The eggs of Utetheisa ornatrix contain pyrrolizidine alkaloids. These compounds are contributed by both parents, who sequester them as larvae from their food plants.Females receive alkaloid from the males at mating, apparently by seminal infusion, and transmit this alkaloid together with alkaloid of their own to the eggs. Field and laboratory tests showed that the alkaloids protect eggs from predators. The alkaloidal contribution of the male, although smaller than that of the female, itself provides significant egg protection. A previously identified pheromone, derived by the male from the alkaloid and emitted during precopulatory behavior, may announce the male alkaloidal worth to the female.

Male Utetheisa ornatrix produce a courtship pheromone (hydroxydnaidal) that they derive from systemic pyrrolizidine alkaloid of planit origin. Pheromone titers in males correlate with systemic levels of alkalid and with the quantity of alkaloid tr itted to the female at mating. The male's emission of pheromone during courtship may therefore communicate his possession of protective akaloids and his capacity to provision the female. By mating preferentially with males endowed with hydroxydanaidal, females may ensure their acquisition of an alkaloid f git for use in egg defense. OH H O-C\ C-_.In many insect species, males contribute resources to the female at mating (2). Benefits to the female from these nuptial gifts include increased fecundity (3-5) and enhanced offspring survivorship (6). When male donations are of variable quality, females may assess the gifts and mate preferentially with males able to bestow the most worthy offerings. Precopulatory gift assessment by the female can occur visually when offerings are presented overtly, as in the form of prey items (3, 7). But if gifts are bestowed covertly, by transfer with the spermatophore, their prenuptial evaluation becomes problematic.Covert gift presentation occurs in the arctiid moth Utetheisa ornatrix, in which the males transmit protective pyrrolizidine alkaloids (for example, monocrotaline; structure I) to the females by seminal infusion (6). Mated females transfer alkaloid thus received, together with systemic alkaloid of their own, to the eggs, which are protected against predation as a result (6). Both males and females obtain their alkaloid from their larval food plants (Crotalaria spp.), thereby acquiring protection both for themselves (8,9) and their offspring. Males, in addition, use the alkaloid metabolically to produce a pheromone, hydroxydanaidal (structure H), that they emit from a pair of brushes (coremata) everted during close-range precopulatory interaction with the female (10). Males endowed with hydroxydanaidal have a higher mating success than those devoid of the pheromone (10). The females possess antennal chemoreceptors by which they could gauge hydroxydanaidal (11).The finding that hydroxydanaidal mediates male acceptance in courtship led to the suggestion that female Utetheisa might assess their suitor's defensive vigor (that is, their alkaloid content), as well as the male's alkaloid donating capacity, by quantitative appraisal of the pheromone (6,8,10). If so, males should contain pheromone titers proportional both to their intrinsic alkaloid load and to the quantity of alkaloid they bestow upon females. We here present laboratory data demonstrating that these quantitative relations hold and that males do indeed advertise their alkaloidal "worth" in the context of courtship. I II MATERIALS AND METHODSOur approach involved rearing males on diets containing various levels of monocrotaline and then assaying chemically for (i) the hydroxydanaidal content of the coremata, (ii) the quantity of monocrotaline transferred to femal...

Pyrrolizidine alkaloid sequestered by adult male Danaus gilippus from plants is transferred in large measure to the female at mating, and by the female to the eggs. The eggs, presumably, are protected as a result. The male's courtship pheromone, danaidone, derived from the sequestered alkaloid, may function to advertise the male's alkaloid-donating capacity.

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