Ecology of Corixidae (Water Boatman) in Lake Poinsett, South Dakota

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Abstract
Corixid populations in the littoral zone of Lake Poinsett, South Dakota [USA], were sampled during the open water seasons, April-Oct., in 1970-72. Seven genera and 15 spp. of the family Corixidae [Palmacorixa buenoi, Trichocorixa borealis, Cenocorixa dakotensis, C. utahensis, T. verticalis, T. naias, Sigara conocephala, S. solensis, S. bicoloripennis, S. grossolineata, S. alternaria, Hesperocorixa vulgaris, Cenocorixa sp. Callicorxa audeni, C. tursalis] were collected. Estimated corixid population density increased from a mean annual standing crop of 4.7/m2 in 1970 to 17.6/m2 in 1971 and 56.9/m2 in 1972. The mean density of P. buenoi Abbott (19.8/m2) was about 5-fold greater than that of T. borealis Sailer (3.8/m2), which ranked 2nd in abundance; the 2 spp. combined represented 95% of the 3-yr mean standing crop (24.7/m2) of Corixidae in Lake Poinsett. Both of these species produced 2 generations each year, but P. buenoi overwintered primarily as 4th-instar nymphs and T. borealis overwintered as adults. Corixids were not prey species of the common littoral zone fishes, and fish predation had no known significant effects on corixid population dynamics. This lack of predation appeared to be primarily related to the fish species composition and to the high densities of more vulnerable prey.

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