Prothoracicotropic hormone
Prothoracicotropic hormone (PTTH) was the first insect hormone to be discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć (1922) and Vincent Wigglesworth (1934), who realized that ligation of the head of immature insects could prevent molting or pupation of the body region excluded from the head if the ligation was performed before a critical age in the lifestage was reached. After a certain point the ligation had no effect and both sections of the insect would molt or pupate. However, implantation of a conspecific brain to a sessile ligated abdomen or an abdomen under diapause would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
Kenneth Callow
In the 1930s Callow became interested in the structure and action of sex hormones and identifying steroids in urine. In a 1936 paper, written with Frank Young, a footnote states "The term steroids is proposed as generic name for the group of compounds comprising the sterols, bile acids, heart poisons, saponins and sex hormones." Callow claimed that this was the first use of the term "steroids". 
He showed that androgens were excreted in the urine in similar amounts in men, women and eunuchs, which at the time was surprising. His conclusion was that these substances were produced by the adrenal cortex as well as by the gonads. This conclusion was supported by findings made jointly with A.C. Crooke, working at the London Hospital, that patients with Cushing's syndrome, caused by a tumour of the adrenals, had very high levels of androgenic substances in the urine.