118 



THE MEXICAN COTTON-BOLL WEEVIL. 



The records for Calvert and Brenham show a very remarkable 1 

 power of endurance in some weevils, the average survival for the two 

 lots of 20 and 8 weevils being over 30 and 60 days, respectively. 



NATURAL CONTROL. 



Considerable attention has been given to the study of the natural 



i'mrr^ which control the boll weevil. These studies have revealed a 

 large amount of important data, some of which have been used in 

 eral bulletins. In the present publication it is possible to give 

 only a summary of the most important results. 



In general, the natural agencies which control the boll weevil may 

 he classified as climatic (consisting principally of heat which kills 

 directly and also indirectly by rendering the food supply unsuitable, 

 and dryness, the effects of which are intermingled with those of heat I, 



Elant resistance, parasites and other insect enemies, diseases, and 

 ink Each of these agencies will be discussed separately, but a 

 general summarization may be of value. Table LV is a summary of 

 t he observations made in the years 1906 to 1900 on weevil stages from 

 many localities. It deals with the mortality of immature stages from 

 all causes exclusive of plant proliferation. 



Table LV. — Annual mortality of immature boll weevils in all classes of cotton forms. 



1906-1909. 



5fear. 



Total 

 forms 

 ex- 

 amined. 



Total 

 stages 

 found. 



Total 



stages 

 dead. 



Number stages killed | Percentages of mortality 

 by— due to— 



Clim- 

 ate. 



Preda- 

 tors. 



Para- 

 sites. 



All 

 causes. 



Clim- 

 ate. 



Preda- 

 tors. 



Para- 

 sites. 



1900 



100,044 

 21,9S0 

 72, 2.34 

 27, 857 



40. 073 

 13,405 

 29, 546 

 11,653 



22, 353 

 7,275 



13, 103 

 4,863 



10. 078 

 3,896 

 6,268 

 3, 012 



10. 547 

 2,263 

 3.878 

 1,231 



1.728 



1,116 



2,957 



620 



55.81 

 54.27 

 44.34 

 41. 73 



25.15 

 29.06 

 21.21 

 25. S4 



26.31 

 16.88 

 13.12 

 10.56 



4.31 



i'.hit. . 



8.32 



1908 



10.00 





5.32 







1906-1909. . . . 



222, 715 



94 ; G77 



47,594 ' 23,254 



17. 919 



6,421 50.26 



24.56 



IS. 92 



6.78 



Inasmuch as the material used in making the examinations was 

 derived from mairy sources and in different proportions each year, a 

 system of weighting the different kinds of material was devised. 

 Table LVI presents a summarization of this weighting in terms of 

 percentages of mortality: 



Table LVI. — Weighted average mortality of the boll weevil, 1906-1909, due to various 



causes. 



Year. 



Prolifera- 

 tion.! 



Climate. 



Preda- 

 tion. 



Parasit- 

 ism. 



Total. 



1906 



Per cent. 

 12.42 

 12.42 

 12.42 

 12.42 



Per cent. 

 24.39 

 28.16 

 17.83 

 23.01 



l\r a nt. 

 24.85 

 L6. 18 



11.77 

 10.92 



Per cent. 

 2.94 

 3.83 

 6.34 

 2.63 



Per cent. 

 64.61 



1907 



60.61 





i^ :;7 



1909.. 



48.99 







1906-1909... . 



12.42 



24.45 



15.93 



3.93 



56.73 







The average determined in 1906 (see Bull. 59, Bureau of Entomology) is used to apply to other- years. 



