Research Project: Improved Systems-based Approaches that Maintain Commodity Quality and Control of Arthropod Pests Important to U.S. Agricultural Production, Trade and Quarantine

Location: Commodity Protection and Quality Research

2022 Annual Report

Objectives
The long-term objective of this project is to improve the quality of specialty crops grown in the western U.S. and increase their domestic consumption and export. All three objectives represent multiple, integrated issues focused on reducing insect damage, maintaining or improving quality and ensuring that exported commodities meet all phytosanitary requirements. Project integration will facilitate successful implementation of systems-based control strategies into current crop production systems, delay the development of resistance to chemicals used for control or disinfestation, overcome trade barriers for the export of fresh fruits and nuts, and minimize deleterious effects of these chemicals on the environment. Objective 1: Develop new or improved preharvest processes that are acceptable to industry and regulatory partners that reduce the incidence of pests in fresh and durable commodities prior to harvest. Sub-objective 1A: Improve current integrated pest management strategies for control of navel orangeworm (NOW) in order to reduce damage and minimize nontarget impacts on environmental quality. Sub-objective 1B: Reduce NOW damage to almond and pistachio orchards by characterizing the environmental and host factors associated with high NOW damage to orchards and develop strategies to eliminate them or mitigate their impact. Sub-objective 1C: Minimize chemical treatment requirements by characterizing and optimizing integrated pest management strategies for monitoring and control of key dipteran and lepidopteran pests. Sub-objective 1D: Improved management of pests of high-value commodities through generation of molecular resources and development of genomics-based approaches. Objective 2: Develop new or improved postharvest processes for the control of arthropod pests, such as handling procedures and treatments, that contribute to food security and food safety while maintaining commodity quality. Sub-objective 2A: Improve semiochemical-based strategies for control of stored product insect pests. Sub-objective 2B: Develop novel postharvest treatments for fresh and durable commodities that maintain or improve commodity quality while protecting the commodity against arthropod pests. Sub-objective 2C: Improve the sustainability of methyl bromide alternatives using molecular toxicology approaches to understand pest physiology, in the context of emergence of insecticide resistance. Objective 3: Ensure that new treatments comply with environmental, human health, sanitary, and phytosanitary regulations, including local, state, national, and international regulations. Sub-objective 3A: Develop treatments for action agencies and industry that satisfy the regulatory requirements of the exporter and importer, ensuring that technology implementation results in market retention or expansion. Sub-objective 3B: Identify agrochemical use strategies and develop novel technologies to ensure residues are compliant with importer and domestic food tolerances. Sub-objective 3C: Develop technologies that reduce or eliminate atmospheric emissions during ventilation of postharvest fumigations to address air quality criteria.

Approach
This project has one overarching theme, maintaining or improving the quality of west coast horticultural commodities in order to maintain or expand market share, by improving existing systems approaches and developing new ones. This complex project contains three objectives, 10 sub-objectives, and 13 research goals. The research focus of Objective 1 is preharvest, and three sub-objectives and four research goals target the navel orangeworm (NOW), the primary moth pest of California tree nuts. Research will evaluate the feasibility of a nonchemical alternative, sterile insect technique and facilitate the integration of another nonchemical technique, mating disruption, into existing management programs. These programs will be improved by enhancing the efficacy of existing insecticides through changes in timing and improvements in coverage, as well as recognizing orchards at increased risk for damage. The final NOW sub-objective determines the feasibility of using RNAi-mediated reduction in target gene expression to improve its control, as well as that of citrus red scale. The final sub-objective in Objective 1 seeks to improve the monitoring and control of dipteran pests such as the spotted wing drosophila, the Mediterranean fruit fly, and the melon fly, by improving existing attractants and developing new ones. The research focus of Objective 2 is improved control of coleopteran and lepidopteran pests of fresh and durable commodities in storage. It contains three sub-objectives and four research goals. The first sub-objective and two research goals are far ranging and involve novel methods to synthesize semiochemicals and develop new methods to dispense them. Additional studies seek to improve mating disruption using the same semiochemicals for both disruption and detection. The final two sub-objectives and two research goals are independent but related to one another. One sub-objective is quite broad; developing novel postharvest treatments for fresh and durable commodities. The control methods assessed include low oxygen controlled atmosphere, cyanide, sulfuryl fluoride, phosphine, and ethyl formate, alone and in combination, as well as irradiation. The focus of the final sub-objective is to identify the insect genes responsible for both ethyl formate toxicity and the combination of ethyl formate and CO2 used as an additive, in brown marmorated stinkbug, in order to improve control. The research focus of Objective 3, which contains three sub-objectives and four research goals, is to ensure that the techniques and technologies developed in the earlier objectives can be adopted. The first sub-objective and research goal ensures that treatments developed for lepidopteran and dipteran pests are in compliance with all pertinent regulations. The second sub-objective and two research goals focuses on generating efficacy and residue data to support the use of ethyl formate and sulfuryl fluoride as substitutes for methyl bromide. The final sub-objective and research goal focuses on developing recapture technologies to reduce or eliminate fumigant emissions into the atmosphere.

