Alteration of fitness components was assessed in the yellow fever mosquito, Aedes aegypti, in automobile tires and vases (ovitraps) under field conditions. Larval numbers were manipulated in both kinds of containers to compare low, high, and control (natural) densities. Densities were set from a census of a wild population, then doubling and reducing to half the mean crowding, m*. Artificially altered densities were not high or low enough to produce differences among treatments. Tires generated more vigorous larval populations and females with higher fecundity than did small containers, although the mortality was more intense.