April, ’18] 
MAXSON: PEMPHIGUS BETiE DISTRIBUTION 
233 
i 
leaf stems and crawling about on the surface of the ground. This was 
especially noticeable after the beets had been irrigated. The wetting 
of the lower levels apparently drove the lice to the surface. During 
their wanderings many became located on beets which were uninfested 
up to this time. 
In order to ascertain to what degree the infestation increased, 300 
beets were pulled once a week from a small plot in the experimental 
field at Longmont and a record made of the number infested. The 
first 300 were pulled on August 12, at which time 68 beets out of every 
100 were infested. One week later the infestation had reached 75 
per cent. By the end of the next week 100 per cent were infested. 
The action of this factor makes it impossible to make some very 
desirable comparisons; however, the survey was made in such a way 
that many interesting comparisons are possible. 
The Previous Crop Factor. —The fact that rotation is of little or 
no value in the control of the sugar beet root-louse has long been 
apparent. The results of this survey seem to prove quite conclusively 
that rotation is of no value as a means of reducing the losses due to this 
insect. 
In the following tables all fields in the Longmont and Eaton terri¬ 
tories are arranged according to the previous crop. 
Longmont Territory 
Previous Crop Per Cent Infestation 
Beets 85.70 
All grains 82.31 
Alfalfa 82.09 
Mixed crops 78.71 
Eaton 
Previous Crop 
Potato 
Alfalfa 
Mixed 
Beets 
All grains 
Territory 
Per cent Infestation 
89.6 
83.7 
82.4 
81.0 
79.5 
A comparison of these tables reveals the fact that the different crops 
do not hold the same relative place in the two territories. This would 
appear to more fully prove the correctness of the statement already 
made that rotation has little if any value as a control for this insect. 
The Winter Host Factor. —This of all the factors thus far studied 
appears to be the most active in the spreading of the sugar beet root- 
louse in northern Colorado. A comparison of the degree of infestation 
in all fields in those parts of the territorial sections where the narrow- 
leafed cottonwood trees are most abundant and those parts where 
these trees are relatively few, results in some very interesting figures. 
All along the foothills and in the canons through which the streams 
