Five nominal species of braconid wasps that parasitize nymphs of five mirid species were studied on farms. The biological data obtained indicate that Peristenus pallipes (Curtis) is likely two (and possibly three) distinct species. In alfalfa and alfalfa-forage grass fields, there were clear parasite: mirid host associations: P. pallipes "A": Leptopterna and Trigonotylus; P. pallipes "B": Adelphocoris; P. pallipes "C": Lygus; P. digoneutis: Lygus; P. conradi: Adelphocoris; P. pseudopallipes: Lygus; and P howardi: Lygus. Diapausing adults of these parasite species do not emerge from their cocoons immediately after the cocoons are removed from cold storage; this delay is referred to here as diapause "duration". Average diapause duration varied from 8 to 61 days, depending on the parasite species, and each duration was statistically different from that of the other species. These durations corresponded to the temporal sequence of appearances of nymphs of the appropriate mirid host species during the growing season, and serve to synchronize the emergence of parasite adults with the hatching of their preferred hosts. All parasites studied except R digoneutis and P. howardi are univoltine. The latter two species produce some non-diapausing progeny in their first generation, which emerge promptly, enabling these species to parasitize second generation mirids. The unusually prolonged emergence period of P. howardi suggests that the second generation of this species may be partly produced by late-emerging (long-duration) parasites from the previous year, or perhaps by a very similar (sibling) species. Diapause rapidly increased in both P. digoneutis and R howardi collected in hosts within two weeks after the maximum photoperiod occurred (June 21) in the field. Peristenus (Braconidae) : Parasite Miridae (Miroidea) : Host Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Nearctic region; North America Miridae; Hymenopteran parasites; Diapause duration in parasites; role in host parasite relationships; Peristenus; USA Peristenus; Diapause; Diapause duration; Hemipteran hosts; Diapause duration in parasites; role in host parasite relationships; Miridae; USA none