On the basis of available information, it is assumed that an average cost of 

 $500 per square mile is necessary to achieve tsetse fly eradication by the application 

 of selective residual insecticides to the vegetation in the tsetse fly environment. The 

 elimination of populations by applying airplane mist sprays would probably average a 

 like amount, or more. Actual cost will no doubt vary greatly, depending on a number 

 of factors, and further research and experience may lead to reductions in cost of 

 eradication by the use of insecticides. 



As previously stated, the difficulties and assumed high cost of rearing tsetse 

 flies are regarded as the major obstacles to the practical utilization of the sterile- 

 male-release method for tsetse fly control. The reproductive potential of tsetse flies 

 is extremely low. There is no doubt that this inherent limitation is an important factor. 

 However, the writer is of the opinion that the importance of this factor has been over- 

 emphasized, and that there is reason to believe that, through a concerted research 

 effort with a view to the development of economical mass-production methods, it will be 

 possible to rear the insects at a cost that would fall well within the range of practicability. 

 Based on information supplied the writer by J. Ford of the Department of Veterinary 

 Services, Salisbury, Southern Rhodesia, it may even be feasible to collect pupae from 

 high-density areas at a cost that would be practical for limited use of sterile flies. 

 Collecting male flies from high-density areas for subsequent sterilization and release 

 in areas to be reclaimed may also be feasible. 



If a rearing cost of 5 cents per male could be attained, and if, as indicated in 

 model 11, only about 1,700 sterile males would be required to eliminate populations 

 averaging 200 flies or less per square mile in the total area requiring treatment, the 

 cost for the flies would amount to only $85 per square mile. This cost plus all other 

 costs, including the distribution of the insects, probably would not exceed $125 per 

 square mile — a highly favorable figure in relation to costs for chemical control. If this 

 estimate is realistic, the sterility method alone would be more economical than chemical 

 control procedures when natural population -density levels exceed 200 tsetse flies per 

 square mile. However, there would appear to be some advantages to the use of at least 

 one insecticide mist treatment when the natural population is moderate-to-high. The 

 release of large numbers of sterile males might, temporarily at least, add to the hazard 

 of the insect. By prior destruction of the existing adult population, the subsequent 

 addition of sterile males in numbers proposed, would not equal the original total popula- 

 tion. 



Even though the low reproductive potential of the tsetse flies will limit the number 

 that can be mass -reared, there are certain compensating factors that, in the final analy- 

 sis, may place tsetse flies in a category comparable to that of certain other insects as 

 favorable candidates for the practical application of the sterile-male technique. 



In considering the release of sterile males for insect species having a high 

 reproductive potential, the writer estimates that the initial natural population of males 

 must be exceeded by at least 10 sterile males in order to achieve a downward trend in 



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