Pollen transfer in apple orchards: tree-to-tree or bee-to-bee?

Gloria DeGrandi-Hoffman, Roger Hoopingarner and Karen Baker

The ability of honeybees to cross-pollinate blossoms is well established, although their methods of acquiring compatible pollen have not always been well documented. Most apple varieties are completely self-incompatible, that is, not even pollen from a different tree of the same variety will set fruit. Pollen must come from a compatible source, usually referred to as a pollinizer. Honeybees working apple usually seem to restrict their foraging areas to a single tree, and at most visit two trees (usually in the same row) during a foraging trip. Because of this behaviour, growers have been advised to interplant pollinizers in the rows of main variety trees to increase the likelihood that honeybees moving between trees will acquire and transfer compatible pollen. This article describes observations on pollen transfer between apple varieties in two Michigan orchards and identification of pollen by scanning electron microscopy.