Data are presented on the nesting and phenology of Canephorula apiformis Friese (Apidae: Eucerini), a monotypic genus of bees endemic to the arid and semi-arid regions of the Argentinian northwest. Aggregations of nests are found in the ground where the surface is horizontal and frequently exposed to the sun. The brood cells, 5–6 cells per nest, are at an approximate depth of 20 cm. Floral hosts include Prosopis strombulifera (Fabaceae), Atamisquea emarginata (Capparidaceae), Larrea divaricata (Zygophyllaceae), and Tessaria absinthioides (Asteraceae) and are visited mainly between 10:00 and 14:00 hr. Adults and immature stages of Melectoides bellus (Jörgensen) (Apidae: Isepeolini) were found in the nests, the first association for this cleptoparasitic tribe with any host other than the genus Colletes. Canephorula apiformis may have two generations per year while the voltinism of its cleptoparasite is uncertain.

The mature larvae of both host and cleptoparasite are described for the first time and compared with known larvae of their respective tribes. Cocoons of the two species are also described, illustrated, and compared to those of related taxa.