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Microstigmus nigrophthalmus Melo, 1992: 663 (Fig. 14 A-D) Holotype: ♀ (# MZSP 61864) ��� Brasil, Minas Gerais, Vi��osa, 06.viii.1989, G.A. R. MELO��� ��� HOLOTYPUS Microstigmus nigrophthalmus, ♀, G.A. R. MELO, 1992 ���. Paratypes: 1 ♀ (# MZSP 61865) ��� Brasil, M[inas] G[erais], Araponga, 13.v.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♀, G.A. R. Melo, 1992 ���; 1 ♀ (# MZSP 61866) ��� Brasil, M[inas] G[erais], Vi��osa, 21.iv.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♀, G.A. R. Melo, 1992 ���; 1 ♀ (# MZUSP 61867) ��� Brasil, M[inas] G[erais], Vi��osa, 24.iv.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♀, G.A. R. Melo, 1992 ���; 1 ♀ (# MZSP 61868) ��� Brasil, M[inas] G[erais], Vi��osa, 09.iv.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♀, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61869) ��� Brasil, M[inas] G[erais], Vi��osa, 17.iv.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61870) ��� Brasil, M[inas] G[erais], Vi��osa, 10.viii.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61871) ��� Brasil, M[inas] G[erais], Vi��osa, 13.xi.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61872) ��� Brasil, M[inas] G[erais], Vi��osa, 05.ii.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61873) ��� Brasil, M[inas] G[erais], Vi��osa, 3.ii.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61874) ��� Brasil, M[inas] G[erais], Vi��osa, 18.v.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61875) ��� Brasil, M[inas] G[erais], Vi��osa, 1.v.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61876) ��� Brasil, M[inas] G[erais], Vi��osa, 15.ix.1888, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61877) ��� Brasil, M[inas] G[erais], Vi��osa, 9.vii.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61878) ��� Brasil, M[inas] G[erais], Vi��osa, 29.xi.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61879) ��� Brasil, M[inas] G[erais], Vi��osa, 1.vi.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 2 ♂ (# MZSP 61880, 61881) ��� Brasil, M[inas] G[erais], Vi��osa, 17.iv.1988, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���; 1 ♂ (# MZSP 61882) ��� Brasil, M[inas] G[erais], Vi��osa, 9.iv.1989, G.A. R. Melo��� ��� Paratype, Microstigmus nigrophthalmus, ♂, G.A. R. Melo, 1992 ���., Published as part of Jesus, Juliana Menezes de, Onody, Helena Carolina, Ramos, Kelli dos Santos, Andrade, Tamires de Oliveira, Santos, Alvaro Doria dos & Brand��o, Carlos Roberto Ferreira, 2019, Crabronidae and Sphecidae (Hymenoptera: Apoidea) type specimens deposited in the Museu de Zoologia da Universidade de S��o Paulo, Brazil, pp. 1-23 in Pap��is Avulsos de Zoologia 59 on page 5, DOI: 10.11606/1807-0205/2019.59.17, http://zenodo.org/record/4613702, {"references":["Melo, G. A. R. 1992. Duas novas especies de Microstigmus Ducke, 1907 (Hymenoptera, Sphecidae). Revista Brasileira de Entomologia, 36: 663 - 670."]}

Altruism in the social Hymenoptera is generally considered to be a feature of females rather than males. A popular explanation for this is that in the solitary ancestors of today's social species, males provided little brood care. Males might therefore lack the preadaptations necessary to evolve altruism in social contexts. While anecdotal observations of male contributions to colony life have been reported, there are few reports of male participation in nest defence. In apoid wasps, there have been several reports of male nest-guarding behaviour in solitary species, potentially setting the evolutionary stage for similar behaviours in social lineages. Here, we present evidence of active and effective nest defence in males of the social apoid wasp Microstigmus nigrophthalmus. Males were observed chasing intruders away from the nest, and the presence of males had a significant effect on nest survival when females were removed. Males potentially obtained direct benefits through defence, so that defence may not represent male altruism. However, our results do show that males can perform acts that benefit their colony.

Fifty-two microsatellite loci were characterized in 22-31 unrelated females of the wasp (Microstigmus nigrophthalmus) collected from the Mata do Paraiso, Vicosa, M.G., Brazil. Fifty-one of these loci were developed from a microsatellite-enriched genomic library derived from M. nigrophthalmus and one was derived from the wasp, Ormyrus nitidulus. The genus Microstigmus represents an independent origin of social behaviour in the Hymenoptera and is thus of great potential in the study of social evolution.

The theory of assured fitness returns proposes that individuals nesting in groups gain fitness benefits from effort expended in brood-rearing, even if they die before the young that they have raised reach independence. These benefits, however, require that surviving nest-mates take up the task of rearing these young. It has been suggested that assured fitness returns could have favoured group nesting even at the origin of sociality (that is, in species without a dedicated worker caste). We show that experimentally orphaned brood of the apoid wasp Microstigmus nigrophthalmus continue to be provisioned by surviving adults for at least two weeks after the orphaning. This was the case for brood of both sexes. There was no evidence that naturally orphaned offspring received less food than those that still had mothers in the nest. Assured fitness returns can therefore represent a real benefit to nesting in groups, even in species without a dedicated worker caste.

The last instar larva of Microstigmus nigrophthalmus Melo, 1992 is described. It markedly differs from that of M. comes Krombein, 1967 the only other species in the genus whose mature larva have been described, for features as follows: presence of spinnerets; setae on the labrum, maxillae and labium; mandibles with tridentate apex and a bidentate lateral projection; lack of the conical supranal processo Notes on habitat, structure, and content of nests are also presented.

In a total of six hours of observation of severalMicrostigmus nigrophthalmus nests with two or more adult wasps, nine buccal contacts, six between females and three between females and males were observed. Except for two cases, these occurred soon after one of the females involved (the apparent donor) had returned to the nest and involved transfer from older to younger individuals. Experimental feeding of colored solution confirmed the occurrence of trophallaxis. InM. nigrophthalmus, trophallaxis seems to have arisen as a prolongation of maternal care since food is transferred from an older to a younger individual.