THE BOLL WEEVIL — LOFTIN 287 



per acre dusted. The cost usually ranges from 25 to 75 cents per 

 acre-application and compares very favorably with ground applica- 

 tions. At present a number of commercial companies maintain an 

 estimated 200 planes equipped for crop dusting at the instant call of 

 growers, and some of the larger commercial dusters have entomologists 

 with each dusting unit who make infestation records and advise 

 growers when to dust. The use of airplanes for boll-weevil control 

 was the basis for the later developments and use for control of mos- 

 quitoes and of various insects attacking commercial vegetable crops, 

 orchards, and forests, as well as for spreading grasshopper poison 

 bait, seeding rice and cover crops, application of fertilizers, chemical 

 defoliation of cotton, and other agricultural uses. A more recent 

 development is the use of concentrated sprays whereby 1 to 3 gallons 

 of concentrate can be finely atomized from a plane to cover an acre 

 of forest or crop land. Airplane spraying has been successfully used 

 in freeing large areas of disease-carrying mosquitoes and other insects 

 and for forest- and crop-pest control. Application of insecticides by 

 airplanes is spectacular but at the same time entirely practical, eco- 

 nomical, effective, and the most convenient method ever devised for 

 treating large acreages. 



For the smaller growers the entomologists and engineers have 

 worked with manufacturers in developing ground machinery of 

 various types, prices, and capacities for dusting any size acreage at 

 4- or 5-day intervals (pi. 8). The rotary-type hand gun (pi. 5, 

 fig. 1) will take care of the dusting of 8 acres of cotton; the saddle 

 gun, 40 to 50 acres; the two-nozzle traction machine (pi. 5, fig. 2), 

 40 to 60 acres ; the four-nozzle traction power cart machine, 75 to 150 

 acres; the power-operated multiple nozzle cart machine (pi. 6, fig. 2), 

 200 to 300 acres ; and the tractor-operated machines with five to eight 

 nozzles (pi. 7), still larger acreages (U. S. Dep. Agr. Farmers' Bull. 

 1729). 



LOSSES CAUSED BY WEEVILS 



As is usual with insects introduced into a new environment, the losses 

 caused by the boll weevil were more severe during the first years while 

 the insects were becoming stabilized and control measures developed. 

 Estimates of the damage have been made by the Bureau of Agricul- 

 tural Economics each year since 1909, based on the reports of thou- 

 sands of volunteer farmer crop reporters and are probably the most 

 accurate records available for any insect. The losses show a general 

 increase as the weevil spread across the Cotton Belt, reaching a maxi- 

 mum of over 30-percent reduction from full yield for the United States 

 in 1921 (fig. 2) . Since that time the cyclic peaks of the damage curve 

 have been lower and the general trend has been downward, especially 

 in recent years. However, in spite of the progress that has been made 



