Mesoleius Holmgren, 1856

Taxonomic History / Nomenclature
Mesoleius Holmgren, 1856: 69. Type species: Tryphon aulicus Gravenhorst, 1829. Subsequent designation by Viereck (1912: 176), selected from several species originally included by Holmgren (1856).

Allocritus Foerster, 1869: 211. Type species: Mesoleius tenuiventris Holmgren, 1858. Subsequent designation by Perkins (1962: 403). Monobasic. Synonymized by Perkins (1962: 403).

Cryptocentrus Walsh, 1873. Type species: Tryphon submarginatus Cresson, 1864. Monobasic. Preoccupied by Cryptocentrus Ehrenberg, 1837. Synonymized by Dalla Torre (1901: 252), who misspelled the genus name and gave an inappropriateAlfkenA senior synonym.

Mesolius Pfankuch, 1906: 85. Type species: Ichneumon integrator Mueller, 1776. Monobasic. Unjustified emendation.

Alfkenia Pfankuch, 1906: 89. Type species: Ichneumon integrator Mueller, 1776. Monobasic. Synonymized by Townes (1945: 508) under a much broader concept of Mesoleius then synonymized under a more restricted definition of Mesoleius, with a query, by Townes (1970: 125).

Habrodemus Schmiedeknecht, 1913: 2799. Type species: Mesoleius elongatus Brischke, 1871. Included by Schmiedeknecht (1914: 2842). Synonymized by Townes and Townes (1951), though they did not indicate this to be a new synonym and so there may be an earlier reference that I have overlooked.

This is a huge genus, Holarctic in distribution, with over 100 valid species.
Diagnosis and Relationships
Mesoleius was often broadly interpreted in earlier literature, but restricted by Townes (1970). who focused on features of the clypeus, hind wing, and notaulus to redefine the genus. Campodorus has historically been challenging to separate from Mesoleius and Perkins (1962: 412) considered it a synonym of Mesoleius. Townes (1970) used the angle of inclination of the first abscissa of CU1 of the hind wing as the first character in his key couplet separating Mesoleius from Campodorus (more vertical in _Mesoleius) but the second character in this couplet, the shape of the clypeus, seems more reliable and is the character emphasized by Kasparyan (2000, 2003, 2005). We have followed Kasparyan in this regard. In Mesoleius, the apical margin of the clypeus is sharp medially (Fig. 1) whereas in Campodorus it is blunt (Figs 2, 3). Essentially, in Campodorus, a median, subapical bulge extends ventrally to obscure the sharp margin medially. The separation is not perfect, and some species are still difficult to place, as nicely explained by Kasparyan (2000), but this is the most reliable character we have found. In specimens of Mesoleius determined by Townes, 25% of the species have the notaulus extending to the anterior margin of the mesoscutum, though not always as sharply as in Campodorus.
Clypeus (Fig. 4) variable but usually narrow, often tall; either flat, weakly concave medially, or strongly bulging medially and subapically; ventral margin sharp throughout, though sharp margin partially overlapped by blunt median bulge in a few species; ventral margin sometimes truncate medially but often weakly (Fig. 4) to strongly bilobed, with sharp lateral margins distinctly angled dorsally; epistomal sulcus varying from sharp and distinct to shallow and indistinct. Malar space in species examined equal to or shorter than half basal width of mandible (Fig. 4). Mandible (Fig. 4) varying from relatively short and broad to moderately long in material examined; curved,sometimes strongly so; either gradually narrowing from base to apex or more or less parallel-sided over apical half; ventral tooth varying from slightly shorter and narrower, to about equal, to slightly longer than dorsal tooth. Inner eye margins parallel to weakly converging ventrally. Ocelli variable; most commonly small, with maximum diameter of lateral ocellus distinctly shorter than distance between ocellus and eye but larger, with maximum diameter shorter than distance to eye in 10 % of species examined. Female and male antennae at least as long as body in material examined, commonly longer than body at least in females; first flagellomere long and slender in many species (nearly twice longer than second), but distinctly shorter and less than twice longer than second in several species (as in Fig. 2). Hypostomal carina joining occipital carina above base of mandible (Fig. 5); occipital carina complete. Epomia absent or pronotum laterally in some species with rugose sculpture that appears epomia-like. Dorsal end of epicnemial carina nearly always extending to anterior margin of mesopleuron but sometimes weaker dorsally and slightly separated from anterior margin in at least a few species; mesopleuron ventrally somewhat variable in sculpture from nearly smooth and polished to finely mat to more coarsely granular-mat. Notaulus varying from absent or nearly so (Fig. 6) to present and either weak or rarely sharply impressed; distinct and extending to anterior margin in about 25% of species examined. Pleural carina nearly always well-developed (Fig. 7), rarely weaker posteriorly; propodeal carinae rarely as poorly developed as in the type species of Mesoleius with petiolar area open anteriorly and lateral longitudinal carinae short, weak; usually with well-developed lateral longitudinal carina extending nearly to anterior margin; petiolar area delimited by tall carinae and varying from small to very large; median longitudinal carinae extending from petiolar area to anterior margin with areola usually distinct and roughly triangular with median carinae then broadening anteriorly to form basal median area; transverse carinae otherwise absent; Legs with apical comb on posterior side of hind tibia short, often poorly developed; hind tibial spurs long, slender, sometimes very long, at least half length of hind basitarsus; all tarsal claws simple in species examined for this description. Fore wing (Fig. 1) with areolet usually absent, sometimes present (one individual of the 40 examined). Hind wing with first abscissa of CU1 usually vertical or nearly so and about as long as or much longer than 1cu-a. T1 varying from short and broad, as in the type species of Mesoleius, to long and slender; strongly to very gradually widening posteriorly, respectively; basal depression for dorsal tendon attachment deep; dorsal carinae always well-developed basally, varying in length: short and not extending to level of spiracle in some species but in other species long, converging at level of spiracle and extending half distance between spiracle and posterior margin; dorsal-lateral carina sharp and distinct from spiracle to apex in all but one species examined; glymma deep, broad basally, narrowing posteriorly. S1 short to very short, usually 0.25-0.4 times length of T1, extending to spiracle in only one of the species examined. T2 thyridium present; laterotergites of T2 and T3 completely separated by creases. Ovipositor short to very short (Figs 1-3, 9, 10), straight, with deep, wide subapical, dorsal notch. Apex of female metasoma as in Figs 2, 3, 9, 10.

