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, theNlGFATandNlPFKwere knocked down through RNA interference (RNAi) inNilaparvata lugens, the notorious brown planthopper (BPH), and the changes in energy metabolism were determined. Knockdown of eitherNlGFATorNlPFKsubstantially reduced gene expression related to trehalose, glucose, and glycogen metabolism pathways. Moreover, trehalose content rose significantly at 72 h after dsGFATinjection, and glycogen content increased significantly at 48 h after injection. Glucose content remained unchanged throughout the experiment. Conversely, dsPFKinjection did not significantly alter trehalose, but caused an extreme increase in glucose and glycogen content at 72 h after injection. The Knockdown ofNlGFATorNlPFKsignificantly 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 dsGFATinjection, most of genes in TCA cycle pathway were upregulated, but after dsNlPFKinjection, they were downregulated. Correspondingly, ATP content substantially increased at 48 h afterNlGFATknockdown but decreased to an extreme extent by 72 h. In contrast, ATP content decreased significantly afterNlPFKwas knocked down and returned. The results have suggested the knockdown of eitherNlGFATorNlPFKresulted 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.