Globally there are nine species in the genus Tomostethus, mostly distributed in the palaearctic region. Only one species is present in both Britain and Ireland.
The genus can be characterised by the following features. The antennal pedicel is about as long as it is wide. The first flagellomere is almost as long as the second and third flagellomeres combined. The post-genal carina is missing. On the forelegs the tibial spur is bifurcate at the tip and the tarsal claws are simple. The prepectus is large and triangular in the same plane as the mesepisternum from which it is separated by a suture. In the forewing the stub vein 2A+3A is straight, or only weakly upcurved, at the apex. Veins M and 1m-cu slightly diverge. In the hindwing, cell M is present.
Larvae feed on trees in the Oleaceae family, especially Fraxinus species.
Tomostethus nigritus (Fabricius, 1804)
Austarå, O. 1991: Severe Outbreaks of the Ash Sawfly Tomostethus nigritus F. (Hymenoptera: Tenthredinidae) on Ornamental Trees in Oslo. - Anzeiger für Schädlingskunde, Pflanzenschutz Umweltschutz, Berlin 64: 70-72
Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London
Liston A, Knight G, Sheppard D, Broad G, Livermore L (2014) Checklist of British and Irish Hymenoptera - Sawflies, ‘Symphyta’. Biodiversity Data Journal 2: e1168. https://doi.org/10.3897/BDJ.2.e1168
Matoševic, D.; Hrašovec, B. & Pernek, M. 2003: Spread and Character of Tomostethus nigritus F. Outbreaks in Croatia During the Last Decade. - In: McManus, M. L. & Liebhold, A.M. (eds.) 2003: Proceedings. Ecology, Survey and Management of Forest Insects.
Meshkova, V.; Kukina, O.; Zinchenko, O.; Davydenko, K. 2017: Three-year Dynamics of Common Ash Defoliation and Crown Condition in the Focus of Black Sawfly Tomostethus nigritus F. (Hymenoptera: Tenthredinidae). - Baltic Forestry 23(1): 303-308.
Smith, D. R. 1969: Nearctic Sawflies. I. Blennocampinae: Adults and larvae (Hymenoptera: Tenthredinidae). - Technical Bulletin, U.S. Department of Agriculture, Washington 1397: 1-176
Stockan, J.; Taylor, A. F. S. 2014: An outbreak of Tomostethus nigritus (F.) (Hymenoptera: Tenthredinidae) on Aberdeen's urban ash trees. - British Journal of Entomology and Natural History, London 27: 190.
Zinchenko, O. V.; Kukina, O. M. 2015: [Some biological peculiarities of the ash black sawfly Tomostethus nigritus Fabricius, 1804 (Hymenoptera: Tenthredinidae).] (In Ukrainian). - Yzvestyya Xar'kovskoho entomolohycheskoho obshhestva 23(2): 70-74.