Ecdysteroids as a component of the genital sex pheromone in two species of hard ticks,Dermacentor variabilis andDermacentor andersoni (Acari: Ixodidae)

Neutering of part-fed females eliminated copulatory behavior inDermacentor variabilis (Say) andD. andersoni Stiles males. Extracts from the anterior reproductive tracts of part-fed (7 days) females partly restored the male copulatory behavior in conspecific neutered females. Similar extracts from unfed females did not restore the behavior, suggesting that the pheromone was produced during feeding. Perception of the genital sex pheromone by sensillae on the male cheliceral digits was confirmed by electrophysiological techniques.Males ofD. variabilis andD. andersoni responsed positively to authentic ecdysone and 20-hydroxyccdysone (20HE) in neutered female bioassays. Responses to sterols were significantly lower than to ecdysteroids. Electrophysiological assays suggest a sensitivity of males to high doses of ecdysteroids. The strongest responses were to 20HE in both species. Ecdysteroids, specifically ecdysone and 20HE were shown to be present in the anterior reproductive tracts in excess of amounts that could be explained by mere hemolymph contamination. Ecdysteroids were also found in washings of the vaginal lumen of these two species.Dermacentor andersoni females contained larger amounts of ecdysteroids thanD. variabilis females. 20-hydroxyecdysone and possibly ecdysone appear to be components of the genital sex pheromone ofD. variabilis andD. andersoni. Species recognition may be facilitated by these components, but the complete mechanism is not yet fully understood.Supported by grant AI10, 986 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Public Health Service, Department of Health and Human Services, Bethesda, Maryland.