Belongs within: Cecidomyiinae.
The Oligotrophini are a group of midges whose larvae cause galls or live freely in flower heads (Gagné 1981). Members include the Hessian fly Mayetiola destructor, a serious pest of wheat crops in many parts of the world.
Juniper gall midges
Published 1 January 2016
Sometimes, the evidence of an insect’s presence may be much more visible than the insect itself. Imagine passing by a common juniper tree Juniperus communis and seeing a structure like the one in the photo above (copyright Jean-Yves Baugnée). You might think it was some sort of reproductive structure. You would be right, though it is not the tree that is reproducing. This is the gall of a juniper gall midge Oligotrophus juniperinus, and were you to cut the gall in half you would possibly find a single gall midge larva lurking within. Many insects (and other animals) cause the development of galls on their host plants, thus providing themselves with both shelter and food in one convenient location.
The adult gall midge is a minute, very delicate fly, unlikely to be spotted by the casual observer. Gall midges are classified in the family Cecidomyiidae, an extremely diverse group of which not all members cause galls as larvae (some feed on plants without causing galls, others feed on fungi, a few are even predators or parasitoids). Cecidomyiids are divided between a number of subfamilies and tribes, with Oligotrophus belonging to the tribe Oligotrophini. In the past, this tribe has been used to cover a heterogeneous mix of relatively unspecialised cecidomyiids, but the most recent classification of the tribe strips it down to two genera, Oligotrophus and Walshomyia, found in the Holarctic region (Harris et al. 2006). Adults of these genera have legs with simple tarsal claws and long empodia (the soft pads between the claws), and as larvae they all live in galls on trees of the cypress family Cupressaceae. The exact form of the gall produced may differ between species, and it is often (though not always) possible to determine the species responsible for a gall by its form. For instance, three species that cause galls on Juniperus communis in Europe are Oligotrophus juniperinus, O. panteli and O. gemmarum. The first two species have galls formed from whorls of leaves pressed into a vase shape, but whereas in galls of O. juniperinus the leaves splay outwards towards the tip, in galls of O. panteli they remain parallel. The third species, O. gemmarum, has much smaller galls formed from only slightly modified buds; though very different from mature galls of the other two species, they may be confused with young undeveloped galls (Harris et al. 2006).
Despite their diversity, and the fact that some species are economically significant to humans, cecidomyiids are not a widely studied group. Part of the reason for this is that their small size and build makes them difficult to handle; diagnostic work on adults often requires slide-mounting them. I have made one not-very-successful attempt at slide-mounting cecidomyiids, and I can confirm that it is a fiddly process. Because the different body parts often have to be examined from different angles, slide-mounting first requires dissection of the animal into sections (so, for instance, the head can be placed on the slide face-on, the body side-on, and the terminalia top-up). In my experience, instructions for slide-mounting animals requiring such dissections will always tell you to arrange the various bits appropriately on the cover-slip before placing the slide (or the other way around, if you prefer). And if you know how to attach slide to cover-slip without having all your carefully arranged body parts immediately zooming off to a completely different spot on the slide from where you put them, then you’re a far more skillful slide preparer than I am.
The gall of it all
Published 20 August 2025
When I wrote the above, I mentioned that the historical concept of Oligotrophini had shifted over the years. Anyone familiar with the ways of invertebrate taxonomy should hardly be surprised to find that has not stopped.
Gall midges and other members of the Cecidomyiidae are doomed to be a taxonomic challenge, considering that they are diverse in terms of species but fairly simple in terms of morphology. Many features that workers on other insect families find useful, such as wing venation, are reduced to the bare minimum in gall midges. Those features that are available for consideration are prone to selective pressures and convergence, so many cecidomyiid subtaxa have been defined not by unique features but by combinations of features. The simple tarsal claws and long empodia that defined Oligotrophini in the restricted sense of Oligotrophus and Walshomyia only were each features that might be found in other gall midges, though not necessarily together. In 2016, Raymond J. Gagné described three new genera of gall midges that he felt blurred the distinction between the restricted Oligotrophini and another vaguely defined tribe, the Rhopalomyiini. As a result, he combined the two into a single tribe, with Oligotrophini being the senior name. Distinctive (but again, not exclusive in and of themselves) features of this slightly broader Oligotrophini included wings with the costal vein closed immediately after its junction with vein R4+5, and a uniformly microtrichose gonostylus (lateral valve of the male genitalia). Also characteristic was the formation of galls in which each larva occupied its own chamber, and emergence from the gall was done by the pupa (as opposed to the larva making a tunnel through which the pupa might emerge).
