Distribution & status of Peristenus digoneutis, an introduced parasitoid of Lygus lineolaris in the Northeast U.S.: an update

W.H. Day and K.A. Hoelmer

Beneficial Insect Introduction Research Unit, USDA-ARS, Newark, DE, USA

Correspondence: Kim.Hoelmer@ars.usda.gov

Nymphal parasitism of tarnished plant bugs (Lygus spp.) by various species of Peristenus (Hym.: Braconidae) in Europe is notably higher (10 to 60 percent) than parasitism of North American Lygus spp. by Peristenus native to the eastern US (4 to 10 percent). Following a series of earlier releases of European Peristenus species elsewhere in North America that failed to result in establishment, a program of releases of Peristenus digoneutis obtained from northern Europe was conducted in the NE US from 1979 to 1983 by USDA. Establishment was evident by 1984 at one release site in northern New Jersey. It is now known to be present in 11 northeastern states and the Canadian provinces of Ontario, Quebec and Nova Scotia. Peristenus digoneutis has reduced Lygus populations in New Jersey alfalfa by 65 percent relative to pre-release levels, and causes moderate to high levels of parasitism in strawberries and apples. However, P. digoneutis has not become abundant south of northern NJ (latitude 40.5 degrees N) since its establishment more than 20 years ago. Its southern distribution limit closely matches the summer temperature/duration isocline in this region of 30 degrees C for a maximum of 30 days. The warm summers that are common south of this latitude appear to limit the survival of the P. digoneutis population that was established in the NE. Consequently, efforts are underway to establish P. relictus (=P. stygicus), a related nymphal parasitoid predominant in southern European Lygus populations, in the Mid-Atlantic states.

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