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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
living aphid could be found in this grove, although the mummified 
bodies of dead aphids were abundant. Unfortunately no counts were 
made at either examination. It is not claimed by the writers that the 
fungus was the sole agent in the eradication of the aphids on this 
grove, for large numbers of ladybird beetles and larvae, and of syrphid 
fly larvae were observed at the time of the first examination. However, 
the fact that such a large number of infected bodies was present, 
when living aphids were absent, proves that the fungus was an im¬ 
portant agency in controlling the aphis. 
Natural Factors in the Control of the Walnut Aphis 
During the week June 11 to June 18, extremely high temperature 
and correspondingly low humidity prevailed throughout Southern 
California. In fact, that week was the hottest period for the time 
of year ever reported in Southern California. Table 2 gives the 
maximum temperatures recorded at various points for the week. 
Table 2— Maximum Temperatures (F.°), Week Ending June 19, 1917 1 
June 12 13 14 15 17 18 
Los Angeles.79 80 100 99 105 85 
Santa Ana.79 87 104 95 97 83 
Pomona.93 99 110 112 117 100 
Riverside.98 105 112 114 117 103 
Santa Barbara..76 80 92 105 115 77 
This extreme heat resulted in the death of a large percentage of 
aphids throughout the walnut growing sections of Southern California, 
and was by far the most efficient check of the season. In only one 
case were any living aphids observed by the writers during the follow¬ 
ing week. This was on the Limoneira Rancho, Santa Paula, where on 
June 19 there was an occasional aphid found. Such aphids were 
found only on leaves well in the interior of large trees, where they 
were protected considerably from the heat. 
Among the natural agents which contribute to the control of this 
aphid, the heat of summer can be mentioned as very important in 
certain sections. To this heat is largely due the credit for the prac¬ 
tical absence of the walnut aphis in such interior sections as Riverside, 
Elsinore and Hemet. In harmony with this is the fact that in cool, 
humid weather the aphids seem to thrive best. The early part of the 
season of 1917 was cool and humid, and this condition lasted until June. 
1 These records were obtained from the Daily Weather Map, United States De¬ 
partment of Agriculture, Weather Bureau, Los Angeles, California, June 13-19, 
1917, with the exception of those for Santa Ana which were obtained from the records 
of a thermograph placed in the Rohrer Grove, by the Department of Plant Pathology 
of the Citrus Experiment Station. 
