The effect of administering different quantities of a JHA topically and orally to the last instar larva ofSpodoptera litura of different ages has been studied. With both modes of treatment the effects comprised prolongation of the life of the instar followed frequently by death; imperfect ecdysis adversely affecting survival; production of non-viable larval-pupal intermediates, and occurrence of extra larval moults. Topical treatment is more effective but ecdysial failure and production of 1-p intermediates are more frequent with oral administration. A single supernumerary larval moult may be caused by administering a large quantity of JHA to 1 day old larva. Supernumerary instars are non-viable. Contrary to expectation, 1-p intermediates produced by early treatment show more pupal characters whereas middle-aged larvae show more larval characters. Prolongation of larval life caused by small quantities of JHA is the largest single effect which results into larval mortality.