Three species of true firs in the Pacific Northwest--Abies gran-dis, grand fir; A. amabilis, Pacific silver fir; and A. lasiocarpa,
subalpine fir--are severely damaged or killed by an imported insect
pest, the balsam woolly aphid (Chermes (Adelges) piceae Ratz.), Infestations of this insect cause abnormalities in the wood and, in...