Research on materials and methods of producing sterility in insects has progressed 

 substantially during recent years, and the probability is good that it will be possible to 

 produce reasonably competitive sterile insects of any species for release. Depending on 

 the sterility methods that may be developed, and through the selection of exceptionally 

 competitive strains, it may be possible, for some species at least, to release insects 

 that are even more competitive than the normal wild strain. Through selections carried 

 out by A. H. Baumhover, of the Entomology Research Division, there is every indication 

 that the strain of screw-worms employed in the eradication programs is more aggressive 

 sexually than the original colony strain. 



Two methods of achieving sterility (dominant, lethal effects in the genetic material) 

 have been investigated most extensively. The use of X-rays or gamma rays from cobalt 

 60, as first investigated on the screw- worm by R. C. Bushland and D. E. Hopkins, and 

 the use of chemicals for sterilization, as reported by G. C. LaBrecque and associates, 

 are the sterility methods of most interest at present. However, these procedures may 

 not necessarily be the only, or the best, ways of producing sterility for any given insect. 

 Conceivably, hybrid sterility could be the preferred method for some insects, and hybrid 

 vigor may actually result in more competitive insects. It is the writer's firm view that 

 if other factors that determine the practicability of using sterile insects are favorable for 

 any given insect species, difficulties encountered in preliminary efforts to achieve 

 sterility without adverse effects on behavior should not deter research on the method. 

 There is every reason to believe that it will be possible to develop satisfactory ways to 

 achieve sterility in insects, in view of the progress that has already been made in the use 

 of radiation, chemicals, or by crossing genetically incompatible varieties or strains of 

 insects. Intensive research may be necessary (and would be fully justified for important 

 insects) to achieve this objective, if all other factors appear favorable. The boll weevil 

 seems to be one of the most difficult insects to sterilize without producing serious 

 adverse effects on the competitiveness of the males, based on studies conducted by the 

 Division entomologists located at College Station, Tex. , and State College, Miss. There 

 are, however, many elements in connection with the boll weevil problem (to be considered 

 later) that would favor the sterility method for integration with other systems of control. 



Practicability of Rearing or Collecting Organisms for Subsequent 

 Sterilization and Release 



Whether or not it will be practical to rear, or otherwise obtain, adequate numbers 

 of an organism to control or eliminate a pest population is a question that can be deter- 

 mined only after careful consideration of a number of factors. As a general working 

 hypothesis, it is submitted by the writer that where the complete elimination of a 

 bisexual insect population is the final objective, and is feasible with current control 

 procedures, there will be circumstances where final elimination can be brought about 

 more effectively by the release of sterile insects, regardless of the cost of producing 

 them. This generalization might also apply to vertebrate pests. At what stage the 

 sterile-insect-release system will become useful will depend on the number of individual 



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