The fourth larval instar and pupa of Dioxys cincta are described and illustrated, and anatomical details of the first and last larval instar are interpreted from cast exuviae. The cocoon of this species is also described. The discovery of a hatched egg containing the first-instar exuviae indicates that the first instar remains mostly surrounded by the egg chorion. The second instar emerges through a hole in the thick dorsal surface of the chorion, presumably by chewing its way out. This discovery and the interpretation of the larval head anatomy of this species and that of D. pomonae Cockerell indicate that the genus has five larval instars. The second, third, and fourth instars are adapted to destroying the host egg or larva and any competing cleptoparasites. The fifth instar is not so adapted.

As with Dioxys, other cleptoparasitic Megachilidae tend to have a sequential series of instars modified for attacking immatures of hosts and competing cleptoparasites, although which instars are so adapted varies. This contrasts with the cleptoparasitic lineages of the Apidae in which only a single instar, usually the first, is hospicidal.