Location: Insect Control and Cotton Disease Research
2023 Annual Report
Objectives
Objective 1: Develop improved boll weevil monitoring/detection technologies, and molecular tools to accurately and rapidly distinguish boll weevils from other weevil species and to determine the geographical association of boll weevils.
Subobjective 1A: Determine feasibility of using satellite imagery for early detection of cotton fields to support boll weevil eradication programs.
Subobjective 1B: Prolong attractiveness of boll weevil pheromone lures.
Subobjective 1C: Develop genomic tools to accurately identify boll weevils and to determine geographical source(s) of re-infestations.
Objective 2: Understand the biological processes and ecological functions of lepidopteran and piercing-sucking insects and determine the nature of their agronomic importance in cotton and other field crops.
Subobjective 2A: Identify the hemipteran complex in a production area following boll weevil eradication.
Subobjective 2B: Elucidate propensity for hemipteran insects to acquire, harbor, and transmit FOV race 4 and related pathogens to cotton bolls.
Subobjective 2C: Evaluation of Bacillus velezensis LP16S as a potential entomopathogenic agent for stink bugs.
Objective 3: Develop novel pest management techniques that include use of natural host plant volatiles.
Subobjective 3A: Exploit natural plant defense traits to reduce insect pest abundance and feeding damage in cotton.
Approach
Novel and ecologically based management of field crop pests is critical for sustaining agricultural productivity/health and for reducing costs and environmental consequences associated with reliance on chemical pesticides. This project focuses on: 1) development of remote sensing techniques, pest trapping/monitoring systems, and genomic tools to rapidly and accurately detect host plant distributions, pest identity, and pest abundance; 2) improved knowledge on the transmission of plant pathogens by piercing/sucking insect pests; and 3) exploitation of host plant defense chemicals to reduce pest damage. Project objectives will be accomplished through three main research areas that lead to development of: 1) technologies to improve detection of pests and host plants; 2) improved knowledge and methods to better understand the multitrophic interactions among insect pests, plant pathogens, and host plants; and 3) novel pest management technologies and strategies that are target-specific, environmentally safe, and effective. Results of project research are expected to provide boll weevil eradication programs, producers, and crop consultants with the appropriate scientific knowledge and technologies to make effective pest management decisions with minimal environmental impact. This project combines entomological, molecular, and genomic expertise to create a research program that defines the distribution and abundance of host plants and insect pests, how insect pests transmit plant pathogens and infect target crops, and how pest activity and feeding damage can be reduced by the use of natural plant defense volatiles.
Progress Report
Work by this project in FY 2023 resulted in significant progress in using remote sensing technologies to detect cotton fields, developing and evaluating new pheromone dispensers for the boll weevil, developing molecular-based diagnostic tools to distinguish boll weevils from other weevil species, understanding the role of stink bugs and plant bugs as vectors of cotton pathogens, and developing novel pest management technologies based on exploitation of cotton defensive compounds. In work addressing Objective 1, different image classification and processing methods, including machine learning techniques, were compared for early identification of cotton fields using satellite imagery (Landsat 7 & 8, and Sentinel 2A & 2B). Best methods were identified, and transfer of associated technology to the Texas Boll Weevil Eradication Foundation is underway. In cooperation with an industry partner, new longer-lasting prototype boll weevil pheromone lures were developed; studies are underway to evaluate the most promising prototype against the standard lure used in eradication programs. In other work addressing Objective 1, a molecular assay based on single nuclear polymorphisms (SNPs) was developed in collaboration with academic and USDA-Animal and Plant Health Inspection Service (APHIS) partners to distinguish boll weevils from thurberia weevils. The assay was >98% accurate in differentiating these two similar looking species, and was recently adopted by USDA-APHIS to confirm the identity of suspect boll weevils captured in eradication programs or intercepted at U.S. ports of entry. Complementary to this work, a similar molecular tool was developed to identify the geographical source of boll weevil re-infestations. Collectively, this work provides the foundation for the development of a broader molecular-based tool to rapidly and accurately differentiate the boll weevil from other similar looking weevils, and to identify potential geographical sources of boll weevil re-infestations. Work addressing Objective 2 provided a clearer understanding of the interactions between stink bugs and cotton pathogens, and the mechanisms by which stink bugs obtain and transmit pathogens that cause disease in cotton. Field surveys of stink bugs and plant bugs in local major crops established that the brown stink bug was the predominant species in cotton, while the brown and red-shouldered stink bugs were the predominant stinkbug species in corn. The rice stink bug and southern green stink bug were the main species in sorghum and soybean, respectively. Efforts are underway to identify pathogens carried by these insects, particularly those collected from cotton, and to determine whether stink bugs can transmit the Fusarium wilt race 4 pathogen (Fov4) to cotton bolls. Work under Objective 3 developed a tri-species cotton hybrid that produces three unique caryophyllene derivatives; caryophyllenes are a type of chemical (sesquiterpene) produced by higher plants and that are commonly used as an ingredient in insect repellents. However, based on small-scale field studies, plants expressing the caryophyllene alcohol or acetate derivatives had negligible impact on thrips injury on cotton. Laboratory studies also indicated that the caryophyllene derivatives had minimal impact on corn earworm larval development and survival. Conversely, plants expressing the alcohol derivative adversely affected fall armyworm larval development under laboratory conditions, and aphid reproduction and colonization on cotton plants under both laboratory and field conditions. Breeding efforts are underway to incorporate the caryophyllene alcohol derivative into previously developed nematode-resistant cotton germplasm lines that also have been shown to possess some level of resistance to the Fusarium wilt disease. To complement this breeding effort, the genomes of two nematode-resistant lines of cotton (BAR 32-30 and BARBREN-713) were sequenced and assembled. Efforts are now underway to sequence and assemble the genome of the most recent parental line (PSC-355) that was used to develop the nematode-resistant lines; success in this effort will expedite development of DNA markers that can be used to efficiently introduce the caryophyllene alcohol derivative, and nematode resistance, into commercially valuable Upland cotton lines.
