Because they are (mostly) above-ground nesters and more commonly attracted to artificial nests, megachilid bees are also more commonly cultivated than ground nesting solitary bees. They accept nesting materials made from hollow stems, tubes, and blocks with preformed holes ("nest blocks"), and several megachilids have become important species for agricultural / horticultural pollination. In North America these cultivated bees include the introduced "Megachile rotundata", (alfalfa leafcutter bees), used extensively in alfalfa pollination, and the western native and frequently raised "Osmia lignaria" (the orchard mason bee or blue orchard bee), used in orchard pollination. Other "Osmia" and "Megachile" species are also in commercial use in North America, Europe and Asia.