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Fir Engraver
Host: All species of true fir including grand fir and subalpine fir.
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| Fir engraver Mortality |
| D. Powell |
Distribution: Throughout range of true firs.
Identification: Light brown boring dust accumulating in bark crevices; distinctive galleries apparent under bark layer; crown fading.
Damage: Beetles feed in phloem and introduce blue-staining fungi which, in combination, girdle the tree.
Ecology: Fir engraver preferentially attack windthrown, weakened, or diseased trees along with slash. In some cases, small numbers of beetles can attack trees, and cause top kill, branch dieback, or patches of damage healed over by the tree.
Life Cycle: Adult beetles emerge from trees and fly between July and August, although weather and location may affect exact timing. Adults attack trees by boring under the bark and excavating a horizontal gallery, laying eggs along the margins. Eggs hatch into larvae that feed on the phloem and disrupt the water and nutrient transport system of the tree. Larvae feed until cold winter temperatures initiate dormancy. Larvae resume feeding in the spring.
Fir engraver generally complete one generation per year in Montana.
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| Fir engraver galleries |
| F. Honing |
Management
Brood trees: Identifying and removing trees currently infested with fir engraver 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.
Windthrow: Fir engraver preferentially attack windthrown, downed material. Removing windthrown trees prior to beetle flight 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).
Trap trees: Fir engraver are preferentially attracted to freshly downed material and therefore, populations can be manipulated using recently cut or windthrown trees to trap beetles. 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.
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| Adult fir engraver |
| D. Owen |
Log decks: Fir engraver 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 fir engraver and must be removed from the site prior to the next flight period. Because logging decks can attract fir engraver, 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 | ||
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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