The Effect of Sterilised Males on a Natural Tsetse Fly Population

The control of an isolated insect population by the release of artificially sterilised males has been successfully carried out by the Entomology Research Branch of the United States Department of Agriculture. The apparent eradication of the screw-worm [Callitroga hominivorax (Cqrl.)] from the island of Curagao was described by Baumhover et al. [1955], and Knipling [1955], in a theoretical analysis of the principle, has examined the biological and economic conditions necessary for its success. The biological prerequisites are: (i) The method of sterilization must not adversely affect the mating behaviour of the males. (ii) Adequate dispersion of the sterilized males amongst the natural female population must be obtainable. (iii) If the females mate more than once, the sperm from sterilized males must be capable of competing with that from normal males. Since the tsetse female normally only mates once, the question was raised' of the effect of this method on a natural tsetse fly population.2 The purpose of this paper is to present a theoretical examination of the method, which though based on numerical data derived from the observed life cycle of the tsetse fly, is sufficiently general to indicate its application to other insect populations satisfying the above conditions. In Section 2 the necessary mathematical background is sketched. A mathematical model of the natural tsetse population is developed (Section 3) and the theoretical effect of sterilized males is considered