Induction of Nlvg and suppression of Nljhe gene expression in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) adult females and males exposed to two insecticides

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a typical pest in which resurgence is induced by insecticides. In the past, studies of resurgence mechanisms have focused on the physiological and ecological aspects of insecticide-induced stimulation of fecundity in adult females. Juvenile hormone (JH) plays a key role in the regulation of growth, development, diapause and reproduction in insects. The fecundity of insects is mainly regulated by the synthesis of vitellin (Vt) and vitellogenin (Vg). The synthesis of vitellogenin, in turn, is regulated by JH. The present study investigated the effects of two insecticides, deltamethrin and triazophos, on the gene expression of vitellogenin (Nlvg) and the juvenile hormone esterase (Nljhe), which is associated with reproduction. Our findings show that the Nlvg mRNA expression in adult females before and after mating is significantly induced by insecticides. Deltamethrin caused Nlvg mRNA expression to be 0.6, 1.7 and 2.1 times the control level at one, two and three days before mating (DBM) after adult emergence, respectively, and 2.5, 4.1 and 5.2 times the control levels at one, two and three days after mating (DAM), respectively. Triazophos exposure induced Nlvg mRNA expression at levels that were 1.2, 2.4 and 2.7 times the control levels at one, two and three DBM, respectively, and 4.1, 5.4 and 6.0 times the control levels at one, two and three DAM, respectively. The transcript level of Nlvg mRNA was higher for triazophos than for deltamethrin both before and after mating. However, the expression of Nljhe mRNA in adult females before mating was significantly suppressed by insecticides. The two insecticides significantly induced Nljhe mRNA expression in females after mating, and this effect increased with increasing insecticide concentration, especially at one and two DAM. The JHIII titer in N. lugens adult females both before and after mating increased with insecticide concentration. The JHIII titer in N. lugens adult males increased before mating and decreased after mating compared to the controls, indicating that JHIII in adult males is transferred to adult females via mating. The JH titer and insecticide concentration could be fitted into a significant regression equation. The present findings provide valuable information for improving our understanding of the molecular and hormone regulative mechanisms of insecticide-induced stimulation of fecundity in N. lugens.