The tarnished plant bug,Lygus lineolaris(Palisot de Beauvois), is one of the two mirids that frequently are abundant on alfalfa in the northeastern United States. This insect also is a pest of numerous fruits and vegetables. We have established the European parasitePeristenus digoneutisLoan in northern New Jersey, and it has spread downwind into two additional counties, one of which is in New York State. Average total parasitism of tarnished plant bug nymphs in 1987–1988 was 36% in the first generation and 29% in the second, each about three times the normal rate of parasitism by native parasites.