A systematic revision of the species of the genus Xylocopa subgenus Neoxylocopa in Argentina is provided. Seven species are included: X. atamisquensis Lucia & Abrahamovich, X. augusti Lepeletier, X. eximia Pérez, X. frontalis (Olivier), X. mendozana Enderlein, X. nigrocincta Smith and X. tacanensis Moure. The males of X. eximia and X. nigrocincta are described for the first time. Xylocopa jujuyensis Brèthes is a new junior synonym of X. nigrocincta. Photographs, occurrence maps, and identification keys for the species are presented. Information on the nest architecture and substratum preference are also given.

Four new gynandromorph Xylocopinae bees from Argentina are described and illustrated; one specimen of Xylocopasplendidula Latreille and three of Ceratina rupestris Holmberg. All specimens are mosaic gynandromorphs as they display mixed female-male characters in different parts of the body.

The nesting biology of the exotic bee Megachile (Eutricharaea) concinna Smith, 1879 and its negative interactions with other insects were studied. Trap nests made of wood were located in an urban environment in Buenos Aires province, Argentina, and surveyed during 26 months. The lifecycle and the structure of the nest of M. concinna are described. We also report six interactions between this bee and native and exotic parasitoids and cleptoparasites. The species Baryscapus megachilidis is recorded here for the first time in Argentina.