generation the treatment kills 900,000 individuals. In the F^ generation the kill is about 

 56,000 individuals. In subsequent generations, each treatment, theoretically, still kills 

 90 percent of the population, but the actual number of insects killed becomes lower and 

 lower. Near the point of extinction for the population, treatments may be required over 

 an extensive area to kill only a few insects. This is typical of pest eradication programs 

 involving the use of insecticides, as observed in actual practice. 



It should be pointed out that to reverse the trend of an insect population that is 

 increasing at a five-fold rate per generation, it would be necessary to destroy or remove 

 more than 80 percent of the individuals in the total population each generation, assuming 

 that all other hazards remain constant. If the level of kill falls below 80 percent each 

 generation, the population will increase in spite of control efforts. 



Trends of an Insect Population Subjected to Competition by 

 Sexually Sterile Insects 



We will now consider the theoretical effect of competing sterile insects on an 

 insect population when the initial release rate is high enough to start a downward trend 

 in the natural population. This is shown in model 3. 



Model 3 . — Trend of an insect population subjected to control by the sustained release of 

 competitive sterile insects, when 90 percent of the total population in the 

 first generation consists of sterile insects that have been released 







Insects per 



unit area 







Fertile 



Sterile 



Ratio of 



Insects 



Generation 



insects 



insects 



sterile to 



fertile 



insects 



reproducing 





Number 



Number 



Ratio 



Number 



Parent 



1,000,000 



9,000,000 



9:1 



100,000 



^1 



500,000 



9,000,000 



18:1 



26,316 



F 

 2 



131,625 



9,000,000 



68:1 



191 



F 

 3 



9,535 



9,000,000 



942:1 



10 



^ 



50 



9,000,000 



180,000:1 







- 6 



