THE BEHAVIOR OF HONEY BEES ON 'DELICIOUS' APPLE BLOSSOMS

The cultivar 'Delicious' is the most widely planted apple (Malus domestica Borkh) in the United States, but it generally yields quite poorly. This study was designed to determine whether ineffective pollinating visits by honey bees (Apis mellifera L.) might be contributing to the shy bearing behavior of this cultivar.;In comparison to topworkers and spreaders, sideworking bees are ineffective pollinators because they fail to contact anthers and stigmas. More than 85% of the honey bees foraging for 'Delicious' nectar were sideworkers. On 5 other cultivars, an average of approximately 60% were topworkers, 35% spreaders, and 5% sideworkers. As a result, only about 10% of the nectar gatherers on 'Delicious' contacted a stigma, compared to about 75% on other cultivars.;The behavior of bees on 'Delicious' is attributable to its unusual floral morphology. In this cultivar and 76 of its sports so far examined, the stamens are irregularly spaced about the nectary, resulting in gaps near the receptacle that allow a bee to insert its proboscis through the stamens to the nectar. On most cultivars, the filaments are pressed tightly together at their bases, forcing bees to forage by either topworking or spreading. An examination of 195 apple cultivars and crabs (Malus spp.) revealed that only 'Northern Spy' and a few other cultivars share the 'Delicious' morphology.;'Delicious' blossom clusters were bagged prior to bloom. During bloom, a few clusters at a time were unbagged, and the methods used by bees in foraging from them were recorded. Other clusters were hand pollinated or left bagged throughout bloom. Visits from pollen-gathering and topworking honey bees were comparable to hand pollination in setting fruit. Fruit set from blossoms receiving sideworking visits was extremely low, similar to fruit set from bagged, unpollinated blossoms.;Foraging behavior was classified by watching bees forage on individual flowers in large plantings of single cultivars. Honey bees collecting either pollen, or both nectar and pollen, actively scrabble over the anthers and nearly always contact stigmas. Bees collecting only nectar employ 3 basic techniques: (a) standing with all legs on the stamens, head down, proboscis extended to the nectary ("top-working"); (b) standing with at least the metathoracic legs on a petal, parting the stamens with head, prothoracic legs, and often mesothoracic legs ("spreading"); or (c) standing with all legs on a petal, reaching between filaments with the tongue ("sideworking").;A unique planting of apple trees in which each planting hole held 3 trees of different cultivars provided an ideal setting for a study of the interactive effects of the 2 basic floral morphologies on honey bee behavior. When bees were first introduced into this block, the presence of nearby 'Rome' and 'Golden Delicious' blossoms led more bees to topwork than had previously been observed in large plantings of only 'Delicious', thus improving pollination efficiency. However, over a 3-day period the proportion of topworkers on 'Delicious' fell steeply. The transience of this inter-cultivar effect was at least partially due to the specialization of a force of bees on 'Delicious' as sideworking nectar gatherers.;Recommendations for improving 'Delicious' pollination include: use of more honey bees to increase the numbers of pollen gatherers and topworkers; use of strong colonies with high pollen demand; elimination of flowering weeds that compete for bee visits; and frequent interplanting of pollinizers to disrupt conditioning of bees as sideworkers.