THE ENDOCRINOLOGY AND BIOCHEMISTRY OF 



INSECT DIAPAUSE 



A. D. LEES 



Agricultural Research Council, Unit of Insect Physiology, 

 Cambridge (Great Britain) 



The blood-sucking reduviid bug Rhodnius invariably under- 

 goes ecdysis after taking a full blood meal. In 1934Wigglesworth^ 

 observed that insects decapitated immediately after the meai 

 failed to moult, although they often remained alive for over a 

 year. He concluded that they had been deprived of a growth 

 hormone produced in the head. His comparison of this experi- 

 mentally induced state with other naturally occurring examples 

 of dormancy has since been shown to have a general validity. 



As knowledge of the humoral control of moulting and meta- 

 morphosis increased, it became apparent that the source of the 

 moult-inducing hormone was the brain or, more precisely, the 

 gi'oups of neurosecretory cells located near the mid-line in the 

 dorsum of the forebrain. The axons of these cells were shown to 

 end in two small organs situated just behind the brain, the 

 corpora cardiaca. Droplets of secretion, presumably transporting 

 the hormone, pass down the axons to the cardiaca and are there 

 discharged into the blood. 



This relatively simple picture was considerably complicated 

 when it was shown that a further endocrine organ — the pro- 

 thoracic glands — also secreted a moult-inducing hormone. 



The apparent contradiction was resolved by WiUiams- who 

 showed that the neurohormone from the brain activates the 

 prothoracic glands. It is the hormone secreted by the latter 

 organs — ecdyson — which stimulates the tissues to undergo a 

 moulting cycle. Since larval and pupal diapause involves the 

 suspension of ecdysis and metamorphosis it is not surprising 

 that the same dual endocrine mechanism controls diapause. 

 Indeed, the material used by Williams for demonstrating the 

 endocrinological relationships of the brain and prothoracic 



