Release of Sterile Males Alone for Eliminating Low- Level Populations 



In estimating the potential possibilities of sterile-male releases for tsetse fly 

 control or eradication, no attempt has been made to consider the many variations in 

 life history, behavior, preferred ecological environments, or other aspects that would, 

 of course, have to be taken into account in developing procedures for specific kinds of 

 tsetse flies. Instead, a hypothetical species and hypothetical conditions have been 

 established, which are assumed to be reasonably representative of the various species. 

 The assumption for the present is that mass-rearing methods for the insect can be 

 developed. It is also assumed that it will be possible to induce complete and irreversible 

 sterility in the males without serious adverse effects on the ability of the released males 

 to compete with normal wild males in mating with the normal wild females . A period of 

 3 months is regarded as the time required for one complete generation, including the 

 average length of life of the flies. The maximum net increase potential of a tsetse fly 

 population is assumed to be 50 percent per generation. In efforts to make an appraisal 

 of the conditions where the sterile-male-release method might prove to be feasible and 

 practical, tsetse fly populations are classified into four categories, as follows: 



(1) High-density population, averaging about 1, 000 flies per square mile for the 

 area as a whole; (2) moderate-density population, averaging about 500 flies per square 

 mile; (3) low-density population, averaging about 200 flies per square mile; and (4) 

 minimum-survival population levels, averaging 10 flies or less per square mile. 



In extremely low population situations, the mere detection of the presence of an 

 infestation may be difficult and costly, because of limitations in detection methods. In 

 this regard, detection of the presence of insects at low-density levels is often one of the 

 most difficult problems to deal with in the final stages of eradication efforts for most 

 insect species. 



From the standpoint of control or eradication, it is assumed that for selective 

 residual spraying, airplane application of mist sprays, or brush clearing, the cost per 

 unit area to achieve eradication will likely be essentially the same whether the tsetse fly 

 populations are high, moderate, or low. 



From the standpoint of eradication by the release of sterile males, however, the 

 assumption is made that the cost of eradication will be in inverse proportion to the 

 natural population density. This is the chief advantage of the sterile-male method that 

 needs to be fully exploited in connection with the eradication or control of tsetse flies, 

 as well as other insects. It represents a feature that may permit practical use of the 

 sterile male method alone, as the primary and most practical means of control or 

 eradication in some situations, but perhaps more often prior reduction of high or 

 moderate populations by the use of insecticides or other methods would be necessary or 

 advantageous. The use of sterile males may then become more economical than con- 

 tinued use of insecticides until eradication is achieved. 



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