Location: Crop Improvement and Protection Research
2022 Annual Report
Objectives
The long-term objective of this project is the development of alternative postharvest treatments that are safe and effective for control of pests and microbes on fresh and stored products. This project builds upon our recent progress in developing nitric oxide (NO) fumigation treatments for control of pests and pathogens, and sulfur dioxide fumigation treatments for control of postharvest pests. Specifically, during the next five years we will focus on the following objective.
Objective 1: Determine the effectiveness of nitric oxide and sulfur dioxide fumigation for postharvest control of pests and pathogens and evaluate the effectiveness of essential oils as alternative fumigants for postharvest pest control.
Sub-objective 1A: Determine effectiveness of nitric oxide fumigation for control of microbes (pathogens) on stored products.
Sub-objective 1B: Evaluate nitric oxide fumigation for control of insects and microbes (pathogens) in large-scale fumigation.
Sub-objective 1C: Determine effective sulfur dioxide fumigation treatments against pests on fresh and stored products.
Sub-objective 1D: Determine effective fumigation treatments with plant essential oils against postharvest pests.
Approach
Sub-objective 1A: Almonds, peanuts, and corn will be fumigated with nitrogen dioxide (NO2) in separate studies to determine microbial loads and effective treatments to control bacteria and fungi. Each product will also be disinfected with NO2 fumigation to kill bacteria and fungi and, then, artificially inoculated with spores of non-aflatoxin producing strain of Aspergillus flavus. Inoculated products will then be cultured and fumigated with NO2 to verify effective control of A. flavus.
Sub-objective 1B: Large scale fumigation tests with NO + NO2 will be conducted in a 246 cm tall mini silo filled with corn to evaluate fumigant penetration and efficacy against rice weevil and Aspergillus flavus fungus. Rice weevil adults and A. flavus infected corn will be positioned at different depths in corn in the mini silo. An air pump will be used to circulate air in the mini silo. After injecting NO under specific ultralow oxygen conditions to have expected NO level for insect control and NO2 level for microbial control, NO and NO2 will be monitored at different heights of the mini silo. Efficacy against rice weevil and A. flavus will be evaluated at the end of fumigation treatment. Fumigations will be conducted with different combinations of NO and NO2 concentrations and treatment times to determine effective NO+NO2 fumigation for control rice weevil and the fungus. NO and NO2 levels will also be measured without air circulation to determine fumigant penetration in the mini silo.
Sub-objective 1C: Small-scale SO2 fumigation tests will be conducted to determine effective combinations of SO2 concentrations and treatment times at different temperatures for control of rice weevil, confused flour beetle, naval orangeworm, and Pacific spider mite. Different life stages of insects/mites will be fumigated to determine the most tolerant life stages and effective treatments will be developed to control the most tolerant life stage for each pest. Once an effective treatment is identified, large-scale SO2 fumigation treatments will be conducted to control each pest on a selected product. Rice weevil, confused flour beetle, naval orangeworm, and Pacific spider mites will be fumigated together with corn, wheat, pistachio, and table grape, respectively, in large-scale SO2 fumigation treatments. The large-scale SO2 fumigation for controlling rice weevil will be conducted in the mini silo. Large-scale SO2 fumigation against other pests on respective products will be conducted in 26 l chambers modified from 7 gal plastic buckets.
Sub-objective 1D: Rice weevil, navel orangeworm, and western flower thrips will be fumigated with plant essential oils (PEO) including anisole and methyl benzoate in glass jars. The pests at different life stages will be exposed to PEO at different doses for different durations at different temperatures to determine effective treatments. For each insect species, once an effective treatment is identified, it will be tested in larger scale fumigation tests with products to verify efficacy. For western flower thrips, effects of PEO fumigation on apple quality will also be evaluated in large-scale fumigation tests.
