Ambrosia beetle

Distribution

British Columbia, Newfoundland and Labrador

Ambrosia beetles, or “pinworms” as they are often called in the forest industry, are a group of beetles totalling over 1000 species worldwide. In British Columbia, there are at least five ambrosia beetle species affecting commercial timber.

Micro-habitat(s)

Lumber

Damage, symptoms and biology

Unlike several species of bark beetles, ambrosia beetles will not usually attack living trees. Also, ambrosia beetles penetrate into the sapwood, producing a whitish sawdust. This white sawdust can be seen in bark crevices and on the ground when logs are on land, and floating on the water around boomed logs. The holes in the wood made by ambrosia beetles are very small and perfectly round. A few days after attack, a dark fungal stain will appear around the holes.

Gnathotrichus sulcatus makes a hole approximately 1.3 mm in diameter. Dark-stained ambrosia beetle galleries with branching pupal niches are evident on plywood veneer or on the tangential face of lumber.

The biggest commercial loss caused by ambrosia beetles is in the degradation of lumber due to the presence of the dark-stained pinholes. The loss is particularly significant because the beetles bore into the sapwood where the most valuable clear lumber is located.

Eggs are laid in niches along the gallery. After the eggs hatch, the larvae feed on fungi and enlarge the niche in which they will pupate and become adult beetles.

Adults overwinter in their galleries. Gnathotrichus spp. appear to have overlapping generations; this results in a first flight slightly later in the spring than Trypodendron spp., and a second major flight period in late summer. Gnathotrichus spp. are less particular about the aging of wood material and will attack trees felled as recently as 2 weeks before their flight. In addition, Gnathotrichus spp. more commonly attack green lumber than Trypodendron spp.

Other information

Ambrosia beetles do not feed on wood, they feed on fungi. The ambrosia fungi associated with these beetles have been identified as Monilia ferruginea Mathiesen-Kaarik (Trypodendron), Ambrosiella sulcati Funk, Raphaella sulcati Funk, and Graphium spp. (Gnathotrichus). The fungal spores adhere to the beetles and quickly germinate in suitable new host material, creating a dark stain around the tunnels.

Main host(s)

Amabilis fir, Rocky Mountain Douglas-fir, western hemlock

Secondary host(s)

Grand fir, lodgepole pine, red alder, Sitka spruce, subalpine fir, western redcedar, western white pine