20 
THE HOP APHIS IN THE PACIFIC REGION. 
FIRST APPEARANCE OF THE HOP APHIS IN THE SEASON. 
The first wingless viviparous aphides of the season at Santa Rosa, 
Cal., at Independence, Oreg., and at Agassiz, British Columbia, 
were invariably observed upon hopvines near shrubby growth 
bordering a watercourse or fence, near a sheltering tree, or near 
buildings. At Santa Rosa and Agassiz, where the writer made 
observations during the early part of the season, the aphides were 
most numerous near shrubbery or buildings, the numbers decreasing 
the center of the 
=jcasp*' 
as 
field was approached. 
This condition is 
shown diagrammati- 
cally in figure 7. In 
fact, at Santa Rosa 
on May 30, 1911, and 
June 6, 1912, the 
aphides occurred in 
numbers only near the 
brush, trees, or build- 
ings, the other parts 
of the field being al- 
most entirely free. 
FAVORABLE AND 
UNFAVORABLE 
CONDITIONS FOR 
THE APHIS. 
Moderately warm, 
moist seasons with an 
occasional rain but 
with little strong wind 
are the most favor- 
able for the develop- 
ment of the hop aphis, 
and the most severe infestations occur during seasons of such 
weather. 
A hot, dry wind is very unfavorable to the aphides and in some 
sections, when followed by dry, warm weather, will materially 
check infestation. 
Fig. 7.— Diagram showing relative number of aphides in different 
parts of a single hopyard, indicating the increased infestation 
near Santa Rosa Creek (a). (Original.) (The numbers repre- 
sent approximate counts of aphides which were present on the 
vines June 1, 1911. On September 1 these vines were grossly 
infested. The row nearest the creek (a) is row 1; the next is 
row 2; and after that the numbers were taken from every fifth 
row. Each number represents the number of aphides found on 
the hill in that location. ) 
EFFECT OF HEAT. 
Some careful observations on the condition of the hop aphis after 
continued hot weather, and especially when the hot weather was 
accompanied by a north wind, were made at Perkins, Cal. 
