Location: Crop Improvement and Protection Research
2020 Annual Report
Objectives
The long-term goal of this project is to develop alternative postharvest pest control treatments that are effective and safe for control of quarantine pests on a wide range of perishable agricultural commodities. This project builds upon our previous success with nitric oxide (NO) and oxygenated phoshine (PH3) fumigations as potential alternatives to methyl bromide fumigation for postharvest pest control on fresh fruits and vegetables. Nitric oxide was found to have higher efficacy than regular PH3 and may also enhance postharvest quality of fresh products. Oxygenated PH3 fumigation was found to control external pests with greater efficacy than regular PH3 fumigation. Successful completion of the project will result in specific NO fumigation and oxygenated PH3 fumigation treatments against four insect species on fresh fruit and vegetables including western flower thrips, light brown apple moth, codling moth, and the fruit fly spotted wing drosophila. Specific objectives are listed below:
Objective 1. Develop nitric oxide fumigation treatments for postharvest pest control.
Sub-objective 1.A. Develop an effective nitric oxide fumigation treatment to control western flower thrips on fresh fruit and vegetables.
Sub-objective 1.B. Develop an effective nitric oxide fumigation treatment to control light brown apple moth on fruit.
Sub-objective 1.C. Develop an effective nitric oxide fumigation treatment to control codling moth in apples.
Sub-objective 1.D. Develop an effective nitric oxide fumigation treatment to control spotted wing drosophila in sweet cherries and strawberries.
Objective 2. Develop oxygenated phosphine fumigation treatments for postharvest pest control.
Sub-objective 2.A. Determine feasibility of oxygenated phosphine fumigation to control codling moth in apples.
Sub-objective 2.B. Determine feasibility of oxygenated phosphine fumigation to control spotted wing drosophila in strawberries.
Approach
Objective 1. Nitric oxide fumigation under ultralow oxygen conditions will be studied for controlling insect pests including western flower thrips, light brown apple moth, codling moth, and spotted wing drosophila on harvested fresh commodities for their exports. Small scale laboratory fumigations will be conducted to determine effective treatments (concentration, time, and temperature) for different insects. Selected treatments will then be tested on specific fresh products to evaluate the impact of the treatments on postharvest quality.
Objective 2. Oxygenated phosphine fumigation under high oxygen conditions will be studied for controlling codling moth larvae in apples and spotted wing drosophila in sweet cherries and strawberries. Small scale laboratory fumigations will be conducted to determine effective treatments to control the most tolerant life stages of the pests in the fruits. Selected effective treatments will then be tested on fresh products to verify their efficacies and impact of postharvest quality of the fresh products.
Progress Report
This is the final report for project 2038-22430-002-00D, which will terminate on September 30, 2020.
In support of Sub-objective 1A, nitric oxide (NO) fumigation for control of western flower thrips and lettuce aphid on lettuce was demonstrated to be effective and safe on commercial packed lettuce. NO fumigation for postharvest pest control must be conducted under ultralow oxygen (ULO) conditions, and the chamber must be flushed with nitrogen to dilute NO before terminating the fumigation in order to prevent injuries to sensitive products, e.g., lettuce, by nitrogen dioxide (NO2). Commercial packaging of fresh products restricts ventilation and may affect establishment of ULO at the start and dilution of NO at the end. A 16-hour fumigation with 0.5% NO effectively controlled both insects and was demonstrated to be safe in regard to product quality of commercially packed lettuce in a large-scale laboratory experiment. NO fumigation has potential for control the both insects on commercially harvested and packed lettuce.
In support of Sub-objective 1B, NO fumigation was found to be efficacious for control of light brown apple moth (LBAM). LBAM larvae, pupae, and eggs were fumigated in 1.9 L jars with NO at different concentrations under ULO conditions for different durations at 2°C to determine their susceptibilities to NO fumigation and effective treatments. A 2.0% NO fumigation achieved complete control of LBAM larvae and pupae in 8 hours. Eggs were more tolerant than larvae and pupae to NO fumigation. Complete control of eggs was achieved in 6-hour fumigations with 5.0% NO, in 12-hour fumigations with 3.0% NO, in 24-hour fumigations with 2.0% NO, and in 48-hour fumigations with 1.5% NO. The study demonstrated good potential of NO fumigation at low temperature to control LBAM.
In support of Sub-objective 1C, research was conducted to determine efficacy and safety of NO fumigation for control of codling moth in apples. NO fumigation treatments were conducted to control codling moth on artificial diet and in infested apples and effective fumigation treatments were determined. Complete control of larvae in apples was achieved with a 24-hour fumigation treatment with 5.0% NO at 2°C. The treatment did not injure or stain the fruit. Fumigated and non-treated control apples were compared for postharvest quality. Treated apples were firmer and retained color better than the controls, suggesting that NO fumigation helped preserve postharvest quality of apples. The study showed that NO fumigation has the potential to control codling moth larvae in apples.
