. ABSTRACT: Laodelphax striatellus damages plants directly through sucking plant sap and indirectly as a vector of rice stripe virus (RSV), resulting in serious losses of rice yield. It is one of the most destructive insects of rice in East Asia. Insecticides are primarily used for pest management, but the sublethal concentrations of insecticides may benefit several insects. The present research attempted to explore the effects of sublethal concentrations of imidacloprid on the fecundity, apoptosis and RSV transmission in the viruliferous SBPH. The results showed that the fecundity of SBPH was significantly increased after treatment with the LC(10) dose of imidacloprid, while the LC(30) dose of imidacloprid reduced the fecundity compared with the control. To further investigate the underlying mechanism of increased fecundity after exposure to the LC(10) dose of imidacloprid, we examined the expression levels of vitellogenin (Vg), Vg receptor (VgR) and caspases in the ovaries of SBPH, and observed the apoptosis by terminal deoxynucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL). qRT-PCR results indicated that the expression levels of Vg, VgR and four caspase genes were all significantly increased by the LC(10) dose of imidacloprid, and TUNEL assays suggested that the frequency of apoptosis was significantly higher in the SBPH treated by the LC(10) dose of imidacloprid, suggesting a potential correlation between the increased fecundity and the apoptosis of SBPH ovarioles. Additionally, the expression levels of RNA3 and capsid protein (CP) were both increased significantly by the LC(10) dose of imidacloprid, whereas were decreased by the LC(30) dose of imidacloprid compared to the control. Therefore, this study clarifies the mechanisms of sublethal effects of imidacloprid on viruliferous SBPH and could be used to optimize pest control strategies.