Effects of Aphid Honeydew on Soil Nitrogen Availability and Net Primary Production in an Alnus rubra Plantation in Western Washington

The effect of honeydew from an aphid (Pterocallis alni DeGeer) infesting a red alder (Alnus rubra Bong.) plantation in western Washington, USA, was studied experimentally. The purpose of the study was to examine the hypothesis that melezitose, an aphid-synthesized sugar in honeydew, causes an increase in the available soil nitrogen which improves tree assimilation thus benefitting the aphids. Aphids were removed from one plot by periodic spraying with Malathion and were left undisturbed on a control plot. The hypothesis was not supported by this study. Honeydew reaching the soil caused a reduction in available soil nitrogen, nitrogen mineralization rates, aboveground net primary production and nitrogen uptake by trees.