Project : USDA ARS

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Research Project: Sustainable Management Strategies for Stored-Product Insects

Location: Stored Product Insect and Engineering Research

2019 Annual Report

Objectives
Objective 1: Identify and describe the functional genomics for physiological systems important to pest management (e.g., the digestive and sensory systems), for key stored product insects (e.g., lesser grain borer, red flour beetle). Sub-Objective 1.A. Sequence the genome of some key stored product pests. Sub-Objective 1.B. Conduct functional genomic studies of stored product pests to identify target genes for bio-rational controls. Sub-Objective 1.C. Evaluation of insect responses to insecticides and mechanisms of recovery and resistance. Objective 2: Develop and improve monitoring technologies, control tactics, and integrated pest management systems for stored product insects (e.g., cigarette beetle, lesser grain borer, red flour beetle, and warehouse beetle). Sub-Objective 2.A. Improve the management of outside sources of stored product insect infestation. Sub-Objective 2.B. Improve protection of bulk stored grain from damage by stored product insects through reduced risk approaches. Sub-Objective 2.C. Improve the effectiveness of reduced risk aerosol insecticides. Sub-Objective 2.D. Improve use of pheromones in integrated pest management programs.

Approach
Our research focus is the management of key pests of stored raw grains and processed grain products. Insect pests cause significant economic loss through direct feeding damage and product contamination throughout food distribution channels. Integrated pest management (IPM) approaches employing a combination of strategies are needed to protect domestic and international food supplies. Our research objectives target important data gaps in IPM programs, with an emphasis on reduced risk products and sustainable strategies that can be integrated to reduce pest infestation issues. We will conduct genome sequencing for several important stored product insect species and use functional genomics to identify targets for new biologically-based insecticides and evaluate insect response to insecticides. We will improve the management of outside sources of insect infestation through an evaluation of population structure and how insects exploit outside food accumulations. For bulk grain protection, we will focus on reduced risk insecticides and aeration to reduce the need to fumigate commodity. Aerosol insecticide usage inside structures is increasing as a structural fumigation alternative, so our research will focus on how applications can be improved. Finally, we will evaluate how pheromone use in monitoring and mating disruption can be improved through a better understanding of insect behavior. Successful completion of this work will result in new methodologies that will improve the quality of stored products, reduce economic loss, and contribute to the improved security of our food supply.

Progress Report
Progress was made toward meeting project objectives, which fall under National Program 304, Component 4, Protection of Post-Harvest Commodities, Quarantine, and Methyl Bromide Alternatives. Under Objective 1, Identify and describe the functional genomics for physiological systems important to pest management, significant progress was made on obtaining genomic sequence information for stored product pest insects. Reference quality genome assemblies have been obtained for the lesser grain borer, yellow mealworm, rice weevil, red flour beetle, house cricket, and banded cricket. Transgenic strains of the yellow mealworm and house cricket were evaluated. Data was mined from the mealworm and cricket genomes for optimization of protein and vitamin A production. Genetic assemblies have been completed for the Khapra beetle, Indianmeal moth, drugstore beetle, larger grain borer, warehouse beetle, hide beetle, cigarette beetle, and confused flour beetle. Due to involvement in the AGPest100 initiative, we also had the opportunity to submit merchant grain beetle and the saw-toothed grain beetle for Pac-Bio long read sequencing, which is being done in cooperation with ARS Stoneville, Mississippi. Under Objective 2, Develop and improve monitoring technologies, control tactics, and integrated pest management systems for stored product insects, we evaluated colonization by stored product insects of outside food accumulations in and around grain milling facilities and tested how treatment of these accumulations could reduce colonization. Better management of these outside sources of insects can reduce infestation of stored products. Studies have also been conducted to improve the tools available for the monitoring of stored product insects, including evaluation of the influence of moldy grain odors on insect behavioral responses, the evaluation of new chemical attractants and traps, and how response to monitoring traps is influenced by environmental conditions. We have conducted studies evaluating how pheromones can be more effectively used in mating disruption programs, by testing how pheromones influence female behavior and determining the fitness consequences of delaying time until mating. We have evaluated new reduced-risk insecticides to control stored product insects and are correlating efficacy data with insect movement when those insects are exposed on a treated substrate. We have conducted further studies evaluating effects of aerosol particle size in the range of 4 to 16 microns, and documented that efficacy begins to decrease at about 8 microns. Field trials show that differential aerosol dispersal in field sites can be somewhat mitigated by optimizing aerosol release points, but structural barriers and equipment inside milling facilities still affects aerosol dispersal. We have shown the potential of using a long-lasting insecticide netting to prevent the dispersal of stored product insects, which could alleviate reliance on fumigants to control insects in packaged grain-based products.

