Wood Borers

Ambrosia Beetles
Trypodendron spp., Platypus spp.,
Gnathotrichus spp., Xyleborus spp.

Hosts:  True fir, spruce, Douglas-fir, pine, aspen, poplar, and maple

Figure 149. Figure 149. White boring dust caused by ambrosia beetles tunneling in the wood of a bark beetle-killed pine.

Symptoms/Signs:  Entrance holes are small for most species (1.5 mm or less) and are marked by piles of white boring dust. Gallery patterns vary by species, but all tunnels run perpendicular to wood grain. The mines of Platypus species penetrate into the heartwood in contrast with most ambrosia beetles in the Scolytinae that mine only the sapwood.

Effects:  Weakened, dying, recently cut or dead trees are attacked. Galleries cause defect in logs. Some species can attack freshly cut lumber before it has been dried. Populations can build up in windthrown and fire-killed trees, bases of trees attacked by bark beetles, logging slash, and logs in storage. These beetles are unique among bark beetles in that larvae feed upon a special type of fungus, known as the ambrosia fungus, which grows in the galleries. Larvae do not feed on wood or phloem as in other bark beetles.

Figure 150. Figure 150. Entrance points of adult ambrosia beetle. Holes are stained by blue stain fungi.

Biology:  Insect appearance varies between beetles. Adult Trypodendron, Gnathotrichus, and Xyleborus beetles are all dark colored, cylindrically shaped beetles, about 2 to 4.5 mm long (depending on the species). Larvae are white, legless grubs with brown head capsules. All three genera belong to the subfamily Scolytinae. Platypus on the other hand belongs to the subfamily Platypodinae, which is closely related to the Scolytidae. Adult Platypus are more elongate, cylindrically shaped beetles than scolytids.

Similar Insects and Diseases:  May be confused with other bark beetles; however, ambrosia beetles are the only ones that bore straight into the bole producing fine, white boring dust.

References:  24, 33