Unlike the spruce bark beetles, the bark breeding beetles on silver fir are not very well known. The fact that most species partly develop within the sapwood makes an effective countermeasure more difficult. All silver fir beetles described in this fact sheet are occasionally found living together and are, in general, secondary pests. This means that they find favorable conditions for their development only on weakened and dying trees. Breeding sites are silver firs which are weakened by wind, snow damage, insect attacks, frost, but particularly by drought and heat. Some of the beetles tend to occur in outbreaks and may attack vital silver firs as well.

needles in the lower parts of the crown are discolored brown

Fig. 1. After the attack by the European fir engraver beetle, the needles in the lower parts of the crown are discolored brown.

Breeding galleries of the silver fir bark beetle

Fig. 2. Breeding galleries of the silver fir bark beetle (Pityokteines curvidens).

 

The silver fir bark beetle (Pityokteines curvidens)
The greatest damage on silver fir is caused by the silver fir bark beetle. It prefers to attack the branch free parts of the stem of weakened and dying older silver firs. It occurs only rarely in stems with a diameter of less than 16 cm. The silver fir bark beetle often occurs as a single species and is the most frequent beetle of the Pityokteines-genus. The nuptial chamber of the beetle is often hidden in the bark and is not clearly visible. The females feed across the grain where they build typical galleries (see Figure).

Pityokteines spinidens
This species colonizes similar stem parts as the silver fir bark beetle. Pityokteines spinidens is the rarest of the three different Pityokteines-species described here.

European fir engraver beetle (Pityokteines vorontzovi)
This beetle prefers the thin upper stem parts and branches with smooth bark. Therefore it mainly colonizes the tops of silver firs. Only with young trees it colonizes the entire stem.

The fir bark beetle (Cryphalus piceae)
The fir bark beetle colonizes the thin branches and twigs of the crown of older and weakened silver firs. It can also be found in broken tree tops and piles of branches. Like the six-spined spruce bark beetle, a high population of the fir bark beetle can cause damage in thicket and pole forests. Like the silver fir bark beetle, they tend to occur in outbreaks.

The European silver fir weevil (Pissodes piceae)
This beetle is a secondary pest and colonizes the most diverse stem densities. It doesn’t leave out wood piles and trunks either. The European silver fir weevil is characterized by high reproductive ability. It is considered to have a high longevity as they can survive as long as three to four years.

 

Infestation characteristics

  • Particularly striking are shining, colorless, fresh drops of sap on stems of healthy looking silver firs which have not yet been colonized for breeding (primary attack).
  • Healthy silver firs with dried-out yellowish old sap drops.
  • Sap flow on stems in March/April.
  • Fine ejected boring dust. This characteristic is difficult to detect because of the amount being significantly smaller than that of e.g. the eight-toothed spruce bark beetle species.
  • Often reddening of the needles in the lower part of the crown (see Figure) with simultaneous crown transparency.

(without the European silver fir weevil)

The fir bark beetle (left) and The European silver fir weevil (right)

Fig. 3. The fir bark beetle (left) and The European silver fir weevil (right). Drawing: C. Chararas and W. Schwenke

Translation: Marcus Schaub (WSL) 

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