Effects of larval mosquitoes (Aedes triseriatus) and stemflow on microbial community dynamics in container habitats

Abstract

The dynamics of the microbial food sources for Aedes triseriatus larvae in microcosms were found to be strongly influenced by larval presence. The total abundance of bacteria in water samples generally increased in response to larvae, including populations of cultivable, facultatively anaerobic bacteria. Additionally, a portion of the community shifted from Pseudomonaceae to Enterobacteriaceae. Bacterial abundance on leaf material was significantly reduced in the presence of actively feeding larvae. Principle-component analysis of whole community fatty acid methyl ester (FAME) profiles showed that larvae changed the microbial community structure in both the water column and the leaf material. Cyclopropyl FAMEs, typically associated with bacteria, were reduced in microcosms containing larvae; however, other bacterial fatty acids showed no consistent response. Long-chain polyunsaturated fatty acids characteristic of microeukaryotes (protozoans and meiofauna) declined in abundance when larvae were present, indicating that larval feeding reduced the densities of these microorganisms. However, presumed fungal lipid markers either increased or were unchanged in response to larvae. Larval presence also affected microbial nitrogen metabolism through modification of the physiochemical conditions or by grazing on populations of bacteria involved in nitrification-denitrification. Stemflow primarily influenced inorganic ion and organic compound concentrations in the microcosms and had less-pronounced effects on microbial community parameters than did larval presence. Stemflow treatments diluted concentrations of all inorganic ions (chloride, sulfate, and ammonium) and organic compounds (total dissolved organic carbon, soluble carbohydrates, and total protein) measured, with the exceptions of nitrite and nitrate. Stemflow addition did not measurably affect larval biomass in the microcosms but did enhance development rates and early emergence patterns of adults.

FIG. 1

Bacterial abundance as DMCs in microcosm leaf material and water columns and CFU in the water column only. Values are means ± 1 standard error (SE); n = 3 or 4 for each point. Arrows denote the times of stemflow additions.

FIG. 2

Composition of cultivable (TSA medium) bacteria from microcosm water columns. Values are mean percentages of total identifications ± 1 SE; n = 3 or 4 for each point.

FIG. 3

Principle component analysis of whole-community FAME profiles extracted from microcosm leaf material and water columns. Numbers near symbols indicate the sampling time (in days) of each point. The total variances for water column PC 1 and PC 2 were 35.7 and 15.4%, respectively, and for leaf material PC 1 and PC 2 were 21.6 and 14.9%, respectively.

FIG. 4

Concentration of major inorganic ions and pH in microcosm water columns. Values are means ± 1 SE; n = 3 or 4 for each point. Arrows denote times of stemflow additions.

FIG. 5

Concentrations of organic compounds in microcosm water columns. Values are means ± 1 SE; n = 3 or 4 for each point. Arrows denote times of stemflow additions.