Phenoloxidase activity at various stages of development in the egyptian cotton worm Spodoptera littoralis

Abstract

The phenoloxidase activity in Spodoptera littoralis was determined at various stages of development. During an instar period the activity of this enzyme was at its lowest after ecdysis, which then increased sharply and reached its maximum at the pharate stage.During larval-pupal development the highest activity occurred at the pharate pupal stage, reaching about fifteen and ten times that of the postecdysed larvae when it was expressed in terms of fresh larval weight and dried cuticle respectively. This activity was far stronger than that obtained in the pharate larvae (peak of activity) of the 4th and 5th instars. After larval-pupal ecdysis the activity dropped sharply and reached in untanned pupae about 40 per cent of that of the pharate pupa.During egg development the phenoloxidase system was at its highest activity compared with other stages of development, i.e., larval or pupal. In fertilized eggs the activity increased with age and reached in 3-day-old eggs, about 130 per cent that of the newly laid eggs. Striking results pointing to a strong phenoloxidase activity in the female genital organs indicate the presence of this enzyme in the early stage of egg development. These findings are strengthened by the fact that unfertilized eggs laid by virgin females exhibit a relatively high activity, albeit lower than in fertilized eggs.The general pattern of the phenoloxidase activity during the different stages of insect development (i.e., egg, larva and pupa) points to the possibility of a hormonal mechanism directing this system.