Location: Cattle Fever Tick Research Unit
2025 Annual Report
Objectives
Objective 1 Develop population genetic and ecological methods to improve cattle fever tick surveillance.
Objective 2: Develop methods to control ticks using biocontrol, botanicals and new acaricides.
Approach
Cattle fever ticks, Rhipicephalus microplus and R. annulatus, are invasive pests that remain a threat to the livestock industry. They were eradicated from the United States in 1943; however, they remain established in Mexico and these populations tend to recolonize suitable habitats north of the Rio Grande. Cattle fever ticks transmit the microbes that cause bovine babesiosis and anaplasmosis. Significant cattle damage and economic loss would result if bovine babesiosis re-emerged in the United States. Research on new technologies to improve Integrated Pest Management (IPM) of cattle fever ticks is needed for implementation in the Cattle Fever Tick Eradication Program (CFTEP). This Program is operated in the Permanent Quarantine Zone established in south Texas along the Rio Grande to eliminate incursions from Mexico. The overall goal of this project is to conduct research on risk assessment and biology, surveillance, control, and monitoring and sustainability to improve integrated cattle fever tick management. The outcomes of this research will be effective, long-term adaptable technological solutions for the challenges that the CFTEP is facing. These include climate variability, acaricide resistance, involvement of native and exotic wildlife as alternative tick hosts, and the economic impact of tick outbreaks. The project will also benefit transdisciplinary efforts to achieve optimal health for animals, humans, and the environment, a concept known as “One Health”, by adapting this research to tick disease vectors expanding their range and exotic ticks that threaten animal and human health in the United States.
Progress Report
This report summarizes progress of research continued under the bridging project from the previous project, 3094-32000-042-000D, “Integrated Pest Management of Cattle Fever Ticks,” which began October 1, 2019 and terminated September 30, 2024, while the next five year research plan, 3094-10400-003-000D, “Improved Methods for the Management of Cattle Fever Ticks on Cattle and Wildlife,” completes the Office of Scientific Quality Review certification process.
Objective 1: Research efforts were continued to develop population genetic and ecological methods to improve cattle fever tick (CFT) surveillance.
To confirm past reports of host avoidance of CFT larvae, ARS researchers in Edinburg, Texas, used game cameras to evaluate avoidance behavior of six Hereford cattle released into a fenced pasture containing differentially infested and non-infested areas. The presence and density of CFTs was not observed to influence visits to infested areas. These observations suggested understanding host avoidance behavior is not feasible for CFT control.
Nilgai antelope and white-tailed deer (WTD) have been associated with the spread of CFTs near the permanent quarantine zone (PQZ) of South Texas, and USDA-APHIS constructed game fencing to limit movement of these hosts. ARS researchers in Edinburg, Texas, used global positioning system (GPS) satellite collars and passive integrated transponder (PIT) tag readers to track movement patterns of WTD and two nilgai populations in a National Wildlife Refuge system containing continuous game fences, finding this fencing effectively restricted movement in areas of high nilgai density. These results indicated game fencing can be an important tool for CFT eradication.
A 28.2-hectare property in the PQZ underwent moderate-to-severe surface fire in April, 2022, providing an opportunity to evaluate the utility of fire as a CFT management tool. Over the course of two years, ARS researchers in Edinburg, Texas, measured tick population regeneration in 60-meter zones adjacent to unburnt refugia. Tick numbers collected before and after this unintentional burn were not significantly different, suggesting fire may not be effective for tick management in South Texas. Further research is warranted with longer periods of pre- and post-burn tick collections over a larger area to improve understanding of the utility of controlled burns for CFT control.
To better understand CFT dynamics and optimize monitoring efforts, ARS researchers in Edinburg, Texas, studied the effects of abiotic and biotic variables on questing abundance of larval CFTs. Colony-reared CFT larvae were collected from experimentally infested mesquite-dominated plots and buffelgrass-dominated plots via tick drag during early mornings and afternoons to capture potential variations of questing activity. A negative association was observed between the numbers of larvae collected and temperature, while significantly greater numbers of larvae were collected from mesquite shaded areas than buffelgrass-dominated plots. Effects of habitat and environmental variables on larval abundance will be instructive for experimental monitoring of CFT larvae.
