ABSTRACT
In this chapter, the authors focus on the tissue localization of the conversions and provide results obtained in their laboratory on two insect species, i.e., one heterometabolous species, Locusta migratoria, and one holometabolous species, Pieris brassicae. Tissues were dissected into an insect saline and thereafter incubated with [H]ecdysone in culture medium: medium S29 for Locusta and T. D. C. Grace's medium for Pieris tissues. The metabolic transformation of ecdysone detected in vitro is 26-hydroxylation. As the formation of 3-dehydro compounds from 3ß-hydroxyecdysteroids is reversible, it is possible that in vivo conditions favor the reduced forms, whereas the in vitro conditions allow 3-dehydro compounds to accumulate. For Pieris and Locusta, ecdysonoic acids are always formed in vivo, at any stage. The major difference between the two species studied concerns ecdysone conjugates, not detected in Pieris tissue incubations, although they are formed in vivo after injection of tritiated ecdysone into larvae, prepupae, or pupae.
