Dietary and phylogenetic correlates of digestive trypsin activity in insect pests
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Because food proteins are crucial for insect survival, growth, and fecundity, enzymes involved in their digestion have attracted the attention of fundamental entomologists studying the mechanisms and patterns of dietary specialization, and applied entomologists searching for more efficient modes of pest control. Most insects digest proteins using trypsin, an endopeptidase that cleaves polypeptide chains on the carboxyl side of arginine and lysine, two basic amino acids. As the most ancestral proteinase, trypsin is wide-spread in the digestive tract of insects from various orders and with various feeding habits. The present review focuses on biochemical and molecular characteristics, mechanisms of regulation, and adaptive/non-adaptive changes of trypsin activity in response to heterogeneous food environments in a phylogenetic context. Within- and among-species variations in trypsin structure and regulation that contribute to better matching with specific food types are emphasized. We also discuss the relevance of these data for choosing an appropriate strategy for control of insect pests. Pest control strategies to reduce trypsin activity by interfering with substrate binding or trypsin synthesis and secretion have been suggested. Successful application of these procedures requires a multi-disciplinary approach and knowledge about digestive physiology of the pest, as well as the structural characteristics of trypsins that determine their interaction with proteinaceous inhibitors and other food compounds, about patterns of developmental changes in trypsin gene expression, adaptive responses of insects to food composition, and various environmental effects on trypsin activity.