Release of Osmia excavata and Osmia jacoti (Hymenoptera: Megachilidae) for apple pollination

Abstract

AbstractTwo species of bees native to China, Osmia excavata Alfken and Osmia jacoti Cockerell, were released in 1991–1993 to observe life-history characteristics and assess pollination efficiency. Osmia excavata successfully established in both coastal (Shandong Province) and interior (Hebei Province) habitats, whereas O. jacoti was only able to establish in the coastal habitat. Sex ratios (female:male) ranged from 1:1.05 for O. jacoti to 1:2.46 for O. excavata. Apple, Malus domestica Borkh (Rosaceae), pollination was enhanced following the release of either species in orchards in Shandong. Fruit diameter increased following the release of either Osmia species in 'Red Delicious' blocks compared with control blocks where no pollination treatment was applied. The number of seeds per fruit was also increased relative to controls, and the percentage of asymmetrical fruit decreased. Release of O. excavata produced the best results for this cultivar. For 'Ralls Janet', the number of seeds per fruit increased following the release of either species and the percentage of asymmetrical apples decreased. Effects on fruit diameter were confounded by poor cultural practices (i.e., lack of adequate fruit thinning) in these 'Ralls Janet' blocks. Fruit set increased relative to controls following release of either Osmia species for both apple cultivars. Release of O. excavata also produced higher fruit set relative to blocks that received hand pollination treatment; release of O. jacoti was better than hand pollination only for 'Red Delicious'. Observations on the behaviour of individuals showed that O. excavata averaged 49.6 foraging trips per day and set an estimated 3108 fruit on 'Ralls Janet'; O. jacoti made fewer foraging trips (average of 31.2) per day and set 1831 fruit. Both species were more efficient pollinators than Apis mellifera. Osmia excavata would appear to be a better candidate for commercial apple pollination than O. jacoti under conditions similar to those in this study.