Higher larval mortality and delayed development of the mosquitoes Aedes albopictus and A triseriatus in container habitats with leaf litter grown in elevated atmospheric CO2

Background/Question/Methods: CO₂-enrichment can impact plants, such as increase growth rates and alter leaf chemistry. Such changes can affect leaf-feeding insects by altering the nutrition or toxicity of leaves. The invasive mosquito Aedes albopictus breeds in water-holding containers where it often competes for food as larvae with the native Aedes triseriatus. Container food mainly consists of allochthonous detritus inputs of leaf litter and associated microbes. We tested the hypothesis that litter grown in CO₂ concentrations representing worst-case but increasingly likely conditions predicted by IPCC climate-change scenarios affects competition among A. albopictus and A. triseriatus. Competition among Ae. albopictus and A. triseriatus was tested in microcosms with litter grown under elevated (~1000-ppm) or ambient (~385-ppm) CO₂ in a response-surface design. In a separate set of microcosms, population parameters for A. albopictus and A. triseriatus were tested with varying amounts of elevated-CO₂ or ambient-CO₂ litter and concentrations of commercial tannic acid under conditions of little competition.

Results/Conclusions:   Consistent with prior research, we found elevated-CO₂ litter had greater biomass, higher carbon, slower decay rate and higher tannin concentrations than ambient-CO₂ litter. Despite these differences, we found no differences in mosquito competition between litter types, with A. albopictus consistently superior to A. triseriatus. Single-species microcosms with elevated-CO₂ litter had lower larval survival and slower larval development than microcosms with ambient-CO₂ litter, but there were no differences between A. albopictus and A. triseriatus. Aedes albopictus and A. triseriatus also experienced similarly lower survival and slower development with increasing commercial tannic acid concentrations. These results suggest that possible future CO₂ conditions may actually suppress mosquito production by increasing the toxicity of leaf litter but that it would not affect population-level competition outcome between A. albopictus and A. triseriatus.