Submitted to: Transactions of the American Entomological Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/20/2005
Publication Date: 7/20/2005
Citation: Day, W.H. 2005. Diapause duration as a synchronizer of parasite (peristenus spp: hymenoptera: braconidae) and host (hemiptera:miridae) life cycles, and its use in separating morphologically-similar parasite species. Transactions of the American Entomological Society. 131:87-99. Interpretive Summary: Plant bugs (Miridae) cause moderate to severe losses to a large number of crops in the United States, including fruits, vegetables, cotton, forage and seed crops, and forestry seedlings. USDA-ARS has been in the forefront of research to develop permanent biological controls of plant bugs, and has established two European parasite species in the northeastern U.S. to reduce damage by LYGUS and ADELPHOCORIS plant bugs. Several of these parasites are difficult to identify, and difficult to separate from native parasites (which are mostly ineffective control factors)- - because of their small size (2-3mm) and similar appearance. This research showed that each of five parasite species differs from the others in one aspect of their life cycle (diapause duration), and that these differences can be used to separate species that look alike. In addition, these measurements suggest that each of two 'species' may be two similar species, so the five species studied may actually be seven species. Data for the two multi-voltine parasite species indicate that decreasing day length ('photoperiod') is the likely initiator of their diapause. Finally, diapause duration was demonstrated to synchronize the emergence of overwintered adult parasites with the hatch of the appropriate plant bug species during the spring and summer.
Technical Abstract: 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 P. 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 P. HOWARDI collected in hosts within two weeks after the maximum photoperiod occurred (June 21) in the field.