southern Appalachians two and occasionally three generations are 
produced (24, 5). 
The balsam woolly aphid feeds at any point on the tree where 
it can reach the parenchyma of the cortex with its mouth parts. 
During feeding, it introduces an irritating salivary substance into 
the tissues which causes an abnormal multiplication of cells and 
excessive growth in the vicinity of the point of attack. Infested 
twigs and small branches become swollen and distorted. Swellings 
are particularly noticeable at nodes and around buds. Branchlets 
may thicken, twist irregularly, and bend down at the ends. The 
main stem tapers rapidly toward the top. The tip becomes bent or 
flattened and is usually killed. This results in a condition com- 
monly known as “gout.” The wood of infested trees becomes hard 
and brittle and its surface is usually marked with dark, reddish- 
brown blotches. This type of wood, which resembles “compres- 
sion’ wood, is produced in greatest amount on moderately infested 
fast-growing trees. Trees suffering from heavy stem attack may 
be killed in 3 or 4 years (fig. 22). 
The balsam wooly aphid is subject to a considerable amount of 
control by low winter temperatures, especially in the northern 
portions of its range. Tree resistance is also an important control 
factor, some trees being less favorable for multiplication of the 
insect than others. So far, no insect parasites of the aphid have 
been found in North America. Quite a large number of predators 
have been recorded, however, but they have proved incapable of 
preventing outbreaks. A few species of introduced predators, such 
as the derodontid beetle, Laricobius erichsonti, offer promise of 
greater benefits in control in the future (7, 27). 
Outlying infestations of the balsam wooly aphid may be 
controlled by clear cutting infested stands, especially if this is fol- 
lowed by burning. The spread of infestations may also be checked 
by the prompt salvage of infested stands during the winter. Short 
rotation and cutting cycles, combined with silvicultural methods 
of reducing the balsam fir content of stands, have helped in re- 
ducing infestations in New Brunswick (28). 
Adelges strobilobius (Kalt.), an introduced species, occurs in 
southern Canada and south and west in the Eastern States to 
Washington, D. C. and the Lake States. Its hosts are recorded as 
larch and spruce, principally red and black. Infestations on larch 
appear as white wooly masses on the needles and as clusters of 
aphids at the bases of needles. Infestations on spruce may be 
recognized by the presence of small galls at the tips of new 
growth. A related species, A. lariciatus (Patch), occurs on larch 
and Norway spruce. It produces galls similar to those produced 
by the eastern spruce gall aphid. Cumming (180) discussed its 
life history. 4 
The pine bark aphid Pineus strobi (Htg.), an introduced species, 
occurs over most of the United States wherever white, Scotch, 
and Austrian pines grow. It is small, dark, and covered with floc- 
culent wax. Infestations may be recognized by the presence of 
spots and patches of white cottony material on the smooth bark 
of the trunks and limbs (fig. 23) or at the bases of needles on 
twigs, or on buds. The trunks of heavily infested trees often ap- 
pear as if whitewashed. 
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