Accomplishments
1. Improving effectiveness of aerosol insecticide treatments for food facilities. With the reduced use of structural fumigations for the management of insect pests of stored food, the food industry has increasingly relied on aerosol insecticide applications, primarily reduced risk materials such as pyrethrins and insect growth regulators. Aerosol treatments disperse the insecticide in small droplets that can provide more even coverage, but little information was available on effectiveness of these treatments. Scientists at ARS in Manhattan, Kansas, along with collaborators at Kansas State University and MRI Global, determined how droplet size impacted insecticide efficacy. Small droplets (2 microns) produced limited mortality, while larger droplets (16 microns) were more effective. Smaller droplets do not as readily impinge on surfaces. Measurements of aerosol treatments in food facilities revealed spatial variation in efficacy that was correlated with uneven distribution of aerosol droplets. Inside buildings like mills, processing plants, and warehouses, distance from release point and structural features which block the movement of aerosol droplets both contributed to reduced number of droplets and an overall decrease in size of droplets. Measurement of how droplets settle over time revealed that exposure times after application could be reduced from two or more hours to less than one hour, which is an economic benefit, since it reduces the time a food facility needs to stop operation to apply the treatment. The lost production time associated with treatments typically exceeds the cost of the treatment itself. Different aerosol release strategies influence droplet distribution and can improve the evenness of droplet coverage. This research provides important insights into how aerosol applications can be applied more effectively and at a lower cost while providing better pest management.

2. Netting with incorporated insecticide as a new pest management tactic. Stored product insect infestations lead to contamination issues and average product loss estimates of up to 30%, so preventing insects from entering structures where food is processed or stored is critical. ARS scientists in Manhattan, Kansas, demonstrated that netting material impregnated with a reduced risk insecticide (deltamethrin), originally developed as bed nets for control of mosquitos that spread malaria, has potential for preventing stored product insect infestations. For netting to be an effective tool it must cause a response after only short periods of time in contact with netting. In laboratory testing, short-term exposure to netting did not cause immediate mortality and openings in netting allowed insects to pass through, but insect movement after exposure was greatly reduced. For a variety of pest species and both adults and immature stages, exposure to netting successfully reduced movement by 2–3-fold and stored product insects were unable to reach food as close as 10 inches away. After the initial reduction in mobility, most insects eventually succumb to the effects of insecticide. In larger scale tests, netting prevented food infestation when netting was placed as a barrier between where insects were released and where bagged food was placed. Netting with incorporated insecticide has potential application as a covering over vents and windows to intercept stored product insects as they immigrate from the surrounding landscape. Larger mesh size should increase airflow and reduce dust accumulation which avoids issues found with netting that is fine enough to physically exclude stored product insects. Netting that incorporates insecticide is a promising management tactic that can be layered onto existing pest management programs to prevent pest infestations and need for other more costly treatments such as fumigation.

3. Reference quality insect genome assemblies and genetic resources developed. Current DNA sequencing technology does not allow the genome to be sequenced all at once, so researchers have to align and merge DNA fragments to reconstruct the original sequence in a process called genome assembly. DNA sequencing can be done using short reads or long reads, short reads are less expensive to generate and work better with poorer quality DNA than long read sequencing. Researchers have struggled to obtain high quality genome assemblies using short read sequencing, because short read sequencing assemblies tend to be error prone and incomplete. ARS researchers in Manhattan, Kansas, demonstrated that assemblies of long read and long-range sequencing data resulted in reference quality genome assemblies (assemblies that contained all genes and were assembled at the chromosome level). A limitation encountered in obtaining long read sequencing and reference quality genome sequences was the need to extract DNA that was not fragmented or damaged. A method was developed to obtain consistent high-quality long genomic DNA from insects. This method was used to isolate genomic DNA from six insects, which were sequenced by PacBio long read sequencing, and resulted in chromosome level reference genomes for four stored product insects and two cricket species. Annotation of these genomes has highlighted new gene pathways that may be targeted for control and this approach was also used as part of a collaborative project with industry and North Carolina State University cooperators to improve insects as a food crop, addressing the need for expanded protein resources for animals. These efforts will help the development of new high-quality genome resources for insects that can be used to understand insect biology, identify novel targets for future pest management tools, and improve insects as a food crop.

U.S. DEPARTMENT OF AGRICULTURE

Stored Product Insect and Engineering Research: Manhattan, KS