Osmia cornuta (Hymenoptera, Megachilidae) as a pollinator of pear (Pyrus communis): fruit- and seed-set

To investigate the possibility of pollinating 'Abate Fetel' and 'Max Red Bartlett' pears with O. cornuta, different pollination treatments were compared in 1998 and 1999: (1) trees caged with O. cornuta bees; (2) open pollination - uncaged trees located at various distances from O. cornuta nesting shelters; (3) trees caged without bees. O. cornuta was the most abundant pollinator species in the orchard (97.6% of the observed insects). Caged trees pollinated by O. cornuta set significantly more fruitlets and matured more fruits than caged trees without pollinators. The fruitlet- and fruit-set in open-pollinated trees was intermediate between caged trees with O. cornuta and caged trees without bees in 'Abate Fetel' in 1998 and 'Max Red Bartlett' in 1999, but did not differ from fruitlet-set in non-pollinated trees in the other two variety-years. Open-pollinated trees had seed-sets comparable to caged trees with O. cornuta. The pollen provisions stored in O. cornuta nests were almost exclusively composed of Pyrus pollen. As evidenced by traces of Prunus pollen some O. cornuta foraged 400 m away from the nesting shelters.