Progress Report
In support of Sub-objective 1A, flight cylinder assays were used to examine the impact of cold exposure on navel orangeworm reared at Parlier, California, because although cold is used to immobilize moths for sterile insect mass release programs, navel orangeworm is particularly susceptible to this method. Adults exposed to 4°C for 24 hours did not perform significantly worse on this test, and three days at this temperature were required for a significant reduction in the number of males leaving the flight cylinder. A separate flight cylinder experiment found a small but significant reduction in performance for males shipped overnight in cold compared to those held in a cold room over the same time. The results indicate that the effect of cold stress is cumulative and that mechanical transport stress contributes to loss of vigor. In further support of Sub-objective 1A, a series of field trials were conducted to determine if the water volume used for insecticide application in pistachios could be reduced from 100 gallons to 80 gallons per acre using organosilicone adjuvants. Trials tested 80 gallons of water per acre at an adjuvant concentration of 0.1%, added to either insecticide combination of chlorantraniliprole+lambda cyhalothrin or methoxyfenozide+bifenthrin. These treatments lasted three weeks. This was the first demonstration that pistachios could be protected by ground application for this period using less than 100 gallons of water per acre. Air application was assessed in both almonds and pistachios for the insecticide chlorantranliprole. Water volume was successfully reduced from 30 gallons to 10 gallons per acre, and this did not affect the duration of control. As a result of this study the label was changed to allow air application at 10 gallons per acre. In support of Sub-objective 1B, in Fresno County, California, orchards participating in a sterile release program for navel orangeworm, the primary lepidopteran pest of California almonds, were identified and information collected on insecticide use and insect trapping data for 2020 and 2021. Analysis of the data is ongoing, and outcomes will be compared to research conducted between 2016-2020, which demonstrated that almond sanitation failure (presence of unharvested nuts) could be successfully mitigated by applying a selective insecticide to these nuts during the period April 21-May 1. Having a baseline will facilitate the multiyear process of identifying indicators for both high and low insect damage. Research to determine the efficacy of sanitation programs and assess insect damage contributes to a reduction of the navel orangeworm population. In support of Sub-objective 1C, four isoprenyl ether analogs, each individually attractive to spotted wing drosophila, were synthesized, formulated in polymeric lures, and the release kinetics investigated. Effective lures are required for trapping and understanding the field dissipation of the lure is critical to improve capture. The kinetic approach yields laboratory predictions of the potential for environmental loss prior to conducting field bioassays. Results were transferred to: USDA-Animal and Plant Health Inspection Service; FAO International Atomic Energy Agency; California Department of Food and Agriculture, and Florida Department of Agriculture. In support of Sub-objective 1D, research continued on development of molecular resources for California red scale (CRS), a major pest of citrus plants. A total of 3.3Gb RNA-seq expression data (87,478,180 150b paired-end reads) obtained from whole body CRS samples were processed through a bioinformatics analysis pipeline. A high-quality transcriptome of CRS containing 49,857 transcripts with a minimum length of 300 nucleotides was obtained. Functional annotation provided a summary of various gene functions and indicated molecular pathways in this insect pest. Availability of this gene expression resource establishes a platform to investigate the molecular basis of biological traits and improve field control of CRS. In support of Sub-objective 2A, a hydrolyzable precursor of warehouse beetle pheromone was synthesized and formulated in polymeric lures. After synthesis the filtrate was concentrated to yield crude (1E,8Z)-14- methylhexadeca-1,8-dienyl acetate. Gas chromatography mass spectrometry was used to estimate a purity of 65%, which provides a source for attraction bioassays. In further support of Sub-objective 2A, a