Probable occurrence of ecdysteroid fatty acid esters in different classes of arthropods

We investigated the fate of injected [³H]ecdysone or [³H]20-hydroxyecdysone in various species of ticks, spiders, scorpions, myriapods, crustaceans and insects. Most of these arthropods were able to convert the ecdysteroids to esterase-labile metabolites with a very apolar behaviour in reverse-phase HPLC. Some of them have retention times similar to the apolar conjugates AP2 of the tick, <i>Ornithodoros moubata</i>, which have been identified recently as ecdysteroids esterified as C₂₂ with palmitic, stearic, oleic or linoleic acid [Diehl et al. (1985a) <i>Int. J. invert. Reprod. Devl. </i><b>8</b>, 1–13]. Others are less apolar and could correspond to the AP1 from <i>O. moubata</i>. The possible function of these metabolites remains to be established. They could represent inactivation products and/or a hormone storage-form for embryos.