[Illustration: Eggs and wool-covered adult balsam woolly aphids.]
The balsam woolly aphid was introduced into northeastern North America
from Europe around the turn of the century. Since then it has become a
pest of major importance to true firs on the east and west coasts of the
continent, and threatens some 60,000 acres of Fraser fir in the southern
Appalachians. Usually the balsam woolly aphid has two generations per
year in the southern Appalachians. Eggs of the first generation hatch in
late June and July followed by the second generation in September and
October. The immature stage of the aphid known as a “crawler” is the
only motile stage in the aphid’s life cycle. Once the crawler begins
feeding, it transforms into an adult and never again moves. Reproduction
is parthenogenic with each female laying approximately 100 eggs during
her lifetime.
In the feeding process the aphid injects a salivary substance into the
host tree, which causes growth abnormalities. Initial symptoms of aphid
attack may include “gouting” of buds or twig nodes and some twig and
branch die-back. Heavy stem attacks reduce the tree’s ability to
translocate food and water. Usually a heavily infested tree dies within
two to seven years.
Chemical control is effective but extremely costly and thus limited to
very high-value areas along scenic road-ways. Other control measures
include removal and destruction of infested material.
[Illustration: Fraser fir infested by balsam woolly aphid.]