20 



BULLETIN 1103, U. S. DEPARTMENT OF AGRICULTURE. 



Counties. The larvae were so numerous that by actual count as 

 many as 17 were found to a square foot in some wheat fields, while 

 the average over the entire infested region was about five cutworms 

 in this same area. They were also very destructive to young corn. 



In Colorado this insect was somewhat more active than usual, 

 particularly in the winter-wheat area east of a line extending from 

 Jackson County to Graham County, in the northeastern part, and 

 Crowley and Las Animas Counties in the southeastern part. 



This pest has been recorded in literature from Wyoming, Utah, 

 Nevada, California, Arizona, and New Mexico, in addition to the 

 States infested in 1921. 



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Fig. 8. — Monthly departures from normal temperature (solid black) and rainfall (white) 

 from September, 1920, to September, 1921, inclusive, in the region infested by the pale 

 western cutworm. (See also Table 4.) 



In the region infested by this pest the temperatures were quite 

 normal during the fall of 1920. During the winter of 1921 very 

 mild weather prevailed, January and February averaging over 6° F, 

 excess temperature. May was below normal, while the remainder of 

 the spring and summer showed substantial excesses up to September, 

 which showed a temperature deficiency of 2.9° F. (See Table 4 and 

 Fig. 8.) 



The rainfall over this region was generally below normal during 

 the fall of 1920 and winter of 1920-21. Only slight excesses of pre- 

 cipitation occurred in April and June. (See Table 4 and Fig. 8.) 



The map (Fig. 7) illustrates the area generally infested in 1921 

 (fine shading), the areas very seriously infested in 1921 (coarse 

 shading), and previous records of occurrence (black dots). 



