Pholetesor viminetorum
Creators: name: Whitfield, James B.
Publisher: name: Zenodo
Year: 2006
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Braconidae
Pholetesor
Pholetesor viminetorum

description: Pholetesor viminetorum (Wesmael)   
(figs. 26, 53, 73, 83)  
 Microgaster viminetorum Wesmael, 1837. Nouv. Mem. Acad. Belg. 10: 50. Type not examined.   
 Microgaster fuliginosus Wesmael, 1837. Nouv. Mem. Acad. Belg. 10: 52–53. Syn. by Wilkinson (1945). Type not examined. See Nixon (1973) and Papp (1983a &b) for additional synonymical information.   
 Females. Body length 2.0– 2.5 mm, forewing length 2.2–2.5 mm.   
 Head. Frons 1.2–1.3x broader at midheight than medially long, weakly punctate; inner margins of eyes strongly convergent. Antennae approximately same length as forewing, very dark brown; all but apical 6 or 7 flagellomeres with 2 ranks of placodes; flagellomere 2 3.2–3.5x as long as broad; flagellomere 14 1.4–1.6x longer than broad. Palpi lighter than antennae but still deep brown. Head in dorsal view approximately 2.0x broader than medially long.   
 Mesosoma. Mesoscutum shallowly but distinctly punctate anteriorly, becoming more indistinctly so posteriorly; surface between punctures moderately shiny without strong metallic sheen; width just anterior to tegulae equal to that of head. Scutoscutellar scrobe relatively coarse, not set in depression. Scuellar disc much less strongly punctate than mesoscutum, shiny between punctures, approximately 1.3x longer than anteriorly broad. Metanotum weakly excavated anteriorly, nearly appressed to scutellum; transverse carinae on either side poorly developed, remnants closer to anterior edge then posterior; transverse depression on either side irregularly sculptured, not deeply impressed. Propodeum approximately 1.8x broader than long at longest point, coarsely rugose posteriorly near nucha, becoming finely rugulose anteriorly and nearly smooth in posterolateral corners; nucha with very short ridges radiating anteriorly.   
 Legs. All coxae nearly black, rest of legs very dark brown except lighter tibial bases; brightness and extent of lighter yellow­brown areas strongly variable geographically. Pines on outer faces of hind tibiae about 30 in number, irregularly distributed. Apical spurs of hind tibiae subequal in length, not more than 0.4 as long as hind basitarsi.   
 Wings. Tegulae very dark brown, weakly translucent. Venation of forewing unusually evenly dark­brown pigmented; stigma entirely dark brown. R1 slightly longer than stigma, about 3x as long as distance from its distal tip to end of 3Rs fold along wing edge; 2r slightly arched, equal to or longer than 1Rs, meeting it at a distinctly knobbed junction. Hindwing with anterior venation distinctly pigmented, posteriorly with pale veins; vannal lobe somewhat flattened but evenly fringed with hairs of moderate length.   
 Metasoma. Tergite I 1.7–2.1x longer than broad at midlength, weakly to strongly narrowing posteriorly, strongly rugose posteriorly, weakly and longitudinally costulate anterolaterally, with weak concentric sculpturing around basal depression; apically with small raised medial polished bump. Tergite II 2.1–2.3x broader posteriorly than medially long, weakly rugulose to costulate, becoming smoother and more polished medially; hind margin distinctly convex to weakly bisinuate. Tergum III longer than tergite II, without obvious sculpturing. Laterotergites medium to dark brown. Succeeding terga of usual unsculptured, overlapping type. Hypopygium medially longer than hind basitarsus, submedailly weakly creased, setting off narrow, medial, more translucent fold; tip bluntly acuminate. Ovipositor sheaths decurved basally, broadly expanded apically into short, asymmetrical paddle shape (longer ventrally); hairs somewhat longer and denser apically; entire length of sheaths slightly longer than hind basitarsi; expanded portions only 0.75– 0.8 length of hind basitarsi. Ovipositor weakly decurved.   
 Males. Similar in coloration to females; body length 1.9–2.5 mm, forewing length 2.2–2.5 mm. Antennae longer and more slender than in females, clearly longer than forewing and with all but apical 2–3 flagellomeres with 2 ranks of placodes. Tergite I narrower, smoother than in females; tergite II usually longer relative to its posterior width. Usually easy to associate with females on shape of metasomal tergites, wing venation and coloration, and somewhat slender overall proportions of body.   
 Variation. I have assigned to this species specimens differing strongly in color and (to a lesser degree) in ovipositor sheath breadth from the above redescription. The leg coloration can be quite light yellow­brown (especially on the femoral apices, tibial bases and tarsomeres, but occasionally more generally) in som eastern populations (esp. Michigan, Minnesota), to extremely dark brown at high elevations and/or latitudes. Several Rocky Mountain series (Colorado) have even broader, more truncate ovipositor sheaths than in the figured Alaskan material, whereas the eastern specimens in general tend to have slightly narrower sheaths. There also exists considerable variation in the width of the first metasomal tergite, but this seems to be intrapopulational more than geographical, suggesting size correlation or some other physiological cause.   
 Final instar larva. Described in part from European material by Short (1953). Apparently with the usual plesiomorphic bedelliae ­group complement of one pair of labial setae and one seta on each maxilla, and has 17 teeth on the mandible, not counting the bifid tip (Short counts 18 but includes one of the tip points).   
None of the nearctic specimens has been reared, so I have been unable to examine any associated cocoons and larvae.  
 Cocoons. The cocoons associated with palearctic material appear to be similar to those of P. bedelliae, but I have seen none from nearctic material.   
 Material examined. 110 females, 176 males: from ALASKA, ALBERTA, BRITISH COLUMBIA, COLORADO, IDAHO, MICHIGAN, MINNESOTA, NEW HAMPSHIRE, NOVA SCOTIA, SOUTH DAKOTA, UTAH (7000' elevation), WASHINGTON, WYOMING, YUKON TERRITORY; mostly July, August records but a few late May, June in some southerly localities.   
I have also examined Palearctic material in the CNC and BMNH, determined by Wilkinson, Nixon and Papp, in the Royal Museums of Scotland (MRS) and from my own collections in Britain and Europe.  
 Hosts. Not known to have been reared in North America. In Europe and Great Britain, P. viminetorum appears to be mainly a parasite of various elachistid miners on grasses and sedges (Nixon, 1973). The Nearctic distribution of this species is consistent with a possible similar host range here.   
 Comments. The broad, asymmetrically truncate ovipositor sheaths and convex posterior margin of the second metasomal tergite are diagnostic for this species. Only P. rhygoplitoides comes close in ovipositor sheath shape, but it differs so strongly in metasomal tergite shapes that confusion is unlikely.   
I have been unable to find consistent differences between nearctic and palearctic series, so have considered them conspecific; biological or genetic data on the nearctic populations could show this to be incorrect. In the light of its evidently northern distribution, it is not surprising that the species appears to be holarctic; this pattern is common in boreal ichneumonoids.
description: Published as part of Whitfield, James B., 2006, Revision of the Nearctic species of the genus Pholetesor Mason (Hymenoptera: Braconidae), pp. 1-94 in Zootaxa 1144 (1) on pages 56-58, DOI: 10.11646/zootaxa.1144.1.1, http://zenodo.org/record/5057957