Does geographic range affect the attractant-aggregation-attachment pheromone of the tropical bont tick, amblyomma...

The tropical bont tick, Amblyomma variegatum, transmits heartwater in sub-Saharan Africa and in the Caribbean. This species has a broad geographic distribution, ranging from Madagascar and other islands in the Indian Ocean through most of sub-Saharan Africa, to several islands in the eastern Caribbean Sea. Blood fed male A. variegatum secrete an attraction-aggregation-attachment (AAA) pheromone which, combined with CO2, excites host finding and formation of feeding clusters of these ticks. However, it is not known whether the composition of the pheromone varies throughout A. variegatum's geographic range. Extracts of fed male ticks were examined for phenols and volatile organic acids by gas chromatography and mass spectrometry to determine whether differences occur in the pheromone components of populations of this species across the geographic range (Guadeloupe, Zimbabwe, Zambia and Rwanda). No significant difference in the chemical composition of the pheromone in relation to geographic range was found. No significant differences in rates of attachment in response to native versus foreign extracts were found in on-host attachment tests comparing ticks from two countries. Guadeloupe (Caribbean) and Zimbabwe (African). This finding was confirmed in more detailed studies with ticks from Guadeloupe and four African countries (Kenya, Rwanda, Zambia and Zimbabwe). On-host attachment assays from these countries did not detect consistent differences in response to extracts from different locations. In an olfactometer bioassay, females were not consistently more attracted to extracts from their native locality than from any of the foreign localities. We conclude that despite the widespread distribution of A. variegatum over both hemispheres, no significant differences in pheromone composition or biological responses to male tick pheromone secretions occur.