Prothoracotropic Hormone of Locusts

Abstract

MOULTING in insects is initiated by neurosecretory cells of the brain which secrete a prothoracotropic hormone. When this hormone is released into the blood it stimulates the prothoracic gland to release ecdyson, which, in its turn, sets off the cycle of processes which culminates in ecdysis. It has recently been suggested¹ that the pro-thoracotropic hormone of the silkworm is cholesterol. This is a surprising conclusion. Alone among animals, insects are incapable of synthesizing their own steroids, so that cholesterol (or β-sitosterol) is an essential constituent of the diet². It is, in fact, a vitamin for insects. There can be little doubt that cholesterol is a major constituent of nervous tissue in insects. But to be stored there it must first be transported from the gut via the blood stream. But if cholesterol has a hormonal function then it must exert this function whenever it is present in sufficient concentration in the blood, a concentration which must be reached after every meal. We have therefore attempted to investigate the effect of cholesterol on moulting in the locust Locusta migratoria migratorioides (Reiche and Fairmaire).