Location: Cattle Fever Tick Research Unit
2024 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
Objective 1: Research efforts to develop population genetic and ecological methods to improve cattle fever tick (CFT) surveillance were conducted over the life of this project. Studies in collaboration with scientists at the Pathogen and Microbiome Institute, Northern Arizona University, focused on integrating CFT genetic data with geographic information system (GIS) tools to enhance understanding of the geographic source and population structure of CFT causing outbreaks. The resulting sequence variations that are associated with CFT resistance to permethrin as well as sequence variations that can be used to compare CFT populations within and between U.S. and Mexico are now generated year-round as outbreaks occur. This critical information is used by the USDA-APHIS-VS Cattle Fever Tick Eradication Program (CFTEP) and the Texas Animal Health Commission (TAHC) in support of their programmatic CFT eradication efforts. To enhance GIS-based tools for CFT surveillance, ARS researchers partnered with the ARS Partnerships for Data Innovations (PDI) team to complete the development of a FieldMaps tool for the CFTEP to streamline data entry and provide real-time access to the CFT infestation database. This FieldMaps tool is being utilized by the CFTEP with over 100 CFTEP field inspectors in eight different county work areas using the tool for real-time entry of CFT infestation data. CFTEP inspectors in the field can record CFT outbreak data from their phones directly to an online map layer that can be instantly accessed by program personnel and ARS researchers. This FieldMaps tool has drastically decreased data entry workflow, enabled rapid identification of at-risk areas in south Texas, and allowed for faster programmatic decision making. ARS researchers also maintain a decades old geographic information system (GIS) database that tracks and archives CFT infestation location and collection data from cattle, equine, and wildlife hosts. This GIS database is used by ARS researchers and the CFTEP to inform operational decisions inside and outside of the Permanent Quarantine Zone (PQZ) in south Texas.
Population models that explore the impacts of host, host habitat use, and eradication practices on CFT population dynamics were developed during this 5-year project. Eradication efforts by the CFTEP along the U.S.-Mexico border in south Texas are complicated by the involvement of wildlife hosts including white-tailed deer and nilgai antelope. ARS scientists in Kerrville, Texas, in collaboration with partners at Texas A&M University, developed two CFT population models that explored infestation scenarios. The first model assessed the potential effects of host species composition and host habitat use patterns on CFT infestations and assessed the risk for CFT infestations across the landscape in the PQZ. The second model investigated the potential role of nilgai in sustaining CFT populations by simulating infestation and eradication scenarios. The developed models generate near-real-time infestation forecasts that can be used to predict and prevent wildlife impacts on CFT eradication efforts.
In further support of this objective, ARS researchers in Edinburg, Texas evaluated several methods to mechanically collect larval CFT from the environment including the “tick-vac” and the “tick bot”. Field studies were conducted in naturally infested CFT habitats to compare these two collection methods to the previously tested “tick trouser” method. Additionally, two other novel tick sampling methods, sampling bovine feces for detection of biochemicals as an indicator of tick infestation and using Raman spectroscopy to sample for tick fecal residues on cattle, were developed and tested in collaboration with Texas A&M University. These methods are effective, non-invasive, and non-destructive technologies to detect tick infestations.
Objective 2. ARS researchers in Edinburg and Kerrville, Texas, developed novel methods to control CFT that utilize biocontrol strategies, botanical compounds, and novel acaricides. Acaricides are an important tool for use in mitigating CFT world-wide. Novel long-acting acaricide formulations are continuously needed to reduce the number of systematic treatments needed to manage CFT infestations. Barn trials with stanchioned cattle were continued as part of an ongoing collaboration with an animal health industry partner to evaluate the therapeutic and residual efficacy of a pour-on formulation of fluralaner for controlling CFT, Amblyomma americanum, and A. mixtum infesting cattle. Additionally, pasture studies were conducted in collaboration with Texas A&M University to evaluate the control efficacy of novel dosing regimens of macrocyclic lactones (doramectin, eprinomectin, and moxidectin) against CFT as well as the synergistic effect of combining these acaricides with the Bm86 vaccine. Studies are currently underway to further evaluate the efficacy of two injectable eprinomectin repeated dosing regimens for use by the CFTEP and TAHC to control CFT.
Alternatives to traditional acaricides are also needed for use in the CFTEP, in particular as concerns about acaricide resistance and overuse increase. Researchers in Kerrville and Edinburg, Texas, evaluated natural botanicals, abrasives, and desiccants against CFT for use in sensitive wildlife areas. In vivo and in vitro studies were completed to evaluate the efficacy of commercially available desiccant dusts (Deadzone®, Drione®, and EcoVia®) and botanical products (nootkatone, cedar oil, and Stop the Bites®) for controlling CFT. Laboratory and cattle stall trials demonstrated that desiccant dust products, Deadzone (renamed Celite 610, a diatomaceous earth product), Drione (silica gel + pyrethrins + piperonyl butoxide synergist), and EcoVia (silica gel + thyme oil), with and without bioactive botanical additives, when applied dry were strongly lethal to larval CFT in the laboratory and after being released on dust-treated cattle. Nootkaone and Stop the Bites® were found to be highly efficacious against CFT in the laboratory and in vivo testing of nootkatone to determine the effective treatment dosage for cattle is underway.
