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 Ta])le 

 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 hj^^othetical illustration shows in a striking way the 

 influence which the class of form may have upon the pro])ortion of 

 weevil stages reaching maturity therein. 



Table XVII. — Illustration of effect of natural control, asfovnd, vpon uecvil develop- 

 ment in each class offonns. 



Class of forms. 



Dried, hanging bolls. . . 

 Dried, hanging squares. 

 Fallen bolls 



Total for 3 classes above . 

 Fallen squares 



! Number 



Numl)er of ^^^''^^ ^? ^^>' 

 wVe^stages P^^P^'^io'is, 



startine ioyxnd at 



theVei^^ examinations 



I given ; 



1 herewith. 



Additional 



nimil)er 



likely still to 



die before 



emergence. 



100 

 100 

 100 



300 

 300 



116 



LSO 



XumlxT 



of adult 



weevils 



emerging. 



125 

 30 



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

 reach maturity are gi-eatest 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 iii'st thi^e 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 probabh^ peld 

 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 gi'ound. Because 

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

 trol to exert their greatest influence in checking the midtiplication of 

 the weevils. Without the" large degi'ee 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 cTiltm-e of cotton tlu'oughout the area which still, in spite of the 

 damage actually done b}^ the weevil, produces m-orc 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 efliciency of any factor in 

 the natural control of the weevil. 



