72 



NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



This may be more clearly understood if we consider a concrete 

 illustration based upon the actual average percentages shown in Table 

 III. In addition to the percentage of weevils found dead at the time 

 of examination, it is reasonable to assume that had the stages been 

 left in the undisturbed forms until all surviving weevils might have 

 emerged, there would have been an increase in mortality fully equal 

 to one-half of the percentage shown by the examinations. Based upon 

 this mortality, a hypothetical illustration shows in a striking way the 

 influence which the class of form may have upon the proportion of 

 weevil stages reaching maturity therein. 



Table XVII. — Illustration of effect of natural control, as found, upon weevil develop- 

 ment in each class of forms. 



Class of forms. 



Dried, hanging bolls 



Dried, hanging squares 



Fallen bolls 



Total for 3 classes above 

 Fallen squares 



Number 



Number of dying as by Additional 



w™ stages Proportions number 

 startin! found at ; likely still to 



therein examinations die before 



given emergence, 

 herewith. 



100 

 100 

 100 



300 

 300 



116 

 180 



Number 



of adult 



weevils 

 emerging. 



125 



From this illustration it may be seen that the chances for a weevil to 

 reach maturity are greatest in hanging bolls, second in fallen bolls, third 

 in hanging squares, 'and least among fallen squares. Starting with 

 three hundred stages, distributed equally among the first three classes 

 of forms, between 40 and 45 per cent may be expected to become adult, 

 while an equal number of stages in fallen squares may probably yield 

 not more than 10 per cent of adults. 



It is fortunate that under normal conditions a large majority of 

 weevil stages develop in squares which fall to the ground. Because 

 of this fact it is possible for the most important factors of natural con- 

 trol to exert their greatest influence in checking the multiplication of 

 the weevils. Without the large degree of natural control, such as has 

 been shown to have existed in 1906, the profitable production of cotton 

 would, apparently, not be possible. Understanding something of the 

 influence of these factors, as we now do, we can appreciate in some 

 measure our indebtedness to them for making it possible to continue 

 the culture of cotton throughout the area which still, in spite of the 

 damage actually done by the weevil, produce's more than one-third of 

 the annual crop in the United States. We can appreciate also the 

 importance of following such methods in the culture of cotton as are 

 found to promote in the greatest degree the efficiency of any factor in 

 the natural control of the weevil. 