Progress Report
Research on sulfur dioxide (SO2) fumigation for control of stored product insects is continuing. Significant progress was made for control of rice weevil and confused flour beetle adults. Adults of these insects were fumigated with SO2 for 3 hours and 24 hours at different temperatures to determine effective treatments. Preliminary results were encouraging and showed that SO2 fumigation can have effective control of both insects in 3 hours. This research is continuing to determine susceptibility of other life stages to SO2 fumigation and effective SO2 fumigation treatments.
Research on SO2 fumigation for control of navel orangeworm (NOW) yielded significant results and is still in progress. A series of experiments were conducted to evaluate SO2 sorption on pistachios and efficacy of SO2 fumigation against different life stages of navel orangeworm. SO2 concentration in fumigation chamber with pistachios declined rapidly after injection, indicating rapid sorption of SO2 by pistachios. Because of rapid decline of SO2 concentration, a short-term fumigation treatment of 3 hours was selected to develop an effective SO2 fumigation treatment against navel orangeworm. Effective controls were achieved against all life stages. Eggs were most susceptible to SO2 fumigation followed by pupae. Larvae were the most tolerant life stage. Confirmation tests with navel orangeworm larvae in infested pistachios together with uninfested pistachios are in progress to verify efficacy of a selected SO2 fumigation treatment. These studies are directly related to Sub-objective 1C: Determine effective sulfur dioxide fumigation treatments against pests on fresh and stored products.
Accomplishments
1. Effects of nitric oxide fumigation against ham mites. Ham mites are important pests on aged hams as well as stored products, such as cheeses, nuts, dried fruits, spices, and semi-moist pet foods, and methyl bromide fumigation has been the main treatment in the past. Nitric oxide (NO) is a recently discovered new fumigant for postharvest pest control and was studied by ARS researchers in Salinas, California, for its potential for controlling ham mites. Ham mites at different life stages on artificial media were fumigated with 0.5 to 2.0% NO under ultralow oxygen conditions for 8 to 48 hours to determine effective treatments. Complete control of eggs, mobile immatures, and adults was achieved and eggs were more tolerant to NO than other life stages. Effective control of all life stages of ham mites on hams was also confirmed in 48 and 24 hour fumigations with 0.5 and 1.0% NO, respectively. The study demonstrated that NO fumigation has potential to be an alternative treatment to methyl bromide fumigation for control of ham mites on cured-ham products in ham aging facilities.
2. Long-term low oxygen storage treatment to control rice weevil and confused flour beetle on stored products. Long-term low oxygen storage treatment was studied by ARS researchers in Salinas, California, to develop alternative treatments against two major stored product insects, rice weevil and confused flour beetle. Eggs of the two insects were exposed to controlled atmospheres with 3 to 8% oxygen for 45 days to determine effects on survival and development. Different life stages of the two insects were also subjected to a 14-day 5% low oxygen treatment to determine variation in susceptibility to the low oxygen treatment. There were considerable differences between the two species, with rice weevil eggs and adults more susceptible to low oxygen treatment than larvae and pupae, and confused flour beetle eggs most susceptible and adults most tolerant to the low oxygen treatment. Results of the study indicated that long-term storage treatments with 5% and 6.5% oxygen are expected to be effective to control rice weevil and confused flour beetle, respectively, and long-term low oxygen storage treatment has potential for grain storage facilities to control rice weevil and confused flour beetle on stored products.
Review Publications
Liu, Y.B., Simmons, G.S. 2021. Effects of nitric oxide fumigation on mortality of light brown apple moth, Epiphyas postvittana (Lepidoptera: Tortricidae). Agricultural Sciences. 12(11):1286-1294. https://doi.org/10.4236/as.2021.1211082.
LeBlanc, N.R. 2021. Bacteria in the genus Streptomyces are effective biological control agents for management of fungal plant pathogens: A meta-analysis. Biocontrol. 67:111-121. https://doi.org/10.1007/s10526-021-10123-5.
LeBlanc, N.R. 2022. Green manures alter taxonomic and functional characteristics of soil bacterial communities. Microbial Ecology. 85:684–697. https://doi.org/10.1007/s00248-022-01975-0.
