The chalcidoid wasps are truly a remarkable array: tiny wonders coming in a bewildering variety of forms. For this post, I’m looking at the members of the chalcidoid subfamily Pireninae.
The Pireninae are currently recognised as one of the subfamilies of the Pteromalidae, a chalcidoid ‘family’ that is long overdue for reclassification as phylogenetic studies have agreed that it is extensively polyphyletic* (e.g. Heraty et al. 2013). The pirenines are very small wasps, about one to two millimetres in length. They’ve always struck me as having a fairly fly-like habitus: they lack the metallic coloration and strong sculpturing of many other pteromalids, often being uniformly black or yellow, and carry upright bristle-like setae on the head and mesosoma. Characteristic features of the Pireninae also include antennae inserted low on the face, reduced numbers of antennal segments (and hence often rather short antennae), a large clypeus that often protrudes ventrally, and a dorsally rounded mesosoma often with deeply impressed notauli (longitudinal grooves on the mesoscutum) (Bouček 1988). About ten genera are currently recognised in the subfamily. Perhaps the most remarkable is the genus Zebe, named by John La Salle in 2005 from a single female that he says, at the time, had stymied multiple hymenopterists as to what it might be for two decades. Zebe has legs with four-segmented tarsi, instead of the five-segmented tarsi of other pteromalids, and the female has a long horn extending forward from the mesoscutum and hanging over the head. As in other micro-wasps with comparable structures, this horn probably provides space for the retraction of an extraordinarily long ovipositor.
*But just in case anyone who stands to have some influence is reading, I will point out that the number of subfamilies that need to excised from the Pteromalidae could be kept to a minimum if the family is expanded to include the Ormyridae, Torymidae, Eucharitidae and Perilampidae. Bonus points that these are the families that are the hardest to distinguish from pteromalids to begin with.
The life habits of most pirenines are very little known. Those whose hosts are known develop as parasites of Cecidomyiidae, gall midges, and may be found in association with the galls produced by those flies on various plants. Species of the genus Macrogelenes attack cecidomyiids associated with grasses, and some have been investigated as control agents for midges on commercial crops. So these tiny little wasps could prove themselves very valuable to humans.
Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).
Heraty, J. M., R. A. Burks, A. Cruaud, G. A. P. Gibson, J. Liljeblad, J. Munro, J.-Y. Rasplus, G. Delvare, P. Janšta, A. Gumovsky, J. Huber, J. B. Woolley, L. Krogmann, S. Heydon, A. Polaszek, S. Schmidt, D. C. Darling, M. W. Gates, J. Mottern, E. Murray, A. D. Molin, S. Triapitsyn, H. Baur, J. D. Pinto, S. van Noort, J. George & M. Yoder. 2013. A phylogenetic analysis of the megadiverse Chalcidoidea (Hymenoptera). Cladistics 29: 466–542.
La Salle, J. 2005. Zebe cornutus gen. et sp. nov., a new Pireninae (Hymenoptera: Pteromalidae) with 4-segmented tarsi and a mesoscutal horn. Acta Societatis Zoologicae Bohemoslovenicae 69: 193–197.