Objective 2: Research efforts were continued to develop methods to control ticks using biocontrol, botanicals and new acaricides.
In support of Objective 2, ARS researchers in Kerrville, Texas, completed studies to characterize mechanisms that confer fever tick resistance to organophosphate (OP) and macrocyclic lactone (ML) pesticide classes. The Rhipicephalus (Boophilus) annulatus acetylcholinesterase 1 gene (RannAChE1), the target of OP pesticides, was expressed in the baculovirus system to study the biochemical properties of this enzymatically active recombinant protein. Three RannAChE1 gene variants with similar enzymatic activity were identified, suggesting differential expression across developmental stages and tissues. Because a known mutation in mosquito AChE, G170S, confers resistance to OP and carbamate pesticides, a recombinant version of the tick enzyme that incorporates this mutation, RannAChE1-G170S, was tested and subsequently found resistant to OP and carbamate pesticides. In collaboration with researchers at Texas A&M University and University of Florida, ARS researchers identified five different variants of the Rhipicephalus (Boophilus) microplus glutamate-gated chloride channel gene, a target for glutamate and the ML, ivermectin. These variants are being evaluated for different ligand binding properties.
Mounting threats of CFT resistance to acaricides used by the cattle fever tick eradication program (CFTEP) necessitated efforts toward novel and alternative treatment regimens. First, in collaboration with the Texas Animal Health Commission, ARS researchers in Kerrville and Edinburg, Texas, are conducting a pasture study to evaluate the efficacy of eprinomectin against CFTs on experimentally infested cattle. Second, a project in collaboration with Texas A&M involved evaluation of the efficacy of CFT extracellular vesicles as vaccine candidates to reduce CFT performance in a pasture study. Third, a different collaboration with Texas AgriLife Research has focused on in vitro analysis of botanical acaricides and repellants, with additional barn and pasture studies planned to evaluate product safety and efficacy. Fourth, in collaboration with the University of Texas at San Antonio, ARS researchers at Kerrville, Texas, developed a liquid chromatography tandem mass spectrometry-based assay for quantification of an orally administered acaricide, diflubenzuron, in blood, plasma and sera from treated cattle and white-tailed deer. These developmental and applied studies each have the advantage of potential near-term implementation by the CFTEP.
Colonies of acaricide-resistant and -susceptible CFT strains are needed for studies to define and mitigate mechanisms of CFT resistance to different acaricides. To reduce effects of genetic bottlenecking, ARS researchers in Edinburg, Texas, have crossed long-term colonies of different acaricide-resistant CFT strains to improve vigor and prolong colony lifespan while preserving naturally selected alleles responsible for the different phenotypes of these strains. These four new multi-resistant strains are undergoing artificial selection for resistance to specific acaricides, and they will be instrumental for identification of genetic loci associated with acaricide resistance and for metabolic and pathogen transmission studies in collaboration with ARS researchers in Pullman, Washington. ARS researchers in Edinburg, Texas, are continuing to monitor acaricide resistance among CFT outbreaks in south Texas, watching for novel resistant or susceptible phenotypes to establish new colonies, and providing specimens to ARS researchers in Kerrville, Texas, for population genetics tracing of these outbreaks in collaboration with researchers at Northern Arizona University.
Tick genetics offer basic, long-term studies with the promise of novel approaches to management of acaricide resistance, as well as targets for designing supplemental control technologies. In collaboration with Texas A&M, ARS researchers in Edinburg, Texas, and Kerrville, Texas, constructed a new, reference-quality genome assembly based on DNA from a single male CFT, which allowed for identification of the CFT sex chromosome. Understanding genetic mechanisms of sex determination and differentiation in CFTs is expected to lead to novel approaches to CFT population control, such as products that interfere with tick reproduction or skew populations toward a single sex. Additionally, it is well-established that hybridization of R. annulatus males with R. microplus females will produce sterile male and fertile female hybrids, so ARS researchers in Edinburg, Texas, are crossing these CFT species to define the genetic mechanism regulating this hybrid sterility, with the goals of genetically engineering a strain with conditionally sterile males and to determine their utility for autocidal CFT control. Preliminary results indicated hybrid males with vestigial testes. Lastly, in collaboration with Baylor University, ARS researchers in Edinburg, Texas, are investigating nanoliposomes as vehicles for delivery of nucleic acids or toxic molecules for functional genetics or novel acaricides, respectively.
