Males of many moths possess scent organs, ranging from simple scales and hair-tufts to complex glands.

The argument is made that such pheromonal assessment of defensive capacity may occur also in other insects, including danaid butterflies, many of which share with Utetheisa a dependence on pyrrolizidine alkaloids for sex-pheromone production.

It is proposed that in addition to signalling male presence to the female, hydroxydanaidal may provide the means whereby the female assesses the alkaloid content of the male and therefore his degree of chemical protectedness.

Evidence is presented indicating that Utetheisa derive hydroxydanidal from defensive pyrrolizidine alkaloids that they sequester from their larval foodplants (Crotalaria spp.). The principal chemical associated with the coremata, identified as a pyrrolizine (hydroxydanaidal), has a proven pheromonal role: males raised under conditions where they fail to produce hydroxydanaidal are also less likely to succeed in courtship, and the compound itself, as its (-)-isomer, is capable of inducing the principal receptive response (wing raising) of the female.

Males experimentally deprived of coremata are less acceptable to females. Males of Utetheisa ornatrix have a pair of brushlike glandular structures, the coremata, which they evert from the abdomen during close-range precopulatory interaction with the female.

Ornatrix hair preparing instances