Female bicoloured; body largely brownish yellow; tarsi, apices of tibiae and apices of femora sometimes paler, abdominal segments I & II also paler; antennal segments I–III yellow, III with a narrow dark brown ring at extreme apex; IV–IX brown; fore wing banded, brown with transverse clear area sub-basally and sub-apically; often slightly paler medially. Head longer than wide; eyes prolonged ventrally; without long setae; maxillary and labial palps with distal segment subdivided. Antennae 9-segmented; III & IV with linear sensorium that curves around distal apex and extends toward base of segment, with internal markings. Pronotum smooth, with no long setae. Mesonotum transversely striate, two pairs of setae medially. Metanotum with sculpture arcuate on anterior half, weakly reticulate on posterior; median setae on posterior half of sclerite. Fore wing wider distally than near base; with two rows of setae; costa with setae but no cilia. Abdominal tergite I constricted at base, tergites without sculpture medially, discal setae small; tergite X with pair of small trichobothria. Sternites III–VII with three pairs of posteromarginal setae, discal setae forming a transverse row.
Male smaller and slender, but similar in colour; abdominal tergite I longer than wide and with two longitudinal ridges on posterior half; X with trichobothria very small.
Intraspecific variation
Not recorded.
Genus and similar species information
Stomatothrips is a New World genus that comprises eight species, half of them described from Central and South America. They are all ant-mimic thrips associated with grasses, and are remarkable in having maxillary and labial palps with the distal segment subdivided into small units. S. rotundus resembles another Brazilian species, S.angustipennis but females can be distinguished by the brown colour of antennal segment IV and the arcuate sculpture on the anterior half of the metanotum.
