ECDYSTEROID RECEPTORS IN LAST INSTAR LARVAE OF THE WAX MOTH GALLERIA-MELLONELLA L

Ecdysteroid receptor levels were determined during the last instar of Galleria mellonella L. (Lepidoptera, Pyralidae). From these larvae, partially purified nuclear extracts were prepared. The ecdysteroid binding protein fulfils the requirements of an ecdysteroid receptor, showing high affinity for ecdysteroids, hormone analogue specificity and a limited binding capacity. Equilibrium dissociation constants are similar to those described for ecdysteroid receptors in flies. The non-steroidal agonist RH 5849 competed 3.5-fold less effectively with [H-3]ponasterone A for ecdysteroid binding sites than 20-hydroxyecdysone. Furthermore, the activity of different brassinosteroids was tested. 22S,23S-Homocastasterone showed a binding affinity similar to that of ecdysone. With G. mellonella a new system for the investigation of hormone-receptor interaction has been established.