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 Cooperative Agreement was established to support objective 1 of the in-house project and is related to finding methyl bromide alternatives for postharvest applications. Dried fruit beetle (DFB) and navel orange worm (NOW) are endemic to California (CA) and are key economic pests of the dried fruit and nut industry. External morphology of DFB and NOW eggs was studied using scanning electron microscopy, which identified structural differences that potentially explain the relative tolerance of eggs of both species to sulfuryl fluoride. We found up to a pair of aeropyles, gaseous exchange portals, in the outer shell of DFB eggs. In contrast, hundreds of aeropyles occur in the outer shell of NOW eggs. A micropyle, an opening for sperm entry that also facilitates gaseous exchange, is absent in DFB and present in NOW. We are currently testing the hypothesis that the rate of fumigant penetration through the insect outer shell is facilitated by the presence of aeropyles and/or a micropyle. Research also continues toward the pursuit of fumigants, such as propylene oxide, which are effective at controlling the egg stage of insects (as well as microbes). Recently, residue levels of propylene oxide, propylene bromohydrin, and propylene chlorohydrin were quantified after fumigation of walnuts with proplylene oxide under conditions currently being used for commercial pastuerization of walnuts.