Tonopah Desert, Maricopa County, Arizona, USA April 4, 2015 Size: 11mm
This bee is in a Prickly Pear Cactus, Opuntia Engelmannii. I think that this is a male Chimney Bee in the Diadasia australis species group.
This bee appears to have a few tiny particles of waxy flakes, pressed onto some of his abdominal hairs, near the center of the last tergite.