Thrinax

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Selandriinae
Tribe: Strongylogastrini
Genus: Thrinax Konow, 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 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 Selandriinae subfamily are relatively small and slender. The range of Selandriinae is worldwide, it occurs on all continents except Antarctica (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.). It is the most common and diverse group of tenthredinids in tropical regions, particularly in Central America, South America, and Southeast Asia (Smith 1969eSmith 1969e:
Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.). Selandriinae contains the only known sawflies that feed on non-vascular plants, specifically ferns (Smith et al. 2013Smith et al. 2013:
Smith DR, Janzen DH and Hallwachs W. 2013. Food plants and life histories of sawflies of the families Argidae and Tenthredinidae (Hymenoptera) in Costa Rica, a supplement. Journal of Hymenoptera Research 35: 17-31. https://doi.org/10.3897/JHR.35.5496).The subfamily can be distinguished from other subfamilies by wing venationvenation:
the network of veins on a wing
(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.).

Thrinax are medium-sized, about 7 mm in length, and generally black and white in color with orange/red legs. The genus is fern-feeding (Smith 1969eSmith 1969e:
Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.).

Diversity

There are 27 described extantextant:
in existence; opposite of extinct
species worldwide. Four occur 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 key to NearcticNearctic:
describing the region of the Northern Hemisphere that includes North America south through northern Mexico
species of Thrinax (as Hemitaxonus) is included in Smith 1969eSmith 1969e:
Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48..

Diagnostic characteristics

Subfamily characters

• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein Rs+M curved near intersection with veinvein:
  a tube-like, often darkened, structure on the wings
  Sc+R (Smith 1969eSmith 1969e:
  Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  veins M and m-cu about parallel (Smith 1969eSmith 1969e:
  Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein 2r-m present (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.)

Genus characters

• antennae long and slender (Smith 1969eSmith 1969e:
  Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.)
• occipital ridge present (Smith 1969eSmith 1969e:
  Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.)
• pedicel pedicel:
  the second antennal segment, between the scape and flagellum
  as long as wide (Smith 1969eSmith 1969e:
  Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.)
• epicnemial furrowfurrow:
  a groove or linear depression
  present and fairly straight, not V-shaped (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.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  vein M meeting Sc+R at intersection of Rs+M and Sc+R (Smith 1969eSmith 1969e:
  Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  anal cellanal cell:
  cell A of either the fore wing or hind wing
  with almost perpendicular crossveincrossvein:
  short section of wing vein that connects two larger veins
  (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.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  anal crossveinanal crossvein:
  a crossvein that goes through the center of the basal anal cell
  located in the apicalapical:
  towards the apex; farthest away from the body
  third of the anal cellanal cell:
  cell A of either the fore wing or hind wing
  (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.)
• somewhat scattered setaeseta:
  hair-like structure
  on the mesepisternummesepisternum:
  the ventral portion of the mesopleuron, located between the forecoxae and mid coxae
  (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.)
• mesoscutum mesoscutum:
  the central and dorsal portion of the thorax between the scutellum and postnotum
  laterallateral:
  of or towards the side of the body
  lobe without pits (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.)
• first tergitetergite:
  a sclerotized segment of the tergum
  wide medially with narrow membranous area (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.)

May be confused with

Thrinax can be confused with similar species in the subfamily Selandriinae or tribe Strongylogastrini. It can be distinguished from most other genera by the perpendicular anal crossveinanal crossvein:
a crossvein that goes through the center of the basal anal cell
, from closely related Eriocampidea by slender 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
and presence of occipitalocciput:
the posterior surface of the head
ridge, and from closely related Strongylogaster by the length of the pedicelpedicel:
the second antennal segment, between the scape and flagellum
(Smith 1969eSmith 1969e:
Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.).

Exotic pest species of concern

none

Host associations

In North America, Thrinax feeds on ferns, including Athyrium (lady fern), Athyrium thelypteroides (silver glade fern), Onoclea sensibilis (sensitive fern), Osmunda, Pteridium (bracken fern), and Matteuccia (ostrich fern) (Smith 1966aSmith 1966a:
Smith DR. 1966a. The Nearctic sawflies of the genus Hemitaxonus Ashmead (Hymenoptera: Tenthredinidae). Proceedings of the Entomological Society of Washington 68(2): 113-120., 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.).

Life history

Specific biology of this genus is not known. Female Thrinax lay eggs onto the upper side of the leaf in groups up to 12 per leaf. LarvaeLarva:
the immature stage of holometabolous insects
feed externally and then overwinter in wood or pith of a nearby plant (Smith 1969eSmith 1969e:
Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.).

Distribution

World: This genus is known from North America and East Asia (Taeger et al. 2010Taeger et al. 2010:
Taeger A, Blank SM, and Liston AD. 2010. World Catalog of Symphyta (Hymenoptera). Zootaxa 2580: 1-1064.). One species occurs in Europe (Blank 2002Blank 2002:
Blank SM. 2002. Taxonomic notes on Strongylogasterini (Hymenoptera: Tenthredinidae). Proceedings of the Entomological Society of Washington 104 (3): 692-701.).

North America: Three species of Thrinax are eastern in distribution, found in eastern Canada and in the United States east of the Mississippi River. Thrinax primaria occurs in British Columbia, Oregon, and California (Smith 1969eSmith 1969e:
Smith DR. 1969e. Nearctic Sawflies. II. Selandriinae: Adults (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1398: 1-48.).

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

Details about data used for maps can be found here.