The down-regulation of salivary protein gene expression by etofenprox partially contributed to reducing the risk of increased fecundity in the brown planthopper.

Etofenprox is a pyrethroid insecticide that acts on the nervous system of insects. Due to its low toxicity to aquatic animals, it is permitted for use in controlling insect pests in rice fields. The brown planthopper (BPH), Nilaparvata lugens, a significant piercing-sucking pest feeding on rice exclusively, secretes various salivary components when feeding. Salivary proteins are essential for BPH feeding, but their response to etofenprox is not well understood. The application of etofenprox down-regulated the expression of 21 salivary protein genes, among which 9 genes (NlShpa, Salivap 3, CA, NlSEF1, Nl12, NlHSC70-3, NlSP1, NlG14, and NlDNAJB9) showed significant differences. Most differentially expressed genes are found important for BPH physiological processes, except Nl12. Here we found that silencing Nl12 impeded ovary development, thereby inhibiting oocyte formation. The potential explanation was that Nl12 was highly expressed in both salivary gland and ovary, and the ovary development abnormality may be due to the direct effect from expression reduction in ovary and/or indirect influence from expression reduction in salivary gland. Altogether, our findings provide a new insight into the mechanism of action of etofenprox on insect pests and explain part of the reason why etofenprox does not stimulate reproduction in BPH.