Location: Insect Control and Cotton Disease Research
2021 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 under this project in Fiscal Year (FY) 2021 resulted in significant progress on 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 methods were compared for early identification of cotton and crop fields using imagery from manned aircraft and satellites (Landsat 7 & 8 and Sentinel 2A & 2B). Several image processing and classification methods were evaluated and best methods were identified; transfer of associated technology to the Texas Boll Weevil Eradication Foundation is underway. In cooperation with an industry partner, new prototype boll weevil pheromone lures were developed and aged under controlled and field conditions. The new prototypes released pheromone more uniformly than the current lures used in eradication programs, but additional field evaluations are needed to assess lures under a broader range of environmental conditions. In other work addressing Objective 1, boll weevils and other closely related species were collected throughout the Americas or obtained from museum specimens. Advanced genetic sequencing techniques were used to identify genetic markers (single nucleotide polymorphisms) that could be used to distinguish boll weevils from other weevil species commonly captured in traps. Collectively, this work provides the foundation for the development of a molecular-based tool for rapidly and accurately distinguishing boll weevils from other weevil species as well as identifying the likely geographic origin of captured boll weevils. 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. Ongoing survey of stink bugs in local major crops revealed that the brown and red shouldered stink bugs were the predominant stink bug species in corn, while the rice stink bug was the main species in milo; survey of stink bug species in cotton are underway. Work under this objective also revealed that the southern green stink bug and brown stink bug could acquire the Fusarium wilt race 4 pathogen (FOV4), but only the brown stink bug transmitted the pathogen 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 they are commonly used as an ingredient in insect repellents. Based on laboratory, greenhouse, and small-scale field studies, plants expressing the caryophyllene alcohol or acetate derivatives had negligible impact on thrips injury on cotton or corn earworm larval development and survival. However, plants expressing the alcohol derivative did adversely affect fall armyworm larval development, aphid population reproduction, and aphid colonization on plants. Efforts are underway to increase seed production of plants expressing these caryophyllene derivatives for larger-scale field trials, and the release of germplasm lines expressing one or more of these derivatives is expected in FY 2022.
Accomplishments
1. Fusarium wilt is vectored by stink bugs. Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is an emerging fungal pathogen that causes Fusarium wilt in cotton. FOV4 was first detected and confined to cotton fields in California, but this particular strain of Fusarium was recently detected in several cotton fields in West Texas and New Mexico. Spread of FOV4 throughout the U.S. Cotton Belt would be catastrophic because there are no effective control methods once the pathogen becomes established in fields. ARS researchers at College Station, Texas, demonstrated that some species of stink bugs can acquire and transmit FOV4 to cotton bolls while feeding. These findings are important because they document for the first time that stink bugs may serve as reservoirs and vectors of the FOV4 pathogen. Comprehensive management of stink bugs may be required to prevent or reduce the spread FOV4 from field to field.
2. Genetically distinguishing boll weevils from different geographical areas. Despite the success of the U.S. Boll Weevil Eradication Program, boll weevil populations that remain in southern Texas and northern Mexico, and to a lesser extent, in Central and South America, continue to pose a threat to previously eradicated areas in the U.S. If an area is re-infested with boll weevils, knowledge of the geographical origin of these weevils will be critical for developing appropriate regulatory and management policies and protocols to facilitate prompt eradication, and to prevent or minimize future re-infestations. ARS researchers at College Station, Texas, working with university and USDA-Animal and Plant Health Inspection Service collaborators, obtained boll weevil specimens from southern Texas, northern Mexico, and Argentina, and identified hundreds of genetic markers (single nucleotide polymorphisms) that can be used to differentiate boll weevil populations based on their geographic origin. This work is foundational to our goal of developing a set of diagnostic tools to determine if a weevil captured in a trap is a boll weevil or some other weevil species and, importantly, to identify the most likely geographical source of any invading boll weevils.
Review Publications
Perkin, L.C., Oppert, B.S., Duke, S.E., Suh, C.P. 2021. Assessment of DNA integrity from trap captured boll weevil (Coleoptera: Curculionidae) for use in a new PCR-based diagnostic tool. Journal of Economic Entomology. 114(3):1321-1328. https://doi.org/10.1093/jee/toab073.
Raszick, T.J., Dickens, M., Perkin, L.C., Tessnow, A., Suh, C.P., Ruiz-Arce, R., Boratynski, T.N., Falco, M.R., Johnston, J.S., Sword, G.A. 2021. Population genomics and phylogeography of the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in the United States, northern Mexico, and Argentina. Molecular Ecology. 14(7):1778-1793. https://doi.org/10.1111/eva.13238.
Hamons, K.L., Raszick, T.J., Perkin, L.C., Sword, G., Suh, C.P. 2021. Cotton fleahopper biology and ecology relevant to the development of insect resistance management strategies. Southwestern Entomologist. 46(1):1-16. https://doi.org/10.3958/059.046.0101.
Esquivel, J.F., Medrano, E.G. 2020. Retention of Pantoea agglomerans Sc1R across stadia of the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae). PLoS ONE. 15(12). https://doi.org/10.1371/journal.pone.0242988.
Suh, C.P., Spurgeon, D.W., Reardon, B.J. 2020. Reproductive and survival responses of overwintered boll weevils (Coleoptera: Curculionidae) to diet. Journal of Entomological Science. 55(1):58-68. https://doi.org/10.18474/0749-8004-55.1.58.
Park, J., Thomasson, A., Gale, C., Sword, G., Lee, K., Herrman, T., Suh, C.P. 2020. Adsorbent-SERS technique for determination of plant VOCs from live cotton plants and dried teas. ACS Omega. 5(6):2779-2790. https://doi.org/10.1021/acsomega.9b03500.
