1a. Objectives (from AD-416):
Objectives of the research are: 1) Establish species-specific efficacies for the Sulfuryl fluoride-propylene oxide mixture at molar ratios that are technically and economically the most feasible over temperature 40-80 F. 2) Quantify the antimicrobial activity of SF-PPO mixture toward pathogens, including salmonella. 3) Determine chemical residues associated with ovicide-SF pairings, particularly those resulting from the PPO-SF mixture. Tailor fumigant-ovicide application to minimize residue formation, as well as, adapt novel residue remediation technologies (e.g. ozone-ethane fumigation) to break PPO-related trade barriers for the walnut industry. 4) Develop novel chemical and physical approaches to kill insect eggs based on an understanding of egg biochemistry and/or the logistical operations of walnut harvest and distribution.
1b. Approach (from AD-416):
Objective 1. The LD 50 of sulfuryl fluoride will be determined at 60 - 80 F for the eggs of dried fruit beetle and warehouse beetle. Objective 2. To facilitate the detection of biomolecular conjugates, mass-labeled propylene oxide will be synthesized via the method of Beckman. The mass-labeled PPO 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. Objective 3. We will then 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).