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, codling 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. Postharvest chamber fumigation provides a biological safeguard against pests and, in many scenarios, is the only available tool for government and industry to guarantee pest-free security and food safety. In general, the eggs of insects are the most difficult life stage to control with fumigants. This research explores species-specific differences in morphology of the egg surface and initiates an attempt to relate theses differences to the relative ovicidal efficacies of fumigants. Eggs of Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae; dried fruit beetle), Lasioderma serricorne (F.) (Coleoptera: Anobiidae; cigarete beetle), Ephestia elutella (Hübner) (Lepidoptera: Pyralidae; tobacco moth), and Amyelois transitella (Walker) (Lepidoptera: Pyralidae; navel orangeworm) were imaged with scanning electron microscopy to explore how respiratory openings on the egg surface may affect the relative efficacy of fumigation. Although confirmatory measurements of fumigant diffusion into eggs are needed, findings suggest that species-specific ovicidal efficacies are related, at least in part, to the surface morphology of eggs and that respiratory structures differentially affect fumigant penetration and/or uptake.