CONTROL OF BOLL WEEVIL IN MISSISSIPPI DELTA. 43 



weevil-control reaction, though this control was by no means com- 

 plete. In 1916, however, with a rapid multiplication of weevils and 

 a heavy infestation, no evidence of control was secured from the 

 weevil collection. The question of the relation of the degree of 

 infestation to the effect secured from practicing these control meas- 

 ures has been raised frequently, and apparently it has a very definite 

 bearing on the difference in the results secured during the two years. 

 It might appear that if a certain amount of benefit is to be derived 

 from the control measures during a year of light infestation, this 

 benefit will be increased proportionately in a year of heavy infestation. 

 The results secured do not support this idea, however, and it seems 

 to the writers that a year of light infestation, such as prevailed during 

 1915, presents the optimum conditions for securing the maximum 

 degree of control from the picking operation. It must be conceded 

 that the most thorough picking operation will not secure all the 

 weevils present ; say, for the sake of discussion, that 75 per cent are 

 secured. If 100 weevils per acre are present in the field at the time 

 of the picking (as would be the case during a light infestation), 25 

 would be left, and this number would be below that 'required to 

 produce serious injury to the crop. On the other hand, assuming 

 that there were 1,000 weevils per acre in the field and 75 per cent of 

 these were collected, 250 would still remain, which would be sufficient 

 to produce great injury to the crop, if not the maximum injury. It 

 must be recognized that the degree of weevil injury in the field is not 

 always directly proportionate to the number of weevils present ; that 

 is, the amount of injury per weevil decreases considerably with the 

 increase of the number of weevils per acre, owing to the lessened 

 chances of each individual for injury and what might be called the 

 "duplication of effort" in the repeated puncturing of the same form. 

 With the average degree of infestation reached in the Delta during 

 midsummer, there is a great excess of weevils for producing the 

 maximum injury to the crop, and a considerable number of these can 

 be removed from the field without increasing the crop secured to any 

 appreciable extent. 



In addition to this consideration, the actual effect of this collection 

 of over-wintered weevils in relation to their propagation is of interest. 

 Under normal conditions, the percentage of squares punctured during 

 the period when the weevil pickings are practiced is comparatively low. 

 The normal shedding of forms in upland cotton is so high that the 

 squares punctured by these hibernated individuals simply serve to take 

 the place of a portion of those which would be shed normally. Con- 

 sequently, these over-wintered weevils do not injure the cotton crop 

 directly ; their only effect on the crop itself in such a case lies in the 

 progeny they produce and the activity of these progeny. Therefore, 

 the only beneficial effect secured from collecting these hibernated 



