. Infestation characteristics of the balsam woolly aphid in the Pacific Northwest. Fir Diseases and pests Northwest, Pacific; Adelges Northwest, Pacific. Nature of Aphid Damage When the aphid feeds, it pumps a salivary substance into the tree (Balch et al. 1964). The saliva is toxic and produces abnormal reactions in the cells of the cambium and differentiating tissues of the phloem and xylem (Doerksen and Mitchell 1965). Cellular damage is always localized within a few milli- meters of where the aphid feeds. Accordingly, the amount of damage to a tree depends not only on the size of the aphid
. Infestation characteristics of the balsam woolly aphid in the Pacific Northwest. Fir Diseases and pests Northwest, Pacific; Adelges Northwest, Pacific. Nature of Aphid Damage When the aphid feeds, it pumps a salivary substance into the tree (Balch et al. 1964). The saliva is toxic and produces abnormal reactions in the cells of the cambium and differentiating tissues of the phloem and xylem (Doerksen and Mitchell 1965). Cellular damage is always localized within a few milli- meters of where the aphid feeds. Accordingly, the amount of damage to a tree depends not only on the size of the aphid population but also where it is located. Populations concentrated in the outer portions of the tree's crown cause less damage than populations on the main stem and large branches. Symptoms of a crown infestation are swelling of the outer nodes and termi- nal buds (called "gouting" in the literature), and inhibition of new growth (figs . 3, 4, and 5). Figure by balsam woolly aphid settling along the twig and around flower buds. Typical of upper crown on large trees, especially around staminate flowers (subalpine fir).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Mitchell, R. G; Pacific Northwest Forest and Range Experiment Station (Portland, Or. ). [Portland, Or. ] : Pacific Northwest Forest and Range Experiment Station, Forest Service, U. S. Dept. of Agriculture
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