Nesting habits of a pollinator: Osmia orientalis (Hymenoptera: Megachilidae)

Osmia orientalis has potential as a crop pollinator and this study examined its curious nesting habits. They were successfully induced to nest in empty snail shells placed in a field (19.8% nesting rate). The nesting rate was higher for larger shells of Euhadra amaliae than for smaller shells of Satsuma japonica. The rate was also higher for intact than damaged shells, but was not affected by the freshness of the shells. As a nesting environment, the insects preferred grass fields rather than denuded areas, spaces adjacent to buildings, or a forest edge. The overall sex ratio of O. orientalis within the shell nests was male biased (59.2% males). The sex distribution within the shell nests was as follows: when O. orientalis nested in S. japonica shells, all cells contained males; when they nested in E. amaliae shells, the innermost and second innermost cells were highly male biased, while the ratio of females increased gradually toward the outermost cells and was highest in the second outermost cells, while the male ratio recovered in the outermost cells. Finally, we discuss the possibility of using and the methods of managing O. orientalis as a crop pollinator.