Feeding rates of Daphniapulex fed a range of levels of the alga Chlamydomonas reinhardi af 15 "C are strongly density-dependent. At lower densities, Daphnia (30 1-l) fed at higher rates than crowded (270 1-l) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 -15.7 x 104 cells d-'h-l (on a volume basis, 12.1 -22.2 x lo6 pm3), at 270 L-r 3.7 -3.9 x lo4 (5.2 -5.5 = lo6 pm3 cells d-'h-l when feeding on algae at 80000 cells ml-' (11.3 x lo6 pm3 ml-'). The feeding rate data best fit an Ivlev feeding function. An "autoallelopath" might be causing the repression. Water preconditioned with crowded Daphnia comnletely repressed feeding in uncrowded Daphnia after six hours.

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The vulnerability of instar I and II larvae of the mosquito Aedes vexans as prey for Chaoborus americanus is much greater than that of the small coexisting prey, Daphnia pulex. Predation on Aedes larvae could reduce Aedes populations in overlapping habitats, and be a selective force in driving Aedes to lay eggs in muds of more temporary wetlands. Predation rates are great (7–25∙d−1) and ingestion times are rapid (0.8–6 s) on Aedes instars I and II. In prey choice experiments, Chaoborus strongly prefers Aedes I over small Daphnia. An Aedes diet promotes growth of Chaoborus at least as well as a Daphnia diet. Larval Aedes behaviors show a distinct difference between the first two and last two instars. Aedes swimming speeds and swimming distances increase with each instar, but when disturbed, the first two instars significantly reduce their swimming distances. Calculated prey vulnerabilities, based on swimming speeds and reciprocal ingestion times, suggest a much greater vulnerability for Aedes I and II than that for small (0.8 mm) Daphnia or for Aedes III and IV (4.6–6.2 mm).

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