Computer simulation of population dynamics of the lone star tick, Amblyomma americanum (Acari: Ixodidae).

Abstract

A comprehensive computer model of the life cycle of lone star tick (LST), Amblyomma americanum (L.), was developed to simulate effects of major environmental variables on population dynamics of this three-host tick in a wildlife ecosystem with whitetailed deer as principal host. The life cycle of LST was incremented in the model into weekly age classes and simulations were run with weekly time steps. The model incorporates 1) temperature-dependent development rates for eggs and engorged larvae, nymphs, and females; 2) influence of habitat type, temperature, and relative humidity on survival rates of free-living ticks; 3) effect of host density, temperature, and daylength on host-finding rates; and 4) density-dependent survival of parasitic ticks during engorgement. General validity of the model was established by comparisons between simulated and actual population densities for a series of years at three areas in eastern Oklahoma using actual weekly weather data for each year as a model input. Using historical-average weather data in the model, we generated population growth rate per generation (R), generation time (T), and equilibrium population densities and seasonal activity profiles for LST at various geographic locations. For areas within the known range of LST, R ranged from 1.13 at Baltimore, Md., to 3.27 at Jackson, Miss., while T ranged from 99 wk at San Antonio, Tex., to 110 wk at Baltimore, Md., and a feasible equilibrium population was established for each area after ca. 8 years of simulation. For each area outside the known range of LST, R was <1 and the equilibrium population was 0. We propose that this model can be used to study various integrated tick management methods and to serve as the framework for further studies on biology and ecology of LST. Furthermore, this model can be adapted to life histories of other important three-host ticks without major modification.