Ecdysteroids during ovarian development and embryogenesis in the cricket,Gryllus bimaculatusde Geer

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Abstract
Ecdysteroid levels in Gryllus bimaculatus eggs have been determined at each of the developmental stages by a radioimmunoassay. Freshly laid eggs contained low amounts of free and conjugated ecdysteroids (c. 120 ng ecdysone equivalents per g wet wt.). A slight increase around day 8/9 (time of cuticle secretion) was followed by a conspicuous rise of free ecdysone, free 20-hydroxyecdysone and polar conjugated 20-hydroxyecdysone at the tenth day, that means one day before hatching of larvae. To examine possible metabolic transformations contributing to this increase in immunoreactive ecdysteroids during late embryogenesis, metabolism of [3H]ecdysone administered to vitellogenic females was investigated. Freshly laid eggs showed low amounts of labelled ecdysteroids, mainly in an apolar conjugated form. This pattern of labelled hormones did not change significantly during embryonic development. Comparable studies with [4–14C] cholesterol administered per os to ovipositing females revealed a similar pattern of (labelled) ecdysteroids as that shown by the radioimmunological method. Obviously, in this cricket species, maternal conjugates do not represent a storage form of hormones in the young embryo. The huge increase in ecdysteroids during late embryogenesis is apparently due to a de novo synthesis of hormones from cholesterol by the embryo.