Species recognition elicited by differences in composition of the genital sex pheromone in Dermacentor variabilis and D. andersoni (Acari: Ixodidae).

The chemical basis for the ability of fed males of Dermacentor variabilis (Say) and D. andersoni (Stiles) to differentiate conspecific and heterospecific females was investigated using a neutered female bioassay. Male D. variabilis responded strongly in a dose-response manner to increasing concentrations of stearic and palmitic acids and an extract of the anterior reproductive tract (ART) of fed D. variabilis females. Mating responses were greatest at 1 microgram of fatty acid and 1 female equivalent (FE) of ART extract. D. variabilis males also responded strongly to D. variabilis females treated with a conspecific ART extract and a mixture of fatty acids simulating the extract; responses were moderate to D. andersoni females treated with the same extract or fatty acid mixture. They also responded moderately to conspecific females treated with D. andersoni extract. Male D. andersoni displayed moderate increases in mating behavior over a range of concentrations of stearic and palmitic acids and conspecific ART extract. D. andersoni males mated only with D. andersoni females treated with a conspecific extract or a mixture of fatty acids simulating the extract. Mating by D. andersoni did not occur in response to D. variabilis females treated with D. andersoni or D. variabilis ART extracts. Stearic acid alone or in combination with 20-hydroxyecdysone, oleic, or myristic acid did not account for the specificity of response of either species. D. andersoni males were much less responsive to fatty acids, alone or in mixtures, than D. variabilis males. These findings indicate that fatty acids are important in mate recognition by D. variabilis, but explain only part of that by D. andersoni. The possibility is raised that another compound is required for mate recognition by D. andersoni.