Nesting Preferences of Osmia orientalis (Hymenoptera: Megachilidae) in the Field and Its Potential as a Strawberry Pollinator in Greenhouses

The western honeybee, <i>Apis mellifera</i>, is used worldwide as a pollinator of crops such as strawberries; however, it is an introduced species in Japan. The mason bee, <i>Osmia orientalis</i> Benoist (Hymenoptera: Megachilidae), is native to Japan, where it nests in empty snail shells and has potential as a crop pollinator. We conducted three experiments to collect information on the nesting habits and potential agricultural use of this species as a pollinator of greenhouse-grown strawberries. Our first experiment investigated the bees' nesting preferences in the field by placing the empty shells of four snail species, <i>Euhadra amaliae</i>, <i>Satsuma japonica</i>, <i>Sinotaia quadrata histrica</i>, and <i>Helix lucorum</i>, in six different environments. The nesting rate was significantly higher in medium-sized, empty <i>E. amaliae</i> shells. Regarding the surrounding environment, <i>O. orientalis</i> preferred tall and short grasslands to bare ground and forest interiors. Our second experiment investigated per-visit strawberry flower pollination efficiency. The results indicated that the efficiency of <i>O</i>. <i>orientalis</i> was equal to or greater than that of <i>A. mellifera</i>. In our third experiment, as a replacement for empty snail shells, which are scarce natural sources, four types of plastic artificial shells were created and placed inside a greenhouse together with <i>E</i>. <i>amaliae</i> shells. The nesting rates in three types of artificial shells were nearly identical to those in <i>E</i>. <i>amaliae</i> shells, implying that these artificial shells may be effective nesting materials. Although many questions remain before practical application, our results indicate the potential for using <i>O</i>. <i>orientalis</i> as a pollinator of greenhouse-grown strawberries.