The phenology of flowering of male-fertile and genetic-cytoplasmic male-sterile upland cottons was observed and compared in detail, and a descriptive sequence which identifies 5 stages of anthesis is proposed. Phenological differences as well as other differences in availability and relative abundance of extrafloral nectar among cotton lines influenced honeybee (Apis melli/era) visits between cotton lines. In cage studies, cotton pollen-collection activity and flower-visitation movements of both honeybees and bees of an unidentified soil-nesting species were observed and recorded. Both species avidly collected loads of cotton pollen although, in open-field studies, it is unusual to find honeybees collecting cotton pollen. In the cage individual honeybees switched between pollen collection and nectar collection during single foraging trips.