SEASONAL HISTORY. 



77 



multiplication would be limited to about 250,000 weevils per acre. 

 It has been shown in this bulletin that on the average over 50 per 

 cent of the weevil stages are destroyed by natural conditions. This 

 means that the theoretical possibilities are never reached. In fact, 

 it is doubtful whether the actual increase from a single pair exceeds 

 2,000,000. 



Prof. Sanderson, in Bulletin 63, of this bureau, estimated that the 

 actual increase in the number of weevils from the 1st of June to the 

 1st of September is about 50 times and certainly not over 65 times, 

 where theoretically it would be 625 times. 



PROGRESS OF INFESTATION IN FIELDS. 



It is of considerable importance to understand the rate of increase 

 of the infestation in the fields. Normally, in a given cotton field the 

 infestation when the squares have just begun to form is under 10 

 per cent, but tins percentage increases very rapidly in proportion as 

 the hibernation was successful. The infestation generally starts 

 in a given field in the vicinity of timber or of buildings where cotton 

 or cottonseed was stored during the winter. It then progresses in 

 increasing circles until the entire field is scatteringly infested. From 

 then on the increase is general until it is almost impossible to find an 

 uninfested square. Table XXIX may be used to illustrate the 

 progress of infestation in a given field. 



Table XXIX. — Progress of infestation by the boll weevil, field 1, Victoria, Tex. 1 



Block. 



Date. 



Number 

 of 



squares, 

 exam- 

 ined. 



Number 

 of 



squares 

 infested. 



Percent- 

 age. 



Remarks. 



I 



l 



II 



1903. 

 f June 8, 9 



July 13 



July 22 



August 4 



[August 29 



July 30 



August 1 



1 August 4 



[August 20 



4,200 

 467 

 249 

 278 

 91 

 358 

 331 

 300 

 699 



675 

 211 

 193 

 224 

 85 

 168 

 148 

 100 

 636 



16.0 

 45.0 

 77.5 

 80.6 

 93.5 

 46.6 

 44.7 

 33.3 

 91.1 



Work of hibernated weevils only. 

 Second generation at work. 

 Third generation beginning. 



About four generations now working. 

 Much cotton dying from root rot. 





Total.... 



6,973 



2,440 



35.0 





1 From Bull. 51, Bureau of Entomology, p. 114. 