Later, representatives of this broader Oligotrophini were included in a molecular phylogeny of gall midges by Dorchin et al. (2019). They found that these taxa did not form a single clade, and so they recommended dropping the Oligotrophini entirely, instead sinking its members in a broader tribe Dasineurini. Unfortunately, this concept of Dasineurini may not be defined by morphological characters only, though it is noteworthy that all species of Dasineurini are completely herbivorous. In contrast, their sister group, containing the remaining tribes of the supertribe Lasiopteridi, produce ‘ambrosia galls’, in which the gall tissue is infected with fungi on which the midge larvae feed. However, it should be noted that Dorchin et al.’s analysis, broad as it is, is still not exhaustive. Even if diagnostic for Dasineurini, herbivory is probably ancestral for the supertribe as a whole, and it remains a possibility that some herbivorous taxa not sampled by Dorchin et al. might have yet more remote affinities.
Systematics of Oligotrophini
Characters (Gagné 1981): Antenna with 7–42 flagellomeres, usually irregular in number within species. Ocelli absent. Tarsal claws rounded at or beyond mid length, all either toothed or simple; empodia as long as or longer than claws. Male genitalia with gonocoxite with elongate mediobasal lobes sheathing aedeagus; mediobasal lobes entire, uniformly setulose or glabrous; gonostylus terminal. Female cerci usually fused medially into a single terminal lamella.
<==OligotrophiniG81 |--Mayetiola destructorG81, CM91 |--ProcystiphoraG81 |--RhabdophagaG81 |--LygocecisG81 |--SackenomyiaG81 |--FiciomyiaG81 |--WalshomyiaG81 |--Rhopalomyia californicaG81, B88 |--Diarthronomyia hypogaeaG81, G17 |--Iteomyia salicifoliaG81 |--Oligotrophus Latreille 1805S-TG10 | |--O. betheli [incl. O. apicis Appleby & Neiswander 1965, Phytophaga sabinae Felt 1935]S-TG10 | |--O. juniperinusS-TG10 | |--O. panteliS-TG10 | |--O. schmidtiS-TG10 | `--O. szepligetiiS-TG10 |--SemudobiaG81 |--CystiphoraG81 | |--C. canadensisG81 | `--C. schmidtiCM91 `--DasineuraG81 |--D. canadensisG81 |--D. corollaeGJ09 |--D. gleditchiaeGJ09 |--D. oxycoccanaG96 `--D. praecox Gagné 1996G96
*Type species of generic name indicated
References
[B88] Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).
[CM91] Colless, D. H., & D. K. McAlpine. 1991. Diptera (flies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 2 pp. 717–786. Melbourne University Press: Carlton (Victoria).
Dorchin, N., K. M. Harris & J. O. Stireman, III. 2019. Phylogeny of the gall midges (Diptera, Cecidomyiidae, Cecidomyiinae): systematics, evolution of feeding modes and diversification rates. Molecular Phylogenetics and Evolution 140: 106602.
[G81] Gagné, R. J. 1981. Cecidomyiidae. In: McAlpine, J. F., B. V. Peterson, G. E. Shewell, H. J. Teskey, J. R. Vockeroth & D. S. Wood (eds) Manual of Nearctic Diptera vol. 1 pp. 257–292. Research Branch, Agriculture Canada.
[G96] Gagné, R. J. 1996. A new species of Dasineura (Diptera: Cecidomyiidae) infesting pinxterbloom azalea flowers in Maryland and Washington, D.C. Proceedings of the Entomological Society of Washington 98 (2): 228–232.
Gagné, R. J. 2016. Three new genera and three new species of Nearctic Lasiopteridi (Diptera: Cecidomyiidae: Cecidomyiinae) from Asteraceae and Caprifoliaceae, and the tribe Rhopalomyiini subsumed under Oligotrophini. Zootaxa 4158 (3): 403–418.
[GJ09] Gagné, R. J., & M. Jaschhof. 2009. Cecidomyiidae (gall midges). In: Brown, B. V., A. Borkent, J. M. Cumming, D. M. Wood, N. E. Woodley & M. A. Zumbado (eds) Manual of Central American Diptera vol. 1 pp. 293–314. NRC Research Press: Ottawa.
[G17] Girault, A. A. 1917. Descriptiones stellarum novarum. Privately published (reprinted: Gordh, G., A. S. Menke, E. C. Dahms & J. C. Hall. 1979. The privately printed papers of A. A. Girault. Memoirs of the American Entomological Institute 28: 80–101).
Harris, K. M., S. Sato, N. Uechi & J. Yukawa. 2006. Redefinition of Oligotrophus (Diptera: Cecidomyiidae) based on morphological and molecular attributes of species from galls on Juniperus (Cupressaceae) in Britain and Japan. Entomological Science 9: 411–421.
[S-TG10] Simova-Tošić, D., D. Graora, R. Spasić & D. Smiljanić. 2010. Oligotrophus betheli Felt (Diptera: Cecidomyiidae), a new species in the fauna of Europe. Arch. Biol. Sci. 62 (4): 1219–1221.