DECLINING ECDYSTEROID LEVELS ARE TEMPORALLY CORRELATED WITH THE INITIATION OF VITELLOGENESIS DURING PHARATE ADULT DEVELOPMENT IN THE INDIANMEAL MOTH, PLODIA-INTERPUNCTELLA

Photo-synchronized pupae were used to determine the titer of ecdystero ids during the pupal and pharate adult stages of the Indianmeal moth, Plodia interpunctella (Hubner). For female pupae that were kept in a 1 6 h light: 8 h dark (long-day) photocycle, there was one major peak of ecdysteroids. The ecdysteroids reached a maximum of 2000-2500 pg/mg w et wt between 28-36 h after pupation. The ecdysteroids declined to <50 0 pg/mg wet wt by 68 h after pupation. For pupae that were kept in con tinuous darkness, the ecdysteroid peak became broader with a maximum a t 24 h (3130 pg/mg wet wt). The composition of ecdysteroids at various times during pharate adult development was determined using gas chrom atograph-mass spectrometry with selected ion monitoring [GC-MS (SIM)]. Ecdysone was the major component (93%) in samples taken 28 h after pu pation, at the maximum of the pupal peak. Thus, high levels of ecdyson e are correlated with the beginning of adult ovarian development. As p harate development progressed, the proportion of 20-hydroxyecdysone in creased so that by 100 h after pupation 20-hydroxyecdysone was the onl y ecdysteroid detected. Previously, the initiation of vitellogenesis w as determined to begin between 96 and 100 h after pupation. In conjuct ion with previous work, these findings demonstrate that the ecdysteroi d titers decline before vitellogenesis is initiated and egg maturation can be completed.