Phosphoglucomutase (PGM) is a key enzyme in glycolysis and gluconeogenesis, regulating both glycogen and trehalose metabolism in insects. In this study, we explored the potential function of phosphoglucomutase (PGM) using RNA interference technology in Nilaparvata lugens, the brown planthopper. PGM1 and PGM2 were found highly expressed in the midgut of brown planthoppers, with different expression levels in different instar nymphs. The glycogen, glucose, and trehalose levels were also significantly increased after brown planthoppers were injected with dsRNA targeting PGM1 (dsPGM1) or PGM2 (dsPGM2). In addition, injection of dsPGM1 or dsPGM2 resulted in increased membrane-bound trehalase activity but not soluble trehalase activity. Furthermore, the expression of genes related to trehalose and glycogen metabolism decreased significantly after injection with dsPGM1 and dsPGM2. The expression levels of genes involved in chitin metabolism in the brown planthopper were also significantly decreased and the insects showed wing deformities and difficulty molting following RNAi. We suggest that silencing of PGM1 and PGM2 expression directly inhibits trehalose metabolism, leading to impaired chitin synthesis.

Glutamine:fructose-6-phosphate aminotransferases (GFATs) and phosphofructokinase (PFKs) are the principal rate-limiting enzymes involved in hexosamine biosynthesis pathway (HBP) and glycolysis pathway, respectively. In this study, the NlGFAT and NlPFK were knocked down through RNA interference (RNAi) in Nilaparvata lugens, the notorious brown planthopper (BPH), and the changes in energy metabolism were determined. Knockdown of either NlGFAT or NlPFK substantially reduced gene expression related to trehalose, glucose, and glycogen metabolism pathways. Moreover, trehalose content rose significantly at 72 h after dsGFAT injection, and glycogen content increased significantly at 48 h after injection. Glucose content remained unchanged throughout the experiment. Conversely, dsPFK injection did not significantly alter trehalose, but caused an extreme increase in glucose and glycogen content at 72 h after injection. The Knockdown of NlGFAT or NlPFK significantly downregulated the genes in the glycolytic pathway, as well as caused a considerable and significant decrease in pyruvate kinase (PK) activity after 48 h and 72 h of inhibition. After dsGFAT injection, most of genes in TCA cycle pathway were upregulated, but after dsNlPFK injection, they were downregulated. Correspondingly, ATP content substantially increased at 48 h after NlGFAT knockdown but decreased to an extreme extent by 72 h. In contrast, ATP content decreased significantly after NlPFK was knocked down and returned. The results have suggested the knockdown of either NlGFAT or NlPFK resulted in metabolism disorders in BPHs, highlighting the difference in the impact of those two enzyme genes on energy metabolism. Given their influence on BPHs energy metabolism, developing enzyme inhibitors or activators may provide a biological control for BPHs.

Excessive zinc (Zn) is toxic to plants, but the effect of zinc-stressed plants on herbivorous insects is still unclear. Hence, we assessed the effect of zinc-stressed rice plants on its feeding pest, Nilaparvata lugens. The soil–rice–N. lugens system was treated with Zn²⁺ solution. Sugar content in rice was measured, and the reproduction and trehalose metabolism in N. lugens were assessed. The trehalase activity in rice significantly decreased at 100 mg·kg⁻¹ Zn²⁺, and the trehalose content increased. The glucose and starch content increased at higher Zn²⁺ concentrations. The fecundity and trehalose content of N. lugens decreased after feeding on zinc-stressed rice, and the glucose content in the high Zn²⁺ group was significantly higher than that in the low Zn²⁺ group. In addition, the soluble trehalase activity of N. lugens significantly decreased under the 125 mg·kg⁻¹ treatment, while the activity of membrane-bound trehalase significantly increased under the 150 mg·kg⁻¹ treatment. Quantitative RT-PCR indicated significantly lower expressions of NlTre1-1, NlTre2, and NITps after Zn treatment. In conclusion, Zn²⁺ treatment significantly altered the sugar content in rice plants; it also decreased the fecundity of N. lugens, which may be mediated by alterations in trehalose metabolism.