| Abstract: | The hemolymph of last instar Manduca sexta larvae contains a protein factor that enhances ecdysone synthesis by prothoracic glands in vitro. The titer of the factor fluctuates during development in a pattern that suggests that it is regulated by juvenile hormone (JH). In untreated control larvae, the titer drops from 2.17 U ml?1 on day 1 to 0.27 U ml?1 on day 3. When larvae were treated with (7S)-hydroprene (a JH analog), the titer remained elevated (2.09 U ml?1 on day 3). JH I, however, was ineffective in preventing the precommitment drop in the titer of the factor. After pupal commitment, the titer of the factor increases in untreated larvae from 0.84 U ml?1 on day 5 to 1.62 U ml?1 on day 7. This increase was blocked when the sources of JH (the corpora allata) were removed on day 5 by head ligation. When head-ligated day 5 larvae were treated with either (7S)-hydroprene or JH I, the titer of the factor was driven to a level (1.88 U ml?1 and 2.05 U ml?1, respectively) that was not significantly different from that found in untreated day 7 larvae (1.62 U ml?1). The combined results indicate the titer of the hemolymph factor is regulated by JH. |
