Abstract.Many kinds of adaptive behavior, including responses to risk of predation, have been documented, but there have been few attempts to translate these behaviors into consequences for populations. We present one of the first models to predict the consequences of adaptive behavior for population size in a specific natural system. Larvae of the mosquito Culiseta longiareolata (Diptera: Culicidae) develop in freshwater pools. They are vulnerable to predation by the backswimmer Notonecta maculata (Hemiptera: Heteroptera), and to intraspecific competition. Adult female C. longiareolata usually avoid ovipositing in pools that contain N. maculata. This is presumably an adaptive response that increases individual fitness, but it is also likely to affect the size of the population. We take a novel approach to understanding the relationship between adaptive behavior and population dynamics in C. longiareolata. We use a nonlinear stage-structured population model to predict the evolutionarily stable oviposition strategy and its consequences for the size of the C. longiareolata population. Our model predicts that female C. longiareolata should always avoid ovipositing in pools with N. maculata. Such avoidance will increase the equilibrium size of the C. longiareolata population, relative to a population in which oviposition is indiscriminate with respect to N. maculata. The qualitative effect on population size is the same even if, as observed, C. longiareolata occasionally oviposit in pools containing N. maculata. These predictions have important practical implications for assessing the effectiveness of predators as biological control agents.