SELECTIVE DIET OF CHIRONOMID LARVAE IN A QUEBEC STREAM.

L. Tall, L. Cloutier, and A. Cattaneo. Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada H3C 3J7

Chironomids are ubiquitous and abundant in benthic communities but their diet is still poorly understood. Although most chironomids are considered generalist feeders, some evidence suggests that they can select algae on the basis of size and life-form. No model exists to predict the diet of different chironomids from taxon, size, or mouth morphology. In this study we test the application of predator-prey models developed in terrestrial and planktonic systems to chironomid communities. In particular, we test if: 1) there is a relationship between prey and predator size, 2) diet breadth and selectivity change with grazer size, and 3) spatially partitioned resources are utilized differently by coexisting chironomids. To this end, we collected throughout the growing season chironomids living on mosses and gravel in a small Quebec stream. We clarified (with peroxide)and permanently mounted the larvae to identify and measure diatoms in their gut while preserving heads with mouthparts to establish larval genus and size. There was a significant positive relationship between larval size and diatom average length in the gut. Comparisons of ambient diatom assemblages with gut content indicated that diet selectivity by chironomids is indeed widespread and largely dependent on larval size.