There are aggressive insects that attack coniferous trees which ultimately cause death or devalue a tree in the urban landscape and rural forest to the point where they need to be cut. Five of the nastiest insects have been suggested by foresters and landowners at About's Forestry Forum. I have ranked these insects according to their ability to cause aesthetic and commercial damage. Here they are:
#1 - Bark Beetles:
Bark beetles are the most devastating insects to attack pines. They exist throughout North America in both eastern and western forms, are commercially destructive and my pick for the worst insect.
The Dendroctonus/Ips sp.
will kill healthy trees and trees already weakened by other factors. The bark beetles girdle trees while building egg-laying galleries. The lack of sap flow immediately kills the tree, the insects move to adjacent live trees and the damage spreads.
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#2 - Pales and White Pine Weevils:
Pales weevil is the most destructive insect of newly planted pine seedlings in the Eastern United States. Adult weevils are attracted to cutover pine lands where they breed in stumps and old root systems. Seedlings planted in freshly cut areas are injured or killed by adult weevils that feed on the stem bark.
The white pine weevil is the "most serious and economically important native insect pest of spruce and pine regeneration in Canada" says Canadian Forest Service.
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#3 - Spruce Budworm:
Spruce budworm is one of the most destructive native insects in the northern spruce and fir forests of the Eastern United States and Canada. Outbreaks occur every few years and balsam fir is the species most severely damaged by the bud-worm. These outbreaks have resulted in the loss of millions of cords of spruce and fir. The newly hatched larva feeds on needles or expanding buds. Severe damage to these structures causes the tree to defoliate and die.
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#4 - Tussock Moth:
The Douglas-fir tussock moth is an important defoliator of true firs and Douglas-fir in Western North America. The larvae feeds on current year's foliage, causing it to shrivel, turn brown and will kill or top-kill the tree. The pest is considered serious and can kill up to one-third of trees in a stand of Douglas-fir and deform significant numbers of trees remaining alive.
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#5 - Wooly Adelgids:
The balsam and hemlock wooly adelgids are threatening entire tree species in parts of the eastern U.S. forest. Although not a commercial timber threat (with the exception of Christmas tree growers) the wooly adelgid attacks balsam fir and the eastern hemlocks killing entire stands on critical sites. The sap-sucking insect feeds where the needle attaches to the twig. Researchers believe the aphid's toxic saliva is the agent that does the damage.
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