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Photo#882432
Male Agapostemon from AZ Gathering - Agapostemon melliventris - male

Male Agapostemon from AZ Gathering - Agapostemon melliventris - Male
Santa Cruz River, Amado-Montosa Road, Santa Cruz County, Arizona, USA
July 26, 2013
Found here on flower heads of mule fat (Baccharis salicifolia) in dry river bed during the AZ gathering_2013.

I was able to ID this beautiful bee fairly easily, and unequivocally, to Agapostemon milleventris in the 1972 revision of the genus by R. B. Roberts (see genus info page for reference details). I lucked out in that this specimen keys out in just three straightforward steps. Salient details are:

1) Male: 11 flagellomeres;
2) Not A. nasutus (a tropical species which ranges up coasts of Gulf of Mexico & Gulf of California, but doesn't reach AZ...and also has dark brown to black bases of metasomal segments);
3) First metasomal tergum yellow to very pale amber basally, not brown or black, and hind basitarsus always slender and simple (Fig. 155); hind leg yellow with small brown or black area apically on femur and basally on tibia....A. milleventris

The description fit well for the characters that are visible.