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 depend ent on honeybees for fruit set. A significant initial fruit set requir ed a density of at least five bees per tree during the female stage of flowering. The early-blooming avocado cultivars were visited by enoug h honeybees on fewer than one-third of their blooming days. Because th ey 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 ex posed to sufficient pollination to set fruit. The late-blooming cultiv ars however, were visited by many bees and exhibited high initial frui t set. The attractiveness to honeybees of various avocado cultivars an d some other plant species, which were found to compete for pollinatio n, was measured by the coefficient ''r'' obtained from correlations be tween bee density and reward measures of these plants, over the course of a day or season. At the beginning of the blooming season, the avoc ado flowers competed for nectar-foraging bees mainly with flowers of C itrus spp, and for pollen foragers with Brassicaceae and Fabaceae, all of which were more attractive to the bees. Since pollination was carr ied out only by nectar-collecting bees, Citrus spp. flowers presented the main limiting factor for initial fruit set in avocado. However, to ward the end of its blooming season, the avocado competed with Poaceae , Asteraceae and Apiaceae flowers, and its relative attractiveness inc reased.