Communication among phlebotomine sandflies: a field study of domesticated Lutzomyia longipalpis populations in Amazonian Brazil

Abstract

Stimulated by laboratory work which has shown that adult male Lutzomyia longipalpis sandflies (Diptera: Psychodidae) possess sex pheromones, this paper describes a field study of communication in domesticated populations in Amazonian Brazil. Comparative observations on adults caught in animal pens, together with a series of mark-release-recapture and aggregation experiments, lead to the following inferences about host and mate-finding by males and blood-sucking females. During early colonization of a new site, males attending a host increase the of recruitment of other flies, males as well as females, but especially females. The pool of female recruits is consequently exhausted before that of males, whereupon the proportion of males increases, culminating in a male-biased sex ratio (in light traps) at equilibrium. Natural site-to-site variation in the sex ratio depends on the number of hosts available; among sheds supporting populations of flies near equilibrium, males are more responsive to host abundance than females. The implication is that, as long-range attractants (and then possibly arrestants) of females, pheromones are of little value to domestic males. Besides pointing to novel selection pressures under domestication, the results have practical significance: putative pheromone traps would need to catch or disorientate sandflies already present in animal pens, because they could not markedly increase female recruitment to pens, or attract a large proportion of females to other sites.