Comparison of the attachment rates of males of the ticks Amblyomma hebraeum and A. variegatum to cattle, sheep and rabbits in the absence of aggregation-attachment pheromone.

Losses in domestic ruminants caused by heartwater (Cowdria ruminantium infection) in Zimbabwe and Mozambique are greater when the vector is Amblyomma hebraeum than when the vector is A. variegatum. It has been suggested that the epidemiology of the disease may be influenced by the rates at which unfed adults of these two tick species attach to uninfested hosts (i.e. in the absence of the male-produced aggregation-attachment pheromone [AAP]). In this study we confined unfed males of A. hebraeum and A. variegatum on uninfested cattle, sheep and rabbits and recorded their attachment rates. Males of both species attached more rapidly on cattle than on sheep or rabbits. Males of A. hebraeum attached more rapidly than males of A. variegatum on all three host species. The differences in the attachment rates between the two species were much greater on sheep and rabbits than on cattle. The findings suggest that in the absence of AAP, pioneer males of both tick species may attach to cattle, and pioneer males of A. hebraeum may also attach to sheep. The differences in the attachment rates of A. hebraeum and A. variegatum provide a possible explanation for observed differences in the epidemiology of heartwater associated with these two vector species.