32 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



of weevil stages to squares, whether hanging or fallen, but that then 

 is a natural tendency on the part of the plant to shed a large number 

 of uninfested bolls soon after their formation and before weevil 

 attack has taken place. Many of the dried hanging bolls also fail to 

 show any sign of weevil attack. The attack of the weevils upon 

 squares is, therefore, of much greater importance in their multiplica- 

 tion than is their attack upon bolls. Here again the importance of 

 natural control is shown by the mortality in all squares, amounting 

 to almost 60 per cent, whereas in all bolls it was but 31.6 per cent. 



These figures show a remarkable similarity in the degree of infes- 

 tation for the corresponding classes of fruit. This agreement is so 

 close as to lead to the conclusion that the attack of the weevil has 

 practically no effect upon the tendency of the plant to retain a portion 

 of its surplus fruit in this way. 



The proportion of hanging to fallen forms is not accurately shown 

 by the figures given here as no effort was made to collect the hanging 

 and fallen forms from the same areas at each examination made. 

 This proportion varies very greatly in different fields and during dif- 

 ferent periods of the season, but it is safe to say that in the exami- 

 nations recorded a much larger proportion of hanging, dri' 

 was collected than would be found in any ordinary field l : cotton, 

 unless it were of some limbless variety, such as the Dickson. Among 

 the forms examined, nearly 70 per cent of the squares and bolls had 

 fallen. These fallen forms contained somewhat more than 70 per 

 cent of all the weevil stages found. The proportion of weevil stages 

 to forms is very closely similar in hanging and in fallen forms, but 

 the percentage of mortality in hanging forms averages 40, while in the 

 fallen forms it averages over 56 per cent. The relative importance 

 of the mortality in the two classes of forms as related to the whole 

 question of natural control is shown to a fair degree by a comparison 

 of the percentages of mortality in hanging versus fallen forms, based 

 upon the total number of stages found in the total number of forms 

 examined. In this way we find that among the 38,891 weevil stages 

 found the 3,877 dead in hanging forms constitute approximately 10 

 per cent, while the 16,408 dead in fallen forms constitute 42.1 per 

 cent. Since, as has been stated, the hanging forms examined are in 

 a greater proportion to the fallen forms than actually occurs in the 

 average field, it follows that it is conservative to say that, as a rule, 

 the total mortality in fallen forms will average to be, at least, four 

 times as great as that occurring in the hanging forms. Consequently 

 the factors of natural control which affect especially the weevil stages 

 in the fallen forms must be given a corresponding!} 7 high rank as 

 compared with those which affect more especially the stages in the 

 hanging forms. Figuring in this way for each of the three factors of 

 natural control given, we find that heat or diying caused a mortality 

 of 3.2 per cent in hanging forms and 17.5 per cent among fallen forms, 



