Competition for nectar between introduced honey bees and native North American bees and ants.

Previous studies (Schaffer et al. 1979) of introduced honey bees foraging at Agave schottii Engelm. flowers suggest that Apis preferentially exploits the most productive patches of flowers and thereby reduces the standing crop of available nectar and the utilization of these sites by native bees. In the present paper, we report the results of experiments undertaken to evaluate this hypothesis. A single 1-ha site was studied. Visitation rates by Apis and native bees were determined, as were rates of nectar secretion and amounts of nectar available to the bees. Nectar available to bees was increased by excluding ants, which foraged on the stalks both during the day and at night. A. schottii flowers secrete 90% of their nectar at night. Prior to this exclusion, ants consumed =85% of the nightly accumulation. At first, the ants were excluded from only 10 flower stalks out of 130. These stalks were visited by greater numbers of both honey bees and bumble bees than were the controls. The experimental stalks also had higher standing crops of available nectar. Next, ants were excluded from all of the stalks on and surrounding the study site by treating them with Tree Tangle- foot. Following this manipulation the number of honey bees again increased, but the numbers of Bombus remained at the level of the controls of the first experiment. A significant increase in the numbers of small solitary bees on the stalks was also observed. These species generally foraged later in the day than Apis and Bombus, which were both active primarily early in the morning and before dusk. During these manipulations, two hives of Cordovan honey bees, a light-colored strain of Apis mellifera, were present on the site. The subsequent introduction of two additional hives had no discernible effect on the number of honey bees visiting the flowers. The final experiment consisted of removing the Cordovan hives. Thereafter the number of darker feral honey bees observed on the flowers increased until it approached the previous combined total of Cordovans (:75% of the total) and ferals. Concomitantly, the numbers of Bombus and small solitary bees first increased and then declined.