490 
Journal of Agricultural Research 
Vol. XXX, No. 5 
Continental Divide there. It has been 
present in southwestern Wyoming for 
eight years and has not crossed the 
climatic limit shown on the map. It 
reached the northeastern corner of 
Idaho in 1917, and has not yet crossed 
the climatic boundary into Montana. 
Within the present range the regions 
of the most severe infestation are the 
lower valleys of Utah, the Colorado 
area, western Idaho and the adjacent 
part of Oregon, and western Nevada. 
It has been abundant in some of the 
other places, but varies greatly in 
substantiates the findings of the studies 
on climatic conditions in the Old World. 
The zones outlined on the map of 
Figure 11 are based upon a detailed 
study of the climatological data from 
several hundred stations in this region 
as published by the United States 
Weather Bureau. 3 The writer wishes to 
express appreciation of the assistance 
rendered by the section directors of the 
Weather Bureau for these Western 
States in furnishing a large amount of 
climatic data and in some cases lend¬ 
ing file copies of the older publications. 
S£££/J£> 0Y 77/£ /££££//. 
BY C0£//VT/£S 
Fig. 12.—Dispersion of the alfalfa weevil in America, 1904-1923 
abundance from year to year. In 
short, it is most abundant in the zone 
of “normal” occurrence, is often injuri¬ 
ous in the zone of “occasional” occur¬ 
rence, but has not as yet reached the 
zone of “possible” occurrence. It is 
spreading at the present time in those 
parts of its range where conditions are 
favorable from a climatic standpoint 
and has ceased to spread when it has 
reached the climatic boundaries. Thus 
the history of the insect in America 
SUMMARY AND CONCLUSIONS 
The general procedure indicated in 
the introduction has been used in the 
present paper. 
The climatic conditions of the origi¬ 
nal home of Phytonomus 'posticus have 
been studied in detail to find the opti¬ 
mum and limiting conditions, which 
were correlated with similar conditions 
in America. 
3 United States Department of Agriculture, Weather Bureau, summary of the climato¬ 
logical data for the united states, by sections. 106 sections, published separately. 1908 and later 
dates. 
United States Department of Agriculture, Weather Bureau, climatological data by sec¬ 
tions. Annual summaries under this general title for various Western States. 1910-1922. 
