The nesting biologies of Monoeca haemorrhoidalis (Smith) and Lanthanomelissa betinae Urban (Tapinotaspidini) are described from southeastern Brazil. Both are ground nesting; the nests of the former are attacked by the cleptoparasite Protosiris gigas Melo (Osirini), and those of the latter are attacked by Parepeolus minutus Roig-Alsina (Osirini). Egg eclosion, larval feeding behavior, and cocoon spinning of M. haemorrhoidalis are detailed. A female of P. gigas opens the closed cell of M. haemorrhoidalis by making a large opening in the cell cap (which is plugged after ovipositioning) through which she apparently extends her metasoma. Indirect evidence suggests that she uses her metasomal apex, and perhaps even the sting, to kill the host egg or early instar. Protosiris eggs are either attached to the cell-wall surface of the nearly vertical host cells or dropped onto the surface of the provisions. First instars of P. gigas, with strongly curved, sharply pointed mandibles, are also capable of killing host immatures or competing cleptoparasites.

Cocoons of all four species are compared and contrasted. The egg, all larval instars, and pupa of Monoeca haemorrhoidalis are described, as are the egg and postdefecating larva of Lanthanomelissa betinae. The egg, all larval instars, and pupa of Protosiris gigas are described, as is the postdefecating larva of Parepeolus minutus.

Both Monoeca haemorrhoidalis and Protosiris gigas have four ovarioles per ovary. The egg indices and other ovarian features of both species are identified and discussed.

The possible phylogenetic relationship of the Tapinotaspidini with the Osirini is briefly explored on the basis of data from this study. Possible phylogenetic relationships of the Osirini with other cleptoparasitic apids are analyzed.

In the ^appendix,, the identity of the species of Monoeca, whose nesting biology is presented in the main paper, is discussed. The species is M. haemorrhoidalis (Smith, 1854), a species closely related to M. schrottkyi (Friese, 1902) and M. xanthopyga Harter-Marques, Cunha, and Moure, 2001. An identification key for distinguishing these three species is presented. Tetrapedia piliventris Friese is placed as a junior synonym of M. haemorrhoidalis (new synonymy). A lectotype is designated for Pachycentris schrottkyi Friese. The species of Protosiris found attacking M. haemorrhoidalis is here described as new, P. gigas Melo sp. nov. It is structurally most similar to P. caligneus (Shanks), from which it differs by its abundant yellow marks, plumose pubescence on the lower paraocular area, protruding anterior mesoscutum, and sparser punctation on the metasomal terga.

Appendix: Taxonomic Notes on Monoeca and Description of a New Species of Protosiris, by Gabriel A. R. Melo