Megachiloides Maybe

Also, at this very nonce several patches of Helianthus annuus (not shown)are in flower at the CB. The Silphiums (not shown)are too. Largish yellow bees have staked out every patch of these sunflowers defending same against all comers. Yes. These fierce bees scrap with everyone. Even with bumblebees, even with the little Mallaphora.

Naturally, Crumby has been mighty curious about these bees. But getting a good picture of the wing venation was not easy. No.

Yet these bees all seem to be males of the genus Megachiloides. Ma! I need a species key for these parts.