Corematal function in Utetheisa ornatrix: interpretation in the light of data from field-collected males

Summary. Males of the moth Utetheisa ornatrix produce a pheromone, hydroxydanaidal, contained in two brush-like organs, the coremata, which they evert during courtship. Hydroxydanaidal is derived chemically by the males from pyrrolizidine alkaloids that they sequester from their larval food plants. It had been shown previously that the amount of hydroxydanaidal in the coremata correlates positively with a number of male parameters that are a measure of the male’s “worth.” Hydroxydanaidal could thus be used by the female as a basis for discrimination in courtship. Experiments carried out with virgin Utetheisa had shown that females do indeed mate selectively with males of high corematal hydroxydanaidal content, thereby accruing the multiple benefits that are the consequence of such selectivity. Unresolved was the question whether corematal hydroxydanaidal could still provide a basis for female appraisal of suitors when these had previously mated. Given the proven promiscuity of the female, male Utetheisa could be expected to be promiscuous as well. Evidence we present here shows that field-collected males, which could be expected to be mostly non-virginal, are of reduced acceptability to females. They are also, on average, in possession of lower quantities of hydroxydanaidal, explaining possibly why they should be held in lesser regard. At low levels, however, hydroxydanaidal does not lend itself for precise assessment of male worth, because as we show herein, at such levels, the compound does not correlate with any of the criteria of male quality (male size, spermatophore mass, male pyrrolizidine alkaloid content, amount of pyrrolizidine alkaloid transmitted to the female). Males that have mated beforehand are therefore likely not to be classed into subcategories by the females, but simply as belonging to one category of “less desirables”. The significance of these findings to our understanding of the mating strategy of Utetheisa is discussed.