Obviously, if the strain of insects used for release were highly resistant to the 

 insecticide, but the natural population was still highly susceptible, both systems could 

 be employed simultaneously for maximum advantage. The application of an insect 

 pathogen, or mass liberation of a parasite or predator that would destroy a high 

 percentage of the immature stages, with the simultaneous release of sterile insects to 

 compete with the normal adults, might be an effective and desirable combination. 

 Mechanical destruction of the immature stages of an insect, such as the boll weevil 

 (Anthonomus grandis Boheman) in squares on the ground, plus the simultaneous 

 liberation of sterile adults in the cottonfields , would be representative of another 

 combination that might be used to advantage without employing insecticides. 



Regardless of the systems employed, the effects of a simultaneous integration of 

 sterile-insect releases with other control methods within the same generation can have 

 a dramatic impact on the insect population in a short time, and when the natural popu- 

 lation is reduced substantially, the liberation of sterile insects alone probably would be 

 the most economical way to achieve final elimination and to maintain control in areas 

 subject to reinvasion of the pest by long-range migrants or by new accidental intro- 

 ductions . 



Model 6 projects the theoretical effect of two systems of control, each 90 percent 

 effective when carried out simultaneously for one generation, followed by the continued 

 release of sterile insects only, in subsequent generations. 



Model 6 . — Trend of an insect population subjected to the combined use of sterile insects 

 and a conventional system of control for one generation, followed by the 

 release of sterile insects alone. All reproducing insects are assumed to 

 result in a five-fold increase 



Genera- 



Normal trend 



Original popu- 



Fertile 



Sterile 



Insects 



tion 





lation reduced 



insects 



insects 



reproducing 







by 90 percent 



remaining 



released 







Number 



Number 



Number 



Number 



Number 



Parent 



1,000,000 



100,000 



100,000 



900,000 



10,000 



^1 



5,000,000 



— 



50,000 



900,000 



2,632 



"^2 



25,000,000 



— 



13, 160 



900,000 



189 



^3 



125,000,000 



— 



945 



900,000 







- 10 - 



