PRINCIPLES INVOLVED 

 Normal Trends of Insect Populations 



The way that sterile-insect releases affect population trends can be demonstrated 

 by the use of hypothetical, but reasonably realistic, models. 



Unless the principles are well understood and appropriately applied in relation to 

 the population trend that is characteristic for the particular insect to be controlled, in 

 its different ecological situations, failure is likely to result in attempts to use sterile 

 insects for practical control. The model that follows is representative of the usual 

 trend of many of our well-established insect populations . 



Model 1. — Theoretical trend of a hypothetical uncontrolled insect population increasing 

 at a five-fold rate per generation 



Generation Number of insects per unit area 



Parent .1,000,000 



F 5,000,000 



F2 25,000,000 



Fg 125,000,000 



The above is re^-sonably realistic for many insect populations that are increasing 

 from a low level in the population cycle. There is a point, however, in the population 

 cycle of any pest, after which no further increase can be expected, because all organisms 

 eventually reach a maximum density that the environment can maintain. The rate of 

 increase for each pest can be expected to vary, depending on many factors, and for most 

 species we cannot identify and properly weigh all of the factors involved. We know very 

 well, however, that the biotic potential of most insects exceeds by far the actual rate of 

 increase from one generation to the next. An insect population already well adjusted to 

 its environment seldom comes even close to achieving its maximum potential increase 

 rate because of the many environmental hazards. Newly established pests are likely to 

 achieve a much higher rate of increase until some degree of natural balance with the 

 environment is attained. It is difficult to determine the normal or representative rate 

 of increase of different insects, even in a well-balanced environment. Such knowledge 

 is of basic importance, regardless of the method of control, but relatively little precise 

 information is available on the subject. , 



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