282 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 5 



In discussing the progress made in developing improved varieties 

 after the coming of the boll weevil, Ware states in the 1936 United 

 States Department of Agriculture Yearbook, 



Considerable impetus was given to cotton breeding about tbis time, largely tbrougb 

 tbe discovery that many of the early-maturing cottons were of inferior quality 

 and that their production was resulting in the loss of special markets which had 

 been using the better cottons of pre-boll weevil days for many years. . . . The 

 greatest improvement has taken place in the medium staples, ir /ic to V/iq inches, 

 inclusive. In 1928, only 39 percent (of the United States crop) was of these 

 lengths, whereas in 1935 this had increased to 50 percent of the crop. On the 

 whole there bas been an increase in the average staple length of the entire crop 

 of approximately %2 inch. 



The time required for setting and maturing a crop of bolls has been 

 so shortened that it is approaching the practical limitations to which 

 it can be carried, and more attention is now being given to varietal 

 resistance to boll- weevil attack. None of the numerous species, varie- 

 ties, or strains of cotton has been found immune to boll weevils. At- 

 tempts have been made at various times to discover a resistant cotton 

 in the native home of the boll weevil, and studies have been made of 

 some of the characters which contribute to resistance, but this impor- 

 tant problem has not received the attention it deserves. Among other 

 plant characters that have been studied in their relation to weevil 

 damage are the shedding of the infested squares and small bolls, 

 proliferation, pilosity, thickness of boll walls, and toughness of carpel 

 lining. The mortality of immature weevils in shed forms is consid- 

 erably higher than in those hanging on the plant owing to exposure 

 to higher temperatures and attack by ants and other predators on the 

 soil surface. The effectiveness of heat in killing the grubs is greatly 

 reduced by shading of the plants late in the season or by abundant 

 moisture, but the mortality often reaches 50 percent after 3 or 4 days' 

 exposure to 95° F. or above. Small plants with few lateral branches 

 and "open" foliage afford less shade and are desirable characteristics 

 of some varieties. Proliferation, or the development of numerous ele- 

 mentary cells in the square and boll, was observed as early as 1902 

 (U. S. Dep. Agr., Bur. Ent. Bull. 59) to kill from 10 to 15 percent of 

 the developing weevil forms by mechanical crushing, but it seems to 

 be present to about the same extent in all upland varieties. Pilosity 

 of stalks and leaves varies greatly among varieties from almost gla- 

 brous sea island varieties to 300 to 400 hairs per square centimeter in 

 some upland cottons but has not been found to hinder the movement 

 of adult weevils over the plant as previously supposed. However, 

 pilose leaves cause better adherence of calcium arsenate, especially 

 when applied to dry cotton, and thus indirectly aids weevil control to 

 some extent. The thickness of the boll walls and toughness of the 



