It may be noted that the sterile-insect releases achieve a much more drastic 

 effect than conventional control methods, when the initial treatment is 90 percent 

 effective in preventing reproduction. The first release at the rate of 9, 000, 000 sterile 

 insects, theoretically, has the same effect as the initial treatment of the population with 

 an insecticide, since this would reduce the reproduction rate by 90 percent. However, 

 the continued release of sterile insects at the initial rate will cause a progressively 

 greater effect in reducing the reproductive rate of each subsequent generation. This 

 is one of the most significant points to keep in mind in appraising the relative merits of 

 the two systems of control. The sterile-insect-release method is highly inefficient when 

 the number of insects in the population is high, but is highly efficient when the natural 

 population is low — just the opposite of the effect of insecticide treatments. This, then, 

 is our clue to how we can profitably integrate the two systems of control. 



It should be emphasized at this point that it is essential that the rate of sterile- 

 insect releases be high enough to start a downward trend in the natural population in 

 order to take full advantage of this method of control. If conventional methods of 

 destroying pest populations and the sterile-insect-release method are equally effective 

 in the first generation, but the level of control in each case is below that required to 

 start a downward trend, the sterile insects become progressively less efficient in each 

 subsequent generation, whereas, the effect of the conventional method remains constant. 

 Thus, the population subjected to sterile insects increases at a more rapid rate. This 

 may be noted by studying theoretical model 4. 



Model 4 . — Comparative trends of two similar insect populations, one subjected to treat- 

 ments each generation by insecticides, the other by sterile-insect releases . 

 The degree of control is equal in the first generation for both treatments 

 but below the level necessary to prevent an increase in population 



Genera- 

 tion 



Uncontrolled 

 population 

 (Increase rate, 

 5X) 



Insecticide 

 treatments , 

 75-percent 

 kill each 

 generation 



Sterile insect releases at the rate of 3, 000, 000 

 each generation 





Natural 

 population 



Natural 

 population 



Sterile 

 population 



Ratio of sterile to 

 fertile insects 





Number 



Number 



Number 



Number 





Parent 



1,000,000 



1,000,000 



1,000,000 



3,000,000 



3.0 :1 



^1 



5,000,000 



1,250,000 



1,250,000 



3,000,000 



2.4 :1 



^2 



25,000,000 



1,562,500 



1,838,235 



3,000,000 



1.6 :1 



^3 



125,000,000 



1,953,125 



3,475,665 



3,000,000 



0.87:1 



^4 



125,000,000 



2,441,405 



9,294,115 



3,000,000 



0.32:1 



- 7 - 



