Project : USDA ARS

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Research Project: Sustainable Management Strategies for Stored-Product Insects

Location: Stored Product Insect and Engineering Research

2018 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
Under Objective 1, “Identify and describe the functional genomics for physiological systems important to pest management”, significant progress has been made on obtaining sequence information for stored product insects. We now have draft genomes for the lesser grain borer, yellow mealworm, and rice weevil. The draft genomes have been analyzed for potential genes and are now in the process of manual annotation. Additionally, we have obtained the transcriptome for different developmental stages of the yellow mealworm, and analysis of differential gene expression is in progress. We also have perfected an extraction procedure for long and intact genomic deoxyribonucleic acid (gDNA) for long read sequencing. Based on this procedure, we are obtaining additional long read sequencing for male red flour beetle adults to improve the genome assembly and identify sequences associated with the Y chromosome. In addition to these three draft genomes, genome assemblies of seven other stored product insects were generated using short read sequences derived from 10X Chromium libraries, including cigarette beetle, warehouse beetle, drugstore beetle, khapra beetle, which has quarantine status in the United States, hide beetle, Indian meal moth, and confused flour beetle. High molecular weight DNA is currently being prepared from larger grain borer for 10X library prep and Illumina HiSeq X-ten sequencing. This insect is a major pest of corn and is commonly found in Mexico and Central America, with some recovery in the southern U.S., but with the potential to move more northerly. To facilitate gene annotations, transcriptomes from larvae, adults, and pupae are currently being generated and antennal transcriptomes are being prepared for each of the eight species to aid in the annotation of sensory genes that could be important for the location of food and mates. We continue to work towards oral ribonucleic acid interference (RNAi) in stored product beetles. Analysis of lesser grain borer populations from different regions of the United States using genotyping-by-sequencing (GBS) analysis was completed and collection of new lesser grain borer adults at different times of year for population genetic analysis is ongoing. Attraction to pheromone and kairomone cues by different red flour beetle strains and lines with antennal mutants was compared using different bioassays, and this information will be used as a foundation for subsequent genetic analysis of attraction. Antenna, whole body, and head transcriptomics from six populations of red flour beetle with differing behavioral responses to pheromone and kairomone lures have been collected and sequences will be compared for candidate genes involved in the insect’s sensory system. Targeted functional genomic analyses will follow to pinpoint genes involved in sensing volatile cues. Under Objective 2, “Develop and improve monitoring technologies, control tactics, and integrated pest management systems for stored product insects,” we conducted tests to show that efficacy of a commercial formulation of the insecticides pyrethrin + the insect growth regulator methoprene was inversely related to aerosol droplet size. As droplet size decreased mortality of adult stored product insects decreased, and residual efficacy of the aerosol particles on a treated surface decreased as well. We conducted studies evaluating different positions for releasing the aerosols in a pilot scale mill, to show how structural composition of milling facilities affects aerosol distribution. We also evaluated new reduced-risk insecticides to control insects in stored raw grains, and showed they could be used to reduce reliance on phosphine fumigant. We also assessed new packaging treatments that have either the insect growth regulator methoprene or the adult insecticide deltamethrin embedded into the packaging matrix. We assessed the utility of long-lasting insecticide netting to prevent the dispersal of stored product insects, and have found that it is very effective at reducing movement and impairing dispersal capacity of adult and immature stages. These new developments in protective packaging and netting could be incorporated as alternatives to methyl bromide fumigation for food facilities. Experiments were conducted to evaluate cigarette beetle response to pheromone traps under different lighting conditions and experiments to evaluate warehouse beetle responses are being conducted. Mating disruption trial data from retail stores was analyzed and laboratory scale tests of mating disruption and mating delay were conducted. We have been involved in determining the optimal lure and trapping device for monitoring the presence of the khapra beetle, which is a quarantined pest in the United States. We assessed a range of potential attractants for inclusion in an attract-and-kill strategy to manipulate the behavior of stored products and provide control while decreasing insecticide inputs. Finally, we have also been involved in evaluating whether fungal volatiles may provide additional attractive cues, or whether specific density-mediated cues may provide effective repellents in a push-pull management strategy.

