In vivo induction of ovarian development in decapitated Aedes atropalpus by physiological levels of 20‐hydroxyecdysone

Abstract

AbstractThe Bass Rock strain of the mosquito Aedes atropalpus is autogenous for the first gonadotropic cycle; i.e. adult females will undergo normal oocyte maturation without the benefit of a blood meal. Yolk deposition can be completely inhibited if these animals are decapitated within 6 hours or abdominally ligated within 8 hours of adult emergence. Injection of 4.8 ng of 20‐hydroxyecdysion into 12‐hour‐old adult females that had been decapitated soon after eclosion restored vitellogenesis in 100% of the treated insects. With this dosage of hormone 50% of the oocytes appeared mature 72 hours after injection. When the amount of hormone administered was increased to 4.8 × 103 ng all of the follicles in 100% of the animals contained yolk, but the average follicle length was 35% less than the vitellogenic follicles of either the non‐decapitated controls or the decapitated females that had received 4.8 ng of hormone.Yolk deposition was not restored in isolated abdomens by 4.8 ng of 20‐hydroxyecdysone. When the dosage was increased to 5 × 103 ng, 100% of the abdomens injected had follicles with yolk, and almost all the follicles contained yolk, but the average follicular length was reduced by 42% compared to intact controls.The vitellogenic activity induced by μg quantities of 20‐hydroxyecdysone in decapitated females or in isolated abdomens is no doubt nonphysiological. However the fact that a single injection of only 4.8 ng of 20‐hydroxyecdysone was capable of inducing in vivo vitellogenesis in decapitated females suggests that this hormone is normally required for this process to occur. Since isolated abdomens did not respond to this amount of 20‐hydroxyecdysone, the possibility that the presence of a thoracic factor, perhaps juvenile hormone, may also be necessary for normal ovarian development in A. atropalpus is discussed.