Larval Aedes japonicus and Aedes triseriatus alter biofilm dynamics in water-filled container habitats

Biofilms in aquatic habitats are formed by algae, bacteria, and fungi on organic and inorganic surfaces. Larvae of the mosquito species Aedes japonicus and Ae. triseriatus feed on biofilms by browsing on surfaces in container habitats. We postulated that larval feeding exerts higher grazing pressure on bacteria and fungi than algae because bacteria and fungi in biofilms may be easier for larvae to harvest and assimilate. In a microcosm experiment, we compared algal biomass in both the presence and absence of Ae. japonicus and Ae. triseriatus. Preliminary results showed a trend of greater benthic chlorophyll a levels in microcosms containing larvae relative to microcosms without larvae. This indicated that biofilm algae potentially were stimulated by larval activity. The observed increase in algal biomass may have resulted via release of biofilm algae from nutrient competition with heterotrophic microorganisms, or via nutrient recycling from larval feeding and excretion. We expanded upon these results by testing the effects of larval feeding on the community composition of biofilms in a laboratory experiment in which we exposed surfaces to different larval grazing pressures. The experiment was conducted with Ae. japonicus larvae alone, with Ae. triseriatus larvae alone, and with half Ae. japonicus larvae and half Ae. triseriatus larvae in order to test for differences in feeding stimulated by interspecific competition. Results from this study and their significance to larval competition and microbial dynamics will be discussed.