June, ’18] 
BURGER AND SWAIN: WALNUT APHIS, FUNGUS 
279 
Field Investigations 
Several groves in the vicinity of El Monte were heavily infested 
and many of them were treated. The observations were confined to 
the groves of the Cogswell Ranch which were dusted with various 
combinations of sulfur and tobacco dust during the latter part of May. 
A few days later the owner noticed that the infestation was con¬ 
siderably lighter. On June 4, the writers examined these groves and 
found that the aphids to a large extent had disappeared. Bodies 
of many dead aphids were observed still clinging to the leaves, and 
these were thought at first to have been killed by the dust, but they 
were also observed on untreated trees. It was further noticed that 
live aphids were no more numerous on the untreated than on treated 
trees. A microscopical examination of the bodies of the dead aphids 
brought out the fact that they were infected with a fungus which 
later proved to be a new species of Entomophthora. 
The discovery of aphids infected with this fungus resulted in a more 
thorough examination of the conditions on June 9. Table 1 gives 
the results of counts made on the various groves. 
Table 1 —Walnut Aphis in Cogswell Groves, El Monte, July 9, 1917 
Number Number of 
of Number of Percentage of living aphids 
leaves aphids per leaf aphids infected per leaf 
A Treated.30 40.07±2.87 87.02d=1.51 5.93±0.65 
B Treated...50 17.56±0.94 73.12i2.27 4.72±0.64 
C Treated.50 28.94=1=1.50 71.73=1=1.73 8.18±0.69 
D Untreated.49 42.18 ±2.80 88.56 ±1.17 5.16 ±0.39 
E Untreated.40 38.60±2.67 83.81 ±1.33 6.17±0.94 
An examination of this table shows that the average number of 
aphids per leaf ranged from 17 to 42 in the various groves, but on 
account of this fungus the average of living aphids was only 5 to 8 
per leaf, the percentage of infection being about the same in all groves, 
both treated and untreated. It must be borne in mind that the 
number of aphids per leaf does not represent a true record of the 
previous infestation, for many of the dead aphids had either fallen to 
the ground or been blown off the leaves. However, this table does 
show that the fungus was a very important factor in the elimination 
of the aphids. 
Observations were made in Ventura County about this time, where 
it was found that aphids were present in great numbers but that the 
fungus was also present. On May 11 one grove near Santa Paula 
was found to be heavily infested. It was also observed that a small 
percentage of infected aphids were present. On June 11 not a single 
