Porpomiris curtulus (Reuter), a plant bug of the mirine tribe Stenodemini, is newly reported from Iowa, Kansas, Minnesota, Missouri, and South Dakota. Additional records from Nebraska (26 counties) and one from New Jersey are presented. All specimens (except those from New Jersey) were taken on switchgrass (Panicum virgatum L.; Poaceae). Nymphs were collected in Nebraska from reproductive structures of switchgrass in roadside plantings in areas of the once-extensive eastern tallgrass prairie, Sandhills prairie of north-central counties, and mixed-grass prairie west to the eastern fringe of shortgrass prairie in the panhandle. Overwintered eggs hatched in mid-June to early July as inflorescences of switchgrass were emerging from leaf sheaths, with adults appearing in July during flower expansion (anthesis). Nymphs of a second generation fed on developing and ripened seeds in mid- to late summer, with late-hatching first instars of a second generation observed in southern Nebraska in early September. Adult females sometimes persisted until late September. At a coastal site in New Jersey, adults were collected from redtop panicgrass (Panicum rigidulum Bosc ex Nees), suggesting that this congeneric grass might also support nymphal development.