A study in Jacksonville, Florida showed that a dense natural population of the predator, Toxorhynchites rutilus rutilus, significantly reduced a natural population of Aedes aegypti in a tire dump, when compared with 2 other tire dumps with very low levels of Toxorhynchites. Production of prey pupae and adults was virtually eliminated by mean levels of 1 to 5 predator larvae per tire during a 10-week study. In these studies the predator was most effective in tires located under trees, and least effective in open areas.