Location: Livestock Arthropod Pest Research Unit
2024 Annual Report
Objectives
Objective 1: Determine parameters such as tick range, movement and suitable habitats, to produce models of the risk of tick-borne disease outbreaks, and potential for introduction of invasive ticks in response to climate change and other perturbations.
Objective 2: Develop methods to prevent, eradicate and control introduction of exotic ticks.
Approach
Ticks are a major threat to the livestock industry and human health. Other than cattle fever ticks, Rhipicephalus (Boophilus) microplus and R. annulatus, threats to livestock by high-consequence foreign pests are always present and one example of this is the recent discovery of the Asian longhorned tick, Haemaphysalis longicornis in seventeen states with an eastern boundary from Rhode Island south to North Carolina and a western boundary from Missouri south to Arkansas. There are other potentially invasive tick vectors (e.g., Amblyomma variegatum, Hyalomma spp., Rhipicephalus appendiculatus) and species that are expanding their ranges within the United States (e.g., A. americanum, A. maculatum, A. mixtum). Likewise, there are high-consequence foreign tick-borne pathogens, like African swine fever, that could devastate U.S. animal agriculture if their emergence involved transmission by native tick species.
The research addresses the following research components in the 2019-2024 Veterinary, Medical, and Urban Entomology National Program (NP 104) Action Plan: Component 1: Veterinary Entomology, Problem Statement 1A Improved Integrated Pest Management of Ticks of Veterinary Importance and Component 2: Medical Entomology, Problem Statement 2D Improved Surveillance and Control of Ticks of Medical Importance. This research addresses ARS Performance Measure for Goal 4.3: Provide scientific information to protect animals, humans, and property from the negative effects of pests and infectious diseases. Develop and transfer tools to the agricultural community, commercial partners, and government agencies to control or eradicate domestic and exotic diseases and pests that affect animal and human health.
Progress Report
Project #3094-32000-044-000D, Management of Ticks of Veterinary Importance, began in fiscal year (FY) 22 due to a realignment Program Direction and Resource Allocation Memo (Nov. 2021). The two objectives in this project were transferred to this project from Project #3094-32000-042-000D, Integrated Pest Management of Cattle Fever Ticks, which has had critical vacancies since FY20.
Objective 1: The interaction and response of ticks to biotic and abiotic factors was investigated over the course of this project, including the impact of Gulf cordgrass and soil salinity on tick survival. An ARS scientist at Edinburg, Texas, demonstrated that Gulf cordgrass aids in tick survival by providing shade that is not available in an otherwise uncovered landscape. Further, humidity and soil moisture in coastal regions was shown to impact tick egg survival. Ant and spider species were observed to exhibit predatory activity against the Cayenne tick and a soft tick species, providing some insight into the role of native species in biocontrol. An ARS scientist at Edinburg, Texas, collaborated with the University of Wisconsin-Madison and the University of Delaware to investigate local populations of the blacklegged tick throughout the U.S. and to characterize the sequence diversity of a virulence gene from the bacterium that causes Lyme Disease, respectively. These collaborations improved our understanding of blacklegged tick movement patterns and the potential risk of infection associated with different variants of the bacterial virulence gene.
Objective 2: Lone star ticks and longhorned ticks are invasive species that impact livestock health, and strategies for controlling these ticks have been the focus of studies throughout this project. Using contact and immersion laboratory bioassays, an ARS researcher at Kerrville, Texas, demonstrated the lethal impact of various desiccant dust products on immature and adult stages of the lone star tick. These results suggest that desiccant dust could be used on a limited basis for tick control. Studies throughout this project also characterized an enzyme (acetylcholinesterase) that is secreted in lone star tick saliva and is also present in the tick brain. While further characterization is necessary, this enzyme could play a role in the transmission and establishment of pathogens in vertebrate hosts. Understanding tick invasion routes is critical to targeting control measures. Given the invasive nature of the longhorned tick, an ARS researcher in Kerrville, Texas, collaborated with Rutgers University to better understand the relationship of different longhorned tick populations in the United States. Three different genetic groups were identified, suggesting introductions into the U.S. from Korea, Australia, and Japan/New Zealand, all of which are the natural range of the longhorned tick. These results highlight using genetic tools to monitor tick population expansions in the U.S.
Accomplishments
1. Development of adult lone star ticks and blacklegged ticks feeding on white-tailed deer. Blacklegged ticks and lone star ticks are of veterinary and medical importance because they are known to transmit disease-causing pathogens, and white-tailed deer are the main bloodmeal source for the adults of these species. Although important to the tick life cycle, only a few studies have described the biology of these ticks upon feeding on this host. Scientists at Texas A&M University collaborated with an ARS scientist at Kerrville, Texas, to experimentally infest white-tailed deer with adult pairs of either blacklegged ticks or lone star ticks to understand these tick-host relationships better. The study expanded on previous collaborative work by this group in which they developed a protocol to artificially infest naïve white-tailed deer with ticks and restrict host grooming throughout the infestation. The number of days for females to become engorged, the weight of engorged females, the length of time to deposit an egg mass, the weight of the egg mass, and the number of eggs laid per tick were recorded for both species. These biological data will be incorporated within dynamic computational models to determine how white-tailed deer influence blacklegged and lone star tick populations in nature. This information is important for understanding how to target on-host host treatments against these tick species.
Review Publications
Baker, A.S., Persinger, K.A., Olafson, P.U., Mulenga, A.O., Johnson, T.L. 2023. Feeding and reproductive parameters of adult female blacklegged ticks (Acari: Ixodidae) and lone star ticks (Acari: Ixodidae) parasitizing white-tailed deer (Odocoileus virginianus Zimmermann). Journal of Medical Entomology. https://doi.org/10.1093/jme/tjad144.
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.
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.