Involvement of 20-hydroxyecdysone on feeding behavior and carbohydrate metabolizing enzymes in the adult stage of the red flour beetle, Tribolium castaneum

Since the red flour beetle, Tribolium castaneum, feeds on starch, α-amylase is an important enzyme for hydrolyzing carbohydrates into sugar to meet energy demands. It has been reported that 20-hydroxyecdysone (20E) involve in the regulation of α-amylase in the red flour beetle. Injection of 20E decreased α-amylase activity in dose- and time-dependent manner. α-Amylase activity in males and females showed different patterns responding to 20E. Adults injected with high concentrations of 20E (300–500 ng/insect) had low levels of food consumption leading to a decrease in body mass. Interestingly, glucose levels in treated adults increased significantly in parallel with the increase in trehalase activity in both males and females. 20E down-regulated Amylase (TcAmy), while Trehalase-1 and -2 (TcTre-1 and -2, respectively) genes were up-regulated. Taken together, 20E caused a decrease in α-amylase activity directly at the level of gene expression and indirectly by repressing food consumption and causing low ingestion levels. However, understanding the mechanism(s) by which feeding behavior suppression is caused by 20E in the red flour beetle needs to be examined in the future.