In model 5 , such a system of prior reduction of the original population was 

 established by the intensive use of insecticides for several generations. In the hj^o- 

 thetical model, three treatments would reduce the natural population to one- eighth of the 

 original level. At this level, it would require sterile-insect-release rates only one- 

 eighth as high as would have been necessary for the original population. A constant 

 release rate for four generations would then provide theoretical elimination, whereas it 

 would have necessitated treatments with insecticides for about fifteen additional 

 generations to achieve theoretical zero population. 



The manner in which the two systems can be integrated for most effective results 

 will depend on the biology of the insect, the control procedures normally employed, the 

 stage of the insect that can be controlled, and other factors. By considering these 

 factors, it should be possible to develop an integrated program that is more effective and 

 practical than the one projected in model 5. If the insects within the same generation are 

 subjected to the two systems of control simultaneously without interference — for example, 

 if the insecticide were applied against the immature stages, and sterile insects were 

 released to compete with the adult progeny that emerge — the combined effect of the two 

 systems would be much more drastic than indicated in model 5 . How to conduct the 

 integrated program for optimum effect would depend on the insect and the control methods 

 used. Different methods of conventional control might be employed. A nonresidual 

 insecticide might be employed for a series of treatments to reduce the natural adult 

 population, immediately followed by the release of sterile insects that would compete with 

 the surviving adults and those that emerge from immature stages until the next insecti- 

 cide treatment is made. 



Model 5 . — Relative trends of insect populations subjected to repeated insecticide treat- 

 ments alone, as compared with a program of insecticide treatments for 

 three generations followed by the release of sterile insects 



Genera- 



Normal trend 



Control by 



Insecticide treatments, followed 



by 



tion 



(Increase rate, 

 5X) 



insecticides 

 at 90-percent 

 level 



sterile-insect releases 







Number 



Number 



Number 





Parent 



1,000,000 



1,000,000 



1,000,000 





"^1 



5,000,000 



500,000 



500,000 





^2 



25,000,000 



250,000 



250,000 





^3 



125,000,000 



125,000 



125,000 : 1,125,000 sterile 





^4 



125,000,000 



62,500 



62,500 : 1,125,000 " 





^5 



125,000,000 



31,250 



16,450 : 1,125,000 " 





h 



125,000,000 



15,625 



1,190 : 1,125,000 " 





h 



125,000,000 



7,812 









- 9 - 



