The Induction and Termination of Facultative Diapause in the Chalcid Wasps Mormoniella Vitripennis (Walker) and Tritneptis Klugii (Ratzeburg)*

Many insects exhibit a facultative diapause which is under the control of specific environmental factors. When the insect enters diapause growth and development cease. The end of diapause is signalled by the resumption of development. In most instances the environmental agencies that cause diapause affect the generation that will enter diapause, but occasionally a stimulus applied to the maternal generation affects the post-embryonic stages of the progeny. Commonly in facultative diapause, normal growth proceeds for several moults after the application of the stimulus, and development ceases only at a later stage. Whatever the mechanism which finally prevents moulting and produces diapause, it does not interfere with intermediate moults. The present report defines the extrinsic factors that cause facultative diapause in the last larval instar of two parasitic wasps and analyses in detail the mechanism of diapause termination.