Absence of Assembly Pheromones in the Hard Ticks Dermacentor variabilis and Dermacentor andersoni (Acari: Ixodidae)

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Abstract
There was no evidence of response to an assembly pheromone when male and female Dermacentor variabilis (Say) and Dermacentor andersoni Stiles were exposed in petri dish assays to filter paper circles contaminated by other ticks (either conspecific or heterospecific), hexane extracts of ticks, tick feces, or tick excreta. These ticks did not assemble in response to the presence of other living ticks. Significant responses to saline extracts occurred in both species. However, D. variabilis did not respond to conspecific saline extracts of the same sex and D. andersoni males did not respond to conspecific saline extracts of females. D. variabilis males and females responded to filter paper circles contacted by conspecific ticks of the same sex, but not to those contacted by any other types. D. variabilis females also responded to saline controls. Ticks allowed to climb rods of a simulated “meadow” did not cluster in response to the presence of other live ticks or rods previously contaminated by ticks. These results do not support the hypothesis of an assembly pheromone in D. variabilis or D. andersoni. Contrasts between the ecology of the two North American Dermacentor species and those ticks for which assembly pheromones have been reported are discussed.