Throughout this project, remotely operated nematode sprayers were evaluated as a non-chemical control option for CFT. ARS scientists in Edinburg, Texas, worked closely with the Animal and Plant Health Inspection Service-Veterinary Services and ranchers in south Texas to conduct large-scale field tests of a nematode sprayer to eradicate CFT on free-ranging nilgai antelope. More than 100 sprayers were deployed over 5000 acres to apply entomopathogenic nematodes (Nemasys-R, BASF Co.) as the nilgai transited through fence crossings. Numbers of cattle fever ticks on nilgai were found to be significantly lower on nilgai at treated vs. untreated control ranches. This technology has been transferred to the CFTEP and will be utilized to treat nilgai and white-tailed deer within the PQZ. Additionally, remotely activated sprayers were utilized in a field study in Cameron County, Texas, to evaluate whether use of the sprayers at corn feeders impacted white-tailed deer use of the feeders. Camera observations indicated that use of the sprayers at the feeders, either only spraying water or the botanical pesticide Stop the Bites®, did not deter the deer from using the feeders indicating that remotely activated sprayers may be operationally feasible for use by the CFTEP for treating deer in south Texas. Additionally, a commercially built, remotely operated sprayer, the 3D Quikhand®, was shown to be effective in treatment of cattle with both Steinernema riobrave entomopathogenic nematodes or the botanical acaricide Stop the Bites®. This sprayer could potentially be used to treat CFT infested cattle or wildlife as they approach water troughs or fence gaps.
In a continued effort to track and mitigate acaricide resistance, ARS researchers in Edinburg, Texas, continually process incoming live CFT samples from outbreak premises in south Texas. Incoming viable engorged female CFT are allowed to lay eggs and the larval stages are then assayed with Larval Packet Tests against a panel of acaricides to determine levels of acaricide resistance. The degree of resistance is measured and reported weekly to CFTEP managers to assist with regulatory decisions. DNA samples from these ticks are also used to assay for genetically determined target resistance as well as using population genetic markers for traceback studies for the source of new outbreaks (in support of Objective 1).
In further support of this objective, ARS researchers in collaboration with international partners in Vietnam, Bulgaria, and Greece, developed and tested methods to collect Ixodiphagous parasitoid wasps using cattle infested with Rhipicephalus spp. ticks, including CFT. Preliminary DNA evidence indicates that Ixodiphagus wasps do parasitize Rhipicephalus spp. tick in Vietnam. Tick exposures were conducted in northern Vietnam and potentially parasitized Rhipicephalus spp. ticks, including CFT, were collected and kept alive or put into ethanol for emergence of the parasitoid for molecular screening. Live-exposed larvae, nymphs, and adults were brought back to the U.S. for visual analyses and molecular screening. Initial molecular screening detected the presence of Ixodiphagus parasitoids and emerged parasitoids have successfully been collected from the closely related species R. sanguineus. Additional CFT collections are planned in Vietnam to maximize the possibility of collecting parasitized CFT. Discovery and establishment of a specialist parasitoid for CFT could have significant impacts and enhance the efficiency and sustainability of the CFTEP in the transboundary region between Texas and Mexico.
Accomplishments
1. Nilgai antelope are not susceptible to infection with a virulent strain of Babesia bovis. Cattle fever ticks (CFT) transmit bovine babesiosis (BB) to cattle. This protozoal parasite can cause mortality rates up to 90% in previously unexposed cattle. In south Texas, CFT readily infest Nilgai in addition to cattle; however, their susceptibility to infection with BB is unknown. ARS researchers in Kerrville, Texas, in collaboration with Texas A&M University demonstrated that Nilgai do not display clinical signs of infection after inoculation with the merozoite or sporozoite stage of BB. This finding indicates that although Nilgai play an important role in the dissemination of CFT in south Texas, they do not play a significant role in the epidemiology of BB in south Texas.
2. Organic alternatives for cattle fever tick control. The cattle fever tick (CFT) is the most economically important tick worldwide. Traditional management of this tick depends on synthetic acaricides; however, the emergence of resistance has resulted in a need for novel compounds. ARS researchers in collaboration with Texas A&M University evaluated the efficacy of five organic compounds (nootkatone, Stop the Bites®, BioUD®, lavender oil, and cedarwood oil) for controlling CFT. Results indicate that NootkaShield™, Stop the Bites, and BioUD led to significant CFT mortality at low concentrations, had strong repellent properties, and significantly impacted CFT fecundity. These organic compounds show great potential for use as alternatives to synthetic acaricides for controlling CFT.