Accomplishments
1. Application position and structural features affects pattern of aerosol insecticide efficacy. The use of aerosol insecticides as part of integrated pest management programs is becoming more widely adopted in food facilities such as flour mills. However, the method of application and the complex structural features within a facility can impact how insecticide particles travel and settle on surfaces and therefore impact the variation in efficacy obtained. Agricultural Research Service (ARS) scientists in Manhattan, Kansas, conducted field trials inside a flour mill, using adults of the confused flour beetle. The scientists released an aerosol insecticide from different locations within the mill and by splitting the release among all the locations. The application method significantly impacted the pattern of insect mortality obtained. The number of beetles affected by the insecticide at locations at various points in the mill varied depending where and how the aerosol was applied. However, regardless of the treatment location there were still areas of a mill where little efficacy was observed, due to barriers created by structures and equipment, so further improvement in application methods is needed. A better understanding of the impact of these factors will improve the effectiveness of aerosols when they are used in management programs. Flour mill managers and pest management professionals can use this information to target specific locations within a mill where aerosol distribution may be limited. Aerosols could be applied more efficiently and more economically.

2. Insecticide-treated netting exposure reduces dispersal by stored product insects. Every year, producers experience 10-30% loss of their commodities after harvest during the storage, transportation, processing, and marketing of food products. Long-lasting insecticide netting has been used to reduce the spread of malaria since the 1990s. More recently, it has been used to manage pests in pre-harvest agriculture in tree fruit and post-harvest agriculture with stored product pests. Because stored product insects are too small for the netting to be an effective physical barrier, Agricultural Research Service (ARS) scientists in Manhattan, Kansas, conducted studies to assess whether brief contact with the netting resulted in reductions in mobility and dispersal capacity of red flour beetle and lesser grain borer, two cosmopolitan and economically destructive stored product pests. Brief 1-minute (min) exposures resulted in the same 3-4-fold decrease in mobility as longer 10-min exposures to insecticide netting compared to controls without insecticide. Similarly, dispersal capacity of red flour beetle was reduced by 20-fold, while dispersal was completely absent in the lesser grain borer after testing thousands of individuals; controls in both cases dispersed without issues. Overall, our results contribute significantly to the prospect of diversifying integrated pest management programs for stored product insects. Results show how mill managers can use the insecticide-treated netting by potentially providing a barrier for insect dispersal into bagged and packaged goods. Using this targeted approach could reduce the need for whole-plant treatments with fumigants, which would result in cost savings.

3. Rapid diagnostic test for evaluation of phosphine resistance. Phosphine is a gas used as a fumigant for the control of insect pests in grain and other materials, but resistance to phosphine has been increasing worldwide. Determining levels of resistance prior to treatment is important in order to determine the phosphine concentration or exposure time that will be effective or if alternative treatments are needed. There are several protocols to detect phosphine resistance, but many are labor, equipment, and time intensive procedures. ARS scientists in Manhattan, Kansas used a new rapid diagnostic test to characterize how quickly two strains of the red flour beetle, one susceptible and one resistant to phosphine, respond to different concentrations of phosphine. At 1000 parts per million (ppm) phosphine, the majority of the adults from the susceptible strain was quickly immobilized after 15 minutes (min), but the majority of the adults from the resistant strain was still active after exposure up to 90 min. At greater phosphine concentration, 3000 ppm, a larger percentage of immobilization occurred with the susceptible strain and the majority of the adults of the resistant strain were immobilized after 90 min. When beetles were removed from exposure to phosphine, the vast majority of the adults of the susceptible strain never recovered and died. In contrast, for the resistant strain, most adults recovered to normal activity after being removed from both the 1000 and 3000 ppm phosphine treatment. The initial immobilization of active beetles during exposure to phosphine and the recovery after exposure both appear to be useful rapid methods to detect phosphine resistance and will be helpful in field evaluations. This method will also be useful for genetic selection and functional genomics research, since the same individual beetles identified as resistant can be used in subsequent procedures.

U.S. DEPARTMENT OF AGRICULTURE

Stored Product Insect and Engineering Research: Manhattan, KS