286 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 5 



trol on cotton having a potential yield of less than one-third bale per 

 acre if no weevils were present or where the expected gains are less 

 than 100 pounds of seed cotton per acre. Unfortunately there is a 

 large acreage of cotton in this category, though the restriction on 

 acreages during recent years has tended to reduce the use of low- 

 production land for cotton. 



While no exact data are available on the amount of calcium ar- 

 senate used for weevil control, a large proportion of the calcium 

 arsenate manufactured is used on cotton, and it is estimated that the 

 2 million acres or more dusted annually for boll-weevil control in- 

 creases the growers' profit by many times the total of $3,500,000 spent 

 by the United States Department of Agriculture on boll-weevil re- 

 search since the work was started in 1894. Despite the benefits derived 

 from the use of calcium arsenate, it is not the perfect insecticide for 

 boll-weevil control. An inexpensive material is needed that is more 

 toxic as a stomach poison or that will kill boll weevils by contact and 

 not cause an increase in aphids or injury to soil. 



DEVELOPMENT OF DUSTING MACHINERY 



Coincident with the rapid expansion in the use of calcium arsenate, 

 it was necessary to develop methods of application. No suitable dust- 

 ing machines were available, and assistance was given manufacturers 

 in improving the efficiency of the existing models and testing new 

 models at the Tallulah laboratory. The possibility of using airplanes 

 for cotton-insect control was suggested by the work of the Ohio 

 Experiment Station in distributing lead arsenate against the catalpa 

 sphinx in 1921. The first airplane tests against cotton insects were 

 made in the fall of 1922 through the cooperation of the Air Service of 

 the United States Army in furnishing planes and personnel (Dep. 

 Agr. Bull. 1204) . In the first flights calcium arsenate was dropped by 

 hand from the planes for control of the cotton leafworm, but it soon 

 became evident that it would be necessary to develop methods of dis- 

 tributing insecticides evenly and at controlled rates. Research by the 

 Bureau of Entomology in cooperation with the then Bureau of Agri- 

 cultural Engineering during the next few years developed specifica- 

 tions for hoppers and distributing apparatus that would effectively 

 dust a 50- to 75-foot swath for weevil control (pi. 4, figs. 1 and 2) . The 

 use of airplanes for weevil control and later for other cotton insects 

 rapidly expanded and soon became an important factor on the larger 

 plantations. Dusting by airplanes is more rapid than from the ground, 

 as one plane can cover from 750 to 1,000 acres a day, an important 

 factor when it is too wet to use ground machinery or when large 

 acreages are to be covered quickly. Most of the airplane dusting is 

 done by commercial operators by contract per pound of insecticide or 



