Can. Ent. 107: 337-342 (1975) Lecanium tiliae ( L . ) is now attacked in British Columbia by three species of parasites, about 18 predators, and a fungus. Parasites are the most important natural enemies but parasitize an average of only 30% of the scales. Reasons for low parasite effectiveness include: hyperparasitism by one species, Coccophagus lycimnia, which is apparently a recent arrival in the district. on itself and on the chief parasite, Blastothrix longipennis; a tendency for C. lycimnia to be relatively abundant in low scale populations; differences in sex ratio of B . longipennis between low and high host populations; and parasite mortality in the scales. It was confirmed that the parasites pass the summer as diapausing adults rather than in alternate hosts. It is concluded that the biological control attempt of 1928 and 1929 that has been widely regarded as a success was in fact probably a failure, as the introduced parasite, B. sericea, did not apparently become established. An attempt in 1969 and 1970 with an introduced fungus also failed.

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