PHEROMONES, KAIROMONES AND THE AGGREGATION DYNAMICS OF THE SANDFLY LUTZOMYIA-LONGIPALPIS

Male Lutzomyia longipalpis (Diptera: Psychodidae) form lek-like aggreg ations on a range of host animals, to which females migrate to mate an d take a blood meal. In so doing, females act as the vectors of Americ an 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 tr ap for fly control, a technique was developed to mark flies with minim um disruption of their natural behaviour, and employed in a set of fie ld experiments to investigate the role of host and fly factors in aggr egation 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 argue d that male behaviour maximizes mating success, whereas female behavio ur depends on the rate of bloodfeeding and the reduction of travel cos ts. 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 o f 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 s uceptible hosts. (C) 1997 The Association for the Study of Animal Beha viour.