Abstract
Ecdysone stimulates the synthesis of vitellogenin in the fat body of mature female mosquitoes. Preparations from newly emerged animals, however, were found to be unresponsive to ecdysone. Responsiveness developed to a maximal level during a 36‐h post‐emergence period of maturation. This maturation could be accelerated with juvenile hormone application, prevented by allatectomy, and restored by corpora allata implants. It is concluded that the development of fat body responsiveness to ecdysone is dependent upon previous post‐emergence exposure to juvenile hormone.