Delta

Delta campaniformis, copyright Graham Winterflood.

Belongs within: Eumeninae.

Delta is a genus of potter wasps widespread in warmer regions of the Old World, characterised by an elongate metasomal petiole, slightly longer than than the mesosoma, with tergum I largely impunctate, a single mid tibial spur, and an apically truncate clypeus. They build jug-like nests in sheltered locations such as the sides of buildings or crevices on tree trunks.

Delta wasp
Published 29 October 2016
Two views of the potter wasp Delta unguiculata, copyright Entomart.

Not so long ago, I found myself struggling with the challenge of identifying potter wasps. Potter wasps are close relatives of the social wasps, close enough that they are usually classified in the same family Vespidae, but they belong to a distinct lineage (the subfamily Eumeninae) of a more solitary bent, each female constructing its own individual nests in which to lay its eggs. The ‘potter’ part of their name refers to their preferred material for said nests which are sculpted from mud. Though they do not form the vexatious swarms that social wasps can, potter wasps still tend to be relatively large and impressive wasps, and like social wasps they are usually strikingly patterned in bold colours to give fair warning of their potentially painful stings.

Nevertheless, despite being the sort of thing that would be likely to attract interest, identifying potter wasps can be a definite challenge. For a large part of the twentieth century, eumenine genera were mostly divided very finely, with the features separating related genera often difficult to distinguish. Here in Australia, I found an approachable identification guide for most eumenines to be nigh on nonexistent. One potter wasp genus that I did successfully pull out, however, was Delta.

Female Delta campaniforme constructing a nest, from Brisbane Insects.

Delta is a genus of about fifty species of potter wasp found in warm regions of the Old World. At least one member of the genus, D. campaniforme rendalli, has become established in Florida after being introduced there from southern Africa (Menke & Stange 1986). Delta belongs to the Eumenes group of genera, in which the first segment of the metasoma (the petiole) is very long and slender. Distinctive features of Delta within this group include the second segment of the metasoma being relatively short with the associated tergum bell-shaped, and the males having the last segment of the antenna bent backwards to form a hook (Nguyen 2015). Females build their mud nests, which they stock with moth caterpillars, cemented to flattened surfaces such as the sides of buildings or along branches. The species introduced to North America possibly arrived in the form of a nest glued to some easily transportable substrate such as a shipment of lumber.

The names of Delta and many other Eumenes-group genera derive from the work of Henri de Saussure, who recognised a single genus Eumenes corresponding to this group but divided it into a number of sections that he labelled Alpha, Beta and so forth. Later authors raised these sections to the status of separate genera though some expressed the objection that Saussure may have never intended these alphabetical designations to be formal names at all. The validity of Saussure’s ‘genus-group names’ was eventually settled by a decision of the International Commission on Zoological Nomenclature but authors such as Menke & Stange (1986) have continued to criticise the recognition of these difficult segregate genera, especially as, whereas the Eumenes group as a whole is probably monophyletic, many of its component genera may not be. Future classifications may yet see Eumenes gathering its prodigals back into the fold.

Systematics of Delta
<==Delta Saussure 1855C85
    |--‘Vespa’ emarginata Linnaeus 1758 [incl. Vespa maxillosa DeGeer 1775, Eumenes (*Delta) maxillosus]C85
    |--D. arcuata (Fabricius 1775) [=Vespa arcuata]C85
    |--D. bicinctus (Saussure 1852) [=Eumenes bicincta]C85
    |--D. caffer (Linnaeus 1767) [=Vespa caffra, Eumenes caffer, E. caffra]GS61
    |--D. campaniformis (Fabricius 1775) [=Vespa campaniformis]C85
    |    |--D. c. campaniformeC85
    |    |--D. c. assatus (Giordani Soika 1934) [=Eumenes campaniformis assatus]C85
    |    `--D. c. esuriensG84
    |--D. higletti (Meade Waldo 1910) (see below for synonymy)GS61
    |--D. hottentotusGS61
    |    |--D. h. hottentotusGS61
    |    `--D. h. concinnus (Saussure 1855) [=Eumenes hottentotus concinnus, E. lepeleterii concinnus]GS61
    |--D. incola (Giordani Soika 1935)C85
    |    |--D. i. incolaC85
    |    |--D. i. aruensis (Giordani Soika 1935) [=Eumenes (Delta) ncola aruensis]C85
    |    `--D. i. teleporus (van der Vecht 1959) [=Eumenes incola teleporus]C85
    |--D. latreillei (Saussure 1852) [=Eumenes latreillei, E. (Delta) pyriformis var. latreillei]C85
    |--D. lepeleterii (Saussure 1853) (see below for synonymy)GS61
    |--D. nigritarsis (Meade-Waldo 1910) [=Eumenes nigritarsis, E. (Delta) pyriformis var. nigritarsis]C85
    |--D. philantes (Saussure 1852) [=Eumenes philantes]C85
    |--D. phthisicus (Gerstaecker 1857) [=Eumenes phthisicus]GS61
    |--D. transmarinum (van der Vecht 1959) [=Eumenes transmarinus]C85
    `--D. xanthurum (Saussure 1852) [=Eumenes xanthura]C85

Delta higletti (Meade Waldo 1910) [=Eumenes campaniformis higletti; incl. E. campaniformis marshalli Bequaert 1926, E. maxillosus pulcherrimus Schulthess 1910]GS61

Delta lepeleterii (Saussure 1853) [=Eumenes lepeleterii, E. lepeletierii; incl. E. campaniformis formosus Bequaert 1926]GS61

*Type species of generic name indicated

References

[C85] Cardale, J. C. 1985. Vespoidea and Sphecoidea. In: Walton, D. W. (ed.) Zoological Catalogue of Australia vol. 2. Hymenoptera: Formicoidea, Vespoidea and Sphecoidea pp. 150–303. Australian Government Publishing Service: Canberra.

[G84] Gauld, I. D. 1984. An Introduction to the Ichneumonidae of Australia. British Museum (Natural History).

[GS61] Giordani Soika, A. 1961. Hymenoptera (Aculeata): Vespidae. In: Hanström, B., P. Brinck & G. Rudebeck (eds) South African Animal Life: Results of the Lund University Expedition in 1950–1951 vol. 8 pp. 440–451. Almqvist & Wiksell: Uppsala.

Menke, A. S., & L. A. Stange. 1986. Delta campaniforme rendalli (Bingham) and Zeta argillaceum (Linnaeus) established in southern Florida, and comments on generic discretion in Eumenes s. l. (Hymenoptera: Vespidae: Eumeninae). Florida Entomologist 69 (4): 697–702.

Nguyen, L. T. P. 2015. Taxonomic notes on the genus Delta de Saussure (Hymenoptera: Vespidae: Eumeninae) from Vietnam. Animal Systematics, Evolution and Diversity 31 (2): 95–100.

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