1a. Objectives (from AD-416):
Complete normal atmospheric pressure testing and then scale vacuum and normal atmospheric pressure fumigation toward commercial scale applications with validation. Specific objectives of the research include: 1) Conduct insecticidal efficacy trials at temperature < 70ºF (i.e., 50 & 60ºF), 2) Begin scaling fumigations toward commercial scenarios, and 3) Determine the environmental factors (e.g., temp, air flushes, etc.) that minimize chemical residues associated with ovicide-sulfuryl fluoride pairings, particularly those resulting from the propylene oxide-sulfuryl fluoride mixture. Tailor fumigant-ovicide application to minimize residue formation.
1b. Approach (from AD-416):
At 70ºF, the optimized ratio for the sulfuryl fluoride-propylene oxide mixture has been identified under vacuum as well as normal atmospheric pressure. We will follow the same experimental procedure and process at 50 and 60ºF. At 70ºF, efficacy studies will transition from 1 cubic foot chambers into nine cubic foot chambers and commodity will be included in the testing. To facilitate the detection of biomolecular conjugates, mass-labeled propylene oxide will be synthesized via the method of Beckman. The mass-labeled propylene oxide will then be used to fumigate inshell walnuts; a mass balance will be generated. Mass-labeled residues that are likely to be formed during walnut fumigations will be characterized in studies on surrogate biomolecules such as: oleic acid, bovine serum albumen, and glutathione. We will expose eggs to fumigants, ovicides, and other physiologically active gases to observe any morphological change that results. Once mechanistic details are gathered, we will tailor chemical and physical approaches to exploit weakness in egg shells. Approaches will only be explored that are amenable to existing infrastructure of the walnut industry.
3. Progress Report:
This Reimbursable agreement was established to support Objective 1 of the in-house project and is related to finding methyl bromide alternatives for postharvest applications. We evaluated the efficacy of propylene oxide (PPO) against eggs of Tribolium castaneum (Herbst) (red flour beetle), Lasioderma serricorne (F.) (cigarette beetle), Plodia interpunctella (Hübner) (Indianmeal moth), Ephestia elutella (Hübner) (tobacco moth), and Amyelois transitella (Walker)(navel orangeworm), at 25°C under a reduced pressure of 100 mm Hg for 2 hours as well as atmospheric pressure for 24 hours. We found that there were differences in susceptibility to PPO among eggs of tested insect species. The goal of this research is to identify the amount of PPO that is required to control the egg life stage of key walnut insect pests, a critical first step in formulating a sulfuryl fluoride - propylene oxide mixture as a postharvest alternative to methyl bromide fumigation. In addition, residues of propylene oxide (PPO), propylene chlorohydrin (PCH), and propylene bromohydrin (PBH) resulting from the fumigation of walnuts were quantified with novel analytical methodology involving solvent extraction followed by gas chromatography (GC).