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, pa rtially purified nuclear extracts were prepared. The ecdysteroid bindi ng protein fulfils the requirements of an ecdysteroid receptor, showin g high affinity for ecdysteroids, hormone analogue specificity and a l imited binding capacity. Equilibrium dissociation constants are simila r to those described for ecdysteroid receptors in flies. The non-stero idal agonist RH 5849 competed 3.5-fold less effectively with [H-3]pona sterone A for ecdysteroid binding sites than 20-hydroxyecdysone. Furth ermore, the activity of different brassinosteroids was tested. 22S,23S -Homocastasterone showed a binding affinity similar to that of ecdyson e. With G. mellonella a new system for the investigation of hormone-re ceptor interaction has been established.