In the absence of definitive data, even a rough estimate of the normal rate of 

 increase is so vital to an appraisal of the potentialities of the sterile-insect-release 

 method, the writer has attempted by devious ways to gain as much information as 

 possible on the question as it relates to specific insects. As a working hypothesis, it 

 has been concluded that a five-fold rate per generation is a reasonably valid rate of 

 increase for most well-established insect pests. It is obvious that the rate of increase 

 will vary, depending on the species and on the conditions under which the insect is 

 existing. Some insects have an inherently low increase rate. The tsetse fly is a good 

 example. The increase rate for these insects probably seldom exceeds two-fold per 

 generation. A ten- or even twenty-fold increase may occur for other insect species 

 under favorable conditions. 



In considering ways to regulate a given insect population, rate of increase is one 

 of the most vital factors to keep in mind. 



Trends of an Insect Population 

 Subjected to Usual Methods of Control 



If we know the normal trends of an insect population, we can then make a good 

 estimate of the effects on such trends of different methods of control. Since the sterile- 

 insect-release method, as well as other methods of control affect population trends in 

 different ways, we should consider this point carefully. 



Model 2 . —Trend of an insect population subjected to control by insecticides or similar 

 means, when the level of kill is 90 percent each generation. An increase 

 rate of five-fold is assumed for the insects surviving the treatment 



Generation Number of insects per unit area 



( Population actually treated) 



Parent 1,000,000 



F^ 500,000 



' F 250,000 



2 



F 125,000 



3 



F 62,500 



If 90 percent of an existing population is destroyed, and the surviving 10 percent 

 increases at a five-fold rate, the net effect will be to reduce the population by half. This 

 is the pattern established for the model. 



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