Tyrosine Metabolism in Gamma-Irradiated Rice Moth, Corcyra cephalonica

Abstract

The last instar rice moth (Corcyra cephalonica) larvae, exposed to 40 kR of gamma rays, failed to pupate and, when exposed to 120 to 200 kR, developed black pigments on the larval body. Following whole-body irradiation, the total tyrosine pool of the body was considerably reduced and the incorporation of tyrosine metabolites into the cuticle was impaired. Marked enhancement in the activities of dopa decarboxylase and phenoloxidase were observed at 4 and 24 hr after exposure to 40 kR though after 48 hr the activities of these enzymes declined considerably. There was also a sharp reduction in the activation period of phenoloxidase in the irradiated larvae. The enhancement in phenoloxidase activity at 24 hr was found to be dependent upon the radiation exposure up to 80 kR as well as on the developmental stage of the insect. At higher doses, however, phenoloxidase was inactivated. The exposure of insect homogenate to 200 kR also caused loss in phenoloxidase activity. These results have been correlated with the radiation-induced inhibition of pupation and blackening of the larval body.