We report here on the diversity and composition of Coreidae and Pentatomidae species, as well as their egg parasitoids collected on cowpea (Vigna unguiculata [L.] Walp) (Fabaceae) plants from a field in Teresina, central-northern Piaui State, Brazil. Weekly sweep net sampling was performed during the phenological cycle of this crop in the rainy and dry seasons. In the pentatomid collections, 14 species were identified from 3 subfamilies (Asopinae, Edessinae, and Pentatominae). Five species of Coreidae also were collected from the subfamily Coreinae. We found that Euschistus heros (F.), Crinocerus sanctus (F.), Chinavia ubica (Rolston), and Piezodorus guildinii (Westwood) (all Hemiptera: Pentatomidae) were the most abundant hemipteran species associated with cowpea. Generally, species richness and diversity of individuals from this order were higher in the rainy season than in the dry season. The parasitoid species identified from field-collected hemipteran egg masses were: Anastatus coreophagus Ashmead (Hymenoptera: Eupelmidae), Neorileya flavipes Ashmead (Hymenoptera: Eurytomidae), Ooencyrtus anasae (Ashmead) (Hymenoptera: Encyrtidae), O. submetallicus (Howard) (Hymenoptera: Encyrtidae), and Trissolcus urichi (Crawford) (Hymenoptera: Platygastridae). We found that about 52% of hemipteran egg masses collected from the cowpea field were naturally parasitized by the above parasitoids, whereas nearly 10% of C. sanctus and C. ubica sentinel egg masses were parasitized.