Effect of pollination by the Osmia bicornis (syn. O. rufa) bee on fruit set, seed set and yield in three apple cultivars

Our study tested the pollination effectiveness of the megachilid bee Osmia bicornis L. (syn. Osmia rufa) on three apple cultivars (cv.): Lobo, Piros and Champion. The following pollination treatments were compared for each cultivar: insect pollination - caged trees with Osmia bicornis (syn. Osmia rufa) bees; open pollination - uncaged trees; self-pollination - caged trees without bees. Pollination success was measured based on the percentage of fruit set, the fruit yield per tree (measured as number of fruits and total fruit weight) and the number of seeds per fruit. Generally, there was a higher percentage of initial fruit-set and fruits at harvest on open-pollinated trees than on caged trees without bees, with an intermediate value recorded for caged trees pollinated by O. bicornis (syn. O. rufa). However, the fruit set on trees pollinated by O. bicornis (syn. O. rufa) was high and ranged from 49 to 69%, depending on the cultivar. The cv. Lobo trees pollinated by O. bicornis (syn. O. rufa) and open-pollinated trees produced higher fruit yields than without bees. Furthermore, the number of seeds per fruit was higher. Fruit yield and the number of seeds per fruit were higher for trees pollinated by O. bicornis (syn. O. rufa) than for caged trees without insects but lower than for open pollination trees of cv. Piros and cv. Lobo.