Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Blennocampinae
Tribe: Tomostethini
Genus: Tomostethus Konow, 1886
Subgenera: none


The Tenthredinidae are the most species-rich family and are found throughout the world, in all continents but Antarctica. They are known as the “common sawflies.” They can generally be recognized by a cylindrical body and long, segmented antennae. Otherwise, they come in a variety of colors, sizes, and forms (Goulet 1992).

Sawflies in the subfamily Blennocampinae have a diverse set of life histories and habits. Many species are restricted to subtropical and tropical regions, but the genus is still fairly species-rich in North America. Blennocampinae includes many sawflies that feed on ornamental and forestry crops. This subfamily can be recognized by wing venation and bidentate mandibles (Smith 1969d).

Tomostethus is monotypic in the Nearctic region. Tomostethus multicinctus is about 7 mm in length and mostly black with white abdominal stripes (Smith 1969d).


There are nine described extant species worldwide. Two species occur in North America (Konow 1904, Taeger et al. 2018).

Diagnostic characteristics

Subfamily characters

Genus characters

May be confused with

Tomostethus can be confused with similar species in the subfamily Blennocampinae. It can be distinguished from most other genera by the developed pulvilli on basal tarsomeres and by the epicnemial area, and from similar genus Tethida by the densely haired mesonotum and the hairless basal area of the clypeus (Goulet 1992).

Exotic pest species of concern

Tomostethus nigritus, the black sawfly, is a pest of Fraxinus excelsior (common ash) and F. angustifolia (narrow-leafed ash) and is responsible for severe defoliation in several locations in Europe (Mitali et al. 2013, Meshkova et al. 2017, Verhyede and Sioen 2019). Outbreaks of this gregarious pest can result in populations in the thousands (Verhyede and Sioen 2019).

Host associations

In North America, Tomostethus feeds on species of Fraxinus (ash) (Goulet 1992). Tomostethus multicinctus specifically feeds on F. americana (white ash), F. latifolia (Oregon ash) (Smith 1969d), and F. pennsylvanica (green ash) (Brakie 2013).

Life history

Tomostethus multicinctus, known as the brown-headed ash sawfly, is a pest of ash trees. Females oviposit into the edge of the leaves as the leaves develop, causing wrinkling of the mature leaf. After hatching, larvae feed on the leaf tissue, first feeding in small pinholes, then feeding on the entire leaf, leaving behind the veins and skeletonizing the leaf (Cranshaw 2006). Larvae are light green with brown head capsules (Smith 1969d). After 2–3 weeks of development, mature larvae fall to the ground and overwinter in cocoons in the soil. Adults emerge in April. Tomostethus multicinctus is univoltine (Langford and McConnell 1935, Cranshaw 2006).


World: This genus is known from North America, throughout Europe, and in Turkey, Morocco, Iran, South Korea, and China (Taeger et al. 2018).

North America: Tomostethus multicinctus occurs on the east coast north to Ontario, through the Great Lakes region and south to Missouri and Texas; it also occurs in California and Oregon in the west (Smith 1969d). Tomostethus kirbyi is recorded from Mexico (Konow 1904, Taeger et al. 2018).

Map data from: (29 October 2019) GBIF Occurrence Download Tomostethus

Details about data used for maps can be found here.

Tomostethus multicinctus female lateral habitus; photo by Q. Baine, WSDA

Tomostethus multicinctus female lateral habitus; photo by Q. Baine, WSDA

Tomostethus multicinctus female face; photo by Q. Baine, WSDA

Tomostethus multicinctus female face; photo by Q. Baine, WSDA

Tomostethus multicinctus fore wing; photo by J. Orr, WSDA

Tomostethus multicinctus fore wing; photo by J. Orr, WSDA