Effect of bisacylhydrazine ecdysteroid mimics (RH-5849 and RH-5992) on chromosomal puffing, imaginal disc proliferation and pupariation in larvae of Drosophila melanogaster

Two bisacylhydrazine insecticides with ecdysone-mimetic action, RH-5849 and RH-5992, have been subjected to several bioassay procedures that are prerequisites for ecdysone action in Drosophila larvae: (a) induction of early ecdysone-specific puffs on the polytene chromosomes of the larval salivary glands; (b) secretion of glycoprotein glue into the lumen of the salivary glands; (c) evagination of imaginal discs of adult wings and legs; and (d) partial rescue of wild-type phenotypic expression in ecdysone-deficient mutants (ecdysoneless1 (ecd1) and suppressor of forkedts67g (su(f)ts67g). In all these bioassays on Drosophila larvae, the two purely synthetic hydrazines exhibited similar dose-response relationships as did the natural steroid hormone, 20-hydroxyecdysone. In assays involving induction of early chromosomal puffs (74EF, 75B) or regression of the preexisting puffs (25AC, 68C), the dosages required for induction of standard ED-50 effects were one order of magnitude larger for the hydrazines in comparison with 20-hydroxyecdysone. In the assays related to glycoprotein glue secretion, evagination of imaginal discs, or rescue of phenotypic expression in ecdysone-deficient mutants, 20-hydroxyecdysone was two orders of magnitude more active than RH-5849 and RH-5992. We conclude that, in spite of these quantitative differences, the two hydrazine compounds studied are able to duplicate in Drosophila larvae the complex of qualitative biological effects that are a prerequisite for ecdysteroid hormones. The hormonomimetic stimulus of RH-compounds has been given at very low, intracellular, chromosomal level.