64 



NATURAL CONTROL OF THE COTTON ROLL WEEVIL. 



DESTRUCTION OF COTTON FORMS BY WEEVIL ATTACK OR BY 



NATURAL CAUSES. 



It seems advisable in connection with this study of factors con- 

 cerned in the natural control of the boll weevil to place on record some 

 of the data which have been obtained, showing the proportion of 

 squares and bolls which have been found to be destroyed by weevil 

 attack or which were shed by. the plant from natural causes without 

 insect injury. 



COLLECTIONS OF FALLEN FORMS IN 1905. , 



During the season of 1905 quite extensive experiments were made 

 to determine the value of a thorough collection of fallen forms in 

 checking the injury done by the weevil. These experiments showed 

 a net loss. The cost of collecting fallen forms exceeded by several 

 dollars per acre the slight increase in yield shown by the plots from 

 which collections were made as compared with plots under similar 

 conditions, but in which no forms were collected. No examinations 

 were made of these forms to determine the proportion which had been 

 attacked by the weevil, but from sample lots as shown in Table XIV 

 the proportion of squares and bolls was determined.- 



Table XlV.—Propor 



tion of squares and bolls among fallen fruit 



Texas, j 



W05. 







Date. 



Total 



forms ex- 

 amined. 



* 



Squares. 

 N«mbe, | JJ"-* 



Bolls. 



Locality. 



Number. 



Per cent 

 of total. 



Gurley, Tex 



Aug. 10-12 



Aug. 17 



Aug. 19 



Aug. 31 



Aug. 24 



Aug. 31 



498 



2,442 



775 



650 



2,542 



4,036 



147 i 29.5 

 411 16.8 



239 30.8 



240 36.9 

 472 18.6 



4,269 31.4 



351 



2,031 



70.5 



Do 



83.2 



Do 



536 1 69.2 



Do 



410 63. 1 



Quinlan, Tex 



2.070 81.4 



Waco Tex 



2,767 68.6 













10, 943 



2, 778 25. 4 



8,165 74.6 











It should be stated that the lots for which figures are given in 

 Table XIV were from the last collections made in those experiments. 

 The picking began early in July, and doubtless a test at that time 

 would have shown a considerably larger proportion of squares. As 

 it was, the average proportion among the nearly 11,000 forms exam- 

 ined was approximately one square to every three small bolls. In 

 the field at Gurley five collections were made in about six weeks. 

 This work extended over one-half of the 16-acre field. Upon this 

 8 acres about 730,000 fallen forms were collected. According to the 

 proportions shown in Table XV, it would seem conservative to esti- 

 mate that in this field at Gurley there were collected fallen squares 

 containing from 100,000 to 125,000 weevil stages, and in the fallen 

 bolls from 100,000 to 115,000 stages. From this 8 acres, therefore, 

 there were collected, during July and August, 1905, in all probability 

 from 200,000 to 250,000 weevil stages. If we apply to this number 



