A Race of Comperiella bifasciata Successfully Parasitizes California Red Scale1,2

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Abstract
For many years investigation has indicated that in China a parasite going under the name of Comperiella bifasciata successfully parasitized the California red scale (Aonidiella aurantii). This same species of parasite was brought from Japan into California where it reproduced successfully in the yellow scale, but failed to reproduce on the California red scale. An interesting problem arose as a result of this experience. Was the California red scale in reality a distinct species from the form in China going under that name; or was the parasite Comperiella bifasciata from Japan, which was successfully established on the yellow scale, distinct from the Chinese parasite recorded as a parasite of the California red scale there? This question might have been answered rather easily several yrs. ago except for the necessity of avoiding the bringing into California of any citrus originating in areas where citrus canker was known to occur. In order to be certain that there was no mistake as to the identity of the California red scale, stocks reared from Calif. citrus groves were established on sago palms and taken to China with the idea that these plants could be brought back to California with the parasitized scale, thus avoiding the canker danger. However, the Chinese parasites failed to develop on these California scales. The conclusion seemed justified that the so-called red scale in China was in reality distinct from the red scale of California. Shortly after this conclusion had been reached, 2 important discoveries were made bearing on this problem: it was discovered, as a result of work with another red scale parasite, that the sago palm tended to make the red scale immune to parasitization; and new and more reliable characters were discovered which made it possible to be practically certain of the specific identity of the various scale insects involved. Reexamination of the scale material in the light of these new characters made it practically certain that the Chinese red scale and the California red scale were identical. It became necessary then to assume that if the two scales were identical the parasite from China must be distinct from the parasite in Japan, although anatomically indistinguishable. To avoid the possibility of the host plant causing the scale to become immune to parasitism, it was decided to ship, from China, red scale on citrus; and to avoid danger of bringing in citrus canker, citrus cuttings bearing parasitized scale were forwarded directly to the U. S. Dept. of Agric. at Hoboken, New Jersey, where the parasites were reared and sent to Calif. Tests showed at once that this Chinese parasite reproduced successfully on the California red scale, and that it was a genetically distinct race, although the same species, Compendia bifasciata, as the Japanese form which has failed to reproduce on the California red scale.

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