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 Allantinae subfamily are mostly black and shining, sometimes with other colors. They have agricultural importance as some species are pests on cultivated and ornamental plants (Smith 1979a). They can be distinguished from other subfamilies by wing venation (Smith 2003a).
Monostegia are small-sized, about 6–7 mm in length. There is a single North American species, M. abdominalis, and it is recognized by completely orange legs, mainly orange abdomen, and orange clypeus (Smith 1979a).
Monostegia can be confused with similar species in the subfamily Allantinae or tribe Empriini. It can be distinguished from most other genera by the lack of genal ridge and tarsal claw basal lobe. It is especially similar to Empria, which can be recognized by paired white spots on the abdomen (Smith 1979a).
In North America, M. abdominalis feeds on Lysimachia nummularia (creeping jenny), L. terretris (earth loosestrife), and L. vulgaris (garden loosestrife) (Smith 1979a).
Female Monostegia lay eggs into the distal portion of the leaf in short rows. At maturity, the larvae drop to the ground and build cells in the soil to overwinter. Monostegia abdominalis is bivoltine in Quebec and may have up to three generations per year further south (Smith 1979a).
Monostegia abdominalis was introduced to North America, likely along with the introduction of its host plants as ornamental garden plants from Europe (Smith 1979a).
North America: Monostegia abdominalis occurs in Quebec, Ontario, Michigan, New York, Pennsylvania, New Jersey, and New England (Smith 1979a).
Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Monostegia
Details about data used for maps can be found here.