The application of organic insecticides in the agrotechnical praxis resulted in a great and unexpected progress in the control of insect pests, and was of a great economical value all over the world. The widespread application of these agents, however, is also accompanied by negative effects. The principal drawback of classical insecticides consists in the lack of their specificity, the useful insects being killed together with insect pests. Furthermore, the broad-scale application for many years led to the formation of more resistant insect strains requiring higher and higher doses of insecticides. The residues of the mostly used chlorinated compounds accumulate in human and animal foods producing directly or indirectly harmful effects in human sub jects. The critical situation led in many developed countries to the restriction in the usage of some types of classical insecticides. Under these circumstances it is quite natural that novel routes for the control of insect pests are investigated. In this connection, attention has been paid especially to the insect endocrinology and insect hormones which regulate the admirable and in many regards specific development from the egg to the adult insect. The recent successful discoveries in this field are thus in close relation to the practical requirements. Isolation and identification of moulting hor mones and juvenile-hormone-like naturally occurring substances not only made possible an exact investigation of their physiological effects but also stimulated the chemical research.