Leaf cutter and sweat bees are some of the best pollinators for Japanese plum trees. In fact they seem to especially like all plum trees. The leafcutters can be managed in your orchard by building simple homes for them. They may not be as big or glamorous as other bees but if you watch carefully you will see they are real work horses. The first link shows how to build the block homes.

http://wildblueberries.maine.e.....on/301.pdf
http://crawford.tardigrade.net.....nth23.html