Location: Insect Control and Cotton Disease Research
2022 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 fiscal year (FY) 2022 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 imagery obtained from satellites (Landsat 7 & 8, and Sentinel 2A & 2B) with different levels of resolutions. 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 prototype boll weevil pheromone lures were developed and aged under controlled and various field conditions. Based on those results, the most promising prototype was evaluated against the standard lure used in eradication programs. Compared with the standard lure, the prototype dispenser generally released more pheromone and standard lure, and the prototype dispenser tended to release pheromone more uniformly over a two-week period. Discussions with the industry partner to commercialize the new dispenser are underway. In other work addressing Objective 1, previous genomic work by this project identified a single nucleotide polymorphism (SNP 317) that could be used to distinguish boll weevils from thurberia weevils and other weevil species commonly captured in traps. TaqMan assays were conducted by three independent labs [ARS, the Animal and Plant Health Inspection Service/USDA (APHIS), and Texas A&M University] to validate the accuracy of the SNP in distinguishing boll weevils from the other focal weevil species collected throughout the Americas or obtained from museum specimens. Overall, the SNP was >98% accurate in identifying boll weevils and thurberia weevils. 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. 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 surveys of stink bugs and plant 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 sorghum. Surveys of stink bug species in cotton and soybeans are ongoing; the predominant species observed thus far in each of the crops appear to be same as those observed in FY 2021. Efforts are underway to identify pathogens carried by these insects, particularly those collected from cotton. 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 that are commonly used as an ingredient in insect repellents. 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 derivative had minimal impact on corn earworm larval development and survival. However, plants expressing the alcohol derivative did adversely affect 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 to help expedite the development of DNA markers that can be used to efficiently introduce nematode resistance into commercially valuable Upland cotton lines.
Accomplishments
1. Feeding apparatus of the southern green stink bug. Stink bugs use needle-like mouthparts known as stylets to transmit plant pathogens and to feed on various plant structures. The mouthparts are composed of an outer pair of stylets which encompasses an inner pair of stylets to form the feeding apparatus. Although the external characteristics of the stylets are known, the internal components, including nerve bundles, have not been reported. ARS researchers at College Station, Texas, used transmission electron microscopy to obtain high resolution images of the internal components of the stylets. The images showed a counterclockwise rotation of the feeding apparatus throughout the entire length of the mouthparts. The images also revealed two types of nerve bundles within the outer stylets and suggested the presence of nerve bundles within the inner stylets, which have heretofore been believed to be void of nerves. These findings improve our understanding of the stink bug needle-like feeding apparatus and, more importantly, provides additional insight on its relationship with the insect's internal anatomy, feeding behavior, and pathogen transmission.
2. Insect herbivory influences extrafloral nectar content in cotton. It is generally accepted that cotton plants produce extrafloral nectar on leaves and reproductive structures to attract parasitoids and predatory insects such as ants. Cotton generally produces more nectar in the bracteals of fruiting structures than in leaves, but when plants are attacked by herbivores, nectar production in leaves increases substantially in response to herbivory. ARS researchers at College Station, Texas, in collaboration with Texas A&M University, established how foliar herbivory systemically changes the carbohydrate composition of bracteal nectar and how these changes subsequently affect ant foraging behavior. Foliar herbivory significantly increased the sucrose content of bracteal nectar while glucose and fructose content remained unchanged. Although sucrose content has been shown to influence ant foraging behavior in other crops, no difference in ant foraging behavior was observed in the field using mock nectar solutions varying in sucrose content. These findings raise new questions regarding the evolutionary relationship between ants and nectar production in cotton, and represent a significant contribution to cotton host-plant relationship research that may be exploitable in developing new cotton types that are resistant to damage from arthropods and other pests.
3. Resistance associated with facultative fungal endophytes in cotton. Cotton plants treated as seeds with facultative fungal endophytes (FFE) are known to deter some insect pests from feeding on the plants, or exhibit a negative effect on the survivorship and development of other insects. However, the underlying mechanism of "resistance" associated with FFE treatments remains unknown. One of the most plausible explanations is that FFEs cause cotton plants to produce more glandular terpenoid aldehydes (e.g., gossypol), which are well known to play an important role in defending cotton plants against insect pests and pathogens. ARS researchers at College Station, Texas, in collaboration with Texas A&M University, measured the terpenoid aldehyde content in the leaves of cotton plants treated with and without FFEs, and before and after herbivory. Given that terpene aldehyde content did not differ between FFE-treated and non-treated plants before and after herbivory, our findings suggest some other mechanism is responsible for the benefits associated with FFE seed treatments. This work is a significant contribution toward a better understanding of how living cotton plants interact with fungi to achieve resistance to damaging pests.
Review Publications
Perkin , L.C., Perez, J.L., Suh, C.P. 2021. The identification of boll weevil, Anthonomus grandis grandis (Coleoptera: Curculionidae), genes involved in pheromone production and pheromone biosynthesis. Insects. 12(10). Article 893. https://doi.org/10.3390/insects12100893.
Gale, C.C., Lesne, Pierre, Wilson, C., Dickens, C., Helms, A., Suh, C.P., Sword, G.A. 2021. Foliar herbivory increases sucrose concentration in bracteal extrafloral nectar of cotton. PLoS ONE. 16(10). Article e0258836. https://doi.org/10.1371/journal.pone.0258836.
Perkin, L.C., Bell, A.A., Hinze, L.L., Suh, C.P., Arick II, M.A., Peterson, D., Udall, J.A. 2021. Genome assembly of two nematode-resistant cotton lines (Gossypium hirsutum L.). G3, Genes/Genomes/Genetics. 11(11). Article jkab276. https://doi.org/10.1093/g3journal/jkab276.
Esquivel, J.F., Droleskey, R.E., Harvey, R.B. 2021. Rotation of the stylet bundle in the southern green stink bug, Nezara viridula (L.). Southwestern Entomologist. 46(4):867-878. https://doi.org/10.3958/059.046.0408.
Esquivel, J.F., Droleskey, R.E., Harvey, R.B. 2022. Innervation of the southern green stink bug [Nezara viridula (L.) (Hemiptera: Pentatomidae)] stylet bundle. Arthropod Structure and Development. 66. Article 101135. https://doi.org/10.1016/j.asd.2021.101135.
Gale, C.C., Suh, C.P., Puckhaber, L.S., Perez, J.L., Sword, G.A. 2021. Analysis of inducible terpenoids in cotton leaves to test for indirect plant-endophyte-herbivore interactions. Journal of Entomological Science. 57(1):114-118. https://doi.org/10.18474/JES21-07.
Gale, C.C., Suh, C.P., Perez, J.L., Lesne, P., Wilson, C., Kramer, Z., Madamba, C., Sword, G.A. 2021. Sampling volatile organic compounds from individual cotton leaves to test effects of fungal endophyte treatments. Southwestern Entomologist. 46(2):299-304. https://doi.org/10.3958/059.046.0201.
