The aim of the this investigation was to study the bioinsecticidal activities of precocenes (I and II) on the berseem grasshopper, Euprepoc­nemis plorans plorans Charp. and the cotton leafworm, Spodoptera 1i:tor­ahs (Boisd.). Scored percentages for mortalities and abnormalities, as well as, the shortened nymphal duration had occurred due to ecdysitrop­ic effect. The complete sterility resulted from grasshopper treatment proved that the insects were as if chemically allatoectomized by preco­cene II. Biochemical assays on the latent stages for total protein, total cholesterol, integument chitin and whole body lipids content, in addition to some biochemical parameters indicated that precocenes can play a role as insecticides and/or chemosterilants.