Hair-covered scent organs of the male arctiid moth Creatonotos produce and dissipate the volatile pheromone hydroxydanaidal. The biosynthesis of this substance depends quantitatively upon the uptake of pyrrolizidine alkaloids (PA) with the larval foodplant. The size of the tubular, eversible scent organ (corema) is also positively correlated with the ingested amount of the same alkaloid, which acts like a specific growth factor. After an assessment of the corema normogenesis by Rick-Wagner (PhD thesis, University of Cologne, 1986) we injected PA into PA-free raised larvae, prepupae, and pupae. We found that the PA competence (sensitivity) of the corema anläge terminates with the first prepupal day. Ecdysone titer determinations (radioimmunoassay) are in agreement with those in other moth species. Ligated (ecdysone-free) pupal abdomina never developed imaginal structures, with or without earlier PA application. Ecdysone injection into ligated pupal abdomina of PA-fed specimens initiated the development of imaginal structures and also of coremata of more than (ecdysone-free) control size. Pupal abdomina without PA pre-treatment only developed very small coremata. With these experiments we have separated and identified two morphogenetic control agents of corema development: the dietary PA specifies the size of the organ whereas ecdysone induces the anlage to proliferate within these PA-dependent ranges and to differentiate adult structures, as it does with other imaginal anlagen.
Keywords: Corema morphogenesis; Creatonotos (Arctiidae); Ecdysone; Growth factor; Pheromone gland; Pyrrolizidine alkaloid; Scent organ.