Termination of vitellogenin synthesis by mosquito fat body, a programmed response to ecdysterone

In the blood‐fed mosquito, peak vitellogenin synthesis occurs 24–32 h after the meal, dropping to resting levels by 40 h. Challenging fat body with ecdysterone in vitro at various times after a blood meal demonstrated a refractory period at about 50 h, when there was also a drastic decrease in mitochondria, rough endoplasmic reticulum, ribosomes, and glycogen in fat body cells. When fat bodies from sugar‐fed females were incubated with continuous ecdysterone in vitro , vitellogenin synthesis reached a peak at 30 h, but then declined even in the presence of ecdysteroné. This was not due to the in vitro conditions since fat bodies were responsive, even if first exposed to ecdysterone, after 80 h in vitro. If ecdysterone was removed, vitellogenin synthesis ceased. If it was replaced, the fat body responded again only if the initial removal was done during the first 30 h. It is proposed that the falling ecdysterone titre is the major cause of cessation of vitellogenin synthesis, but that synthesis is programmed to decline even if exposure to ecdysterone is abnormally prolonged.