Time sequence in the expression of various developmental characters induced by ecdysterone in Drosophila hydei

Abstract

The effect of injection of different ecdysterone concentrations into third instar larvae of Drosophila hydei at various stages was studied with regard to changes in genome activity, secretion of mucopolysacharides by the salivary gland cells, and pigmentation. It is found that the level and period of activity of puff 78B, a representative of the first series of changes in genome activity, depends upon the concentration of the steroid applied. For the second series of changes in genome activity, represented by puff 77BC, it is established that not only the level and period of its activity, but also its time of appearance depends on the age of the larvae and the steroid concentration administered. Younger animals are less responsive to the steroid than older ones. Glue secretion and pigmentation occur with a longer delay in young than in old larvae. This delay can be reduced by raising the steroid concentration. The possible relationships between the reaction of the various processes upon experimental administration of the steroid are discussed.