Juvenile hormone and 20-hydroxyecdysone as primary and secondary stimuli of vitellogenesis in Aedes aegypti

Female Aedes aegypti that were fed blood and immediately abdominally ligated did not deposit yolk. Injection of 20‐hydroxyecdysone (1.5–5.0 ng) or topical application of juvenile hormone (JH) analogue methoprene (25 pg) did not induce vitellogenesis in these abdomens. When blood‐gorged ligated abdomens were treated with both hormones, however, vitellogenesis was stimulated in 60% of treated animals. Rocket immunoelectrophoresis indicated that vitellin concentration per follicle in treated animals was similar to that in intact controls. When ligated abdomens were first treated with methoprene and immediately injected with a crude head extract of egg development neurosecretory hormone, vitellogenin synthesis was induced at a rate similar to that in blood‐fed controls. Methoprene at this concentration (25 pg), did not cause an increase in whole‐body ecdysteroid titers. Larger amounts of methoprene (1.65 ng) were needed to stimulate egg development and ecdysteroid production. Implantation of ecdysone‐secreting ovaries into ligated abdomens did not stimulate vitellogenesis in the recipients. However, in recipients that were first treated with methoprene (25 pg), implantation of ecdysone‐secreting ovaries resulted in normal egg development. These experiments indicate that the appearance of JH precedes 20‐hydroxyecdysone in stimulating vitellogenesis following blood feeding in Ae. aegypti.