should reduce the natural population to levels that could then be readily managed with 

 relatively few sterile males. We will assume a natural adult population of 1, 000 and a 

 like number of pupae of all ages in the soil that will complete emergence within 30 days, 

 and a prelarvipositional period of 15 days for newly emerged females . A series of adult 

 spray treatments at 15-day intervals should virtually eliminate all adults present before 

 treatment, and the adults that emerge from pupae present in the soil, prior to treat- 

 ment. Such insecticide treatments in all probability would destroy 99 percent of the 

 adults, and reduce reproduction to this extent. If we assume a daily emergence rate of 

 30 flies per day (15 males and 15 females) before treatment began, we can assume that 

 the daily emergence rate during the 31st to 60th day would be reduced to an average of 

 not more than 0. 3 flies per day. 



The liberation of a few hundred sterile males per square mile during a period of 

 about 6 months after the last insecticide treatments, should eliminate the remaining 

 population, and achieve the same result as three to five additional insecticide mist 



treatments . 



If, through research, a rearing and release cost factor of 5 cents per male fly 

 could be realized, and if 300 sterile males per square mile would be adequate to com- 

 plete eradication of the remaining population, an investment of $15 for sterile males 

 would be equal to an investment of from $300-$500 in additional insecticide treatments. 



The potential value of sterile male tsetse flies in an integrated program of the 

 type proposed is clearly indicated. However, by taking full advantage of the effect of 

 properly timed, sterile-male releases, in relation to the biology of tsetse flies, it 

 would seem likely that moderate-to-high populations of tsetse flies could be readily 

 eliminated by employing only one insecticide mist treatment, followed by the release of 

 sterile males. 



We might assume a natural population density of 500 tsetse flies per square mile, 

 and an emergence rate of 16 flies per day from pupae already in the environment. A 

 single mist spray should destroy 99 percent of the reproducing adults. Thus, sterile 

 males released would have to compete only with the fertile males emerging from pupae 

 and the few survivors of the insecticide treatment. 



At an emergence rate of 8 males and 8 females per day, the release of 300 

 sterile males per square mile would provide an estimated ratio of about 30 sterile to 1 

 fertile male on the first day after the insecticide treatment. These males would be 

 competing for matings with 8 newly emerged virgin females. By the 30th day, when 

 pupal emergence from the pretreatment population has been completed, the number of 

 fertile males that have accumulated would approach the number of sterile males. 

 However, allowing for some natural mortality, it is likely that the ratio of sterile to 

 fertile males would still be as high as 300 to 200. Thus, on the 30th day, about 3 of the 

 8 newly emerged, virgin females would be expected to mate with fertile males. It is 

 estimated that the maintenance of a sterile male population at a level of about 300 per 

 square mile would, during the first 30 days, lower the reproductive potential of the 

 natural population by about 90 percent, 



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