234 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
which water the eastern plains make their way out of the mountains 
great numbers of narrow-leafed cottonwood trees are to be found. 
Normally these trees are very heavily infested with the gall form of 
Pemphigus hetee. As we go eastward following the water courses, 
these trees gradually give place to the broad-leafed cottonwood, Populus 
occidentalis. Thus we find that in a strip 100 yards wide passing 
through the timber belt along the St. Vrain River at the west end of 
the river section there were 282 narrow-leafed cottonwoods and 6 
broad-leafed ones. In a similar strip passing through the center of 
this section there were 429 narrow-leafed and 30 broad-leafed cotton¬ 
woods, while in a strip passing through the eastern portion of the 
section contained 185 narrow-leafed trees as against 134 broad-leafed 
ones. 
Comparing all fields in the western half of this section with those in 
the eastern, we find that of those of the former portion 100 per cent 
have an infestation of over 70 per cent and of those of the latter but 
97.5 per cent have an infestation of 70 per.cent or above. 
When we compare all fields within one-half mile of the river with all 
those more than this distance from it we find that those nearest the 
river and the narrow-leafed cottonwood trees in the timber belt along 
it have the heaviest infestation. Of the beets in those fields within 
the one-half mile limit, 87.07 per cent were above 90 per cent infested 
while of those in the fields outside of the one-half mile limit but 76.75 
per cent were infested to a like degree. 
An examination of the central section of the Longmont territory 
brings out the relation of the winter host and the infestation still more 
strongly than the preceding. 
In the western half of this territory there are 244 host trees and in 
the eastern half but 25. The per cent of all fields in the two halves of 
this section which have an infestation of over 70 per cent was 46.6 for 
the western and 35.7 for the eastern half. If we divide this section 
into halves by drawing a line from east to west, we find that the per 
cent of fields with an infestation of over 70 per cent is 56.6 for the 
north and 34.2 for the south half. There are 187 narrow-leafed trees 
in the north half and but 82 in the south. Now if we place all fields 
in this territory into two groups, one including all fields within one-half 
mile of narrow-leafed cottonwoods and the other including all fields 
at a greater distance from these trees, we find that of those within the • 
one-half mile limit 46.42 per cent have an infestation of over 70 per 
cent while of those outside this limit but 36.95 per cent are infested to 
this degree. 
Likewise in the eastern section 69.7 per cent of all fields in the west 
half, with 571 narrow-leafed trees, have an infestation of over 80 per 
