Reproduction in the leaf-cutting bee Megachile (Chrysosarus) pseudanthidioides Moure was studied by trap nesting in secondary Atlantic rain forests on Santa Catarina Island, southern Brazil. Nests were built in borings of hardwood blocks, in small wooden boxes and bamboo canes. The brood cells consisted of an outer layer of overlapping small leaves or pieces of leaves cut oval. They covered a chamber formed of clay. Pieces of flower petals served as the innermost lining of the cells. Nests were constructed October through February. Emergence pattern indicates a bivoltine life cycle with a spring generation emerging December and early January and a second (summer) generation diapausing as prepupae from fall through winter. Metamorphosis then takes place in late winter and imagines emerge only in the following spring, September and October. A cleptoparasitic megachilid, Coelioxys (Acrocoelioxys) tepaneca (Cresson), was found to attack nests of Megachile (C.) pseudanthidioides. This host-parasite relationship was previously unknown.