Effect of dissolved water cations on treehole insect communities

Christopher J. Paradise and William A. Dunson

Abstract.

We monitored water [Na], water volume, and larval densities of insects in natural treeholes and larval insects in simulated treeholes. In natural treeholes, water [Na] was inversely correlated with mosquito and helodid beetle densities; water [Na] was positively correlated with water volume in 1996.

The culicid mosquito Aedes triseriatus (Say), the ceratopogonid Culicoides guttipennis (Coquillett), and the syrphid Mallota posticata (F.) were the first to colonize simulated treeholes. Helodid beetle (Coleoptera: Helodidae) densities were significantly higher and mosquito populations had a significantly higher proportion of early instar larvae in microcosms that were lower in [Na] and [Mg]. On the other hand, more early instars of midges were found in microcosms higher in [Na] and [Mg].

The consistency of the relationship between low [Na] and high insect density in natural treeholes, and the effects of [Na] on microcosm communities suggest that [Na] and perhaps other cations may be important resources and cues to treehole organisms, and may partially determine treehole community structure.

KEY WORDS

sodium, Aedes, Culicoides, helodids, treeholes, microcosms

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