Biologic control with natural enemies of CFTs offers more alternatives to chemical acaricides. In collaboration with international partners in Vietnam, ARS researchers in Edinburg, Texas, optimized methods to collected parasitoid wasp-parasitized engorged female Rhipicephalus ticks from a region near where R. microplus may have originated. Colony-reared CFTs and other species of ticks from the United States have been exposed to parasitoid wasps emerging from the Vietnamese ticks. More work is needed to optimize conditions for establishing and maintaining parasitoid colonies. In vitro studies with entomopathogenic nematodes (EPNs) from different commercial sources were also tested with colony-reared CFT larvae. Different CFT mortality rates were observed after exposure to EPNs from these different commercial sources. Work is underway to explain this discrepancy, which is expected to improve our understanding of the mechanism of action of these EPNs against CFT larvae.
Accomplishments
1. 01 Sex chromosome identified in cattle fever tick genome. Fully characterized tick genetics would enable advanced, genome-informed approaches to population control, including sex-specific suppression methods. However, the sex chromosome of Rhipicephalus (Boophilus) microplus had not been genomically confirmed, hindering genetic control research. ARS scientists at Edinburg and Kerrville, Texas, constructed a new genome assembly from a single male R. (B.) microplus and identified the X chromosome by aligning sex-determination genes. This achievement represented the first genomic confirmation of cattle fever tick sex chromosome structure and laid the foundation for development of genetic control strategies.
2. 02 Analytical method developed for quantification of diflubenzuron in blood. Cattle fever tick-infested stray cattle and wild ungulates repeatedly cross the southern U.S. border. Diflubenzuron has been evaluated as an orally administered acaricide for use at bait stations to mitigate the spread of cattle fever ticks by wildlife and stray cattle from the permanent quarantine zone. ARS researchers at Kerrville, Texas, used liquid chromatography and tandem mass spectrometry to develop a quantitative assay for diflubenzuron in toxicologic samples. This assay is expected to be instrumental for future work to monitor host treatment with the acaricide.
Review Publications
Maestas, L.P., Zavala, M., Tidwell, J.P., Goolsby, J.A. 2024. Observations of tick predation by native insects in the Lower Rio Grande Valley. Subtropical Agriculture and Environments. https://drive.google.com/file/d/1SqB6wv9Cz15yrCmSDBr9u2tvd30JbnP2/view.
Mays Maestas, S.E., Maestas, L.P., Kaufman, P. 2025. Pathogen and host associations of soft ticks collected in South Texas. Journal of Medical Entomology. https://doi.org/10.1089/vbz.2023.0135.
Leal-Galvan, B., Kumar, D., Karim, S., Saelao, P., Thomas, D.B., Oliva Chavez, A. 2024. A glimpse into the world of microRNAs in hard ticks. Frontiers in Cell and Developmental Biology. https://doi.org/10.3389/fcell.2024.1460705.
Maestas, L.P., Goolsby, J. 2024. Effectiveness of a botanical pesticide in a motion activated 3-D Quik Hand™ sprayer for treatment of cattle for cattle fever ticks in a pen trial. Southwestern Entomologist. https://doi.org/10.3958/059.049.0427.
Jellick, G., Lohmeyer, K.H., Bach, S. 2025. Development of an analytical method for the analysis of diflubenzuron in whole blood, plasma, and serum using liquid chromatography tandem mass spectrometry. Journal of Chromatography B. https://doi.org/10.1016/j.jchromb.2025.124506.
Maestas, S.M., Tidwell, J.P., Zavala, M., Goolsby, J.A., Maestas, L.P. 2024. A new record of fleas from nilgai antelope in south Texas and fleas from other wildlife. Journal of Medical Entomology. https://doi.org/10.1093/jme/tjae116.
Tidwell, J.P., Bendele, K.G., Bodine, D.M., Holmes, V., Johnston, J., Saelao, P., Lohmeyer, K.H., Teel, P., Tarone, A. 2024. Identifying the sex chromosome and sex determination genes in the cattle tick, Rhipicephalus (Boophilus) microplus. Genes, Genomes, Genetics. https://doi.org/10.1093/g3journal/jkae234.