Monostegia

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Allantinae
Tribe: Empriini
Genus: Monostegia Costa, 1859
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 antennaeantenna:
the sensory organ emerging from the front of the head, usually between the compound eyes and above the clypeus; includes the flagellum, scape and pedicel
. Otherwise, they come in a variety of colors, sizes, and forms (Goulet 1992Goulet 1992:
Goulet H. 1992. The genera and subgenera of the sawflies of Canada and Alaska: Hymenoptera. Symphyta. The insects and arachnids of Canada. Part 20. Agriculture Canada Publication.).

Sawflies in the Allantinae subfamily are mostly black and shining, sometimes with other colors. They have agricultural importance as some species are pests on cultivated and ornamental plants (Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.). They can be distinguished from other subfamilies by wing venationvenation:
the network of veins on a wing
(Smith 2003aSmith 2003a:
Smith DR. 2003a. A Synopsis of the sawflies (Hymenoptera: Symphyta) of America south of the United States: Tenthredinidae (Allantinae). Journal of Hymenoptera Research 12 (1): 148-192.).

Monostegia are small-sized, about 6–7 mm in length. There is a single North American species, M. abdominalis, and it is recognized by completely orange legs, mainly orange abdomenabdomen:
the third and last segment of an insect's body; in sawflies this is usually made up of 11 segments (segments 9 and 10 often fused)
, and orange clypeusclypeus:
sclerotized area on the front of the head located between the antennal insertions and labrum
(Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.).

Diversity

There are five described extantextant:
in existence; opposite of extinct
species worldwide. Only one occurs in North America (Taeger et al. 2010Taeger et al. 2010:
Taeger A, Blank SM, and Liston AD. 2010. World Catalog of Symphyta (Hymenoptera). Zootaxa 2580: 1-1064.).

A NearcticNearctic:
describing the region of the Northern Hemisphere that includes North America south through northern Mexico
key to species is included in Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172..

Diagnostic characteristics

Subfamily characters

• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein M and 1m-cu parallel (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein 2A+3A complete, connected to 1A by crossveincrossvein:
  short section of wing vein that connects two larger veins
  (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• anal crossvein anal crossvein:
  a crossvein that goes through the center of the basal anal cell
  angled (Smith and Schiefer 1997Smith and Schiefer 1997:
  Smith DR and Schiefer TL. 1997. A new genus and species of Allantinae (Hymenoptera: Tenthredinidae) from southeastern United States. Proceedings of the Entomological Society of Washington 99 (3): 472-476.)

Genus characters​

• mandibles bidentatebidentate:
  having two teeth; often used in descrbing mandibles or tarsal claws
  (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• clypeus clypeus:
  sclerotized area on the front of the head located between the antennal insertions and labrum
  shallowly notched (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• genal ridge absent (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• second antennal segment as long as wide (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein 2r present (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein M intersecting Sc+R at the intersection of Sc+R and Rs+M (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)
• tarsal claw tarsal claw:
  sharpened appendage emerging from the apex of the tarsus
  without basalbasal:
  towards the base; closest to the body
  lobe, with small inner tooth (Smith 1979aSmith 1979a:
  Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.)

May be confused with

Monostegia can be confused with similar species in the subfamily Allantinae or tribe Empriini. It can be distinguished from most other genera by the lack of genal ridge and tarsal clawtarsal claw:
sharpened appendage emerging from the apex of the tarsus
basalbasal:
towards the base; closest to the body
lobe. It is especially similar to Empria, which can be recognized by paired white spots on the abdomenabdomen:
the third and last segment of an insect's body; in sawflies this is usually made up of 11 segments (segments 9 and 10 often fused)
(Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.).

Exotic pest species of concern

none

Host associations

In North America, M. abdominalis feeds on Lysimachia nummularia (creeping jenny), L. terretris (earth loosestrife), and L. vulgaris (garden loosestrife) (Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.).

Life history

Female Monostegia lay eggs into the distaldistal:
furthest from the body, opposite of proximal
portion of the leaf in short rows. At maturity, the larvaelarva:
the immature stage of holometabolous insects
drop to the ground and build cells in the soil to overwinter. Monostegia abdominalis is bivoltinebivoltine:
describing a life cycle with two generations per calendar year
in Quebec and may have up to three generations per year further south (Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.).

Monostegia abdominalis was introduced to North America, likely along with the introduction of its host plants as ornamental garden plants from Europe (Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.).

Distribution

World: This genus is known from North America, the United Kingdom, southern Europe, West Asia, and Siberia (Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172., Taeger et al. 2010Taeger et al. 2010:
Taeger A, Blank SM, and Liston AD. 2010. World Catalog of Symphyta (Hymenoptera). Zootaxa 2580: 1-1064.).

North America: Monostegia abdominalis occurs in Quebec, Ontario, Michigan, New York, Pennsylvania, New Jersey, and New England (Smith 1979aSmith 1979a:
Smith DR. 1979a. Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.).

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

Details about data used for maps can be found here.