1a. Objectives (from AD-416):
Quantify spotted wing drosophila distribution in geographically distinct Western U.S. commercial stone fruit orchards, index this distribution relative to other suitable host crops, and enumerate the probability of SWD removal and/or mortality as a function of harvesting, cleaning, packing, and shipping procedures employed by the stone fruit industry, particularly with respect toward Australian and New Zealand export. In addition, low-temperature high-concentration phosphine fumigation will be evaluated for its technical and economic potential to serve as a final element of mitigation against spotted wing drosophila.
1b. Approach (from AD-416):
This project is planned in 3 compounding phases as indicated below with corresponding objectives and hypotheses. Phase 1, year 1. Perform host trials to demonstrate status in peach, plum, nectarine and apricot for spotted wing drosophila and designate categories of host preference (such as, stage of maturity, commercial export grade or physical condition of the fruits) in stone fruits. Phase 2, year 2. Design, refine and execute experiments that allow spotted wing drosophila population densities to be traced through chemical and physical processes that are consistent with Western US stone fruit production and distribution to Australian and New Zealand markets. Phase 3, year 3. Determine the mortality of spotted wing drosophila eggs, larvae, pupae and adults in infested stone fruit, as well as, the phytotoxicological impact that results from Vaporphos phosphine at 3-5 C and index relative to methyl bromide at 15.6 C.
3. Progress Report:
This Trust agreement was established to support objective 1 of the in-house project and is related to finding postharvest methyl bromide alternatives and techniques for improving methyl bromide fumigations. A Host Suitability Index (HSI) was developed that ranks the relative potential of peaches to serve as a spotted wing drosophila (SWD) host based on the degree of fruit maturity. Peaches were removed from orchards at 4 stages, two weeks prior to harvest, at harvest, one week postharvest, and two weeks postharvest. Peaches from each stage of maturity were ranked as a SWD host using the HSI based on Host Suitability Scores (HSS) that distinguish key elements of SWD behavioral biology: 1) host attractiveness via flight response to volatile chemical cues, 2) rates of successful oviposition (as diagnosed by adult emergence) by a single SWD female exposed to representative peaches from each stage of maturity, 3) rates of successful oviposition (as diagnosed by adult emergence) from a population of SWD females exposed separately to peaches from each stage of maturity, and 4) degree of maturation-specific nutritional quality assessment arising from developmental rates and average pupae size. A field study will begin June 2012 using an orchard of Elegant Lady yellow peaches located at University of California Kearney Agricultural Research and Extension Center, Parlier, California. The experiment will be repeated later this summer using Summer Flame yellow peaches from a commercial orchard located in Fresno County, California.