pseudoacoustic detection device was used to assess the distance that almond moths and Mediterranean flour moths flew to mating disruption dispensers. This information is important to the use of pheromones for monitoring and controlling moth pests. Multiple (10-12) replicates in time (generations of moths) were used for each species. Data analysis is underway to verify wing frequencies associated with approach of these moths to the pheromone source. In support of Sub-objective 2B, laboratory-scale evaluations of fumigant toxicity were conducted, and the dosage, duration, and temperature parameters required to control 95% of a population were predicted. The most fumigant-tolerant life stage was identified. The concentration-time (Ct) exposures of 20, 25, and 18 grams (g) meter (m)-3 hour (h) ethyl formate were required to respectively control adult female (flat mites) Tarsonemus bakeri, Brevipalpus californicus and B. lewisi at 10° C. A Ct exposure of 500 g m-3 h sulfuryl fluoride was required to control eggs of confused flour beetle at 10° C. Eggs of the cigarette beetle at 10° C were controlled when phosphine levels were maintained between 0.7 and 1.5 g m-3 4 days. Eggs of the cigarette beetle at 28° C were controlled when oxygen levels < 2% were maintained for four days. In support of Sub-objective 2C, the physiological response of brown marmorated stink bug (BMSB) to Ethyl formate (EF) exposure was assessed. EF is under evaluation as a methyl bromide alternative to control BMSB. Researchers at Parlier, California, conducted fumigation trials and estimated the median lethal concentrations of EF, along with carbon dioxide as an additive, as 50 milligram (mg)/liter (l)/hour (h) and 25 mg/l/h for third instar nymphs and adults, respectively. The gene expression measurements in EF-exposed BMSB will reveal various molecular players involved in the insect’s physiological response to fumigation. In support of Sub-objective 3A, laboratory-scale evaluations of fumigant toxicity were conducted, and dosage, duration, and temperature parameters required to control 95% of specimens in the target pest population were predicted. A concentration-time (Ct) exposure of 170 g m-3 h methyl bromide was required to control internally feeding larvae of Oriental fruit fly and blueberry maggot in blueberries at 15°C. A Ct exposure of 20 g m-3 h hydrogen cyanide was required to control internally feeding larvae of Oriental fruit fly in citrus at 10° C. Internally feeding larvae of Western cherry fruit fly at 8°C were controlled when phosphine levels were maintained between 0.7 and 1.5 g m-3 for a duration for five days. In support of Sub-objective 3B, ARS scientists at Parlier, California, collaborated with the U.S. Environmental Protection Agency and California Department of Pesticide Regulation in research on registration, experimental procedures, and modeling techniques for the postharvest fumigant EF. Investigations focused on EF efficacy, fate, and transport related to bulk citrus (i.e., lemons, oranges, and grapefruit) treatment in field bins, during storage, and through the marketing pathway. These results enhanced the understanding of how EF impacts human health, particularly along pathways of applicator, worker, and bystander exposure. In support of Sub-objective 3B, capillary electrophoresis (CE) with indirect ultraviolet detection and the use of fluoride-ion sensitive electrodes (ISE) were compared as methods to analyze fluoride. If CE is to be used as a replacement for ISE analysis, improvements must be made to either instrument sensitivity or sample preparation. CE offers potential efficiency gains compared to ISE due to the reduced amount of manual labor required to analyze large numbers of samples. In support of Sub-objective 3C, research continued to minimize or eliminate atmospheric emission of fumigants in ventilation effluent. In a pilot study, sulfuryl fluoride was effectively removed from ventilation effluent, and could be effectively scrubbed using a solution of sodium hydroxide. Two container types were evaluated including an empty shipping container using a commercially available vertical liquid air scrubber. Its HLT (time to remove half the gas from the emission stream during aeration for sulfuryl fluoride) was 17.6 minutes and addition of a hydrogen peroxide catalyst reduced HLT to six minutes for a 33.1 m3 shipping container while retaining a high scrubbing efficiency of approximately 95%.

