As primary vectors of feared arboviral diseases such as dengue, chikungunya, and Zika viruses, invasive Aedes aegypti and Aedes albopictus are arguably two of the world’s most important mosquito species. In their invasive ranges, interspecific encounters are common, as both species lek at bloodmeal hosts for mating and as aquatic immatures occupy common container habitats, especially those provided by humans. Despite frequent documentation of interspecific competition between these species, spatial models of their global distributions do not consider population displacements and reductions attributable to competition. This presentation describes competitive displacements between these species; identifies probable mechanisms; and models their post-displacement distributions based on our research in Florida. We draw from distributional data on these species where they co-occur on islands; in tropical cities; in Florida and Bermuda, where rapid displacements of A. aegypti by A. albopictus are well documented; and in locations where one or the other species is absent. Based on our own experiments we show how reproductive interference by adult males and resource competition among larvae account for these displacements and propose explanations for observations where displacement was not detected, or the two species co-exist sympatrically. A statistical model identifies environmental correlates of species co-existence in south Florida.
Results/Conclusions
In the Hawaiian Islands where both species are invasive, between 1966 and 2012 A. aegypti ceded habitat to A. albopictus; interspecific competition as well as insecticides targeting A. aegypti may have both contributed. Changes in distributions of the two species favoring A. albopictus on South West Indian Ocean islands are associated with the less competitive feral, non-domestic phenotype A. aegypti formosus on Madagascar, Reunion, Seychelles, and Mayotte islands. In tropical cities, such as Kolkata, Kuala Lumpur and Bangkok, native A. albopictus was displaced by domesticated A. aegypti in the 1800s. A similar outcome has been observed more recently in Leticia, Colombia. Following competitive displacements of A. aegypti by A. albopictus in south Florida, the evolution of resistance to interspecific mating in A. aegypti females facilitated co-existence, and differential tolerances of habitat-dependent desiccation, seasonal fluctuations of resource inputs that reduce fitness differences, and intraspecific aggregation across containers that reduce interspecific crowding are likely contributors to local coexistence and habitat segregation in sympatry. Results underscore the importance of context-dependent interspecific competition for explaining the distributions of invasive mosquito vectors, which may have epidemiological consequences for disease transmission and should be incorporated into spatial models of global distributions.