Accomplishments
1. High quality reference genome for the boll weevil. The boll weevil has arguably been the most destructive pest of commercial cotton in the United States since it was first detected in Texas in 1892 and began its spread throughout the U.S. Cotton Belt. Although national eradication efforts have essentially eliminated this insect pest in the United States, eradication progress in South Texas and Tamaulipas, Mexico, have been at a standstill for the past decade. Consequently, remaining boll weevil populations continue to pose a threat to previously eradicated areas, and there is concern that boll weevils may develop resistance to insecticides. Thus, there is a need to identify or develop alternative boll weevil management strategies that are safe and effective. ARS researchers at College Station, Texas, as part of the Ag100 Pest Initiative, sequenced, assembled, and annotated the boll weevil genome. The high-quality reference genome will be foundational to gaining a better understanding of boll weevil biology and ecology, genetic diversity, and for identifying novel genes that may be targeted or exploited with gene disruption technologies (e.g., CRISPR, RNAi) to develop alternative boll weevil management strategies that are safe, effective, and target specific.
2. Molecular tool to identify boll weevils. Although the boll weevil has been eradicated from the United States with the exception of the southernmost portion of Texas, eradication programs in cotton-producing states continue to operate pheromone traps to detect possible boll weevil re-infestations. These traps occasionally capture other similar looking weevils such as the thurberia weevil, which is a variant of the boll weevil but not a pest of commercial cotton. Non-pest weevils misidentified as boll weevils could lead to unnecessary and costly mitigation efforts. Conversely, misidentification of boll weevils could delay or preclude necessary remedial actions. ARS researchers at College Station, Texas, in collaboration with academic and USDA-Animal and Plant Health Inspection Service (APHIS) colleagues, developed a single nuclear polymorphism (SNP)-based TaqMan assay that can rapidly and accurately determine whether a weevil is a boll weevil or a thurberia weevil. This molecular tool was recently adopted by USDA-APHIS and is currently being used to confirm the identity of suspect boll weevils captured in traps, or intercepted at U.S. ports of entry.
3. A biocontrol agent for stink bugs. Stink bugs continue to plague producers of cotton and other crops because they reduce yields through direct feeding damage and can transmit pathogens that cause plant diseases. Control of stink bugs in cotton typically requires repeated pesticide applications which can drive up production costs. ARS researchers at College Station, Texas, established that a bacterium, Bacillus velezensis LP16S, already in use to control sorghum fungal diseases, can significantly reduce mean survival and shorten stink bug longevity. Additional efforts to characterize B. velezensis LP16S efficacy on other stink bug biotic parameters (e.g., frequency and duration of feeding, effects on reproduction) are underway to better understand the potential and utility of this bacterium as a biological control agent of stink bugs. Success in this work will provide a complementary or alternative stink bug management strategy that is both environmentally sound and cost-effective.
Review Publications
Perkin, L.C., Hamons, K.L., Suh, C.P., Sword, G.A. 2023. Amplicon sequencing of plant material links cotton fleahopper to host plants. Insects. 27(1):1-9. https://doi.org/10.56454/WBSD2203.
Cohen, Z.P., Perkin, L.C., Sim, S.B., Stahlke, A.R., Geib, S.M., Childers, A.K., Smith, T.P., Suh, C.P. 2022. Insight into weevil biology from a reference quality genome of the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae). G3, Genes/Genomes/Genetics. Article jkac309. https://doi.org/10.1093/g3journal/jkac309.
Thompson, M.N., Grunseich, J.M., Marmolejo, L.O., Arguirre, N.M., Bradicich, P., Behmer, S.T., Suh, C.P., Helms, A.M. 2022. Undercover operation: belowground herbivory modifies systemic plant defense and repels aboveground foraging herbivores. Frontiers in Ecology and Evolution. Article 1033730. https://doi.org/10.3389/fevo.2022.1033730.
Pandeya, D., Campbell, L.M., Puckhaber, L.S., Suh, C.P., Rathore, K.S. 2022. Gossypol and related compounds are produced and accumulate in the aboveground parts of the cotton plant, independent of roots as the source. Plants. 257. Article 21. https://doi.org/10.1007/s00425-022-04049-0.
Perkin, L.C., Cohen, Z.P., Carlson, J.W., Suh, C.P. 2023. The transcriptomic response of the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), following exposure to the organophosphate insecticide malathion. Insects. 14(2). Article 197. https://doi.org/10.3390/insects14020197.
Hamons, K., Suh, C.P., Sword, G.A. 2023. Reassessing temporal patterns of cotton fleahopper, Pseudatomoscelis seriatus (Reuter), emergence from diapausing eggs. Southwestern Entomologist. 48(2):321-324. https://doi.org/10.3958/059.048.0204.
Raszick, Tyler J., Perkin, Lindsey C., Shirley, Xanthe A., Ruiz-Arce, Raul, Kramer, Zoey A., Suh, Charles P.-C., Sword, Gregory A. 2023. Source tracing of Anthonomus grandis captured in areas of the USA where the species had previously been eradicated. Journal of Pest Science. https://doi.org/10.1007/s10340-023-01656-y.
