Pheromones, kairomones and the aggregation dynamics of the sandfly Lutzomyia longipalpis

Male Lutzomyia longipalpis (Diptera: Psychodidae) form lek-like aggregations on a range of host animals, to which females migrate to mate and take a blood meal. In so doing, females act as the vectors of American visceral leishmaniasis in humans and canids. Host kairomones and a male pheromone are thought to be important for aggregation formation. Stimulated by interest in the development of a semiochemical-baited trap for fly control, a technique was developed to mark flies with minimum disruption of their natural behaviour, and employed in a set of field experiments to investigate the role of host and fly factors in aggregation dynamics. Males arrived at aggregations earlier than females, at a rate dependent on the abundance of resident flies and hosts. The immigration rate of females was dependent on fly abundance alone. The emigration rate of males decreased as fly and host abundance increased. The emigration rate of females was greater than males, and increased with host abundance, but decreased with female abundance. It is argued that male behaviour maximizes mating success, whereas female behaviour depends on the rate of bloodfeeding and the reduction of travel costs. Between nights, most males returned to the site of their previous night's activity, suggesting that flies may memorize a 'familiar area map'. These results raise the possibility that, without the addition of pheromone baits, insecticide spraying programmes that do not achieve blanket coverage of aggregation sites would not significantly reduce the fly population, and might increase parasite transmission between suceptible hosts. (C) 1997 The Association for the Study of Animal Behaviour.