Africanized and European honeybees (Apis mellifera) responded differently to daily fluctuations in nectar resources. In side-by-side comparisons, the relative energy content of the nectar loads collected by the two geographical types varied with day. Daily variation was found in the volume of nectar collected but not in its concentration. Africanized bees collected more highly concentrated nectar. The success rates of foragers of the two types differed considerably. European bees generally were more successful in securing a load of nectar but their percentage of successful foragers tended to be either high or low. Africanized bees returned more often to their nest without a nectar load but had intermediate as well as high and low percentages of successful foragers. Finally, European colonies had greater numbers of foragers under the nectar-resource conditions of the study.