141 



to encounter a number of new conditions, and such questions as the 

 rate of development and the degree of destructiveness which it may 

 show under these conditions are of much interest, as there is now 

 apparent no factor w^hich promises to permanently check the onward 

 movement of the pest before it will have reached the limits of cotton 

 cultivation in the United States. 



During the past century the attention of many botanists and zool- 

 ogists has been drawn to the relations existing between geographic 

 areas and the distribution of plants and animals. In this country 

 the limits of the well-defined zones and the laws governing the distri- 

 bution of plant and animal life through those zones have been most 

 carefully determined by Dr, C. Hart Merriam, Chief of the Division of 

 Biological Survey of the United States Department of Agriculture.^ 

 A few 3^ears before the publication of Doctor Merriam's completed 

 results Dr. L. O. Howard, Chief of the Bureau of Entomology, first 

 applied the principles underlying geographic distribution to a study 

 of the probable spread of a number of species of very injurious 

 insects, most of which had been imported into this country,^ and 

 recently he has made a more extensive study of a very practical nature 

 concerning the geographic distribution of the yellow-fever mosquito.^ 

 Many observations have shown that in general the limits of the spread 

 of an imported insect pest may thus be approximately determined. 

 It is therefore not out of place to consider at this time some points 

 in regard to the probable status of the boll weevil in the cotton belt 

 outside of Texas. 



According to the map published by Doctor Merriam, the entire 

 cotton-growing area of the United States lies within the Lower Austral 

 Zone, the northern limit of which is marked by the isothermal line 

 showing a sum of normal positive temperatures (above 32° F.) amount- 

 ing to 18,000° F. The weevil has already become established near 

 Sherman, Tex. As nearly as can be told from data at present avail- 

 able, the isothermal line passing through Sherman, if extended east- 

 ward, would pass along the Red River Valley, through the extreme 

 southern part of Arkansas, across central Mississippi and Alabama, a 

 little south of Atlanta, Ga., and thence curve northeastward through 

 South and North Carolina. It therefore becomes evident that "tem- 

 perature" will not prevent the spread of the weevil eastward. Even 

 if it should not go beyond the isothermal line within which it now 



"Bulletin 10, U, S. Dept. Agr., Division of Biological Survey, Life Zones and Crop 

 Zones of the United States. 



?>Proc. Entom. Soc. Washington, Vol. Ill, No. 4, pp. 219-226. ''Notes on the 

 Geographic Distribution in the United States of Certain Insects Injurious to Culti- 

 vated Crops." 



c Treasury Department — Public Health Reports, Vol. XVIII, No. 46. "Concern- 

 ing the Geographic Distribution of the Yellow Fever Mosquito." 