In support of Sub-objective 1D, research was conducted to determine efficacy and safety of NO fumigation for control of spotted wing drosophila on harvested strawberries. Spotted wing drosophila is a major pest of strawberries and other soft fruit. In a laboratory study, 8-hour fumigation with 3.0% NO under ULO conditions effectively controlled spotted wing drosophila with 100% mortality of eggs and larvae and 98.8% mortality of pupae at 2°C. A 16-hour fumigation with 3.0% NO had no negative effects on strawberry quality and reduced mold on strawberries. The study showed that NO fumigation has the potential for controlling spotted wing drosophila in strawberries as well as extend strawberry storage and shelf-life.
Sub-objective 2A was not completed due to unavailability of codling moth supply from our collaborating Animal and Plant Health Inspection Service Plant Protection and Quarantine lab after we successfully developed NO fumigation treatment to control codling moth larvae in apples. Sub-Objective 2B was abandoned due to the fact that an effective NO treatment for controlling spotted wing drosophila in strawberries was successfully developed and research emphasis was shifted to NO fumigation as summarized below.
NO fumigation research was expanded to determine its efficacy and safety for control of bulb mites on flower bulbs. Bulb mites are important pests of flower bulbs and difficult to control. Fumigations with 2.0 and 3.0% NO for 24 hours at 20 and 10°C, respectively, achieved complete control of bulb mites. A more severe 24-hour fumigation treatment with 3.0% NO at 20°C was tested on bulbs of four flower species. The treatments had no negative impacts on bulb germination, growth or blooming. The study demonstrated that NO fumigation has potential to be used for control of bulb mites on flower bulbs.
NO fumigation research was expanded to include analyses of NO residues on fumigated fresh and stored products. Twenty fresh fruit and vegetables, and nine stored products were fumigated with NO in two studies. Each product was subjected to two identical fumigation treatments. One of the treatments was terminated with a nitrogen gas (N2) flush in order to dilute NO before exposing products to ambient air so as to prevent NO2-induced injuries to fresh products, and the second treatment was terminated with air flush to allow reaction with oxygen. NO2 in headspace, nitrate, and nitrite in liquate samples were measured 24 hours after fumigation. NO2 levels from fumigated fresh products declined dramatically over time. For most fresh products, NO2 desorption in the treatment flushed with N2 was the same as the controls 24 hours after fumigation, and neither nitrate nor nitrite was elevated by the treatment. Elevated nitrate was detected on some products in the air flush-terminated treatment. This study indicated that NO fumigation, when terminated with an N2 flush, did not alter nitrate or nitrite levels in fresh products and did not, therefore, create any safety concerns. For stored grains and nuts, NO fumigation terminated with N2 flush did not significantly increase nitrate or nitrite levels on fumigated products and there was also no significant difference in nitrogen dioxide desorption rates between the treatment and the control 21 days after fumigation. NO fumigation terminated with air flush had significantly higher residue levels as compared with controls. These results showed that terminating NO fumigation with N2 flush prevents: 1) NO residues on stored products, and 2) nitrate or nitrite residues on fresh and stored products.
NO fumigation research was expanded to determine effectiveness of NO and NO2 fumigation on spores of Aspergillus flavus. Infection by microbial organisms such as A. flavus is a serious problem for many stored products because the fungus produces carcinogenic aflatoxins. NO fumigation containing NO and NO2 has potential to control insects and microbes, and was studied for effects in inactivating A. flavus spores. Fumigation treatments at 0.1% NO2 or 1.0% NO at 15°C achieved complete inactivation of A. flavus spores in 3 hours. The study indicated that NO fumigation for pest control also has potential to control fungal spores on stored products.
NO fumigation research was expanded to evaluate efficacy of NO2 fumigation in controlling microbes on stored almonds. Postharvest control of both insects and microbes is critical for stored products such as almonds. NO fumigation under ULO conditions can have desirable levels of NO and NO2 and, therefore, has potential to control insects by NO and microbes by NO2. A laboratory study was conducted to evaluate potential of NO2 fumigation for controlling bacteria and fungi on stored almonds. Unpasteurized almonds were subjected to 1- and 3-day fumigations with 0.1%, 0.3%, and 1.0% NO2 at 25°C. Microbes on fumigated almonds and untreated control were sampled after fumigation and microbial loads were determined using a rapid enumeration test system. All treatments effectively controlled bacteria and fungi, and 1% NO2 completely controlled bacteria and fungi on almonds. The study adds further evidence on the potential of NO fumigation for control of pests and microbes on stored products.
