Heterarthrus

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Heterarthrinae
Tribe: Heterarthrini
Genus: Heterarthrus Stephens, 1835
Subgenera: none

Background

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 Heterarthrinae subfamily are generally small and dark-colored. Many species of this family are economic pests of trees and shrubs and can be characterized by their skeletonizing or leaf-mining larval feeding behaviors. Heterarthrinae adults can be distinguished from those of other subfamilies by wing venation (Smith 1971a).

Heterarthrus are small sawflies, about 4.5 mm in length, and mostly black with either yellow abdominal spots and a yellow costa, or with a partially reddish-brown abdomen (Smith 1971a, Humble 2010).

Diversity

There are 23 described extant species. Two species occur in North America (Taeger et al. 2018).

A key to birch-feeding Heterathrinae that includes both Nearctic Heterarthrus species is included in Humble 2010.

Diagnostic characteristics

Subfamily characters

Genus characters​

May be confused with

Heterarthrus can be easily distinguished from other genera in the subfamily by the complete anal cell with crossvein, number of antennal segments, and relatively large malar space (Smith 1971a).

Exotic pest species of concern

Heterarthrus ochropoda has been determined to be a pest of Populus tremula (European aspen) and Populus nigra (black poplar) in Turkey, with recorded levels of foliar damage as high as 70% in some locations (Çalmaşur and Özbek 2004). Several species of Heterathrus in Central Europe feed on species of Acer (maple) (Altenhofer and Zombori 1987), and in Japan feed on Salix (willow) (Smith and Naito 2005).

Native or introduced pest species

Heterarthrus nemoratus, the late birch leaf edgeminer, can occur in large populations, leading to extensive foliar damage (Digweed et al. 2009)Heterarthrus vagans can be a pest of red alder pest (Humble 2010).

Host associations

Heterarthrus nemoratus feeds on species of Betula (birch), including B. alleghaniensis (yellow birch), B. glandulosa (resin birch), B. lenta (sweet birch), B. nigra (river birch), B. occidentalis (water birch), B. papyrifera (paper birch), B. populifolia (gray birch), and B. pumila (bog birch). There are also records of H. nemoratus completing larval development on Alnus viridis (green alder) (Goulet 1992, Digweed et al. 2009). Heterarthrus vagans feeds on Alnus rubra (red alder) (Humble 2010).

Life history

Females oviposit into the margin of the leaf. The hatched larvae feed inside the leaf on the parenchyma as leaf miners, creating blotch mines. The feeding stage lasts about 30 days. Unlike leaf miners of the Fenusini tribe, which drop to the soil, mature Heterarthrus larvae remain in the leaf and build a papery cocoon in which they overwinter and subsequently pupate (Smith 1971a, Digweed et al. 2009). Heterarthrus nemoratus is univoltine, and males are not known (Smith 1971a, Digweed et al. 2009). Heterarthrus vagans is bivoltine (Humble 2010).

Distribution

World: This genus is represented in North America, Europe east through Siberia, Asia through China, Japan, India, and Myanmar (Smith and Naito 2005, Humble 2010, Taeger et al. 2018).

North America: Both species of North American Heterarthrus are introduced from Europe. Heterarthrus nemoratus was first discovered in Nova Scotia in 1908. It is now widespread in the northeastern United States and southeastern Canada, and is present in Alberta, British Columbia, Washington, Northwest Territories, and Alaska (Smith 1971a, Snyder et al. 2007, Digweed et al. 2009, Looney et al. 2016). Heterathrus vagans was first discovered in British Columbia in 2009 and is now recorded in Washington State as well (Humble 2010, Looney et al. 2016).

Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Heterarthrus

Details about data used for maps can be found here.

Heterarthrus vagans female lateral habitus; photo by J. Orr, WSDA

Heterarthrus vagans female lateral habitus; photo by J. Orr, WSDA

Heterarthrus vagans female dorsal habitus; photo by J. Orr, WSDA

Heterarthrus vagans female dorsal habitus; photo by J. Orr, WSDA

Heterarthrus vagans female face; photo by Q. Baine, WSDA

Heterarthrus vagans female face; photo by Q. Baine, WSDA

Heterarthrus vagans male lateral habitus; photo by J. Orr, WSDA

Heterarthrus vagans male lateral habitus; photo by J. Orr, WSDA

Heterarthrus vagans male dorsal habitus; photo by J. Orr, WSDA

Heterarthrus vagans male dorsal habitus; photo by J. Orr, WSDA

Heterarthrus vagans male face; photo by Q. Baine, WSDA

Heterarthrus vagans male face; photo by Q. Baine, WSDA

Heterarthrus vagans wings; photo by J. Orr, WSDA

Heterarthrus vagans wings; photo by J. Orr, WSDA