3. Off-host longevity of cattle fever ticks in south Texas. As part of the U.S. program to eradicate cattle fever ticks (CFT) Rhipicephalus (Boophilus) annulatus (RA) and R. (B). microplus (RM), from south Texas, premises infested with CFT are subject to regulatory oversight that includes acaricide treatment and pasture vacation. Current pasture vacation duration time is based on tick degree-day data far from south Texas. ARS researchers in Edinburg, Texas, in collaboration with Texas A&M University assessed the impact of thermal stress on the longevity of RA and RM larvae in south Texas pastures. Results demonstrated that RA can survive in the pasture for 142 days in shady habitat in the winter and 130 days in the summer. RM can survive in winter for 113 days in the shade and 103 days in exposed habitat. These results indicate that temperature is a key variable in off-host survival of RA, but not RM. These results suggest that a reduction in the Texas pasture vacation period from 9 to 6 months would be justified for RM, giving cattle producers additional time to access pastures for grazing.
4. South Texas nematodes control cattle fever ticks. Entomopathogenic nematodes are roundworms that parasitize and kill arthropods. ARS researchers in Edinburg, Texas, and Poplarville, Mississippi, evaluated the control efficacy of an entomopathogenic nematode from south Texas, Steinernema riobrave, for controlling larval cattle fever ticks (CFT). Weekly applications of in vitro-reared S. riobrave (BASF- Nemasys-R) sprayed on CFT-infested potted buffelgrass killed significantly more larval ticks than water or the no treatment check. Use of a native nematode species like S. riobrave that occurs in the south Texas environment and has few effects on native plants and animals may be an environmentally friendly option for mitigating CFT in the environment, especially in areas inhabited by threatened or endangered species.
Review Publications
Schoville, S.D., Dong, D., Paskewitz, S., Maestas, L.P., Tsao, J., Burke, R.L., Ginsberg, H. 2024. Genome resequencing reveals population divergence and local adaptation of blacklegged ticks in the United States. Molecular Ecology. https://doi.org/10.1111/mec.17460.
Goolsby, J., Maestas, L.P., Adamczyk Jr, J.J. 2024. Evaluation of the efficacy of Steinernema riobrave against Rhipicephalus microplus larvae at semi-field conditions. Southwestern Entomologist. https://doi.org/10.3958/059.049.0116.
Thomas, D.B., Gaff, H., Leal Galvan, B. 2023. Mechanical devices for census and detection of off-host larval ticks (Acari: Ixodidae) with emphasis on the cattle fever tick. Subtropical Agriculture and Environments. 74:13-20.
Arocho, C., Leal, B., Thomas, D.B. 2023. Degree-days and off host longevity of cattle fever ticks, Boophilus spp. (Acari: Ixodidae) in south Texas pastures. Journal of Economic Entomology. https://doi.org/10.1093/jee/toad237.
Johnson, T.L., Persinger, K.A., Taus, N.S., Davis, S.K., Poh, K.C., Kappmeyer, L.S., Laughery, J.M., Capelli-Peixoto, J., Lohmeyer, K.H., Ueti, M.W., Olafson, P.U. 2024. Nilgai antelope display no signs of infection upon experimental challenge with a virulent Babesia bovis strain. Parasites & Vectors. 17. Article 245.. https://doi.org/10.1186/s13071-024-06316-3.
Casey, T., Shifflett, S.A., Kennedy, A., Maestas, L.P., Ellis, V.A. 2024. Similar microbiome compositions of nymphal black-legged ticks (Ixodes scapularis) infected and uninfected with Borrelia burgdorferi in Delaware. Parasitology Research. https://doi.org/10.1016/j.ttbdis.2023.102139.
Showler, A. 2023. Interactions of gulf cordgrass, Spartina spartinae (Trin.) Merr. ex Hitchc., habitat with ixodids on the South Texas coastal plain. Environmental Entomology. https://doi.org/10.1186/s40068-023-00311-w.
Oliva Chavez, A. S., S. Guzman Valencia, G. E. Lynn, C. A. Rosario, D. B. Thomas, and T. L. Johnson. 2023. Evaluation of the in vitro acaricidal effect of five organic compounds on the cattle fever tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae). Exp Appl Acarol 89: 447-460.
Goolsby, J., Maestas, L.P., Garcia Iii, R., Cruz, M., Feria, T. 2024. Nilgai, Boselaphus tragocamelus and white-tailed deer, Odocoileus virginianus use of water troughs with and without remotely operated field sprayers for potential treatment of cattle fever ticks. Subtropical Agriculture and Environments. 74:21-25.