Additional research determined the effectiveness of ULO atmosphere for control of bed bugs. Bed bug nymphs, adults, and eggs were subjected to ULO treatments established with nitrogen flush and vacuum treatments at different temperatures. Ultralow oxygen treatments and vacuum treatments were very effective against all life stages of bed bugs. The efficacy of the treatments increased with reduced oxygen level, increased temperature and treatment times. Complete control of bed bug nymphs and adults and >98% control of bed bug eggs was achieved in the 8-hour treatment in a 0.1% oxygen (O2) atmosphere at 30°C. Complete control of all life stages was achieved after 12 hours in a -982 mbar (-29.0 inHg) vacuum at 30°C. This study demonstrated that bed bugs are very susceptible to low O2 stresses, and the potential for ULO as an effective and safe treatment to decontaminate bed bug-infested objects.
Additional research determined efficacy of sulfur dioxide (SO2) fumigation for control of grape mealybug and vine mealybug on harvested table grapes. Sulfur dioxide has not traditionally been used as a fumigant for pest control. Three and 4-day fumigations with 100 ppm SO2 and 24-hour fumigations with 400-500 parts per million (ppm) SO2 controlled all life stages of both mealybug species with >95% mortality of eggs and 100% mortality of nymphs and adults. Effective treatments did not negatively impact table grape quality. The study suggests that sulfur dioxide has potential for postharvest pest control on harvested table grapes.
Accomplishments
1. Essential oil methyl benzoate is a potential fumigant for postharvest pest control. Perishable fresh products for export markets are subject to a quarantine requirement of zero live insect contaminants. Methyl benzoate, an essential oil, was reported to be insecticidal and has, therefore, potential to be an environmentally friendly pesticide for perishable fresh products. Methyl benzoate as a fumigant in laboratory tests conducted by researchers in Salinas, California, completely killed four postharvest pests in 8 to 72 hours, depending on pest species: western flower thrips, lettuce aphid, rice weevil, and bulb mites. Methyl benzoate fumigation did not adversely affect apple quality. The study demonstrated that methyl benzoate was effective as a fumigant against insects and mites and, therefore has potential to be used as an alternative fumigant for postharvest pest control.
2. Comparison of NO fumigation under N and CO2 atmospheres for efficacy against two stored product insect pests. Stored products suffer quality and quantity losses from insect pests. Nitric oxide (NO) is a recently discovered, efficacious fumigant for postharvest pest control, but NO fumigation must be conducted under ultralow oxygen (ULO) atmosphere because NO reacts with oxygen and damages stored products. Nitrogen has been used to establish ULO atmospheres in NO fumigation studies in the past, but carbon dioxide may be a cheaper alternative to nitrogen. ARS researchers in Salinas, California, discovered that NO fumigations under ULO conditions established with nitrogen gas and carbon dioxide (CO2) were effective against all life stages of two stored product insects, granary weevil and confused flour beetle. Granary weevil pupae and confused flour beetle eggs were more tolerant to NO fumigation than other life stages for each respective species, but >99% mortality of granary weevil pupae and 100% mortality of confused flour beetle eggs were achieved in 24-hour fumigations with 2% and 1% NO, respectively. This study showed that CO2 can be used to establish ULO atmospheres for NO fumigation.
3. Nitric oxide fumigation controls navel orangeworm in walnut. The navel orange worm (NOW) causes postharvest losses to stored tree nuts. Nitric oxide (NO), a recently discovered fumigant for postharvest pest control was evaluated by ARS researchers in Salinas, California, for efficacy against eggs, larvae, and pupae of NOW. NO fumigation was effective against NOW on artificial diet and in infested walnuts. Susceptibility to NO fumigation varied among different life stages with eggs being most tolerant, followed by pupae and then larvae. Treatment time needed for complete control of NOW decreased with increasing NO concentrations, and complete control of NOW eggs was achieved in - and 16-hour fumigations with 3.0 and 2.0% NO, respectively. The study demonstrated that NO fumigation was effective against NOW on walnut and has potential to be an alternative treatment for postharvest control of NOW on tree nuts.
Review Publications
Yang, X., Liu, Y.-B. 2019. Residue analysis of nitric oxide fumigation in nine stored grain and nut products. Journal of Stored Products Research. 84:101521. https://doi.org/10.1016/j.jspr.2019.101521.
Yang, X., Liu, Y.-B., Feng, Y., Zhang, A. 2019. Methyl benzoate fumigation for control of post-harvest pests and its effects on apple quality. Journal of Applied Entomology. 144(3):191-200. https://doi.org/10.1111/jen.12723.
Oh, S., Liu, Y.-B. 2020. Effectiveness of nitrogen dioxide fumigation for microbial control on stored almonds. Journal of Food Protection. 83(4):599–604. https://doi.org/10.4315/0362-028X.JFP-19-281.
Liu, Y.-B. 2020. CA requirements for postharvest pest control. In: Gil, M.I., Beaudry, R., editors. Controlled and Modified Atmospheres for Fresh and Fresh-Cut Produce. San Diego, CA: Academic Press of Elsevier. p. 65-74.
