1a. Objectives (from AD-416):
Ensure pest-free security and food safety of walnuts in postharvest marketing channels via the development of efficient, economical, and environmentally benign chemical treatments. Evaluate ovicides, such as propylene oxide, to use in concert with sulfuryl flouride fumigations.
1b. Approach (from AD-416):
Phase 1. The LD 50 of sulfuryl fluoride has already been determined in our lab at 60 - 80 F for the eggs of the following target species: navel orangeworm, coddling moth, and dried fruit beetle. Using these mortalities as benchmark indices, we will quantify how mortality changes as a function of increasing the molar proportion of ovicide to sulfuryl fluoride over the range: 1:100, 1:10, 1:1, and 10:1. Propylene oxide will be the first ovicide examined. Phase 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. Phase 3. Using core microscopy facilities at SJVASC, we will comparatively evaluate the egg physiology of stored product insect pests including, dried fruit beetle, codling moth, indianmeal moth, and navel orangeworm. We will then expose eggs to fumigants and ovicides to observe any physiological 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 Assistance Type 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; Carpophilus hemipterus) and navel orange worm (NOW; Amyelois transitella) 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 microscope, which identified key structural differences that explain the relative tolerance of eggs of both species to sulfuryl fluoride. We found that at most a pair of aeropyles, which enable gaseous exchange by living embryo, are present in DFB eggs. In contrast, aeropyles are numerous in NOW eggs. The 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 rate of fumigant penetration through the egg surface is related to diffusion through aeropyles and/or a micropyle. We also found that DFB eggs have a smoother surface than the navel orange worm, which has a sculptured surface.