A NEW THRIPS-HUNTING M ICR OS TI GM US 
FROM COSTA RICA 
(HYMENOPTERA: SPHECIDAE, PEMPHREDONINAE) 
By Robert W. Matthews 
Department of Entomology 
University of Georgia, Athens, Ga. 30601 
In the two years since the discovery (Matthews, 1968a, b) of the 
first social member of the Sphecidae, Microstigmus comes Krombein, 
which preys on Collembola, I have received a number of additional 
preserved nests of this genus from the same Costa Rican locality. 
Two of these, collected by Miss Robin M. Andrews and Dr. Daniel 
H. Janzen, are quite distinctive and have proven to be those of a 
new species whose prey is Thysanoptera. O. W. Richards has very 
graciously consented to describe this new species; I have added notes 
on the unique prey and distinctive nest structure. 
Microstigmus thripoctenus O. W. Richards, new species 
Female. Pale testaceous; disc of metanotum, propodeum just above 
petiolar attachment, distal end of petiole, two oval spots on gastral 
tergite 2 and sometimes a central spot on tergite 1, blackish suffused. 
Antennal segment 12 sometimes darker. Tips of mandibles piceous. 
Most of prothorax, tegulae, coxae, trochanters and narrow bases of 
femora, white. Wings hyaline-iridescent, venation very pale, ptero- 
stigma with a large dark distal spot. Eyes evidently green in life. 
Length ca. 2.5 mm. 
Head between eyes nearly as broad as mesoscutum, with eyes 
clearly broader than distance between outer edges of tegulae. Anten- 
nal scape not extending quite halfway to median ocellus; segment 2 
clearly longer than 3, about two and a half times as long as broad, 
3 almost one and a half times as long as broad, 3-1 1 very gradually 
decreasing in length, penultimate segments hardly more than quad- 
rate, 12 a little longer than 2 but considerably thicker. Head smooth 
and shining, area above antennae with a fine reticulation; clypeus 
transversely rather convex, ventral margin feebly emarginate and 
like the outer edge of mandibles with very long pale hairs. Ocelli 
in a triangle somewhat narrower than equilateral. Oculo-malar 
space considerably wider than long. Ventral tooth of mandibles 
long, four times as long as the subtruncate dorsal one, but both 
* Manuscript received, by the editor December 8, 1969. 
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