Distribution and Characteristics of Balsam Woolly Aphid Infestations in the Great Smoky Mountains

The balsam woolly aphid was inadvertently introduced into North America in Maine around 1900 and has subsequently spread throughout the eastern spruce-fir forests. Within the past 20 years the aphid has become a serious pest of Fraser fir in the Southern Appalachians, causing concern for the scenic and scientific resources of the spruce-fir forests. Fraser fir is highly susceptible to attack by the aphid with mortality occurring within 2 to 5 years following colonization. This rapid mortality in combination with the phenomenal reproductive potential of the aphid threatens the existence of Fraser fir. Investigations were conducted within the Great Smoky Mountains National Park to determine the history, current distribution, and level of damage of balsam woolly aphid investigations. The relationship of levels of infestations with selected community structure and environmental factory was also investigated.

The balsam woolly aphid arrived in the Great Smoky Mountains around 1960. The initial infestation was on Mt. Sterling, located on the eastern boundary of the spruce-fir distribution within the Park. Analysis of the aerial infrared transparencies revealed that the aphid is distributed throughout the entire spruce-fir forest type. Infestation intensity, as determined by the extent of fir mortality and the size of the infestation, was highest in the eastern portion of the spruce-fir distribution, lower in the middle portion, and lowest in the western portion. Detailed information of the location and size of infestations was recorded on 1:24000 topographic maps.

Permanent plots were located throughout the spruce-fir forests in the Park in areas of varying infestation levels. Sampling was proportional to the area involved in each level. Low levels of balsam woolly activity were associated with dense, pure, young, even-aged stands of Fraser fir growing on eastern and northeastern aspects at the higher elevations of the spruce-fir distribution within the Park. High levels of aphid activity were more common in less dense, mixed, mature, uneven-aged stands located on western and southwestern aspects at the lower elevational limits of Fraser fir's distribution. Initial infestations occurred at the northern hardwood-fir ecotone and gradually expanded upslope.