Mimosine, a nonprotein amino acid, inhibits growth and enzyme systems in Tribolium castaneum

Abstract

The potency of mimosine is much greater in inhibiting growth and development of first-instar larvae of Tribolium castaneum than of fourth-instar larvae as expressed in suppression of larval weight gain and retardation in pupation. Approximately 70% suppression in weight gain of first-instar larvae was obtained at 0.06% mimosine and close to 100% at 0.08%. A dose-dependent decrease in the activity of trehalase, invertase, and amylase of fourth-instar larvae was obtained in vivo with the increase in mimosine concentration. At 0.3% dietary concentration, reductions of 58, 63, and 25% in trehalase, invertase, and amylase activity, respectively, were obtained after 2 days' feeding on treated diet, and of 65, 83, and 35%, respectively, after 5 days' feeding. On the other hand, increases of 27, 77, and 93% in protease activity were obtained in larvae fed for 5 days on diet containing 0.1%, 0.2%, and 0.3% minosine, respectively. The reduced activity of the trehalase enzyme might hamper the energy supply needed for growth and development, and that of the invertase and amylase enzymes for the feeding process. At concentrations of 10 −4 and 10 −3 M, mimosine had no effect on any of the carbohydrase enzymes in vitro. Hence, the observed effect on these enzymes in vivo could result from disturbances in protein synthesis leading to alteration in enzyme activity. Our study indicates that mimosine is a potent suppressor of growth and development of T. castaneum and may promote the development of a new group of insecticides.