78 THE MEXICAN COTTON-BOLL WEEVIL. 



Additional illustrations are .furnished in Table XXX. 

 Table XXX. — Observations upon infestation bi/ the boll weevil, various localities, 1904. 1 



1 From Bull. 51, Bureau of Entomology, p. 116. 



Prof. Sanderson 1 has estimated that usually 50 per cent of the 

 squares will be punctured by about two months after the cotton com- 

 mences to square, at which time there would normally be about 100 

 squares to the stalk. When one-half of the squares are punctured it 

 may be readily concluded that there are probably sufficient weevils 

 present to prevent any more squares from forming fruit. It will be 

 seen, therefore, that the critical period in the relation between natural 

 increase of squares on the plant and increased injury by the boll 

 weevil is during the period of six to eight weeks after the first squar- 

 ing, which usually coincides more or less closely with the time between 

 the appearance of the second and third broods of the weevils. Thus, 

 if we consider six weeks as the average time for cotton to begin to 

 square after planting, it will be seen that the bulk of the fruit must 

 be set in 85 or 95 days after planting. In other words, to escape 

 injury by the boll weevil, cotton must be so grown that the bolls will 

 commence to open in about 100 days after planting and that all the 

 fruit which will probably be secured must be set within 45 days after 

 the squares begin to form. The advantage of early planted cotton 

 and rapid-maturing varieties becomes, therefore, very apparent. 



Field examinations have shown that the period of maximum infes- 

 tation is reached between August 1 and 20, and that from 6,000 to 

 10,000 adult weevils per acre is sufficient to cause maximum infesta- 

 tion within a few days. The highest number of weevils per acre which 

 has ever actually been recorded from a locality during the summer was 



1 Bull. 63, Bureau of Entomology, p. 38. 



