Entomologists with Federal and State research institutions have gained a great 

 deal of precise information on the population dynamics of the boll weevil since 1958, 

 which indicates that the original appraisal of the potential value of sterile male boll 

 weevils was well within the realm of feasibility. Much additional research is needed, 

 especially on methods of producing reasonably competitive sterile males. However, 

 there is good reason to believe that sterile-male releases can eventually play a vital 

 role in boll weevil eradication. The manner in which they might be used for highly 

 effective population control will be considered in another section of the report. 



The writer made similar studies to estimate the general magnitude of the population 

 of hornworms on tobacco. In this instance, published data on the number of eggs depos- 

 ited on tobacco plants during different times of the year were analyzed, the writer taking 

 into account the number of tobacco plants per acre, and the egg-production potential of 

 the moths. An estimate was made that for the spring brood, a moth population averaging 

 about 40 per acre was fairly realistic. On the basis of research by tobacco insect 

 workers, there was every reason to believe that it should be practical, through a co- 

 ordinated cultural and/or insecticide program to reduce such a population to a level of 

 about 8 moths per acre. On the basis of this level of moth density, and by taking into 

 account the acreage of tobacco and tomatoes (the two principal host plants) , the present 

 costs for control, and losses caused by the pest, it was concluded that it would be 

 practical to adequately overflood the natural population and obtain virtual elimination of 

 hornworm populations, even if rearing costs for the moths were as high as 10 cents 

 each. It appeared certain that through research it should be possible to develop methods 

 of rearing the insect at a cost substantially less than this figure. 



F. R. Lawson and associates of the Oxford, N.C. tobacco insects research labora- 

 tory have, during recent years, obtained a good quantitative estimate of the number of 

 tobacco hornworm moths per acre of tobacco. Their data indicate that the rough estimate 

 made by the procedure described was reasonably close, but probably a conservative 

 estimate of the natural population density of the hornworm in the spring brood. Moreover, 

 progress in research on rearing methods, conducted by the Oxford laboratory, indicates 

 that the insect can be reared at a cost of less than 1 cent per moth, a figure one- tenth 

 that regarded as practical in the original appraisal. Thus, through further research it 

 should be possible to develop the sterile-insect method for controlling the tobacco 

 hornworm population in the principal tobacco- growing areas at a cost which would be only 

 a fraction of the current cost of control, plus losses. A more detailed appraisal of the 

 potentialities of the method for tobacco hornworm control will be considered later. 



Similar appraisals were made which suggested the feasibility of utilizing sterile- 

 insect releases for controlling or eliminating such insects as the codling moth, pink 

 bollworm, sugarcane borer (Diatraea saccharalis (F.)) , and tsetse flies. As research 

 advances on these and other species, it becomes evident that population densities of 

 many insects are sufficiently low, or can be reduced to levels that will permit the use of 

 sterile-insect releases as a final means for eradication or control. 



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