|Bogner, FX; Grant, AJ; O'Connell, R: A Potential Kairomone Signal Stimulates Pheromone-Responsive Neurons in Utetheisa ornatrix (Lepidoptera: Arctiidae)., Journal of Chemical Ecology, 18, 427-439 (1992)|
The olfactory receptor neurons in basiconic sensilla on the antennae of Utetheisa ornatrix, which, in females, had earlier been shown to be responsive to stimulation with hydroxydanaidal (HD), are here shown to be responsive to valatile substances in samples of pyrrolizidine alkaloids (Pas). These latter substances are secondary plant metabolites present in the host plant of the larvae. Their sequestration during larval life serves to protect all life stages from predation. In males, the Pas also provide precursors for the production of the male pheromone, HD. In females, basiconic receptor neurons begin to respond to stimulus cartridges containing 1 ng of ®-(-)- hydroxydanaidal, 100 ng of ist isomer, (S)-(+)-hydroxydanaidal, and to volatiles emanating from 10 µg of the alkaloids monocrotaline and heliotrine. Receptor neurons in males are generally responsive to the same array of substances but with reduced sensitivity. The dietary background of the adult moths with respect to prior ingestion of Pas does not influence the response capabilities of basiconic receptor neurons to arctiid (Rhodogastria), had indicated that trace amounts of HD are present in Pas, presumably as their hydrolysis product. Thus we assume that, under natural conditions, HD may be an active component of the volatiles from Pas and may serve as both a male pheromone and kairomone. Sensitivity to HD could thereby provide information about the location and PA content of potential mates and food plants. Mechanisms that may have resulted in the evolution system with these properties are discussed. Keywords Insect olfaction, electrophysiology, pyrrolizidine alkaoids, Utetheisa ornatrix, Lepidoptera, Arctiidae, hydroxydanaidal, male-produced pheromone, olfactory receptor neurons.