26 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



exact location of this cork area is shown by the scar left by a fallen 

 leaf or sqiiare. It frequently happens, however, that for some reasoD 

 the severance is incomplete arid that the square or boll remain^ 

 slightly attached to the plant though cut off as far as the vital con- 

 nection is concerned (PI. IV, figs. 2 and 36). The difference in these 

 two conditions may be seen and better understood by reference to 

 Plate IV, figures 1 and 2. 



The tendency to retain dead squares and bolls seems to be a charac- 

 teristic of individual plants in nearly all varieties, but is most strongly 

 marked in those which approach the limbless, cluster type of growth. 

 In some fields the hanging, dried forms may be found very abun- 

 dantly, while in others at the same time they may be very rare. 



The retention of squares and bolls bears no definite relationship to 

 the boll weevil injury, as many of the small bolls, especially, have 

 never been attacked. 



It is evident that the immature weevil stages in those forms which 

 remain hanging upon the plant will be subjected to very different 

 influences by the factors of natural control from those in fallen forms. 

 This difference is especially marked as regards the exposure to the 

 effect of sunshine and to the attacks of predaceous and parasitic 

 enemies, and should be kept in mind in considering the data pre- 

 sented in the following tables. 



An explanation should also be given regarding the counting of 

 stages. Besides each weevil stage, living or dead, which was actually 

 found, one stage was counted for each case where there existed unques- 

 tionable evidence of its previous presence. This evidence would 

 include the emergence hole made by an adult weevil, the cell within 

 a square or boll from which some stage of the weevil had been re- 

 moved by ants, and also the cases of parasitism. Since dead stages 

 accumulate through a considerable period of time, or so long as the 

 forms remain intact, and will be found and counted upon examina- 

 tion, it becomes necessary in determining percentages of mortality to 

 count emergence holes as representing living adults which, of course, 

 is really the case. 



It would require too much space to give the detailed results of each 

 of the examinations made. For each locality, therefore, all the obser- 

 vations made have been combined. This means in most cases that 

 the figures given in these tables represent an average of several fields 

 in each locality, and in seventeen of the twenty-eight localities where 

 observations were made the figures combine the results of examina- 

 tions upon from two to nine dates. 



NATURAL CONTROL, IN VARIOUS CLASSES OF FORMS. 



In collecting the forms for these examinations all were taken as they 

 came, whether fallen, or dried and hanging to the plants. The green, 

 growing forms were not examined. 



Separate collections were made to secure hanging or fallen forms. 



