The Wharton Lab

Physotarsus Townes, 1966: 139, 330.

Type species: Tryphon maculipennis Cresson, 1874, by original designation.

Townes 1966

: 139, 330 (catalog; new combinations; original description).
Townes 1970: 102-103 (key to genera; copy of original description).
Carlson 1979: 592 (catalog).
Gauld 1997: 181-184, 190-199 (key to genera; revision of Physotarsus of Costa Rica; detailed redescription of genus; illustrated descriptions of 6 new species from Costa Rica).
Yu and Horstmann 1997: 455 (catalog).
Zhaurova and Wharton 2009: 1-52 (revision of genus; descriptions of 18 new species, redescriptions of all previously described species; keys to all species).

The species of Physotarsus are differentiated primarily on the basis of size, color patterns, and the extent of pubescence and punctation. Other characters useful for differentiating species are found on the hind wings and the hind legs. Gauld (1997) provides a key to the species known from Costa Rica. Zhaurova and Wharton (2009) recognized 25 valid species, 18 of which they described as new, and provided a key to all known species.

Physotarsus is not demonstrably monophyletic. A large number of undescribed species available only as singletons renders the task of delimiting the genus more difficult. At present, Physotarsus is best recognized by the absence of the clypeal features that define the other genera of Scolobatini s. s.

Diagnosis – Ventral margin of clypeus thickened medially but never with sharply pointed median tooth. Occipital carina absent mid-dorsally, present at least ventrally. First flagellomere with tyloid laterally bearing 15 or fewer sensilla. Fore wing areolet always absent. Hind tarsi swollen, at least in male.

Physotarsus lacks the sharply pointed median tooth on the clypeus that characterizes Scolobates and Onarion, and is therefore most similar to Catucaba. The apical margin of the clypeus is variously thickened in Physotarsus and uniformly thin and sharp in Catucaba. Physotarsus is extremely color variable. Wings are largely hyaline in most species, although yellow and extensively fuscous patterns occur in some, such as in the type species.

Description. Length: body (Figs 1, 2) 3.2-9.7 mm, fore wing 3.0-10.4 mm. Shape of clypeal margin varies (Figs 3-9), but never with a sharply pointed median tooth as in Scolobates and Onarion nor uniformly thin and sharp as in Catucaba. Clypeus 2.4-4.0 times as broad as long, weakly convex in profile, sometimes separated medially by a weak transverse ridge, separated from face dorsomedially by a sulcus that varies from distinctly impressed to barely visible. Anterior tentorial pits oval to slightly elongate with lateral corners pointed laterad or upcurved. Malar space 0.2-0.8 times basal width of mandible. Mandible with ventral tooth slightly longer than dorsal tooth, mandible tapering over basal 0.3-0.5, almost parallel-sided apically. Mouthparts simple to weakly haustellate, labiomaxillary complex never elongate as in Onarion. Face smooth (Figs 3, 4) to quite strongly punctate (Fig. 5), 1.2 to 2.3 times as wide as long, with a small median tooth or tubercle dorsally. Inter-antennal area flat to slightly concave, anterior margin of torulus situated at about 0.6-0.8 of eye height. Widest diameter of torulus 1.0-1.6 times widest diameter of median ocellus. Area between lateral ocelli flat to quite strongly depressed, distance between lateral ocelli 0.4-1.5 times their widest diameter, distance from lateral ocellus to eye margin 1.4-2.8 times widest diameter of lateral ocellus. Area behind ocelli regularly rounded to sharply declivitous. Antennae with 22-47 flagellomeres, quite long, longer to much longer than length of body. First flagellomere with a small tyloid laterally (Fig. 10), second flagellomere 0.4-0.8 times length of first. Occipital carina incomplete, present on ventral 0.2 to 0.8 of head, rarely joining hypostomal carina at or before mandibular base, the two carinae most often widely separated. Pronotum dorsally with distinctly impressed transverse groove, anterior margin truncate to quite strongly emarginate, and narrow to exceptionally narrow dorsomedially, anterior margin rounded to abruptly upcurved dorsolaterally. Lateral groove of pronotum absent to complete, its length thus highly variable. Pronotum glabrous to variably punctate, sometimes partially rugose. Mesoscutum (Fig. 11) glabrous to densely punctate; notauli absent. Epicnemial carina extending dorsally along ventral 0.2-0.4 of posterior margin of pronotum, sometimes turned towards but only very rarely reaching anterior margin of mesopleuron. Mesopleuron always lightly pubescent ventrally, smooth to densely punctate laterally. Propodeum with pleural carinae absent to complete, median longitudinal carinae sometimes present as posterior vestiges; punctation on propodeum variable, punctation absent posteromedially, sometimes present anteromedially. Posterolateral edge of propodeum somewhat upcurved. Hind trochanter less than 3.0 times as long as basally wide, apical margin of trochanter reaching apical margin of trochantellus. Pectination of claws varying from the presence of stout setae only at the extreme base to fully or almost fully pectinate. Fore wing with abscissa of Cu1 between 1m-cu and 2cu-a about 0.35-1.0 times length of 2cu-a. Marginal cell about 2.5-3.3 times as long as wide. Hind wing with distal abscissa of 1A usually entirely absent, more rarely present as a weak basal stub (as in the type species). T1 (Fig. 12) about 1.5-2.4 times as long as broad, spiracles sometimes slightly protruding in profile. Cerci (Fig. 2) sessile to quite prominent.

Distribution – restricted to the New World, occurring from Saskatchewan (Canada) to Argentina.

Species of Physotarsus are thought to be larval-prepupal parasitoids of sawflies of the family Argidae, but only one host record actually exists as of 2009: Physotarsus adriani Gauld, 1997 was reared from the “pupae” (or more likely cocoons) of the sawfly Trochophora lobata (Erichson) in Costa Rica (Janzen (website)). The only record of a live [male] parasitoid states that it was observed to “have a behavior of a housefly – buzzing flight” (Janzen (website)). Parasitoids were recorded as emerging from the sawfly pupae on November 7, which is the end of the rainy season in Costa Rica.

This page was assembled by Bob Wharton. It is part of a revision of the genera of Westwoodiini and Scolobatini conducted by Kira Zhaurova as part of her M. S. thesis in Entomology at Texas A&M University, completed in 2005, parts of which are published in Zhaurova and Wharton (2009a and 2009b).

This work owes much to the groundwork provided by Ian Gauld’s study of the Australian and Costa Rican faunas, and we are particularly grateful for his assistance in many aspects of this study. We also thank the following curators and researchers for extended loans of the material used for this revision: David Wahl (AEIC), Jason Weintraub (ANSP), Ian Gauld and Gavin Broad (BMNH), Andy Bennett (CNC), Gabriel Melo (DZUP), Anders Albrecht and Pekka Malinen (FMNH), Ronald Zúñiga (INBio), and Dave Furth (USNM). Matt Yoder provided considerable assistance along the way, particularly with databasing. Images used here were obtained through the combined efforts of Kira Zhaurova, Heather Cummins, and Patricia Mullins. Our use of PURLs (http://purl.oclc.org) follows the example of their use in publications by Norm Johnson. This content is based upon work conducted at Texas A&M University and supported by the National Science Foundation’s PEET program under Grant No. DEB 0328922 and associated REU supplement nos DEB 0723663 and DEB 0616851. Page last updated April, 2011.

This material is based upon work supported by the National Science Foundation under Grant Number DEB 0328922 with REU supplements DEB 0723663 and 0616851.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.