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 this 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 



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



