THE SIZE AND DISTRIBUTION OF THE HONEY-BEE (APIS-MELLIFERA L) CROSS-POLLINATING POPULATION ON MALE-STERILE SUNFLOWERS (HELIANTHUS-ANNUUS L)

The size of the honey bee (Apis mellifera) population carrying sunflower (Helianthus annuus) pollen on their bodies while foraging on male-sterile (MS) plants was recorded. When equal numbers of MS and male-fertile (MF) rows were planted, all foragers had some sunflower pollen on their bodies, and the amount did not differ among MS rows at various distances from MF plants. When MS rows outnumbered MF by 3 to 1, 97.7% of the honey bees foraging on the MS row farthest from the MF plants had sunflower pollen on their bodies, but the amount was significantly less than on foragers on MS rows closer to MF plants. Seed set on MS rows adjacent to MFs did not differ from that on MF plants, but set decreased in MS rows further away. The percentage of pollen-collecting honey bees moving from MF to MS rows indicates one means by which the cross-pollinating honey bee population can be created, but these bees represented only 6.5-12.8% of all foragers. Pollen-free honey bees either released in hives located near sunflower fields or pinned at the hive entrances obtained sunflower pollen grains on their bodies, but the amount was much less when MS rows outnumbered MF by 3 to 1. Pollen transfer in the hive may be a component in the creation of the cross-pollinating honey bee population on MS sunflowers, but the impact may vary with MF: MS row ratios and the amount of sunflower pollen entering the hive.