It's time for another post on crabronid wasps! The hard-working individual in the photo above is Clitemnestra bipunctata, a species found in the United States of North America. This is the only species of this genus found north of Mexico; other species are found in South America and in Australasia (Australia, New Guinea and New Caledonia). Clitemnestra belongs to the Gorytini, a closely related tribe to the Bembicini featured in an earlier post, though C. bipunctata is smaller than the average bembicin. You can find a good description of the biology of C. bipunctata at Bug Eric's website.
When Bohart & Menke (1976) prepared their revision of the Sphecidae (which then included the current Crabronidae), they included Clitemnestra in the genus Ochleroptera. Ochleroptera was recognised as closely related to Clitemnestra, but the two genera were distinguished by the shape of the metasoma (the effective abdomen). In Ochleroptera, the first segment of the metasoma is relatively long and narrow, and there is a distinct constriction between it and the remainder of the metasoma (you can see this clearly in the picture above). In Clitemnestra, this segment is shorter and broader, and it is not so divided from the other segments. Because the latter arrangement is the more primitive, Bohart & Menke suggested that Ochleroptera was descended from Clitemnestra, and because both genera were found in both South America and Australasia, they suggested that the two genera had both originated in Australasia and dispersed independently to South America.
However, it was soon realised that the distinction between the two genera was not as clear as had been thought. A number of species were identified in South America in which the segment shape was intermediate: a bit long and narrow for 'Clitemnestra', but not narrow enough for 'Ochleroptera'. As there were no other significant features distinguishing the genera, they were eventually synonymised. Subsequently, Ohl (2002) described another species, Clitemnestra noumeae, from New Caledonia that also has an intermediate metasomal form. Though no formal analysis has yet been done to confirm things one way or another, it seems likely that 'Clitemnestra' and 'Ochleroptera' do not represent independent dispersals between Australasia and the Americas. Instead, 'Ocheroptera' species have probably arisen independently within Clitemnestra on more than one occasion.
To date, Clitemnestra bipunctata is the best studied species in the genus natural history-wise; other species have only been described on sporadic occasions. Clitemnestra species nest in burrows in vertical banks, which they primarily stock with various species of leafhoppers. In the case of one Australian species, C. plomleyi, it was suggested that the burrows it was seen using were not dug by the wasp itself, but had been left behind by beetles or other wasps (Evans & O'Neill 2007). It remains to be seen whether this is typical behaviour for the species, or it may have represented opportunistic behaviour by one enterprising individual.
Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World: a generic revision. University of California Press.
Evans, H. E., & K. M. O'Neill. 2007. Sand Wasps: Natural History and Behavior. Harvard University Press.
Ohl, M. 2002. A new species of the wasp genus Clitemnestra Spinola, 1851 from New Caledonia (Hymenoptera, Apoidea, Crabronidae, Bembicinae). Deutsche Entomologische Zeitschrift 49 (2): 275-278.