The control of tsetse flies in relation to fly movement and trapping efficacy.
Abstract
The control of tsetse fly (Glossina) populations using traps or targets depends on the movement patterns of the flies, which determines how many flies find the traps, and on the efficiency of the traps, which determines the proportion of these flies that are killed. Models were developed to predict population loss rates under various trapping regimes. The parameters in the models are the range of attraction of the traps, the mortality rate imposed by the traps, the rate at which the flies diffuse through an area, the fly population growth rate, and the distribution of the traps or targets. Analytical results derived for 2 limiting cases: very mobile flies and inefficient traps; relatively immobile flies and very efficient traps. It is shown that if the flies are very mobile and the traps relatively inefficient, the rate at which the fly population is reduced is limited by the range of attraction, the trapping mortality rate and the population growth rate; if the flies are relatively immobile and the traps very efficient, the rate of reduction is limited by the mobility of the flies and the population growth rate. The actual situation will lie within these limits. Numerical simulations are used to test the validity of the analytical results. Data from field studies in Africa were used to test the predictions of the models and to confirm their validity. The efficiency of barriers constructed from lines of traps or targets depends on the width of the barrier, the mobility of the flies and the mortality rate within the barrier. The distance beyond the range of attraction of a trap over which the trap will reduce the fly population density significantly is calculated. The relationship between trap catches and population densities was investigated, and the factors that affect the calibration of traps as sampling devices for the 2 limiting cases were determined. The rate at which a fly front will advance into country cleared of or previously unoccupied by flies was investigated and an explanation provided for observations regarding the relatively slow rate at which fly fronts advance. Extending the models to inhomogeneous habitats and combining them with knowledge of tsetse biology and information on climate and vegetation should make it possible to predict spatial and seasonal changes in tsetse fly densities and so to provide a sound basis for planning tsetse control operations.