Density-dependent feeding success in a field population of the sandfly, Lutzomyia longipalpis

1. A two-stage observational study of sandfly populations in chicken sheds was conducted on Marajo Island, northern Brazil, to identify determinants of feeding success within populations of female Lutzomyia longipalpis Lutz & Neiva during the dry and wet seasons. 2. We show, for the first time for a sandfly population, that per capita feeding success, measured as bloodmeal size, decreases with increasing density of other 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 success varies between sheds suggests that, with respect to bloodfeeding, female sandflies are not distributed according to the Ideal Free Distribution (IFD), i.e. they do not maximize individual resource gains. Probable costs of reduced bloodmeal size are discussed in terms of female fecundity and mortality. 5. By fitting a generalized version of Sutherland's interference model, which allows patch quality as well as female interference to vary non-linearly, we infer that bloodfeeding within sheds is predominantly on a subset of the available fowl. This too is consistent with the view that female flies disobey IFD. 6. We also demonstrate that increasing densities of female mosquitoes are associated with smaller bloodmeals in female Lu. longipalpis, suggesting that competition for bloodmeals can also occur between families of bloodsucking insects.