Thus, the daily emergence rate from the 46th to 90th day would probably not 

 exceed 2 flies per day (one male and one female). In view of the assumed 15-day 

 prelarviposition period, relatively few flies would emerge during the 31st to 45th day, 



A rough estimate indicates that the continued maintenance of a sterile-male 

 population at a level of 300 per square mile, would further reduce the reproductive 

 potential of the population during the 46th to 90th day by about 80 percent. Even though 

 the emergence rate of new flies would be low during this period, a considerable number 

 of the males accumulating during the first 30 days would be expected to survive. In 

 order to assure a further substantial lowering of the reproductive potential of the popu- 

 lation, it would be necessary to maintain a fairly high sterile male population during the 

 period mentioned. 



If the reproductive potential of the population emerging during the 46th to 90th 

 day is reduced by 80 percent, the emergence rate per square mile on the average should 

 not exceed one fly each 2 to 3 days during the 6-week period following the 90th day. By 

 that time, most of the relatively few fertile females that did mate and most of the males 

 emerging during the first 30 days would have disappeared owing to age. Therefore, it is 

 estimated that the maintenance of a sterile male population at a level of about 100 per 

 square mile for 3 additional months, and at a level of 50 per square mile for the subse- 

 quent 3 months, should eliminate the hypothetical population. 



The establishment of a model to calculate the effects more precisely would be 

 rather difficult. The writer will not attempt to develop such a model. However, the 

 estimated effect of such an integrated program on a tsetse fly population is probably 

 sufficiently accurate to conclude that about 1, 000 to 1, 500 fully competitive sterile males 

 per square mile would be adequate to eliminate a moderate population of tsetse flies 

 following one insecticide mist treatment. However, if we assumed that 1,500 would be 

 required, and if the cost per male insect released were 5 cents each, the total cost for 

 the sterile insects would be only $75. If the single mist treatment costs $100, the total 

 cost for elimination would be $175 per square mile. This would represent a highly 

 favorable cost figure in comparison with the estimated $500-$800 that would be required 

 if insecticides alone were employed. 



Mass-Rearing of Tsetse Flies 



If the foregoing is a realistic appraisal of the number of sterile males that would 

 be required to eliminate tsetse fly populations under different circumstances, it then 

 becomes a matter of major importance to develop methods of rearing tsetse flies at 

 reasonable cost. There should, however, be other advantages besides cost. A program 

 of eradication based primarily on the use of sterile insects would avoid or minimize the 

 adverse effects on other natural fauna that can result from the use of insecticides, 

 brush clearing, and game destruction methods. 



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