Bidigitus

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Heterarthrinae
Tribe: Fenusini
Genus: Bidigitus D.R. Smith, 1967
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 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 venationvenation:
the network of veins on a wing
(Smith 1971aSmith 1971a:
Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.).

Bidigitus is monotypicmonotypic:
describes having only one representative; ex. a genus that includes only one species
. Bidigitus platani has a very small recorded range and is fairly uncommon. The adults are small, about 4 mm, and mostly black with white markings on the legs (Smith 1971aSmith 1971a:
Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.).

Diversity

There is a single described species, and it is North American (Taeger et al. 2018Taeger et al. 2018:
Taeger A, Liston AD, Prous M, Groll EK, Gehroldt T, and Blank SM. 2018. ECatSymmdash;Electronic World Catalog of Symphyta (Insecta, Hymenoptera). Program version 5.0 (19 Dec 2018), data version 40 (23 Sep 2018). Senckenberg Deutsches Entomologisches Institut (SDEI), Muuml;ncheberg. https://sdei.de/ecatsym/ Accessed: 28 Jan 2020.).

Diagnostic characteristics

Subfamily characters

• angle of intersection of veins Cu1 and 1m-cu between 80°–110° (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.)
• cell cell:
  1. a membranous area of the wing between veins, 2. a small cavity or closed space
  M slightly constricted at apexapex:
  the end or most distal area of any structure
  ; veins m and 1m-cu not parallel (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.)
• intersection of M and M+Cu and intersection of Rs+M and R widely separated (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 2r 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

• third antennal segment longer than fourth (Smith 1967cSmith 1967c:
  Smith DR. 1967c. A review of the subfamily Heterarthrinae in North America (Hymenoptera: Tenthredinidae). Proceedings of the Entomological Society of Washington 69: 277-284.)
• fore wing fore wing:
  the anterior wing of each pair of wings; usually the largest wing of the pair
  veins 2A and 3A incomplete and curved upwards at apexapex:
  the end or most distal area of any structure
  (Smith 1971aSmith 1971a:
  Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.)
• hind wing hind wing:
  the posterior wing of each pair of wings
  anal cellanal cell:
  cell A of either the fore wing or hind wing
  present (Smith 1971aSmith 1971a:
  Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.)
• hind wing hind wing:
  the posterior wing of each pair of wings
  anal petiolepetiole:
  stalk or stem; used to describe basal vein stalk in wing OR basal stalk of a leaf.
  markedly longer than anal cellanal cell:
  cell A of either the fore wing or hind wing
  (Smith 1971aSmith 1971a:
  Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.)
• hind wing hind wing:
  the posterior wing of each pair of wings
  cells Rs and M both absent (Smith 1971aSmith 1971a:
  Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.)
• tarsal claw tarsal claw:
  sharpened appendage emerging from the apex of the tarsus
  bifidbifid:
  divided or forked into two branches or parts
  ; teeth of claw about equal in length (Smith 1971aSmith 1971a:
  Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.)
• tarsal claw tarsal claw:
  sharpened appendage emerging from the apex of the tarsus
  with large basalbasal:
  towards the base; closest to the body
  lobe (Smith 1971aSmith 1971a:
  Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.)

May be confused with

Bidigitus can be confused with other genera in the subfamily, especially the similar genus Profenusa. It can be distinguished by the bifidbifid:
divided or forked into two branches or parts
tarsal claw and the hind winghind wing:
the posterior wing of each pair of wings
anal cellanal cell:
cell A of either the fore wing or hind wing
length to petiolepetiole:
stalk or stem; used to describe basal vein stalk in wing OR basal stalk of a leaf.
length ratio (Smith 1967cSmith 1967c:
Smith DR. 1967c. A review of the subfamily Heterarthrinae in North America (Hymenoptera: Tenthredinidae). Proceedings of the Entomological Society of Washington 69: 277-284., Smith 1971aSmith 1971a:
Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.).

Exotic pest species of concern

none

Host associations

Bidigitus platani feeds on Platanus racemosa (California plane tree) (Smith 1971aSmith 1971a:
Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.).

Life history

Females oviposit into the upper side of leaves in early spring. The hatched larvaelarva:
the immature stage of holometabolous insects
feed gregariously inside the leaf on the parenchymaparenchyma:
in plants, the soft, thin-walled, inner tissue that performs functions such as photosynthesis, storage, and secretion; as opposed to dermal and vascular tissues
as leaf miners, creating blotch mines. The feeding stage lasts about 30 days, and when the larvaelarva:
the immature stage of holometabolous insects
are mature, they fall to the ground and build cocoons in which to pupate, or they overwinter and then pupate. Because of this quick life cycle, this species is multivoltinemultivoltine:
describing a life cycle with many generations per calendar year
with 3–5 generations in a single year (Smith 1971aSmith 1971a:
Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.).

Distribution

World: This genus is North American (Taeger et al. 2018Taeger et al. 2018:
Taeger A, Liston AD, Prous M, Groll EK, Gehroldt T, and Blank SM. 2018. ECatSymmdash;Electronic World Catalog of Symphyta (Insecta, Hymenoptera). Program version 5.0 (19 Dec 2018), data version 40 (23 Sep 2018). Senckenberg Deutsches Entomologisches Institut (SDEI), Muuml;ncheberg. https://sdei.de/ecatsym/ Accessed: 28 Jan 2020.).

North America: Bidigitus occurs in California, specifically the southern region of the state, with records in Santa Barbara and Anaheim (Smith 1971aSmith 1971a:
Smith DR. 1971a. Nearctic Sawflies. III. Heterarthrinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1420: 1-84.).

Map data from the Smithsonian National Museum of Natural History Entomology Collection (USNM)

Details about data used for maps can be found here.