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Efficacy with the Combination of Sulfuryl Fluoride and Propylene Oxide as Replacement for Methyl Bromide Fumigation of Stored Food Products

Wample, Robert
California State University - Fresno
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This research will provide fundamental information regarding combinations of SF & PPO & will determine if the combinations will be more efficacious & cost effective especially towards egg stage of several economically important species that infest dried fruit & tree nuts. In addition to individual attributes of each fumigant towards certain life stages the possibility that some combinations may be synergistic will be studied. Synergies or contraindications created by combining the 2 fumigants will be studied & determined by gas chromatography mass spectrometry(GCMS).

This part of the study will be in collaboration with Calif. State Univ Fresno. In addition to combining the fumigants the potential exists for greater effectiveness if the fumigants were used sequentially i.e., 4 hours under vacuum with SF, 1 hour aeration & 4 hours under vacuum with PPO. With this fumigation method exposure time would be about 9 hours, far less than the 24 hrs now required. This procedure will be studied to a more or less degree depending on findings from combining the 2 fumigants. Because vacuum fumigation is used for PPO microbial fumigation of nuts & spices & is readily available to many packers it will also be studied along with conventional NAP fumigation. Recent trials (Muhareb, 2004) have shown vacuum fumigation with SF increases mortality with less fumigant - economically important.

Objs: i. Find the LD5o & LD95 with the combined fumigants at 26.7oC plus/minus 2.0 on the 3 species: eggs, larvae, pupae & adults of each: Indian meal moth (IMM), Plodia interpunctella (Hubner) red flour beetle (RFB), Tribolium castaneum (Herbst); warehouse beetle (WB), Trogoderma variabile (Ballion).

ii. Under VAC and NAP determine the LD5o & LD95 at temperatures of 15.6 plus/minus 2.0 & 26.7oC plus/minus 2.0 with the combined fumigant on the 3 species: eggs, larvae, pupae & adults: Indian meal moth (IMM), Plodia interpunctella (Hubner); red flour beetle (RFB), Tribolium castaneum (Herbst), warehouse beetle (WB), Trogoderma variabile (Ballion).

iii. Find the LD5o and LD95 under field condition temperatures ranging from 10oC-50oC plus/minus 2.0. In laboratory commodity fumigation with insects determine if dosage will be adjusted as required based on sorption by the commodity.

iv. Based on results from the laboratory studies take selected treatments with SF & PPO & apply them in a commercial real live scale test on appropriate stored food(s).

v. Educate members in the industry about safety & other prudent issues concerning the use & application of the combined & sequential use of these fumigants if sequential use is actually studied.

vi. Provide & promote to commercial concerns of the applicability of this research through presentations at industry & scientific conferences.

vii. Study the cost effectiveness when combining SF with PPO as opposed to using either alone for all insect stages & further comparisons to MB. Efficacy with the new proposed alternative will be compared to MB in research completed in a grant for EPA. This study directly compared efficacy of MB, SF, PPO, phosphine to the same species & stages proposed in this study (Muhareb at el. 2004).

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Non-Technical Summary: The loss of methyl bromide as a post-harvest fumigant has created a demand for alternative practices and fumigants. Current alternatives are cost prohibitive. The use of sequential or combined use of sulfuryl fluoride and propylene oxide is being examined as an alternative to methyl bromide post harvest fumigation of stored food products. It is anticipated that combinations of these compounds may be more efficacious than when applied individually. This project will potentially contribute to the elimination of the "Critical Use Exemptions" currently in place for dried fruit and tree nut crops.

Approach: Objective i. Previous studies will be used to establish appropriate dosages (mg/L) ranges of SF and liquid PPO to investigate CT products to achieve LD50 and LD95. Fumigation chambers are 28.42L vacuum desiccators modified for fumigation. These are placed in a walk-in temperature plus/minus 2.0oC controlled box. Exposure time will be 24 hours for NAP. There will be three replications for each dosage plus two untreated controls for each test. Gas concentration will be determined periodically during the fumigation using gas chromatography. CT products will be determined using the method described by Bond (1984). Insects will be reared at the DFA Laboratory at 28 plus/minus 1.5oC and 65-70% RH. Active IMM adults will be used to provide eggs for testing. The WB and RFB eggs will be obtained by selecting young adults from fresh cultures. Plastic cups with insects will be placed in chambers at least 2 hours before treatment for temperature acclimation. SF and PPO will be introduced via a syringe into each chamber. Aeration of NAP fumigations will be accomplished by forcing air at the treatment temperature, through the chamber for about one hour. Post-treatment evaluation of insect mortality will occur following aeration and storage of the jars in an incubator at 26.7oC, 60-65% RH and 16:8h photoperiod. Objective ii: All conditions from objective i will remain the same for objective ii except for the temperatures and added dosages. Fumigations will be done at100 mm Hg (VAC). Exposure time will be 4 hours for VAC. For VAC treatments, concentrations will be taken after fumigation and after the chambers have been satisfied but before the chambers are opened. Aeration of vacuum treatments aeration will be accomplished by releasing the vacuum after exposure to NAP, reduce the pressure to 100mm and release. This procedure is repeated three times. Objective iii: All conditions from objective i will remain the same for objective iii except for temperature changes. This part of the study will simulate a wide variety of field conditions to show unforeseen effects of temperature changes. Objective iv: These studies will be facilitated by DFA members (i.e., Diamond Walnut Incorporated (VAC) fumigation, Valley Fig Growers (NAP) fumigation). This will include all aspects developed in the laboratory fumigation trials. Dosages will be determined from the laboratory results and the concentrations as well as the CT products will be reported. Gas concentration will be taken at the beginning and at the end of the fumigation. Objective v: Twice a year workshops, held by DFA in Fresno and Yuba City, CA, will educate industry members and make them aware of new fumigation technologies and specifically how to safely use these combined fumigants. Objective vi: Results will be presented at national and international conferences. Scientific and industry input will be solicited. Objective vii: The cost effectiveness of combining these two fumigates will be carefully evaluated. Statistical analysis of the data will use SPSS software.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Chemical Contaminants
Nuts, Seeds