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ARS Home » Plains Area » Kerrville, Texas » Knipling-Bushland U.S. Livestock Insects Research Laboratory » LAPRU » Research » Research Project #434725

Research Project: Nilgai Modeling

Location: Livestock Arthropod Pests Research

Project Number: 3094-32000-039-93-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jul 1, 2018
End Date: Sep 30, 2019

Objective:
To carry out cooperative research to address the role of nilgai as a potentially confounding factor in cattle fever tick (CFT) eradication protocols. We hypothesize that the presence of nilgai antelope render tick eradication protocols focused exclusively on cattle, or on cattle and white-tailed deer (WTD), ineffective. One way research can test that hypothesis is by modeling cattle-nilgai-deer interactions. Besides assessing the impact on the efficacy of standard tick eradication protocols, the cattle-nilgai-deer interactions model will help determine how nilgai maintain cattle fever ticks across landscapes in south Texas. To address this knowledge gap, this project will: 1. Establish the threshold ratio of nilgai-to-cattle for sustaining cattle fever tick populations. 2. Assess overlapping habitat use by nilgai, cattle, and WTD in the formation of refugia for tick populations. 3. Determine whether sufficient spatial and temporal overlap exists between nilgai and cattle to support using treated cattle as a “trap host”. 4. Determine whether nilgai social behaviors associated with the distribution and habitats of communal dung piles could be exploited for tick suppression tactics.

Approach:
The current CFT simulation model will be further developed to meet the project objectives. The current model simulates CFT population dynamics in response to CFT control measures in the presence of cattle and/or WTD on hypothetical heterogeneous landscapes in south Texas. The model will be expanded 1) to include nilgai as an alternative host species and 2) to include rangeland landscapes in/around the CFT quarantine zone along the U.S.- Mexico border. To represent nilgai in the model, information on nilgai life history and ecology, including patterns of habitat use and efficacy as a CFT host will be analyzed. Results of these analyses will be used to estimate nilgai demographic parameters, to describe movement rules quantitatively, and to estimate on-host CFT survival/development. To represent real landscapes in the model, georeferenced land cover/use data will be obtained for real landscapes in/around the quarantine zone representative of the habitat heterogeneity found in the region. Data will be imported into NetLogo. Model performance will be evaluated by comparing simulated population dynamics, movement patterns, and CFT loads of nilgai to an independent set of analogous field observations. If necessary, the model will be recalibrated based on these comparisons to obtain a more accurate representation of the real system. The potential impact of nilgai on the maintenance of CFT will be assessed by simulating the daily spatial/temporal dynamics of off-host larval CFT populations and the temporal dynamics of adult CFT on each host species over a 4 year period under a variety of tick eradication protocols. Standard protocols will include use of various combinations of pasture vacation, dipping, and acaricide treatments targeted at white-tailed deer. Novel protocols will include the addition of acaricide treatments targeted at nilgai. Each protocol will be simulated under a variety of assumptions regarding cattle stocking rates, WTD densities, nilgai densities, and environmental conditions (temperature, RH and precipitation). Analysis of simulation results will include: 1) off-host larval tick densities and 2) frequencies of presence of each tick host species in each of the habitat types within the landscape. The following will be analyzed: 1) post-treatment off-host larval tick densities within the landscape (to establish the threshold ratio of nilgai-to-cattle for sustaining CFT populations), 2) the cumulative number of days of co-occurrence of cattle, WTD, and/or nilgai in each habitat cell within the landscape (to assess overlapping habitat use by nilgai, cattle, and WTD in the formation of CFT refugia), 3) the cumulative number of days of co-occurrence of cattle and nilgai in each habitat cell within the landscape (to determine if sufficient spatial and temporal overlap exists between nilgai and cattle to support using treated cattle as a trap host), and 4) the number of days of occurrence of nilgai in each habit cell within the landscape containing a communal dung pile (to determine if nilgai social behaviors associated with communal dung piles could be exploited for CFT suppression tactics).