Quantitative and qualitative variation in male pheromones ofPhragmatobia fuliginosa andPyrrharctia isabella (Lepidoptera: Arctiidae).

The dihydropyrrolizine pheromones, hydroxydanaidal and danaidal, were identified from the scent organs of malePhragmatobia fuliginosa (L.) andPyrrharctia isabella (J.E. Smith). Qualitative and quantitative GLC analyses were conducted on ca. 80 field-collected males of each species. The total pheromone titer was distributed bimodally in each species with most males having either a small amount (< 10 ng) of pheromone or a large amount (1-10 μg inPyrrharctia and 0.3-3 μg inPhragmatobia).Pyrrharctia males in the 1- to 10-μg range had a predominance of hydroxydanaidal, with little if any danaidal. MostPhragmatobia males in the 0.3- to 3-μg range had danaidal with little if any hydroxydanaidal. These compounds elicited a courtship response in sexually receptive females of both species. A bioassay based on this response was used to measure the thresholds of female response to these compounds.Pyrrharctia females were more sensitive to (R)-(-)-hydroxydanaidal than to danaidal.Phragmatobia females were more sensitive to danaidal then to (R)-(-)-hydroxydanaidal.