organisms remaining in the environment, the number of sterile organisms required to 

 achieve final elimination, and the relative cost of achieving elimination from a given 

 population level by the available systems . 



In appraising the feasibility of controlling or eliminating insect populations by the 

 release of sterile organisms, we might regard the tsetse fly (Gloss ina spp. ) as a good 

 example of an insect problem to carefully analyze. On casual consideration, this group 

 of related species in Africa might be ruled out for practical consideration of the sterile- 

 release method, because of the inherently low reproductive potential of the flies, and the 

 difficulties that can be anticipated in developing mass-rearing procedures. For this 

 reason, these insects have been regarded by many as poor candidates for the practical 

 application of the sterile-male-release method. The writer has studied this matter in 

 some depth, and has prepared a special report on the subject, which was submitted to 

 WHO for consideration. The conclusion reached was that, in spite of limitations imposed 

 by the rearing factor, the method should prove to be highly favorable and entirely practi- 

 cal as the principle means for the elimination of the insects in most situations. If 

 developed, the method should have advantages over current methods for the elimination 

 of incipient tsetse infestations in areas of spread, as well as for low-level, established 

 populations. The greatest value, however, should be derived by integrating sterile- 

 insect releases with other methods of control. Hypothetical models were established 

 and tested, which suggest that even if it costs as much as one dollar to rear or collect 

 males for sterilization and release, their use would be more practical in some situations 

 than the use of insecticides. If rearing or collecting costs within the range of 5 cents 

 for each male could be realized, the use of sterile male tsetse flies should be advanta- 

 geous under a wide range of circumstances. The manner in which sterile male tsetse 

 releases might be employed will be considered further in another section of this report. 



Entomologists and insect nutritionists have made outstanding progress during 

 recent years in developing methods for the mass production of insects. With few 

 exceptions, it seems safe to conclude that a determined research effort will lead to 

 success in developing practical methods for rearing insects. We might include in such 

 category heel flies (Hypoderma spp,), Japanese beetles ( Popillia japonica Newman), or 

 almost any insect that is different to rear, but which, in the final stages of an eradica- 

 tion effort, would require costly or undesirable treatments to destroy only a few insects. 

 In considering this subject, we should not disregard the feasibility of rearing the 

 organism on its natural hosts in sufficient numbers to be useful and practical in relation 

 to costs for eliminating low-level populations of the pest by other means . 



For most insects, it seems reasonable to conclude that methods can be developed 

 for rearing insects in almost unlimited numbers. It then becomes a question of deter- 

 mining under what circumstances sterile-insect releases can be used to advantage over 

 other systems of control, or integrated in a control program. The screw- worm was the 

 first insect to be mass-produced for the sole purpose of utilizing the insects in a sterile- 

 insect-release program. The cost of rearing screw- worms, for use in the eradication 

 and control program in the southwestern United States, which is conducted jointly by the 

 U. S. Department of Agriculture and the livestock industry, is less than $500 per million, 



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