Female. Length 1.4 mm. Head twice as wide as long, not emarginate behind, the cheeks strongly convex, shagreened above; occiput transversely aciculate; interocellar triangle very low, not distinctly sculptured; space around lateral ocelli finely shagreened; frons not distinctly sculptured above, sometimes with extremely faint aciculations, diagonally aciculate below.
Antennae elongate and rather slender; pedicel two and one-half times as long as wide, as wide as joint six apically; joint three longer than wide, half as long and half as wide as the pedicel, two-thirds as long and very little narrower than four; four and five subequal, one and one-half times as long as wide, a little shorter than six; joints seven to nine as long and as wide as six, about twice as long as wide; ten a little wider and longer, twice as long as wide, subacute apically, the sides rounded. [Note that A IV is deformed in the male of the specimen drawn here. This is a common ocurrence in this and in some other species - MwM].
Thorax two-thirds as wide as long, flattened above, as wide as the head; pronotum finely longitudinally aciculate below on the sides, above polished,
without sculpture; mesonotum flattened finely shagreened on anterior half, polished posteriorly; notauli distinct on basal two-thirds, widely separated, the median lobe broadly rounded posteriorly; scutellum transverse, subconvex, highly polished, narrowly margined laterally.
Abdomen as long as the head and thorax united; first and second tergites without pubescence; median area on first longer than wide; lateral foveae on second striate, the striae extending very slightly beyond their apices; interfoveal area with three short carinae, one median; tergites beyond the second not sculptured, with a row of hairs across each; wings hyaline, extending the length of the last segment past the apex of the abdomen.
Amber-colored; antennae dark brown; legs yellowish brown.
Male.—Length 1 mm. Differs little from the female in general structure and color; antennae elongate, all the joints longer than wide; pedicel broad, twice as long as wide, as wide as any of the flagellar joints except the second and last; third joint half as long as the pedicel, a little over half as wide; fourth joint slightly wider apically than the pedicel, much widened at the apex, one and one-fourth times as long as wide, the proportions varying with different degrees of shrinkage (usually one and one-half times as long as wide).
Abdomen as long as the head and thorax united, long-ovate, as wide as the thorax, twice as long as wide, rounded posteriorly; wings hyaline, extending the length of the last four segments past the apex of the abdomen.
Color lighter than in the female, the legs often bright yellow; antennae brownish.
Type locality.—Milwaukee, Wisconsin.
Type.—Cat. No. 2274, U.S.N.M. Type male and allotype female selected.
Host.—Cecidomyia antennaria Wheeler.
Redescribed from the types, fifteen females and ten males. It seems likely that the specimens were killed too soon after emerging to attain their normal oolor. The shrinkage of the male antenna lends support to this view. The sculpture on the second tergite is subject to variation, the striae being more numerous and stronger in some individuals than in others.
References.
Fouts, R.M. 1924, Revision of the North American wasps of the subfamily Platygastrinae. Proc. U.S. Natl. Mus. 63 (15): 98, 99.