Bark Beetles
Fir Engraver
Scolytus ventralis (LeConte)

Hosts:  True firs

Figure 129. Figure 129. Egg and larval galleries of fir engraver. Galleries are horizontal with two branches radiating out from entrance point.

Symptoms/Signs:  Freshly attacked green trees have tiny holes in the bark, reddish-brown boring dust in bark crevices, and streams of clear pitch exuding from entrance holes. Needles change from green to yellow-green to sorrel and then red to brown. Larvae, pupae, and egg are found in the inner bark; egg and larval galleries deeply score the wood, creating characteristic horizontal egg galleries and vertical larval galleries. Adult beetles are small, shiny, black beetles about 4 mm long. The abdomen is incurved at the rear.

Figure 130. Figure 130. Adult fir engraver beetle. Note the sawed-off appearance of the beetles' abdomen.

Biology:  In warm locations, the fir engraver completes one generation and a partial second generation each year. In cooler sites, the beetle needs 2 years to complete its life cycle. Adult flight occurs throughout the summer, but peaks in July and August. Fir engravers overwinter primarily as young or mature larvae. In the spring, they feed for a short period and then construct pupal cells at the end of their galleries.

Effects:  Fir engravers are a major mortality agent of true firs, usually attacking pole-sized to sawtimber-sized trees. Outbreaks often occur during and following droughts. Root diseases are often associated with attacked trees. The fir engraver can also breed in slash and wind-thrown trees. Flagging (death of branches) may occur on fir trees that have been only partially attacked.

Figure 131. Figure 131. White fir mortality caused by fir engraver on Mormon Mountain, Arizona.

Similar Insects and Diseases:  Other bark beetles attack subalpine fir, including species of Dryocoetes and Pseudohylesinus. They may be separated by gallery patterns and characteristics of adult beetles.

References:  3, 20, 24