102 



weevil will ultimately spread over the entire cotton belt in spite of 

 any measures which may be adopted to retard its progress. 



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 distrib- 

 ution 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 

 A few years before the publication of Doctor Merriam's completed 

 results Dr. L. O. Howard, Chief of the Division of Entomolog}^ 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, 5 and 

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

 nature concerning the geographic distribution of the yellow fever 

 mosquito. 6 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 alreadj 7 become established near Sher- 

 man, Tex. As nearly as can be told from data at present available, the 

 isothermal line passing through Sherman, if extended eastward, 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 " temperature " 

 will not prevent the spread of the weevil eastward. Even if it should 

 not go beyond the isothermal line within which it now thrives, its 

 territory would still include most of the great cotton belt of the United 

 States. Furthermore, there is no evidence to show that the weevil has 

 yet reached its most northern limit, and the probabilty remains that it 

 may yet show itself capable of existing anywhere within the Lower 

 Austral Zone where cotton can be grown. 



A comparison of the positive temperatures of various localities in the 



a 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 Cul- 

 tivated Crops." 



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

 cerning the Geographic Distribution of the Yellow Fever Mosquito.'* 



