Top 5 Conifer-Killing Insects

Although forest fires are capable of killing large numbers of trees in a short amount of time, they're not the only thread conifers face in nature — they also have to fend off poisonous insects that invade their bark, roots, and leaves, sucking the very life from them.

The following list details the top five conifer-killing insects, from the bark beetles that lay eggs in the trunks of trees and stop their sap from flowing to woody adelgids. These bugs might just haunt not only your dreams but your backyard woods! Be on the lookout for these insect pests and alert local park rangers if you fear an outbreak of these poisonous critters is occurring in your neighborhood.

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. We have ranked these insects according to their ability to cause aesthetic and commercial damage. 

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Bark Beetles

Bark beetle
Flickr/Katja Schulz

Bark beetles are the most devastating insects to attack pines, and they exist throughout North America in both eastern and western forms, are commercially destructive and my pick for the worst insect.

The Dendroctonus will kill healthy trees and trees already weakened by other factors by girdling trees while building egg-laying galleries. The lack of sap flow immediately kills the tree, and the insects move to adjacent living trees to spread more damage.

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Pales and White Pine Weevils

White pine weevil
Wikimedia Commons

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 the Canadian Forest Service.

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Spruce Budworm

Spruce budworm
Wikimedia Commons

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 budworm; several of these outbreaks have resulted in the loss of millions of cords of spruce and fir.

This occurs in such large numbers as the newly hatched larval often appear by the thousands to feed on needles or expanding buds, causing severe damage to these structures which, in turn, causes the tree to defoliate and die.

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Tussock Moth

Tussock Moth
Wikimedia Commons

The Douglas-fir tussock moth is an important defoliator of true firs and Douglas-fir in Western North America because the larvae feed on current year's foliage, causing it to shrivel, turn brown and possibly 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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Wooly Adelgids

Wooly Adelgids
Wikimedia Commons

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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Your Citation
Nix, Steve. "Top 5 Conifer-Killing Insects." ThoughtCo, Aug. 27, 2020, Nix, Steve. (2020, August 27). Top 5 Conifer-Killing Insects. Retrieved from Nix, Steve. "Top 5 Conifer-Killing Insects." ThoughtCo. (accessed October 18, 2021).