Role of white-tailed deer as a host for the cattle fever tick (Rhipicephalus (Boophilus) microplus) in south Texas, USA: A spatially-explicit model
Tick vector systems are comprised of complex climate-tick-host-landscape interactions that are difficult to identify and estimate from empirical observations alone. As vectors of Babesia bigemina and B. bovis, pathogens of bovine babesiosis, Rhipicephalus (Boophilus) annulatus and R. (B.) microplus pose a significant threat to the economic security of the cattle industry in the US. White-tailed deer, Odocoileus virginianus, is a recognized host for both species of cattle fever ticks (CFTs). Hence, we developed a spatially-explicit, individual-based model, parameterized to represent ecological conditions typical of the south-central United States, to assess the role of white-tailed deer in the maintenance of CFT populations. We first calibrated several versions of the model representing different assumptions regarding the densities of CFTs that would be maintained by white-tailed deer in the absence of cattle, and then evaluated the sensitivity of the resulting simulated densities of on-host CFTs to the uncertainties embodied in these assumptions.
Simulation results from the various baseline versions of the model indicated that as the mean maximum densities of off-host larval CFTs decreased approximately linearly from roughly 70,000 to roughly 3,000, the mean maximum numbers of on-host adult CFTs decreased approximately linearly from roughly 70 to roughly 2. Mean minimum densities of off-host larval CFTs also decreased approximately linearly from roughly 20,000 to roughly 500, and the mean minimum numbers of on-host adult CFTs decreased approximately linearly from roughly 25 to roughly 1. In all of the simulations, both mean densities of off-host larval CFTs and mean densities of on-host adult CFTs exhibited a seasonally-varying dynamic equilibrium. Our model should provide valuable information for those interested in management of CFTs as well as a framework for the development of future efficacy test of proposed tactics.