282 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 11 
Table 3— Walnut Aphis in Cogswell Groves, El Monte, September 12,1917 
Number Number of 
of Number of Percentage of living aphids 
leaves aphids per leaf aphids infected per leaf 
B. 30 84.57± 5.14 1.42±0.27 83.33± 5.14 
D.10 63.10±12.71 1.43 ±0.96 62.20±12.81 
F.20 51.30=1= 6.11 3.51 ±1.46 49.50=fc 6.17 
An examination of this table shows that practically three months 
after the hot period, the aphids had been able to reinfest these groves 
quite extensively. At that time, however, the fungus, although 
present, was a negligible factor in control, since less than 2 per cent of 
the aphids were infected. The practical absence of the fungus was 
due undoubtedly to the summer heat and drought. However, at 
that season of the year, aphid infestations are of no commercial im¬ 
portance. ' 
Observations at Santa Ana 
In Santa Ana, Orange County, the Department of Plant Pathology 
of the Citrus Experiment Station had two walnut trees enclosed in a 
frame covered with cheesecloth for the purpose of studying walnut 
blight. Temperature and evaporation records were kept throughout 
the summer both within one of these frames and outside in the grove. 
It may be noted that the temperatures from August 1 to September 20 
(the period of observations on the aphids) were practically the same 
outside as inside the frame, being but one or two degrees lower on the 
average inside. However, the humidity as obtained by the amount 
of evaporation recorded by the Livingston atmometers was higher 
within the tent than without. In fact, there was marked difference 
(see chart I). 
It was noted (see Table 2) that in this locality the maximum sum¬ 
mer temperature was 104 degrees F, which was considerably lower 
than in most of the sections of Southern California where any ob¬ 
servations were made. Also the humidity there is comparatively high. 
As a result the infestation was not so depleted in June as in other 
localities. On July 26 under tent 1, a count of the aphids on 35 leaves 
showed an average of 44.51 =*=4.09 aphids per leaf, with a mortality 
of 94.43 =»= 0.25 per cent caused by the fungus. On August 1 no live 
atphids could be found on this tree. 
About every two weeks, from August 1 until September 20, counts 
were made of the number of aphids on leaves from the tree under tent 
2, and on trees in the surrounding grove. The results of the counts 
are included in Tables 4 and 5. 
