1. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U.S.A.: Department of Zoology, La Trobe University, Bundoora, Victoria, Australia 3083.
2. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U.S.A.
3. USDA-ARS Carl Hayden Bee Research Center, Tucson, Arizona 85719 and Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U.S.A.