Euura

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Nematinae
Tribe: Nematini
Genus: Euura Newman, 1837
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).

Nematinae is the second-largest subfamily of Tenthredinidae, with over 1250 species (Prous et al. 2014). They are most diverse in northern Eurasia and North America; only a few species occur in the Southern Hemisphere. Nematinae sawflies have a variety of feeding habits including external leaf feeding, leaf mining, and gall forming, and feed on a variety of hosts (Smith 2003b).

The Nematinae have been subject to numerous revisions in recent years. As of 2021, there are no comprehensive keys to many of the North American species of Nematinae (Prous et al. 2014). Because of changing taxonomy and extreme variability in morphology, identifying genera and species in the Nematinae may be more challenging than in other subfamilies of Tenthredinidae. For this reason, knowing the host or behaviors of a specimen can be extremely helpful for identification within this subfamily.

Euura is an extremely species-rich genus with a widespread distribution. In recent years, several genera including Amauronematus, Pontania, Pachynematus, Pikonema, Phyllocolpa, and many species of Nematus were collapsed into Euura based on molecular phylogenetics. This makes the genus especially difficult to key based on morphology (Prous et al. 2014).

Euura are generally small (<10mm), but have a variety of colors and forms. Many species are gall-inducers, so if the larval feeding habits are known, this can be a more useful character for identification than the external morphology (Prous et al. 2014).

Diversity

There are 658 described species worldwide. About 257 species occur in North America (Taeger et al. 2018).

Diagnostic characteristics

Subfamily characters

Genus characters

Euura is very morphologically diverse, so some characters only apply to some species:​

May be confused with

Euura has several shared morphological characters with Nematus and Pristiphora, and in some cases cannot be easily distinguished. Together, these three genera can usually be distinguished from other Nematinae by the lack of fore wing vein 2r-rs, incomplete vein 2A+3A, and asymmetrical outer surfaces of the mandibles. Euura and Nematus can usually be distinguished from Pristiphora by the ovipositor sheath evenly tapering toward the apex in dorsal view, long subapical tooth of the tarsal claw, emarginated clypeus, and fore wing vein C not enlarged apically (Prous et al. 2014). Some species of Euura can be recognized by the lack of fore wing vein 2r-m (Prous et al. 2014). Some species of Euura have the ovipositor sheath deeply emarginate and wide apically (i.e., the former Amauronematus (Pontopristia)), but these can be distinguished from Pristiphora by the deeply emarginate clypeus and long subapical tooth of the tarsal claw.

Exotic pest species of concern

Euura ruyanus is a pest of willow in China. The multivoltine species pupates on the plant during the summer and in the soil in winter. The infested trees were seriously damaged by repeated feeding (Xingyu et al. 2007).

Euura salicis also feeds on willow and is recorded as a pest in Turkey. Though the species is univoltine, the damage inflicted in one cycle can defoliate significant portions of the host (Çalmasur and Özbek 2006).

Euura desantisi is a serious pest of willow and poplar in a few countries in South America, Africa, and New Zealand. This multivoltine species appears to reproduce via parthenogenesis (where only females are produced from unfertilized eggs), and as such it is very successful and can spread quickly where hosts and climatic conditions are favorable (Ovruski and Smith 1993, Koch and Smith 2000).

Euura mucronata is also considered a pest of willow in Europe, and is known to be unusually polyphagous (Urban 1993, Nyman 2002). This species may be present in sub-arctic North America, specifically Alaska and Manitoba (Benson 1962).

Host associations

Most Euura feed on species of Salix (willow) (Smith and Middlekauff 1987). Other species feed on a variety of plants, including Rhododendron, Picea (spruce), grasses, and sedges (Goulet 1992, Smith 1974c). Known host plant species include Robinia hispida (rose acacia), Robinia pseudoacacia (black locust) (Darling and Smith 1985), Trifolium wormskioldii (cows clover) (Poinar and Smith 2003), Populus balsamifera (balsam poplar) (Zinovjev and Smith 2000a), Populus grandidentata (big tooth aspen), and Populus tremuloides (quaking aspen) (Zinovjev and Smith 1999).

Life history

Life histories are varied in the genus Euura; some are gall formers, and some are external leaf feeders (Smith and Middlekauff 1987). Species range in number of generations per year (Darling and Smith 1985).

Many species of Euura, including those previously placed in Pontania, are gall-inducers on stems, petioles, twigs, leaves, or buds (Smith and Middlekauff 1987, Zinovjev and Smith 1999). The leaf galls formed come in many shapes and sizes: round leaf galls, sausage-shaped leaf galls, leaf rolls, and midrib galls (Zinovjev and Smith 1999). The majority of gall-inducing species are monophagous (Nyman 2002).

In the cases of stem or petiole galls, the gall-inducer (e.g., E. amerinae) can cause significant damage to the plant; the leaf or stem beyond the location of the gall often dies due to interruption in the phloem pathway, or due to fungal infection in the vacated gall (Liston 1982).

Euura atriceps larvae feed on the floral inflorescences of the host plant, an uncommon habit in sawflies (Poinar and Smith 2003).

Euura ribesii, also known as the common gooseberry sawfly, is a pest of currant and gooseberry plants in the genus Ribes. The gregarious larvae are small and green with black spots. As they mature they go from feeding on the underside of the leaf, resulting in small holes, to feeding on the entire leaf. E. ribesii is multivoltine, usually with 3 generations per year, so it is common to see larvae of different stages of development on the same plant at the same time. The final generation will overwinter in the soil in cocoons (Gratwick 1992).

Distribution

World: The genus is known from North America, throughout Europe, east through Turkey, the Russian Far East, Central Asia, and North Africa (Liston et al. 2017b). Euura desantisi is introduced in various localities in the Southern Hemisphere, including Argentina, Chile, South Africa, Lesotho, and New Zealand (Koch and Smith 2000).

North America: Euura occurs throughout the United States and Canada north into Alaska, Yukon, the Northwest Territories, and Nunavut (Goulet 1992, GBIF). A few species are recorded from coastal Greenland (Vilhelmsen 2015). One species, E. mexicana, occurs farther south in northern Sonora, Mexico (Smith 2003b).

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

Details about data used for maps can be found here.

Euura ribesii female lateral habitus; photo by Q. Baine, WSDA

Euura ribesii female lateral habitus; photo by Q. Baine, WSDA

Euura oligospila female dorsal habitus; photo by J. Orr, WSDA

Euura oligospila female dorsal habitus; photo by J. Orr, WSDA

Euura oligospila male face; photo by Q. Baine, WSDA

Euura oligospila male face; photo by Q. Baine, WSDA

Euura ribesii male lateral habitus; photo by Q. Baine, WSDA

Euura ribesii male lateral habitus; photo by Q. Baine, WSDA

Euura sp. male face; photo by Q. Baine, WSDA

Euura sp. male face; photo by Q. Baine, WSDA

Euura sp. fore wing; photo by J. Orr, WSDA

Euura sp. fore wing; photo by J. Orr, WSDA