pest is most abundant, and disregard levels when the insect is least abundant. Another 

 factor that seems to have been given little thought is a quantitative estimate of the popu- 

 lation level that would remain in the environment after available methods of control have 

 been applied. Research on the natural population density of various insects under differ- 

 ent circumstances needs much more attention than has been given to it in the past. Until 

 such information is available, especially for periods of scarcity, and after the use of 

 stringent control measures for the insect under consideration, it will not be possible to 

 make even a reasonable estimate of the role of the sterile-insects-release method in 

 control or eradication efforts. 



In attempts to appraise the sterility procedures, the writer has employed various 

 ways to estimate a pest population. Examples of procedures followed in making such 

 estimates may be helpful to others. 



For one example , extensive information has been available for years on the 

 percentage of cotton squares punctured by the boll weevil. Information has also been 

 published indicating the number of squares boll weevils puncture each day. Cotton 

 agronomists and entomologists have good information on the number of squares per plant 

 and per acre at different fruiting stages. By considering such information, it was possi- 

 ble to estimate, with reasonable confidence, that a 5-percent square-infestation level at 

 a given stage of fruiting would represent a certain number of boll weevils per acre. A 

 reasonably reliable estimate of the number of insects present can be made at any 

 infestation level and fruiting stage of cotton. By such means, the writer estimated that 

 a typical overwintering population of boll weevils probably is about 200 insects per acre. 

 In some areas one could expect this number to be exceeded, but in many areas the number 

 of insects present could be expected to be substantially below this level. The second 

 important factor was an estimate of the level of infestation that could be expected to 

 occur during periods of scarcity after insecticides had been applied for boll weevil 

 control. Although much information is available on the percentage of squares punctured, 

 this had not been related to the number of insects remaining per unit area after the 

 insecticides had been applied. However, the writer concluded, as early as 1958, that 

 following a rather rigid program of insecticide use, the natural population should fall 

 below 10 boll weevils per acre. There was also evidence that the rate of increase would 

 range between 2.5- and 7.5-fold per generation. It was further judged that following a 

 rigid insecticide program, the release of 100 to 200 reasonably competitive sterile male 

 boll weevils per acre, per week, should provide an adequate ratio of sterile to fertile 

 insects to force a further downward trend in the population. 



Although successful methods for rearing boll weevils in the laboratory had not yet 

 been developed, there was every reason to believe that even if rearing had to be done on 

 cotton in artificially infested fields, it would be practical to produce and release several 

 hundred boll weevils per acre, per week, at a cost readily competitive uath the cost of 

 applying insecticides each week. Accordingly, the writer advanced the hypothesis that 

 the use of sterile male boll weevils could provide a more effective, a more economical, 

 and a more desirable way to eliminate low-level populations than to employ insecticides 

 for this purpose. 



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