Low attractiveness of avocado (Persea americana Mill.) flowers to honeybees (Apis mellifera L.) limits fruit set in Israel

Avocado in the Western Galilee region of Israel was found to be dependent on honeybees for fruit set. A significant initial fruit set required a density of at least five bees per tree during the female stage of flowering. The early-blooming avocado cultivars were visited by enough honeybees on fewer than one-third of their blooming days. Because they were visited mostly at the end of their blooming season, and due to rainy days, not more than 5% of their entire season's flowers were exposed to sufficient pollination to set fruit. The late-blooming cultivars however, were visited by many bees and exhibited high initial fruit set. The attractiveness to honeybees of various avocado cultivars and some other plant species, which were found to compete for pollination, was measured by the coefficient "r" obtained from correlations between bee density and reward measures of these plants, over the course of a day or season. At the beginning of the blooming season, the avocado flowers competed for nectar-foraging bees mainly with flowers of Citrus spp, and for pollen foragers with Brassicaceae and Fabaceae, all of which were more attractive to the bees. Since pollination was carried out only by nectar-collecting bees, Citrus spp. flowers presented the main limiting factor for initial fruit set in avocado. However, toward the end of its blooming season, the avocado competed with Poaceae, Asteraceae and Apiaceae flowers, and its relative attractiveness increased.