232 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 11 
ment of better means of controlling this pest than we have at the pres¬ 
ent time. 
This work was undertaken for the express purpose of studying the 
relation of previous crops and the presence of the winter host tree, 
Populus angustifolice, to the degree of infestation. 
The areas covered will be known in this report as the Longmont and 
Eaton territories. The former extended from the foothills of the 
Rocky Mountains, in Boulder County, eastward a distance of 18 
miles, contained 44,800 acres and 410 beet fields. The latter, which is 
in Weld County, was 14 miles long, lay parallel to the mountains with 
its western boundary 24 miles to the east of them. This territory con¬ 
tained 32,000 acres and 253 beet fields. 
Owing to the topography of the country and the shape of the beet 
growing areas these territories are naturally divided into sections. The 
Longmont territory is divided into 3 sections. What will be known as 
the river section is the most westerly and extends in a narrow strip 
each side of the St. Yrain River from the foothills to the city of Long¬ 
mont, a distance of 9 miles. Northeast of this is the central section,, 
a rectangular area 4 miles east and west and 5 miles north and south. 
East and a little north of the central section is the eastern section. 
This is also a rectangular area. It is 5 x 6 miles, the 6-mile side running 
east and west. 
The Eaton territory is divided into a north and a south section. The 
former lies north and west of the town of Eaton. It is rather irregular 
in shape, being 8 miles north and south with an average width of 3.5 
miles. The latter lies south and east of Eaton. North and south it is 
6 miles and has an average width of 3.75 miles. 
As already stated, the main object in making this survey was to 
study the relation of previous crops and the presence of the winter 
host to the degree of infestation. However, it was found that another 
factor would have to be taken into account in working up the results 
of the survey, i. e., what the writer calls the “time factor.” The 
effect of this and the “previous crop” and “winter host” factors will 
be considered in the following pages. 
The Time Factor. —There is no doubt that the original infestation 
in all beet fields is due either to the hibernating, wingless lice or the 
spring migrants which come from the winter host. This being the case, 
the number of infested beets should not change after migration from 
the trees ceases (which is about August 1 at the latest with us), unless 
the lice migrate from beet to beet in the field. That this actually takes 
place is shown by the following observations. 
An examination of several beet fields during August and September 
revealed many wingless lice and pupae leaving the soil, climbing up the 