Accomplishments
1. Limiting the impact of postharvest fumigation on greenhouse gas emission. Sulfuryl fluoride (SF) is a key methyl bromide alternative that is used around the world to treat durables such as tree nuts and logs. The five largest ports in the European Union and Australia required that SF emission be curtailed due to its greenhouse gas potential. ARS researchers at Parlier, California, conducted research to enhance the understanding of how fumigants impact human and environmental health. A commercial scrubbing technology was developed to reduce SF emissions and this technology is now in widespread use. This research preserves the use of SF across the globe and reduces greenhouse gas levels.

2. Mating disruption and reduced-risk insecticides provide synergistic control of the navel orangeworm. The navel orangeworm is the most important insect pest of the $8 billion dollar almond and pistachio crops in California. Mating disruption is widely used for this pest, but industry seeks to further expand the role of this environmentally friendly technique in overall management of navel orangeworm. ARS researchers at Parlier, California, in collaboration with a colleague from Trece, Inc., used a 10-year data set from an overall area of 2,400 acres of commercial almonds comparing plots treated with mating disruption only, insecticide only using a reduced risk ovi-/larvicide, or both. The two treatments together yielded significantly lower navel orangeworm damage than either over the entire study, and this trend was evident in nine of the 10 years in the study. Demonstration that mating disruption enhances control with a widely-used insecticide will improve adoption of mating disruption and reduce insecticide use in the long run.

3. Using selective insecticides to mitigate sanitation failure in California almonds. The navel orangeworm, a moth, is the primary pest of California almonds and sanitation that includes the removal and destruction of unharvested nuts is the foundation of its control. However, there are times when sanitation fails due to weather restricting orchard access or environmental conditions causing nuts to stick, resulting in too many nuts left on the tree. ARS researcher at Parlier, California, conducted studies between 2016-2020 and determined that the period from April 21 to May 1 was the optimum time to spray unharvested nuts with selective insecticides to disrupt oviposition during spring. This in turn reduces summer pest pressure in July when the almonds are vulnerable, ensuring reduced insect damage and maintaining almond quality so growers get the highest price for their crop.

4. Baseline susceptibility in gill’s mealybug for insecticide resistance monitoring. The gill’s mealybug (GMB) has emerged as serious threat to California’s pistachio industry. Pistachio growers experienced control failures for three successive seasons (2019-2021) after using recommended chemicals and lacked the tools to determine the cause of failure. ARS researchers at Parlier, California, established a baseline for susceptibility to the insecticides spirotetramat and acetamiprid in GMB populations collected from five different locations in the state. This research provided a tool for resistance monitoring and for implementation of alternative chemicals or control practices that can manage the shifts in insecticide susceptibility. Overall, this research has implications to improve the effectiveness and sustainability of GMB management program.

5. Traps and attractants for improved detection of navel orangeworm movement between crops. The navel orangeworm (NOW) is a key pest of the almond, pistachio, and walnut crops, worth over $8 billion annually in California. Movement of NOW between these crops is an important part of NOW’s pest potential, and reliable detection of this movement from earlier-harvested almonds to later-harvested walnuts improves environmentally responsible reduction of economic harm from NOW. ARS researchers at Parlier, California, in collaboration with colleagues from University of California, Riverside, and University of California Agriculture and Natural Resources, conducted a three-year study using fatty acid profiles to distinguish between moths that developed as larvae in almonds and those that developed in walnuts. Female ovipositional baits and phenyl propionate (PPO), a synthetic chemical attractant, detected movement and correlated with damage better than pheromone lures. The development of a method to reliably detect movement of NOW populations will improve protection of walnuts from NOW damage and reduce the use of residual insecticides applied as a precaution.

6. Methods developed to control invasive and quarantine horticultural pests. ARS researchers at Parlier, California, developed novel postharvest methyl bromide fumigation to control codling moth in over 50 new varieties of fresh plum exported from California to Japan, valued at $12 million annually. A novel postharvest methyl bromide fumigation was also developed to control codling moth infesting inshell walnuts exported from California to Korea valued at $20 million annually. The research contributed to market retention and/or expansion and served as the basis for technical interaction between industry, USDA Foreign Agricultural Service, USDA Animal and Plant Health Inspection Service, U.S. Environmental Protection Agency, and their respective counterparts in foreign governments to maintain trade.

