GEOGRAPHIC VARIATION IN THE PHEROMONE SYSTEM OF THE SATURNIID MOTH<i>HEMILEUCA EGLANTERINA</i>

Abstract

The common sheep moth,Hemileuca eglanterina (Boisduval), appears to have at least two distinct pheromone types. Male moths from the population in the San Gabriel Mountains of southern California are attracted optimally to a blend ofE10,Z12-hexadeca-10,12-dien-1-yl acetate (acetate);E10,Z12-hexadeca-10,12-dien-1-ol (alcohol); andE10,Z12-hexadeca-10,12-dienal (aldehyde), whereas males from the population at Robinson Summit, northwest of Ely, Nevada, are attracted to the two-component blend of alcohol and aldehyde. Populations along the eastern edge of the Sierra Nevada Mountains are composed of individuals of both pheromone types and a type intermediate between the two. Antennae from male moths from the different pheromone types give distinctly different electroantennographic responses when challenged with blends of the pheromone components, with San Gabriel Mountains males showing a large response to acetate and lesser responses to alcohol and aldehyde. In contrast, antennae from Robinson Summit males, which are attracted to lures containing only alcohol and aldehyde, exhibit a large response to alcohol, a smaller response to aldehyde, and minimal or no response to acetate. Male moths from the eastern Sierra Nevada Mountains give antennal responses similar to those of either San Gabriel Mountains or Robinson Summit males. However, eastern Sierra populations also contain an intermediate type that does not occur in areas where the major pheromone types do not occur together. This third type may be a hybrid between the two other pheromone types, and it is attracted in approximately equal numbers to synthetic pheromone lures with and without acetate. The antennae of male moths in all populations tested responded toE10,E12-16:Ac, a major pheromone component of the congenerH. nuttalli, which is sympatric with someH. eglanterina populations, and in mostH. eglanterina populations tested, the addition ofE10,E12-16:Ac antagonized responses to otherwise attractive lure blends. Overall, the existence of different pheromone types in the differentH. eglanterina populations may represent a case of reproductive character displacement.