Oncerometopus atriscutis Knight and Prepops rubroscutellatus (Knight) are plant bugs of the tribe Restheniini and subfamily Mirinae, largest of the eight mirid subfamilies. Both species were described in the late 1920s from a few locales in Arizona and New Mexico (also Colorado in the case of P. rubroscutellatus); their host-plant relationships have remained undocumented. We give additional distribution records of O. atriscutis from Arizona (3 counties, 6 sites), New Mexico (11 counties, 35 sites), and Texas (3 counties, 3 sites; new state record) and P. rubroscutellatus from Arizona (3 counties, 3 sites) and New Mexico (9 counties, 29 sites). Their seasonal histories are based mainly on regular sampling of Apache plume, Fallugia paradoxa (D. Don) Endl. ex Torr.; Rosaceae), from mid-July 2009 to mid-May 2012 at a Chihuahuan Desert site east of Las Cruces (Doña Ana Co.), New Mexico, where the bugs were syntopic. Supplemental data on seasonality were obtained from periodic collections from Apache plume in southwestern states. Regular sampling near Las Cruces, as well as supplemental collecting, indicated that both restheniines are bivoltine. Overwintered eggs hatched during the last two weeks of March at the main study site, and first-generation adults of both species appeared by mid-April and were present until early May. Nymphs of a second generation were present from early June to October (fifth instars occasionally were found in November), with adults present as late as the end of November. In the Southwest, both plant bugs were found only on Apache plume; the 1926 record of O. atriscutis from “Cowania sp.” (Rosaceae) in the Chiricahua Mountains of Arizona is considered an incidental occurrence of adults or a misidentification of Fallugia paradoxa.