Testing hypotheses of seasonal species coexistence or displacement in two Aedes mosquitoes along an urban/suburban gradient

Variations in species coexistence or displacement can be observed in the effects of an invasive species on controphic resident organisms.  One such invasion is the spread of the Asian tiger mosquito (Aedes albopictus) into the range of the resident yellow fever mosquito (Aedes aegypti) in Florida, USA.  Following initial range reductions of the resident species attributable to the recent invader, field studies demonstrated considerable habitat segregation, and laboratory studies have hypothesized a mechanism for these patterns: in wetter areas, larval A. albopictus outcompete A. aegypti, but in drier areas, superior egg survivorship favors desiccation-resistant A. aegypti.  This hypothesis suggests two predictions of seasonal patterns of relative abundance in southern Florida, where there is a pronounced wet and dry season: 1) late in the wet season, there will be an increase in the relative abundance of A. albopictus, as it replaces A. aegypti through larval competition and 2) early in the wet season, A. aegypti will be more abundant, relative to A. albopictus, because of higher egg survival during the dry season.  To examine these predictions, we established 6 transects from the urban, coastal fringe to the suburban/rural edge of Palm Beach County, Florida.  We have found significant geographic differences in average temperature (urban>suburban), humidity (urban<suburban) and ratio of A. aegypti to A. albopictus (urban>suburban).  To date, we have observed a general decrease in both species and a decline in ratio of A. aegypti to A. albopictus from August to December 2006 which supports prediction 1.