Effects of Vegetation on Notonecta (Hemiptera) Distribution in Ponds with and without Fish

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Abstract
The distribution of Notonecta in relation to aquatic vegetation and water depth was studied in two ponds, one with predaceous fish, another without. Notonectid density was lowered but the number of species was greater in the pond with fish. The dominant species in the fish pond (N. lonata) was strongly associated with vegetation throughout its life cycle, while the dominant species in the pond without fish (N. undulata) was associated with vegetation only during the early instars. N. undulata also occurred in the pond with fish, but at greatly reduced densities. The overall distribution of the two dominant notonectid species was random among the three water depth classes studied (< 15 cm, 15-30 cm, 30-65 cm) in both ponds. Each pond also contained a large notonectid species in low densities. The large species in the pond without fish (N. insulata) was characterstically found in open, deeper water where the substrate was bare or sparsely vegetated. The large species in the fish pond (N. irrorata) appeared to be randomly distributed with respect to vegetation density and water depth, and was mainly restricted to heavily shaded parts of the habitat.