BIOLOGICAL-ACTIVITY AND RECEPTOR-BINDING OF ECDYSTEROIDS AND THE ECDYSTEROID AGONISTS RH-5849 AND RH-5992 IN IMAGINAL WING DISKS OF SPODOPTERA-EXIGUA (LEPIDOPTERA, NOCTUIDAE)

The effects of 20-hydroxyecdysone (20E), ponasterone A (PoA) and both dibenzoylhydrazine-based ecdysteroid agonists RH-5849 and RH-5992, wer e tested on in vitro-cultured imaginal wing discs of last-instar larva e of the beet armyworm, Spodoptera exigua (Hubner). In each case, the response was qualitatively similar to that induced by 20E, although th e concentrations required to induce response varied widely. The EC(50) of both ecdysteroids 20E and PoA to elicit wing disc evagination in 5 0% of the discs was 89.8 and 2.57 nM, respectively; for both nonsteroi d agonists RH-5849 and RH-5992 this was 870 and 11.7 nM, respectively. Binding competition studies using whole imaginal wing discs, showed t hat I-50 of 20E, PoA, RH-5849 and RH-5992 to displace 50% of [H-3]PoA- binding was 290, 7, 1100 and 33 nM, respectively, which is in the same order as the respective concentration to elicit a biological response .