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What Is a Spruce Beetle?

Cindy Quarters
Cindy Quarters

A spruce beetle, Dendroctonus rufipennis, is a very small beetle that digs into the bark of certain types of spruce trees. The species is native to North America with high concentrations found in Nova Scotia, British Columbia, Ontario and Quebec; it is also found in some northern areas of the US. Full grown spruce beetles are no more than 0.75 inches (0.64 cm) in length and are often hard to spot. Typically the way the presence of these pests is first known is by the serious damage caused to the trees they inhabit. Trees infested with these destructive insects frequently die.

The spruce beetle favors some types of spruce, including white and Sitka trees, but it tends to avoid the black spruce; on occasion it will infest them as well. It lives in the phloem, a relatively thin layer of actively growing wood. This layer is between the bark and the solid wood core of the tree. The spruce beetle kills many of the trees it infests, but because it does not dig deeper into the wood of the tree the wood can often be salvaged after the tree dies. All of the inner wood can typically be used commercially, as long as it is harvested within a reasonable time frame.

The spruce beetle lives in phloem, a relatively thin layer of actively growing wood.
The spruce beetle lives in phloem, a relatively thin layer of actively growing wood.

A large tree that is hosting a population of spruce beetles may have 100 or more of these insects for every square foot of bark. In the summer the spruce beetle will come out of an existing host tree and fly to other trees in the area. They typically live in dying or damaged trees, but if these are unavailable the spruce beetle will establish residence in any spruce it can find.

The spread of spruce beetles can be reduced by storing firewood for intervals of no longer than one year.
The spread of spruce beetles can be reduced by storing firewood for intervals of no longer than one year.

Human activity often encourages the spread of the spruce beetle. They can live in firewood and slash piles of debris left over from logging operations. When conditions are favorable, the insects will emerge from these places and find new homes in living trees elsewhere in the forest. Once established in an area, the pests can kill trees year after year, causing harm to both the trees and the economic stability of a region.

There are high concentrations of spruce beetles found in Nova Scotia, British Columbia, Ontario and Quebec.
There are high concentrations of spruce beetles found in Nova Scotia, British Columbia, Ontario and Quebec.

The spruce beetle causes a great deal of damage in areas that it infests. In the US, Alaska has lost millions of acres of forest, and in the 1990s Maine reported a loss of about 90% of the larger trees in some areas. People can help minimize the spread by not storing firewood for more than a year. Any cut wood should be de-barked, split, and dried to kill any spruce beetles that may be infesting it.

Frequently Asked Questions

What is a spruce beetle and where can it be found?

The spruce beetle (Dendroctonus rufipennis) is a species of bark beetle native to the forests of North America, particularly in the western United States and Canada. These insects primarily infest Engelmann, white, and other spruce trees. They play a natural role in the life cycle of forests but can become pests when their populations surge.

How does a spruce beetle infestation affect spruce trees?

A spruce beetle infestation can severely damage or kill spruce trees. The beetles bore through the bark to lay eggs, and the developing larvae feed on the tree's phloem, disrupting the flow of nutrients and water. This can lead to foliage discoloration, crown thinning, and ultimately, the death of the tree if the infestation is severe.

What are the signs of a spruce beetle infestation?

Signs of a spruce beetle infestation include pitch tubes on the bark, sawdust-like frass around the tree base, and woodpecker activity as they feed on the larvae. Infested trees may also show yellowing or reddening of needles, and eventually needle drop, indicating the tree's declining health.

What factors contribute to spruce beetle outbreaks?

Outbreaks of spruce beetles are often linked to factors such as dense forests, older trees, and stressed trees weakened by drought, windthrow, or previous pest infestations. Climate change, with warmer temperatures and drought conditions, has also been implicated in increasing the frequency and severity of spruce beetle outbreaks.

How can spruce beetle infestations be managed or prevented?

Management of spruce beetle infestations includes practices like sanitation logging to remove infested trees, pheromone traps, and maintaining tree health to resist beetles. Preventative measures involve thinning dense stands of trees and diversifying forests with different species to reduce the likelihood of large-scale infestations.

Are spruce beetles harmful to humans or animals?

Spruce beetles are not directly harmful to humans or animals, as they do not bite or sting and are not known to carry diseases. However, their impact on forest ecosystems can have indirect effects, such as altering wildlife habitats, increasing the risk of wildfires, and affecting industries reliant on healthy forests.

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    • The spruce beetle lives in phloem, a relatively thin layer of actively growing wood.
      By: designua
      The spruce beetle lives in phloem, a relatively thin layer of actively growing wood.
    • The spread of spruce beetles can be reduced by storing firewood for intervals of no longer than one year.
      By: beeandbee
      The spread of spruce beetles can be reduced by storing firewood for intervals of no longer than one year.
    • There are high concentrations of spruce beetles found in Nova Scotia, British Columbia, Ontario and Quebec.
      By: Iryna Volina
      There are high concentrations of spruce beetles found in Nova Scotia, British Columbia, Ontario and Quebec.