LAUSR

Abstract In animals, feeding can regulate release of digestive enzymes. Digestive enzymes are produced and released in response to specific ratios of nutrients, so the quality and quantity of food ingested are important factors in the secretion and activity of digestive enzymes. In general, the enzyme activity and secretion in the fed insects are relatively higher than that in the unfed insects. Neuropeptides and peptide hormones are important regulators of enzyme activity. In several insects, the neuropeptide sulfakinin (SK) is known to be a regulator of feeding and digestion similar to cholecystokinin in mammals. However, the roles of diet and SK in regulation of activity of digestive enzymes in the important pest insect, the brown planthopper (Nilaparvata lugens), are unknown. In this study, we identified six genes encoding different digestive enzymes and cloned three of these. We found that enzymatic activity and transcriptional levels of digestive enzymatic activity genes were upregulated by refeeding animals for 5 hours after 24 hours starvation. Furthermore, injection of N. lugens SK reduces digestive enzyme activity and leads to a downregulation of digestive enzyme gene transcripts. This study provides new views into the action of diet and SK in regulation of digestive enzymes in (hemimetabolous) insects. Taken together with the roles of SK in inducing satiety, our data strongly suggest that SK signaling is important in regulation of food ingestion and processing.