2012 Annual Report
1a.Objectives (from AD-416):
Evaluate the potential for permanent establishment of a Moroccan strain of Peristenus relictus in the southern San Joaquin Valley of California by.
1)assessing the incidence of parasitism within a localized population of immatures of the western tarnished plant bug (Lygus hesperus) resulting from inoculative releases of P. relictus, and.
2)documenting the persistence of P. relictus populations following releases.
1b.Approach (from AD-416):
A plot of alfalfa 1-2 acres in area and divided into three sub-plots will be established and managed without insecticides. Alfalfa will be regularly mowed in narrow, alternating strips to maximize survival of lygus nymphs. Parasitoids will be introduced through periodic inoculative releases (once or twice per month) during spring and summer months. During the first two years, population indices for lygus nymphs will be obtained by sampling before initial parasitoid release (early spring) and after the final release (August or September) and the incidence of parasitism will be estimated from the dissection of late-instar nymphs. During the third year of the project, lygus population indices and estimates of parasitism will be obtained periodically (biweekly) throughout the spring and summer months. Overwintering potential and establishment of the parasitoid will be determined based on the incidence of parasitism observed in late-winter or early-spring lygus collections.
Perennial alfalfa plots were maintained for three years to facilitate development of high lygus population levels. Population indices of lygus nymphs obtained during each spring and summer indicated high nymph population densities. Multiple releases of a Moroccan strain of Peristenus into the field were accomplished during the spring and summer of each year, and in 2010 and 2011 releases were augmented by caging Peristenus over lygus nymph-infested alfalfa. Assays of field-collected lygus nymphs in the spring of 2009, 2010, and 2011, and the fall of 2009 and 2010, failed to detect parasitism by Peristenus before or after parasitoid releases. Results indicated that the parasite failed to establish self-sustaining populations in alfalfa in the southern San Joaquin Valley of California. Per the FY2012 Consolidated Appropriations Act (H.R. 2112) passed by Congress and signed by the President on November 18, 2011, the Western Integrated Cropping Systems Research Unit has been terminated.