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Spruce Beetle
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| Spruce beetle outbreak |
| A. Munson |
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| Spruce beetle damage |
| D. Blackford |
Distribution: Throughout range of Engelmann spruce.
Identification: Red-brown boring dust accumulating in bark crevices and at base of tree; distinctive galleries apparent under bark layer; crown fading to yellowish-green one year after attack; woodpecker activity often apparent.
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| Spruce beetle pitch tube |
| A. Munson |
Damage: Beetles feed in phloem under the bark and girdle the tree.
Ecology: Spruce beetle preferentially attack large, mature trees along with windthrown trees and logging decks.
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| Spruce beetle larvae |
| DNRC |
Life Cycle: Spruce beetle typically requires two years to reach full maturity. The adults attack new trees in June through July, create vertical galleries, and lay eggs along the margin. The eggs hatch into larvae that feed in circuitous galleries radiating out from the parental gallery. Spruce beetle spend the first year overwintering as larvae. The larvae resume feeding in the spring until pupation. The adults emerge in August through September and re-enter the same tree near the base of the tree or root collar. Spruce beetle spend the second year overwintering as adults.
Spruce beetle requires two years to develop in Montana.
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| Spruce beetle galleries |
| E. Holsten |
Management
Brood trees: Identifying and removing trees currently infested with spruce beetle offspring can directly reduce populations in the stand. Accurate identification is critical for this tactic to be successful. Infested trees will commonly have an apparently healthy, green crown. Closer inspection will reveal boring dust in bark crevices and galleries under the bark. Look for larvae, pupae, or adults under the bark to determine current infestation. Brood trees must be removed from the stand as immature beetles can successfully continue development in a cut tree.
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| Adult spruce beetle |
| E. Holsten |
Windthrow: Spruce beetle prefer windthrown, downed material over standing green trees. Removing windthrown trees prior to beetle flight (June through July) will inhibit beetle attack and reproduction in available material. Windthrown trees can also be left on site to attract beetles and can be effectively used as “trap trees”(see below).
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| Spruce windthrow |
| DNRC Photo |
Trap trees: Spruce beetle are preferentially attracted to freshly downed material and therefore, populations can be manipulated using recently cut or windthrown trees. Large trees (greater than 15 inch diameter) should be cut in the early spring and piled individually in the shade with limbs intact. These trap trees will draw beetles from the surrounding stand and may spill over into adjacent standing trees. Trap trees and infested surrounding trees must be removed from the site prior to the following summer when the next generation disperses to new trees.
Log decks: Spruce beetle will continue to develop in trees even after they are cut. Therefore, it is critical to remove infested logs from the site well before the next beetle flight period in order to inhibit dispersal. Log decks can also attract spruce beetle and must be removed from the site prior to the next flight period. Because logging decks can attract spruce beetle, they can be used as trap trees as a means of reducing beetles in the area (see above).
Links |
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| Forest Insect and Disease Leaflet (FIDL) | Field Guide - Identification | Management Guide | ||
| More Information on MCH | ||||
Additional Common Forest Insects in Montana
| Douglas-fir Beetle | Red Turpentine Beetle |
| Douglas-fir Tussock Moth |
Spruce Beetle |
| Fir Engraver | Western Pine Beetle |
| Mountain Pine Beetle | Western Spruce Budworm |
| Engraver Beetles (Ips species) |
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