The Food of Larvae of Tipula sacra Alexander in a Series of Abandoned Beaver Ponds (Diptera: Tipulidae)

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The work described here forms part of a study of the ecology of a series of abandoned beaver ponds in the Kananaskis Forest Reserve of Alberta. Pritchard & Hall (1971) should be consulted for details of the study site and for a description of the study organism, the aquatic cranefly Tipula sacra Alexander. The thesis of this particular investigation was that sex, instar, season, and location of habitat were all factors capable of influencing the food of larvae of T. sacra, and quantitative investigations of larval gut contents with reference to these factors were carried out. The relationship between the availability of suitable food in the habitat and the quantities of this food ingested by the larvae was also investigated. Previous work on the food of aquatic herbivorous insects has generally shown little or no selectivity in ingestion. Mecom & Cummins (1964), for example, determined that Trichoptera larvae in five streams ingested algal cells in densities proportional to those in the environment. Brown (1960), however, investigating the algal food of Chloeon dipterum (L.) (Ephemeroptera), showed some selectivity in the food habits on the basis of size of larvae; large larvae ingested large species of algae with greater frequency than did small larvae. Brown also showed (1961) there were changes in the diet with seasonal changes in the environment, and also gave a useful review of methods used in the study of food habits. The importance of such studies and the current problems are reviewed by Cummins (1973).