Examining the impacts of Wolbachia in laboratory mosquito populations

Wolbachia pipientis is an intracellular á-proteobacteria that occurs naturally in the mosquito Aedes albopictus and many other invertebrates. Wolbachia infections have been shown to impart both costs and benefits to hosts in terms of development, survival and fecundity. Here we use an experimental model system to test (1) the sustainability of closed laboratory populations of the mosquito Ae. albopictus and (2) examine the population-level effects of Wolbachia infection. The experimental protocol employs a two-cage design, with one cage for immature rearing and one cage for adult breeding. Replicate populations of infected and aposymbiotic Ae. albopictus were maintained and monitored for 720 days. Both infected and aposymbiotic populations reached stable population sizes within the model system. Population sizes for aposymbiotic cages were significantly higher at equilibrium than that of the naturally infected cages. The average sex ratio of the infected populations was close to 1:1, while aposymbiotic populations was female-biased. Death rates and fecundity in the infected populations were greater than aposymbiotic populations. Our results offer evidence for general fitness effects upon naturally infected Ae. albopictus adults that may in part explain of the widespread persistence of Wolbachia in natural populations of Ae. albopictus.