Family common name: common sawflies
Genus: Aneugmenus Hartig, 1937
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 Selandriinae subfamily are relatively small and slender. The range of Selandriinae is worldwide; it occurs on all continents except Antarctica (Goulet 1992). It is the most common and diverse group of tenthredinids in tropical regions, particularly in Central America, South America, and Southeast Asia (Smith 1969e). Selandriinae contains the only known sawflies that feed on non-vascular plants, specifically ferns (Smith et al. 2013). The subfamily can be distinguished from other subfamilies by wing venation (Goulet 1992).
Aneugmenus are small, about 5 mm in length and mostly black. The genus is a fern-feeding sawfly with some unique behaviors (Smith 1969e, Smith 2003).
Aneugmenus can be confused with similar species in the subfamily Selandriinae or tribe Aneugmenini. It can be distinguished from most other genera by the absence of a fore wing anal crossvein and from closely related Birka and Nesoselandria by the occipital ridge and pitted mesoscutellum (Smith 1969e).
In North America, Aneugmenus feeds on Pteridium aquilinum (bracken fern) (Smith 1969e).
Non-native A. padi was likely introduced from Europe or western Asia and is now established in the Pacific Northwest. It is recorded as parthenogenetic in North America, and as such, no male is known (Smith 1969e).
Aneugmenus padi and some other Aneugmenus spp. larvae in Europe, and A. merida in Venezuela have defensive behaviors to limit predaceous ants that live on bracken fern to feed on extra-floral nectaries (Heads and Lawton 1985, Naya et al. 2016). When a larva is first cut by an attacking ant, it bleeds out hemolymph that is extremely sticky and distasteful to the ants. The larvae usually can heal after the initial attack, and the associated ants do not return (Heads and Lawton 1985). Bracken fern is toxic to many animals, but it is unclear if the distastefulness of the sawfly’s hemolymph is due to compounds bio-accumulated from the host plant (Naya et al. 2016).
Because of the toxic properties and commonality of bracken fern, land managers in the United Kingdom have tried to control its growth. Aneugmenus padi was considered as a potential biocontrol insect due to its ability to heavily damage the plant from feeding behaviors. However, the damage was not sufficient to prevent fern re-growth (Lawton 1988).
A unique adult behavior, known by some authors as “nuptial feeding,” is recorded in A. flavipes. A female was observed attaching her mouthparts to a modified gland of the male’s seventh tergite, known as the sinus sexualis. From that location, the male can transfer nutritional secretions to the female. Other Aneugmenus species and one other genus, Neostromboceros, have an observable sinus sexualis, but A. flavipes and Neotropical A. merida are the only species where this behavior has been observed. Even more remarkably, no other sawflies are recorded exhibiting courtship activities like this. In A. merida, nuptial feeding is pre-copulatory, and though the timing is not known for A. flavipes, it is likely the same (Smith 2003, Avila-Núñez et al. 2007).
Adults of A. merida in Venezuela also feed as adults on extrafloral nectaries of the host fern. North American species with the same host may also have this behavior (Avila-Núñez et al. 2007).
World: This genus is known from North and South America, throughout Europe, North Africa, western Asia, eastern Russia, Japan, China, Taiwan, and Southeast Asia (Lacourt 1990, Taeger et al. 2010, Niu and Wei 2013).
North America: Most North American species of Aneugmenus have distinct ranges. Aneugmenus flordidella is known from Florida, A. scutellatus from southern Arizona and northern Mexico, A. nigritarsis from Puebla, San Luis Potosi and the state of Mexico, and A. leucopoda from Guatemala (Rohwer 1911, Smith 2003, Smith 2005). Aneugmenus padi is established in British Columbia, Washington, and Oregon, and A. flavipes occurs in eastern Canada and United States, as far north as Newfoundland, south to North Carolina, and west to Manitoba (Smith 1969e). The range of A. diversicolor is only described as “Mexico” (Rohwer 1911).
Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Aneugmenus
Details about data used for maps can be found here.