Metallus

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Heterarthrinae
Tribe: Fenusini
Genus: Metallus Forbes, 1885
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).

Metallus are generally small, about 4–5 mm in length, and all black or black and orange (Smith 1971a, Smith 1988). The Fenusini tribe are all leaf miners (Goulet 1992).

Diversity

There are 21 described extant species worldwide. Four species occur in North America (Taeger et al. 2010).

A key to Nearctic species is included in Smith 1971a.

Diagnostic characteristics

Subfamily characters

Genus characters​

May be confused with

Metallus can be confused with other genera in the subfamily, especially similar genus Fenusella. It can be distinguished by the bifid tarsal claw, antennal pedicel width, and haired mesonotum (Smith 1967c, Goulet 1992). The males have distinctly widened and flattened third and fourth antennal segments (Smith 1971a).

Exotic pest species of concern

none

Host associations

Metallus capitalis and M. rohweri feed on species of Rubus (blackberry, raspberry, etc.), and M. lanceolatus feeds on Geum (avens) (Goulet 1992, Eiseman and Smith 2017).

Life history

Females oviposit into the upper surface of a leaf. After hatching, larvae feed on the inner leaf tissue and create blotch mines, which sometimes combine into one because they are not able to establish mines on new leaves. At maturity, the larvae exit the mines and fall to the soil to build a cell, then burrow and pupate, or overwinter. (Eiseman and Smith 2017). Other Fenusini larvae lack larval prolegs, but prolegs are present on Metallus abdominal segments 2–7 and 10 (Smith 1971a). The species native to North America are univoltine or bivoltine (Eiseman and Smith 2017).

One species, M. ochreus, can overwinter as an early instar larva. This habit has not been recorded in any other leaf-mining or externally leaf-feeding sawfly (Eiseman and Smith 2017).

Metallus lanceolatus was introduced from Europe. This potential pest species is multivoltine (Looney et al. 2016, Eiseman and Smith 2017).

Distribution

World: This genus is known from North America, Europe, and Asia, with records as far south as Nepal and Myanmar (Smith 1976b, Taeger et al. 2010).

North America: Metallus occurs throughout the northern United States and southern Canada, as far south as Oregon in the west, and Virginia in the east (Smith 1971a). One introduced species, M. lanceolatus, was first collected in British Columbia in 1933, then in several northeastern states and provinces in the 1960s, and is now also recorded from Washington (Looney et al. 2016).

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

Details about data used for maps can be found here.

Metallus capitalis female lateral habitus; photo by J. Orr, WSDA

Metallus capitalis female lateral habitus; photo by J. Orr, WSDA

Metallus capitalis female dorsal habitus; photo by J. Orr, WSDA

Metallus capitalis female dorsal habitus; photo by J. Orr, WSDA

Metallus capitalis female face; photo by Q. Baine, WSDA

Metallus capitalis female face; photo by Q. Baine, WSDA