Male A. variegatum ticks release a mixture of o-nitrophenol (ONP) and methyl salicylate (MS) from dermal glands that develop soon after infesting a host. These products serve to attract conspecifics to the attachment site. The behavioural responses of A. variegatum adult males and females were recorded on a servosphere to vapours of both these compounds presented in an air stream. In the absence of the air stream A. variegatum adults walk on all eight legs but with long halts. An air stream causes continuous walking and induces a reaching response where the first leg pair is used to actively sample the air. This increases the angular velocity of the displacement and reduces walking speed. Air-current effects on behaviour are amplified in the presence of vapours of ONP and MS in the air flowing over the ticks. Males and females are equally attracted to low source doses of ONP and MS presented alone. Vapours from a 1:1 binary mixture of ONP and MS attract over the 10 4 -fold source dose range of 10ng to 100µg (10 9 -10 14 molecules/ml of air), but attraction to vapours from the binary mix is significantly reduced at source doses over 100µg. Attraction was higher to this 1:1 mixture than to the natural ratio released from the dermal glands of males, where ONP vapour predominates. This indicates that A. variegatum adults are sensitive both to the quality and quantity of the odour presented. Although the response to ONP vapour is variable on its own, it is consistently attractive when delivered with steer hair odour - unattractive on its own. Moreover, no change in angular velocity or speed was observed in the the upwind walk to this combination. This supports the hypothesis that the response to the pheromone is enhanced by host odour.

Index terms: Amblyomma, pheromone, host relations, behaviour

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