DIFFERENTIAL DIAGNOSIS.
This species runs directly to P. rufipes (Ashmead, 1893) in Fouts' (1924) key, differing in the following respects.
Antennal segment III is 2/3 as long as IV, not equal as in P. rufipes; V subtrapezoidal, not spherical; VII, VIII and IX all longer than wide, not wider than long; [X, 2-3 times as long as wide, lanceolate, not less than twice as long as wide and blunt as in P. rufipes; lateral lobes of mesonotum entirely shagreened, without the bare median areas of P. rufipes]; abdomen longer than, not equal to, thorax; tergite II longer than wide at apex not the opposite as in P. rufipes.
FEMALE. Length 1.25 mm. Head from above deeply excavated posteriorly, 2.8 times as wide as long at center of excavation, 2.1 times as long as wide at widest point behind eyes; head from front broadly elliptical, exactly the width of the eye wider than high; 6 strong striae between lateral ocelli and occipital sulcus, occiput strongly striate; cheeks shagreened, sparsely setaceous; postgenae setaceous; ocellar space coarsely, heavily shagreened; frons above and on sides finely shagreened; center of face with several fine, wavy aciculations, very minutely shagreened; frons above antennal insertions densely shagreened, weakly striate.
Scape long, sinuate, narrowed basally, about as long as the following six segments united; pedicel twice as long as wide; III, 2/3 as long as pedicel, 4/5 as long as IV; VI, 2/3 as wide at apex as long, narrowed proximally; VII, 3/4 as wide as long; VIII, slightly over l/2 as wide as long; IX, slightly longer than wide, tapering slightly to apex; X, 1 1/5 times as long as pedicel, lanceolate, 3 times as long as wide.
Thorax 3/4 as wide at widest point as long, slightly narrowed behind tegulae; mesonotum a little longer than wide; notauli weakly indicated, extending 2/3 the length of the mesonotum, absent on the anterior one-third; median lobe heavily shagreened anteriorly, finely shagreened posteriorly; truncate tongue over scutellar fovea bare, shining; lateral lobes entirely, finely shagreened; entire mesonotum with rows of whitish setae, with dense tufts at posterior angles of lateral lobes; scutellum convex, not elevated, semi-circular in outline, densely covered with decumbent whitish hairs; metapleura with thick mats of long hairs originating mainly at their anterior margins; propodeum densely hairy.
Abdomen spatulate, 1 1/2 times as long as thorax; tergite I with lateral tufts of whitish setae, a dense patch of white hairs beneath; diagonal linear depressions extending from anterior corners to medial posterior border; tergite II slightly longer than broad at apex, basal foveae distinct, slightly less than 1/2 as long as tergite; foveae finely shagreened, each mesal border with a diagonal row of minute punctures; posterior portion tergite II with minute, irregular scratches scattered over surface; tergites III, IV, V all broader than long, equal in length to each other, each with a median transverse row of white setae: tergite VI, 1 1/2 times as wide at base as long, triangular, sharply rounded at apex, white setae scattered over entire tergite, more densely so at tip.
Head, thorax, shining black- abdomen piceous anterolaterally, black and shining posteriorly and medially; all coxae piceous; fore and mid legs entirely ochraceous, hind legs medium to light brown; hind femora expanded, apex club shaped, with a light band before expanded portion; tarsi pale yellow to whitish; first five segments of antennae light yellow, remaining ones piceous.
Wings extending well beyond apex of abdomen, brownish, heavily, evenly pubescent; fringe at hind margins of fore wings equal to width of tegulae viewed from above, inconspicuous toward anterior margin.
MALE. Length 1.18 mm. Similar to female; face strongly transversely striate throughout; antennal ratios (length to width): scape, 6.4:1; pedicel, 2.5:1; III, 1.7:1; IV, 2.0:1; V, 1.4:1; VI, 1.3:1; VII, 1.8:1; VIII, 1.4:1; IX, 1.5:1; X, 2.6:1. III, 3/4 as long as IV; IV, cylindrical, notched apically; V, subtrapezoidal; X, conical, pointed; all segments with stout hairs about l/2 as long as the width of the segment of origin. Legs and antennae light honey yellow throughout, all coxae piceous.
TYPES. Holotype, female, Franklin, Me., spring 1969, M. W. MacGown (U.S.N.M. No. 71216).
Paratypes. 29 females, 10 males, same locality and date as holotype, Coll. U.S.N.M.; 39 males reared same locality and date as holotype, 224 females collected Mariaville, Franklin, Edinburg, Me., at various dates in spring, 1968-69, Coll. Univ. Me.
REMARKS. P. ahicollis is quite variable, based on observations of 274 specimens from the type series. Striae of vertex vary from occasionally obsolete and replaced by shagreening to 2 to 6 strong striae without shagreening. Supra-antennal striae may be obsolete exteriorly, indicated interiorly; diagonal aciculae may occur between the bases of the antennae and ocular sulci; notauli may be weakly or strongly indicated. In some specimens the bare area of the median lobe over the scutellar foveae may extend one-half of the median lobe; basal foveae of tergite II may be very shallowly or quite strongly impressed. Coxae vary from piceous in some members to rufous in others.
Platygaster abicollis, diagramatic aspects of thorax and Tergites I and II. Ax, axillary region; BF, basal foveoli; Col, collar of pronotum; L, propodeal lamella; LL, lateral lobe of mesoscutum; ML, middle lobe of mesoscutum; Mpl, median, or middle plate of tergite II, Mscl, marginal sclrerite of scutellum; Mspl, mesopleuron; Mssct, mesoscutum; Mtpl, metapleuron; Nx, notaulix (or notaulus); Pnt, pronotum; Sctl, scutellum; Teg, tegula; T-I, tergite I; T-II, tergite II
References
Ashmead, W.H., 1893, Monograph of North American Proctotrypidae. Bull. U.S. National Museum 45: 287, Pl. 12 Fig. 5 (As Synopeas).
Fouts, R.M. 1924, Revision of North American Wasps of the subfamily Platygasterinae. Proceedings of the U.S. National Museum 63 (15): 36.
MacGown, M.W. and E.A. Osgood, Jr. 1971. Two new species of Platygaster (Hymenoptera: Proctotrupoidea, Platygastridae) parasitic on balsam gall midge, Dasineura balsamicola (Diptera: Cecidomyiidae). Can. Ent. 103 (8): 1143