Thyanta Stal

Rider, David A. & Chapin, J. B., 1992, Revision of the genus Thyanta Stal, 1862 (Heteroptera: Pentatomidae) II. North America, Central America, and the West Indies., Journal N Y Ent Soc 100 (1), No. 1, pp. 42-98 : 45-46

Subgenus Thyanta Stal

Diagnosis. Punctures minute, dense. Posterior terminations ofbucculae evanescent. Anterolateral pronotal margins straight to concave, sometimes marked with piceous; humeral angles rounded to angulate, often spinose; pronotal cicatrices sometimes marked with piceous in mesial angles. Ostiolar canals acuminate apically. Superior surface of each tibia sulcate.

Posterior margins of basal plates sinuous, posteromesial angles entire ( Fig. 13). Distal end of sclerotized rod cone-shaped ( Fig. 14); spermathecal bulb digitiform; cylindrical structure below proximal flange ( Fig. 15). Pygophoral opening small, subtended on posteroventral surface by a rectangular or semicircular impression; posterior margin of pygophore straight to concave in caudal view, with medially incised protuberance in middle ( Fig. 9). Each paramere F-shaped, obtuse protuberance on shaft usually prominent, apex spinose, ectal surface convex ( Fig. 3), roughened spiculate area on lateral surface linear ( Fig. 5). Each lateral conjunctiva} lobe of aedeagus with single spinose diverticulum ( Fig. 6); dorsomedial conjunctiva} lobe usually well-developed ( Fig. 7), theca large; subtriangular in lateral view, with dorsolateral protuberance on each side near caudal limit ( Fig. 8); medial penial lobes and penisfilum moderate in size.

Comments. Species of the subgenus Thyanta have the pygophoral opening subtended by a semicircular or rectangular impression, and the posterior margin is distinctly emarginate medially. Species of Phacidium have the posteroventral surface of the pygophore arcuately rounded or sulcate, and the posterior margin is not emarginate medially. The posteroventral surface of the pygophore in species of Argosoma is produced into a blunt, chin-like protuberance. The ectal surface of each paramere is concave in Argosoma and convex in both Phacidium and Thyanta .

The female genitalia are also useful in separating species ofThyantaandPhacidium. In Thyanta , the distal end of the sclerotized rod is cone-shaped, and the spermathecal bulb is digitiform. In Phacidium , the distal end of the sclerotized rod is swollen subapically and narrowed distally, and the spermathecal bulb is globose. The female genitalia ofboth Phacidium and Argosoma are very similar, but females can usually be separated by dorsal punctation which is relatively dense in Phacidium and less dense and more coarse in Argosoma .