Sodium limitation in treeholes: effects on mosquitoes and micro-organisms

Christopher J. Paradise and William A. Dunson

Abstract.

1. A two-factor field microcosm experiment with two levels of water chemistry, with and without mosquito larvae was performed to test the hypothesis that Na is limiting to the treehole mosquito Aedes triseriatus Say (Diptera: Culicidae) at concentrations observed in the field. This experiment also tested the effects of both water chemistry and mosquito larvae on populations of protozoa and bacteria.

2. Female mosquitoes emerging from microcosms with high [Na] and [Mg] were significantly larger than females emerging from low [Na] and [Mg] microcosms. There was no effect of water chemistry on size of males; however males had higher body [Na] than females in both water chemistry treatments. Rates of development and survival were not affected by the treatments.

3. Presence of mosquitoes to some degree affected ciliates and bacteria. There was a mosquito x water chemistry x time interaction for densities of spirilla and ciliates; mosquitoes depressed densities of microbes and water chemistry had varied effects. Densities of bacterial rods and cocci were affected by the mosquito main effect and, for rods, a water chemistry by time interaction.

4. It is concluded that the effects of cation levels on mosquito populations are mediated both through direct uptake mechanisms and through some indirect effects on food sources. This experiment agrees with field observations suggesting that [Na] can be a limiting nutrient in some treeholes.

Key Words.

Aedes triseriatus, sodium, water chemistry, treehole, gender differences, protozoans, bacteria, microcosms

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