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August, ’24] SIEGLER AND BAKER: SCALE PARASITISM 
PARASITISM OF SCALES—SAN JOSE AND OYSTER SHELL 
By E. H. Siegler, Entomologist , and H. Baker, Junior Entomologist , 
Bureau of Entomology , U. S. Department of Agriculture 
Abstract 
The San Jose scale, Aspidiotus perniciosus Comst., and occasionally the Oyster 
Shell scale, Lepidosaphes ulmi L., are serious pests in many fruit growing districts. 
Parasites often play an important role in reducing these scales. 
In order to determine what species of parasites were present, samples of infested 
twigs were collected from several regions and the following species of parasites were 
bred: From San Jose scale— Prospaltella perniciosi Tow., Aphelinus fuscipennis How., 
Aphelinus mytilaspidis LeB., Signiphora pulchra Gir., Perissopterus sp., and Ablerus 
clisiocampae Ashm.; from Oyster Shell scale— Aphelinus mytilispidis LeB. 
During the last few years the San Jose scale (Aspidiotus perniciosus 
Comst.) has attracted considerable attention in many important fruit 
growing districts. It has multiplied in such enormous numbers as to 
cause alarm among orchardists. In some of the more heavily infested 
districts many hundreds of trees were killed or badly injured before the 
seriousness of the situation was fully realized and effective spraying 
measures brought into play. 
In connection with the study of the scale problem it was thought 
desirable to ascertain the parasites present. With this in view ten lots 
of twigs infested with the San Jose scale and one lot infested with the 
oyster-shell scale (Lepidosaphes ulmi Linn.) were received at the Sligo, 
Md., laboratory in late August and early September of 1922. The 
twigs were securely wrapped in waxed paper and upon receipt were 
at once placed in glass test tubes stopped with cotton. The parasites 
soon commenced to emerge, the total period of emergence extending for 
about three weeks. 
An examination of the parasites showed the presence of six species 1 
from the San Jose scale and one from the ovster-shell scale. One of the 
species, Aphelinus mytilaspidis LeB., was common to both of the scales. 
In table I, will be found a list of all the parasites that emerged and 
the number of each. 
determined by Mr. A. B. Gahan of the U. S. Bureau of Entomology, Wash., D. C. 
