Mar. 1, 1925 
Distribution of the Alfalfa Weevil 
489 
has been limited on the north by 
purely climatic factors for a long period 
of time. There is no physiographic 
barrier at its northern limit in Russia 
and Siberia, and it seems probable 
that it has reached its limit of adapta¬ 
bility by the present time, so that little 
or no further adaptation to cold and 
moisture will take place. 
persal of the weevil by approximately 
five-year periods. This map does not 
show the present distribution accurately, 
as a county has been recorded as 
infested when weevils have been found 
in any portion of it. The infestation in 
southern Wyoming, for example, does 
not cover more than a third of the area 
shown in Figure 12. 
Fig. 11. —Probable distribution of the alfalfa weevil in America, based on climatic limitations 
Present Distribution 
Through the kindness of George I. 
Reeves, of the United States Bureau of 
Entomology, the writer obtained a 
detailed statement of the annual spread 
of the alfalfa weevil by counties since 
its introduction and discovery at Salt 
Lake City in 1904. This information 
has been summarized and a map pre¬ 
pared (fig. 12), which shows the dis- 
19974—25f-7 
This map brings out several interest¬ 
ing facts. All regions infested at the 
present time are within the rainfall 
area of the sub-Pacific type. The 
weevil is still spreading northward and 
westward in Idaho and Oregon and 
southward in Utah. On the other 
hand, it reached its climatic limits in 
Colorado in 1917, and its dispersion 
has been only local in that region since 
that time. It has not crossed the 
