Trophic Relations of Aquatic Insects

Abstract

One of the most ubiquitous features of freshwater habitats is their present rate of change in response to man-engendered perturbations. Any rehabilita­ tive or management strategy characterized by a high probability for success must rely on fundamental knowledge of the intricacies of freshwater ecosys­ tem structure and function. A basic facet of this structure and function is material cycling and energy flow. In turn, a significant portion of such cy­ cling and flow involves the processing of various forms of organic matter by freshwater invertebrate animals, especially insects. This constitutes a basis for interest in aquatic insect trophic relations-food intake, tissue assimilation, and waste release-with implications ranging from theoretical questions, such as the efficiency of energy transfer, to very specific practical problems: for example, population control of pest species represented either by the food or the feeder. As Bates (2) put it, trophic relationships constitute the ce­ ment holding biological communities together. Aquatic ecologists have noted (e.g. 31) that the diversity of the ingested food greatly exceeds the diversity of the aquatic insects. Since the majority of species appear to be generalists (polyphagous) rather than specialists (mono­ or oligophagous), statements about food habits are subject to considerable variation and require qualification with regard to habitatand age-specific differences. Therefore, the present focus is on the level at which generaliza­ tions are possible and the ecological importance of such generalizations, rather than the food habits of particular species. For those data reviewed, a bias toward North American stream species will be apparent. Because of the latitude of previous usage, the defiIl:ition of certain terms is necessary. The compartmentalization of the basic components of food en-