This description is modified from that of Townes (1970) and based on about 15 species in the Texas A&M University Collection.

1.Mesoleius habitus
2. Mesoleius habitus...
3. Mesoleius habitus...
4. Mesoleius face and clypeus...
5. Mesoleius back of head...
6. Mesoleius habitus mesoscutum...
7.Mesoleius propodeum
8.Mesoleius T2
9. Mesoleius ovipositor...
10. Mesoleius ovipositor...
No referenced distribution records have been added to the database for this OTU.
Biology / Hosts
As part of a biological control program directed against larch sawfly in Canada, the biology of Mesoleius tenthredinis Morley was studied in Europe by Pschorn-Walcher and Zinnert (1971) and embryogenesis was described in considerable detail for the same species by Bronskill (1960, 1964).

There are no specimens currently determined for this OTU, or those specimens determined for this OTU are not yet mappable.

This page was assembled by Bob Wharton as part of a larger collaborative effort on the genera of Ctenopelmatinae. Page last updated May, 2015.

This work would not have been possible without 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 thank David Wahl of the American Entomological Institute, Gavin Broad of The Natural History Museum, London, and Andy Bennett of the Canadian National Collection for extended loans of the material used for this study. We also thank David Wahl for useful feedback throughout our study, Dave Karlsson for sending valuable material from the Swedish Malaise Trap Survey, and Dmitry Kasparyan for discussions on generic limits. Matt Yoder provided considerable assistance with databasing issues, and our use of PURLs ( in this regard follows the example of their use in publications by Norm Johnson. Heather Cummins, Andrea Walker, Patricia Mullins, Caitlin Nessner, Amanda Ladigo, Karl Roeder, Mika Cameron, Danielle Restuccia, and Cheryl Hyde graciously assisted with image processing, formatting, and literature retrieval. This study was supported by the National Science Foundation’s PEET program under Grant No. DEB 0328922 and associated REU supplement #s DEB 0616851, 0723663, 0923134, and 1026618.

This material is based upon work at Texas A&M University supported by the National Science Foundation under Grant Number DEB 0328922 with REU supplements DEB 0616851, 0723663, 0923134, and 1026618. 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.