DENSITY-DEPENDENT FEEDING SUCCESS IN A FIELD POPULATION OF THE SANDFLY, LUTZOMYIA-LONGIPALPIS

1. A two-stage observational study of sandfly populations in chicken s heds was conducted on Marajo Island, northern Brazil, to identify dete rminants of feeding success within populations of female Lutzomyia lon gipalpis Lutz & Neiva during the dry and wet seasons. 2. We show, for the first time for a sandfly population, that per capita feeding succe ss, measured as bloodmeal size, decreases with increasing density of o ther females at the feeding site, and increases with host density. 3. Interference with sandfly feeding is evidently host-mediated, as with some other bloodsucking insects. 4. The fact that female feeding succe ss varies between sheds suggests that, with respect to bloodfeeding, f emale sandflies are not distributed according to the Ideal Free Distri bution (IFD), i.e. they do not maximize individual resource gains. Pro bable costs of reduced bloodmeal size are discussed in terms of female fecundity and mortality. 5. By fitting a generalized version of Suthe rland's interference model, which allows patch quality as well as fema le interference to vary non-linearly, we infer that bloodfeeding withi n sheds is predominantly on a subset of the available fowl. This too i s consistent with the view that female flies disobey IFD. 6. We also d emonstrate that increasing densities of female mosquitoes are associat ed with smaller bloodmeals in female Lu. longipalpis, suggesting that competition for bloodmeals can also occur between families of bloodsuc king insects.