Review Publications
Kawagoe, J.C., Abrams, A.E., Lourie, A.P., Walse, S.S. 2022. Ethyl formate dilution in carbon dioxide for fumigation control of the brown marmorated stinkbug Halyomorpha halys, Stål (Hemipitera: Pentatomidae). Pest Management Science. 78(7):3090-3097. https://doi.org/10.1002/ps.6935.
Walse, S.S., Cha, D.H., Lee, B.Y., Follett, P.A. 2021. Postharvest quarantine treatments for Drosophila suzukii in fresh fruit. In: Garcia, F.R.M, editor. Drosophila suzukii Management. Cham, Switzerland: Springer. p. 255-267. https://doi.org/10.1007/978-3-030-62692-1_13.
Siegel, J.P., Gilcrease, G. 2022. Augmenting sanitation with insecticides to improve control of navel orangeworm (Amyelois transitella Walker) (Lepidoptera: Pyralidae) in California tree nuts. Pest Management Science. 78(5):2034-2042. https://doi.org/10.1002/ps.6827.
Oppert, B.S., Muszewska, A., Steczkiewicz, K., Šatovic-Vukšic, E., Plohl, M., Fabrick, J.A., Vinokurov, K.S., Koloniuk, I., Johnston, J., Smith, T.P., Guedes, R.C., Terra, W.R., Ferreira, C., Dias, R.O., Chaply, K.A., Elpidina, E.N., Tereshchenkova, V., Mitchell, M.F., Jenson, A.J., Mckay, R., Shan, T., Cao, X., Xiong, C., Jiang, H., Morrison III, W.R., Koren, S., Schlipalius, D., Lorenzen, M.D., Bansal, R., Wang, Y., Perkin, L.C., Poelcheau, M., Friesen, K.S., Olmstead, M.L., Scully, E.D., Campbell, J.F., et al. 2022. The genome of Rhyzopertha dominica (Fab.) (Coleoptera: Bostrichidae): Adaptation for success. Genes. 13(3). Article 446. https://doi.org/10.3390/genes13030446.
Poosapati, S., Poretsky, E., Dressano, K., Ruiz, M., Vazquez, A., Sandoval, E., Estrada-Cardenas, A., Duggal, S., Lim, J., Morris, G., Szczepaniec, A., Walse, S.S., Ni, X., Schmelz, E.A., Huffaker, A. 2022. A sorghum genome-wide association study (GWAS) identifies a WRKY transcription factor as a candidate gene underlying sugarcane aphid (Melanaphis sacchari) resistance. Planta. 255. Article 37. https://doi.org/10.1007/s00425-021-03814-x.
Burks, C.S. 2022. Comparison of navel orangeworm adults detected with optical sensors and captured with conventional sticky traps. AgriEngineering. 4(2):523-532. https://doi.org/10.3390/agriengineering4020035.
Abrams, A.E., Alvarez, A., Rodriguez, M., Kron, C.R., Bellamy, D., Walse, S.S. 2022. Greenhouse rearing methods for brown marmorated stink bug (Hemiptera: Pentatomidae) on live cowpea plants. Journal of Economic Entomology. 114(6):2297-2306. https://doi.org/10.1093/jee/toab201.
Rodriguez, M., Tebbets, J.S., Walse, S.S. 2021. Methyl bromide vacuum fumigation of California USA in-shell walnuts packaged in fiberboard cartons. Journal of Stored Products Research. 94. Article 101879. https://doi.org/10.1016/j.jspr.2021.101879.
Yokomi, R.K., Delgado, J.K., Unruh, T.R., Barcenas, N.M., Garczynski, S.F., Walse, S., Perez de Leon, A.A., Cooper, W.R. 2021. Molecular advances in larval fruit moth identification to facilitate fruit export from western United States under systems approaches. Annals of the Entomological Society of America. 115(1):105-112. https://doi.org/10.1093/aesa/saab040.
Obenland, D.M., Cranney, J., Tebbets, J.S., Walse, S.S., Arpaia, M. 2021. Fumigating citrus with phosphine does not impact marketability or eating quality. Plant Health Progress. 22(4):516-523. https://doi.org/10.1094/PHP-03-21-0053-RS.