278 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
OBSERVATIONS ON A FUNGUS ENEMY OF THE WALNUT 
APHIS IN SOUTHERN CALIFORNIA 1 
By O. F. Burger, Instructor in Plant Pathology 
and 
A. F. Swain, Assistant in Entomology 
Introduction 
In the spring and early summer of 1917 the walnut aphis ( Chroma- 
phis juglandicola Kalt.) was very abundant in the various walnut 
growing sections of Southern California. In many places the infesta¬ 
tions were so severe that control measures were inaugurated. This 
was especially true in the vicinities of Santa Barbara, Santa Paula, 
El Monte and Tustin. Several growers dusted their trees with com¬ 
binations of dry sulfur and tobacco dust, in an attempt to control 
both the aphids and the walnut blight. Under the direction of the 
Department of Entomology of the Citrus Experiment Station, por¬ 
tions of the walnut groves of the San Joaquin Fruit Company, near 
Irvine, Orange County, were sprayed in the latter part of May, with 
nicotine sulfate and lime sulfur, and with nicotine sulfate and soap, 
with excellent results in controlling the aphids. A grove near Santa 
Paula was sprayed about the same time with nicotine sulfate and soap 
under the direction of the Ventura County Horticultural Commissioner, 
with equally good results. 
As stated above the infestation of walnut aphis was exceedingly 
heavy, and gave promise of causing considerable loss. Even in 
Riverside County where ordinarily this aphis is of no importance 
whatever, a severe infestation occurred during the latter part of May 
and in June. One hundred leaves from a tree in Riverside on June 8, 
showed an average of about 70 aphids per leaf, which is an extremely 
large infestation for that vicinity. On June 6, in a grove in Santa 
Ana, an average of 106 aphids per leaf was counted, while the grower 
informed the writers that two weeks earlier there had been many 
more present. In the Thorpe grove near Santa Paula on June 11, 
there was found to be an average of 62.5 aphids per leaf, and on the 
Limoneira Rancho a few days later, about 22 per leaf were noted. 
The great abundance of aphids was also observed in Santa Barbara 
County at Carpenteria, Naples and Santa Barbara; in Los Angeles 
County at El Monte, Spadra and Walnut; and in Orange County at 
Anaheim, Orange and Tustin. 
1 Paper No. 49, University of California, Graduate School of Tropical Agriculture 
and Citrus Experiment Station, Riverside, California. 
