Olfactory responses of adult Amblyomma hebraeum and A. variegatum (Acari: Ixodidae) to attractant chemicals in laboratory tests.

Unfed adults of the African ticks, Amblyomma hebraeum Koch and A. variegatum (Fabricius), important vectors of human and animal diseases, were exposed to volatile compounds in an olfactometer in efforts to identify both tick-produced or synthetic chemicals capable of eliciting an attraction response. A formula, relative efficacy of attraction, was devised for comparison of responses between species and sexes to a particular test stimulus, or within a homogeneous population to different stimuli. Adults of both species responded strongly to known tick-pheromone constituents, nonanoic acid, methyl salicylate, 2.6-dichlorophenol and benzyl alcohol, as well as to a commercially produced antiseptic, TCP (Pfizer), and its major components, chlorinated and iodinated phenols. Benzaldehyde, a proposed tick-pheromone component, and heptadecane, not known from ticks, were markedly attractive to adults of A. hebraeum but not to those of A. variegatum. Males of the former species, but neither conspecific females not either sex of the latter species, responded significantly to salicylaldehyde (known from males of four species of ticks, including A. variegatum). o-nitrophenol, a major component of the aggregation-attachment pheromone of males of both A. variegatum and A hebraeum and a proven long-range attractant for them in the field, was only partially attractive to either species in the olfactometer. Neither species was attracted to 2-methylpropanoic acid, previously identified in volatile effluents form feeding male A. hebraeum. It is concluded that these important disease vectors respond positively to a variety of volatile chemicals, which may conceivably be used to attract them to traps, animals or acaricides in efforts to control ticks or the diseases they transmit.