Responses of the tropical bont tick, Amblyomma variegatum (Fabricius), to its aggregation-attachment pheromone presented in an air stream on a servosphere

Male Amblyomma variegatum ticks feeding on a host release a mixture of o-nitrophenol and methyl salicylate which serves to attract conspecifics. The behavioural responses of A. variegatum on a servosphere to these volatiles presented in an air stream are detailed hers. In still air, ticks walked on all eight legs, but with long halts. In contrast, the air stream caused continuous walking and induced a reaching response where the forelegs actively sampled the air. Such reaching increased the angular velocity and reduced walking speed, effects that were amplified in the presence of vapours from o-nitrophenol and methyl salicylate in the air flowing over the ticks. Vapour from a 1:1 mixture of o-nitrophenol and methyl salicylate was attractive over a 10(4)-fold concentration range providing an increase in upwind displacement of 20-40%, significantly higher than the natural ratio where o-nitrophenol vapour predominates. Although the responses to o-nitrophenol vapour were variable when presented alone, this chemical was consistently attractive when delivered with steer hair odour - unattractive on its own. Moreover, the upwind walk to this combination did not cause a change in speed or angular velocity. This supports the hypothesis that the response to the pheromone is enhanced by host odour.