Pollination of macadamia: Review and opportunities for improving yields

Macadamia nuts are a valuable culinary resource, but yields can vary substantially between varieties, orchards and seasons. The nuts are harvested from commercial varieties derived from two endemic Australian tree species; Macadamia integrifolia Maiden & Betche and Macadamia tetraphylla L.A.S. Johnson. While some aspects of crop management for this relatively new crop are well known and generally well applied—including variety selection, irrigation and pesticide application—progress towards increasing quantity and reliability of yield has proven elusive. Hand pollination studies indicate that inadequate cross pollination contributes to low nut set and thus low yield. Typically just 0.3% of flowers develop into harvestable nuts. Lack of nut development after flowering and early abscission are indicators of poor fertilisation of the ovule. Honey bees ( Apis mellifera Linnaeus, 1758) are routinely reported as the most common insect visitor to macadamia flowers, and are widely regarded as the most important agent for transferring pollen between flowers. Stingless bees, beetles, flies and birds also visit flowers and have been considered as pollinators. In this review, we aim to collate what is currently known about the pollination of macadamia varieties, assess the factors that may hinder effective pollination and subsequent yield, and identify opportunities to improve both pollination and yield in commercial macadamia orchards.