134 



THE MEXICAN COTTON-BOLL WEEVIL. 



Table LXII. — Summary of observations showing increased mortality of the boll weevil 

 in squares and bolls caused by proliferation. 1 



1 From Bulletin 59. Bureau of Entomology, p. 27. 



2 Weighted average. 



It will be seen that in the case of squares there was a range of from 

 9 to 31 per cent increase in the mortality due to proliferation, the 



feneral average being 13 per cent. In bolls the range is not so great, 

 eing only from 7 to 15 per cent, while the average increase in mor- 

 tality in bolls was found to be 6 per cent. This is slightly less than 

 one-half as great a mortality as was found to be the case in squares. 

 A number of interesting experiments were performed to determine 

 whether artificial punctures were as frequently followed by prolifer- 

 ation as those made by the weevil. One thousand one hundred and 

 three needle punctures were made, resulting in proliferation in 36 per 

 cent of the cases. This percentage is not so large as in the case of feed- 

 ing punctures of the weevil, but it is as large as could be expected when 

 the difference between a clean needle puncture and the rough, lacerating 

 puncture by the weevil is considered. It consequently appears that 

 it is the mechanical injury of the weevil rather than any secretion 

 which causes the growth. A further series of experiments showed 

 that injections of caustic potash, formic acid, and other chemicals did 

 not appear to increase the number of cases in which proliferation 

 followed. It did appear, however, that unsealed artificial punctures 

 resulted in more frequent proliferations than sealed punctures of the 

 same kind. 



A number of experiments were instituted to show the possible 

 effect of heavy fertilization of the cotton plant upon its tendency to 

 form proliferous tissues. It was supposed that some such cultural 

 expedient as fertilization might increase the resistance on the part of 

 the plant. In the case of over 8,000 observations made on fertilized 

 cotton growing in two localities, however, it was found that prolifer- 

 ation followed attack by the weevil practically as frequently in the 

 one case as in the other. Squares on fertilized plats showed prolifer- 

 ation in 50.5 per cent of the cases; on unfertilized plats in 49.5 per 



