Bacterial and fungal biomass responses to feeding by larval Aedes triseriatus (Diptera : Culicidae)

We investigated the effect of different densities (0, 20, or 40) of develop ing larval Aedes triseriatus (Say) on bacterial abundance, bacterial produc tivity, and leaf fungal biomass in a microcosm experiment. Larvae in the lo w-density treatment developed normally, but larvae at the high density were significantly slower to develop. Both bacterial abundance (direct microsco pic counts) and bacterial productivity (H-3-leucine incorporation rates) on leaf material were significantly lower in the presence of larvae. Bacteria l abundance in the water column did not change significantly with treatment , but bacterial productivity varied with time and declined significantly at both larval densities. Bacteria on the walls and bottom of the containers also were less abundant and significantly less productive in the presence o f larvae. Aside from presence/ absence effects, there was no clear evidence that larval impacts were density-dependent. Leaf-associated fungal biomass , as measured by ergosterol levels, varied with time but was not significan tly affected by any treatment, suggesting most fungal tissue was incorporat ed in the leaf matrix and unavailable to larvae. Based upon estimated bioma ss accrual and respiration of larvae, it appears that bacterial biomass and production were insufficient to account for carbon demands of growing larv ae. Because fungal biomass and leaf mass likely contributed little to gross larval demands, other carbon sources (e.g., protozoa and extracellular mic robial components) were probably used by larvae. Although apparently insuff icient for all larval carbon demands, bacterial and leaf fungal biomass may be adequate for other larval nutritional needs (i.e., nitrogen and essenti al lipids).