Stemflow chemistry: Effects on population dynamics of detritivorous mosquitoes in tree-hole ecosystems.

Experimental studies support four main conclusions about the effects of the chemical composition of stemflow on the growth, development, and survivorship of larvae of the tree hole mosquito Aedes triseratus Say, a vector of human encephalitis. (1) The presence and type of leaf litter is more critical for larval growth and development than the type of stemflow found in tree holes. (2) However, variations in stemflow chemical composition within the natural range of concentrations have substantial effects on growth, development, and survivorship of the larvae. Effects of pH, ammonia, nitrate, and sulfate are especially pronounced. (3) Acidification of stemflow caused increased mortality, prolonged development times, and reduced size of individual pupae, similar to effects of acid precipitation on the insect detritivores of lakes and streams. The stimulatory effects of nitrate and sulfate in acid precipitation do not compensate for the deleterious effects of the acidity. (4) Changes in stemflow characteristics sometimes had opposite effects on detritivores and detritus. The vigor of the larval population was not dependent on litter decomposition alone. In general, emergence patterns of adult treehole mosquitoes depend strongly on the chemical composition of stemflow.A fractional factorial experiment was successfully used. Fractional designs are advocated for experiments that screen a large number of nutrients or toxins for their effects on ecosystem components.