Fenusa

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Heterarthrinae
Tribe: Fenusini
Genus: Fenusa Leach, 1817
Subgenera: Fenusa, Kaliofenusa

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).

Fenusa are very small, about 3.5–4 mm in length and entirely black with slightly darkened wings (Smith 1971a). The Fenusini tribe are all leaf miners (Goulet 1992). The North American Fenusa species are all pests of economically significant tree genera (Smith 1971a).

Diversity

There are 12 described extant species worldwide. Three occur in North America (Taeger et al. 2018).

A key to North American species is included in Smith 1967c and in Smith 1971a.

Diagnostic characteristics

Subfamily characters

Genus characters​

May be confused with

Fenusa can be confused with other genera in the subfamily, especially similar genera Profenusa and Fenella. It can be distinguished by the number of antennal segments, large membranous area behind the first tergite, open cell R1 of the hind wing, and lack of a completely haired mesonotum (Goulet 1992).

Exotic pest species of concern

none

Host associations

Each of the three Fenusa species in North America are associated with a tree genus: F. dohrnii feeds on Alnus spp. (alder), F. pumila on Betula spp. (birch), and F. ulmi on Ulmus spp. (elm) (Smith 1971a).

Life history

Females oviposit into the upper surface of leaves. Larvae feed on the inner leaf tissue and create blotch mines in the process. At maturity, the larvae drop to the ground and burrow into the soil to overwinter and subsequently pupate (Scannell 2000, Miller and Ware 2014). All three species present in North America are introduced and established from their native range in Europe and western Asia (Taeger et al. 2018).

Fenusa dohrnii, known as the European alder leaf miner, and Fenusa pumila, birch leaf miner, are pests on elm and birch, respectively (Smith 1971a). Fenusa ulmi, the elm leaf miner, is a common pest of elms and has been reported causing extensive damage on elm trees. The larvae are dorsoventrally flattened and have reduced thoracic legs. In infestations, over 100 eggs and larvae can be found in a single leaf at a time. Like many leaf miners, internal feeding behaviors protect the larvae from classical chemical control, making them difficult to control (Miller and Ware 2014).

Distribution

World: This genus is known from North America, throughout Europe into Russia, Turkey, and Iran, and in southeastern Asia in China and Myanmar (Taeger et al. 2018)

North America: Fenusa occurs throughout northern United States and southern Canada. All three species were introduced from Europe. Fenusa dohrnii was first discovered in North America in Ottawa in 1891 and has since spread to the extent of the genus’ range today. Fenusa pumila was first found in Connecticut in 1925 and now is recorded in eastern states and provinces, and in Oregon, Washington, and Alaska in the west. Fenusa ulmi was first found in New York in 1898 and now occurs in northeastern United States west to the Great Lakes region and southeastern Canada (Smith 1971a, Snyder et al. 2007, Miller and Ware 2014).

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

Details about data used for maps can be found here.

Fenusa dohrnii female lateral habitus; photo by J. Orr, WSDA

Fenusa dohrnii female lateral habitus; photo by J. Orr, WSDA

Fenusa sp. female dorsal habitus; photo by J. Orr, WSDA

Fenusa sp. female dorsal habitus; photo by J. Orr, WSDA

Fenusa ulmi female face; photo by Q. Baine, WSDA

Fenusa ulmi female face; photo by Q. Baine, WSDA

Fenusa ulmi wings; photo by P. Jones, WSDA

Fenusa ulmi wings; photo by P. Jones, WSDA