Flower structure and nectar availability in Aloe greatheadii var davyana : an evaluation of a winter nectar source for honeybees

Abstract

The winter-flowering Aloe greatheadii var. davyana is a major indigenous bee plant in South Africa, widely distributed across the northern summer rainfall areas. Migratory beekeepers take advantage of its highly nutritious pollen for colony increase and strong nectar flow for honey production. We looked at variation on different levels in assessing this nectar resource for bees. There were no significant differences in nectar volume and concentration between the basal swelling (bulb) and the floral tube, only between flower stages. Nectar was continuously available, with volume and concentration remaining relatively constant throughout the day despite pronounced diurnal temperature changes and very low afternoon humidities. Bee foraging reduced mean nectar volumes in unscreened flowers by 50%, from 30.7 to 14.7 mL; bees are unable to access nectar in the bulb. Nectar volume was lowest and nectar concentration highest late in the flowering season, while the highest sugar content (3.54 mg per flower) was recorded in the middle of the flowering season. Aloe greatheadii var. davyana nectar, although dilute from a bee perspective (ca. 20% w/w), is more concentrated than that of many bird-pollinated Aloe species and is an ideal source of energy and water for honeybees during dry winter months.