Time-course of pyrrolizidine alkaloid processing in the alkaloid exploiting arctiid moth, creatonotos transiens

Abstract

The processing of dietary pyrrolizidine alkaloids by larvae and adults of the arctiid moth Creatonotos transiens was studied in time-course experiments: In larvae, pyrrolizidine alkaloid uptake is quickly followed by the transformation of the alkaloids into their N-oxides. Furthermore, if 7 S-heliotrine is applied, a stereochemical inversion of the hydroxyl group at C7 to 7R-heliotrine can be observed within 48h of feeding. The rate of this biotransformation is substantially higher in males which use the 7R-form later as a precursor for the biosynthesis of 7R-hydroxydanaidal, a pheromone. The resorbed pyrrolizidine alkaloids are deposited in the integument within 48h, where they remain stored during the larval, pupal and partly also the imaginal stages. Virtually no alkaloids are lost during ecdysis. Some pyrrolizidine alkaloids can be recovered from the meconium which is released at eclosion by the imagines especially when disturbed. In the adults pyrrolizidine alkaloids are processed in different ways by the two sexes: In females, about 50-80% of total alkaloids are transferred from the integument to the ovaries and the eggs within 2-3 days after eclosion. If females mate with alkaloid-rich males they additionally receive with the spermatophore up to 290|ig pyrrolizidine alkaloid, which are further translocated to the eggs. A biparental endowment of eggs with acquired defence alkaloids is thus achieved. In males, 30-50% of pyrrolizidine alkaloids remain in the integument; about 10–30% are transferred to the scent organ, the corema, where they are converted into 7R-hydroxydanaidal. Another part (about 40%) is passed to the spermatophore. In the laboratory experiments, the sizes of the coremata and their respective 7R-hydroxydanaidal contents are strongly dependent on the availability of dietary pyrrolizidine alkaloids during L6 and especially L7 stages. In the L7 stage even short-term feeding (4-6h) on Senecio jacobaea is sufficient to induce large coremata. © 1990, Walter de Gruyter. All rights reserved.