Foraging behavior and pollinating effectiveness of Osmia cornuta (Hymenoptera: Megachilidae) and Apis mellifera (Hymenoptera: Apidae) on Comice pear

We studied the pollinating effectiveness of Osmia cornuta and Apis mellifera on 'Comice' pear. Osmia cornuta visited more flowers per minute (13.8) than A. mellifera (7.1-9.8). Both species visited similar numbers of flowers per tree (6.7-7.9), and switched rows with similar frequency (4.0-7.9%). Rate of stigma contact was 98.7% for O. cornuta, 51.8% for A. mellifera pollen-nectar foragers, and 19.0% for A. mellifera nectar foragers. Fruit-set in flowers visited once was 28.9, 29.3, and 12.9%, respectively. Seed-set was similar (7-8 seeds per fruit) in all three types of flowers. Osmia cornuta females provisioned their nests with 94.4% pear pollen. Stepwise multiple regression showed that fruitlet-set across the orchard was mostly related to tree size ( trees with fewer flowers set more fruit per flower) (beta = - 0.64; P < 0.001), whereas seed-set at harvest was best explained by O. cornuta (beta = 0.47; P < 0.005) and A. mellifera (beta = 0.35; P < 0.05) spatial distribution.