Propagation, release, and evaluation of Peristenus stygicus, a newly imported parasite of lygus bugs [Lygus hesperus, alfalfa].

Peristenus stygicus Loan, a parasite of Lygus , was released in an alfalfa hay field near Bakersfield, Calif., in 1973. The program was evaluated by dissecting a large number of 3rd to 5th instar Lygus (primarily L. hesperus Knight) to determine percent parasitization. Four peaks of parasitized lygus bug nymphs occurred in 1973. The 1st 3 peaks were of increasing magnitude while the 4th peak was much lower. P. stygicus survived the winter of 1973 to 1974 and was active in the release plot in 1974. There were 4 generation peaks of parasite larvae in 1974. However, the 4 peaks were of decreasing magnitude and irregularly spaced. The parasite also survived the following winter and was active in the release plot in the spring of 1975. However, its population did not increase in 1974 and in the spring of 1975 when compared to the number of larvae found in 1973.