Forest Insects Essay, Research Paper
BALSAM WOOLLY ADELGID (Adelges Piceae)
Today’s forests are under a continuous compound of physical stresses. In North America examples of this are evident in all regions, whether it be the subjection of Great Lakes woodland’s to acid precipitation, the submission of hundreds of thousands of forested acres out west to fire of the catastrophic level, or annual gypsy moth defoliation of entire mountain sides in north central Pennsylvania. These dangers are out there and they are only a handful of the prospective damaging agents that exist in forested areas.
The focus of this term paper will be on the nature and characteristics of an insect that inhabits a coniferous species of North America. Adelges piceae, commonly known as the balsam woolly adelgid/aphid, exists by means of a parasitic relationship with specific trees native to the United States and Canada. The insect is a damaging factor that must be dealt with before it claims victims our coniferous forests and ecosystems can’t live without.
Adelgis piceae was accidentally introduced to North America from Europe and has become an important pest of true firs (Abies sp.). The range of the adelgid includes all of the Maritime Provinces, New England, down through the Appalachians, and is found throughout the Pacific Northwest. Currently it devastates stands of subalpine fir (Abies lasiocarpa) and severely affects growth of silver fir (Abies amabilis) in many areas. This insect is now an urban pest of ornamental firs and a major Christmas-tree plantation problem, especially with Fraser fir (Abies fraseri) growing in the Appalachians (Edmonds, 2000). Presumably it is capable of spreading over much of the range of its host. Although, the aphid generally does not survive temperatures below -34 degrees C, but may persist at lower temperatures on the lower parts of tree boles protected by snow (Harris, 1978).
A summarized life history of Adelgis piceae would read as follows. The immature adelgid (nymph) over-winters on the bark of trees. Depending on climatic conditions, the nymph will come out of hibernation in late April to early May. By July the nymph reaches adulthood and begins laying eggs. Females, there are no males, may lay over 200 eggs throughout a six week period (Harris, 78). The adelgid that hatches is called a crawler and represents the only mobile stage of the insect’s life. The dark purple to black nymph is very small and is blown about the wind as it moves around on the tree. This is how the insect spreads to other trees.
While in the crawler stage, the nymph searches for a desirable location to settle down and feed. When a favorable location is found, the adelgid attaches itself to the tree by inserting its long mouthparts into the living bark. Once it is attached and begins feeding, it becomes sedentary and starts secreting the white waxy material that covers it’s body.
In late September and early October the second generation matures and begins laying eggs. It is the nymphs that hatch from these eggs that attach themselves to the bark and hibernate during the winter, laying the next seasons eggs the following July. Two generations are common in most areas, but as many as four generations may occur in lowland valleys (Holtrop, 95).
The aphid sucks the sap from the living bark of the tree. As it feeds, it injects saliva, which causes increased tissue growth of the tree. This tissue growth results in differing damage depending on the location of the injury. Infestations of the tree most often occur in the following locations: under lichens or in cracks on the bark of main stems or large branches, along branch nodes of stems in the crown of the tree, and around new growth buds of twigs (Holtrop, 95).
Heavy infestations on the trunk and main branches are whitish, appearing as a mass of tiny cotton balls or bits of wool. The adelgid injury on the trunk obstructs the flow of water and nutrients between the roots and crown of the tree. It is noted by Mr. Harris that swelling may also occur, but this usually goes unnoticed because the tree dies within two to three years.
Damage to the buds and crown is more obvious. Enlarged and contorted stems and twigs stand out from the healthy ones as foliage dies out. Buds are killed or growth is inhibited by the adelgids, and as old needles are shed they are not replaced by new growth. Holtrop notes that as a result the tree becomes increasingly thin, and that this type of damage may persist for many years before the tree dies.
Direct control of the Adelgis piceae in forest stands is impractical by methods known at present. High value trees in parks and nurseries can be treated successfully with insecticides if all above-ground parts of trees can be thoroughly drenched. This isn’t to say that there is no hope for infected forest stands. Losses in forest stands can be minimized by intensive cutting of trees of the genus Abies before serious tree mortality occurs and before dying trees become unsuitable for salvage.
Of prime concern is the prevention of spread to uninfested areas. Strict regulation of tree movement will help to restrict infestation spread. It should also be noted that several species of imported predacious insects have not been successful in reducing the problem (Harris, 78).
In conclusion, I would like to explain what first turned me on to the thought of researching this insect. This past summer I took a week’s vacation to The Great Smoky Mountains National Park in Tennessee and North Carolina. I was stunned by the abundance of wildlife and vegetation present throughout the park and was amazed at how healthy and vigorous each species appeared to be. Then we hiked to the highest point in the Smokies, Clingman’s Dome.
It was evident immediately that something was affecting the trees surrounding the 6,700 feet tall work of nature. Upon further investigation, I was informed that it was the fir trees, Frasier fir to be specific, that lined the mountainsides with their decaying remains. My initial reaction was to curse a common predator of our coniferous species present at higher elevations, acid rain. To my surprise though, I later read that it wasn’t the acid precipitation claiming the lives of the magnificent firs, it was the balsam woolly adelgid. An insect less than 2mm long was responsible for the demise of hundreds of old-growth Frasier firs. At that moment I felt the thirst for knowledge and I have now quenched that thirst through the writing of this paper.