Wood Borers

Several insect orders commonly cause wood boring damage to trees, logs and processed wood products, including:

Coleoptera

Three groups of beetles will be covered:

Ambrosia Beetles

Ambrosia beetles (primarily Trypodendron and Gnathotrichus) are the most destructive wood borers for the timber industry in BC.  Several millions of dollars of damage are caused by the degraded value of attacked logs in BC every year.  This is pest is covered separately and will not be discussed here.

Longhorned Beetles (a.k.a. roundheaded woodborers)

Longhorned beetles belong to the family Cerambycidae (entomology types call them cerambicids).  These beetles generally attack weakened or dead and down trees.  The adults, as the name implies, have long, conspicuous antennae – often longer than its body.  The grubs are called roundheaded borers, as their head and tunnels are round.  (This is in contrast to the flatheaded borers, which, as you guessed it, have a flattened/oval head and tunnels).  The most common longhorned wood borers belong to the Monochamus genus – commonly known as sawyer beetles.

Monochamus (sawyer) beetles primarily attack pine, spruce, Douglas-fir and larch.  Aside from the damage to the sapwood, the other serious concern of longhorned beetles is that they are able to vector the pinewood nematode.  The pinewood nematode occurs rarely in Canada, but the pest is known to cause mortality in pine in Japan.  This has serious trade implications, especially with Europe, as there is great concern regarding the importation of this pest.

Metallic Beetles (a.k.a. flatheaded woodborers)

Adult metallic beetles are brightly coloured and have a metallic sheen.  They belong to the family Buprestidae (but you can call them buprestids).  The larvae have flattened headed (and a wide thorax, followed by a narrower abdomen - reminds me of Sylvester Stallone) and create oval shaped tunnels – hence the name flatheaded borers.  These buprestids attack healthy trees.  There is little external evidence. 

The most common species of metallic woodborers are the golden buprestid and the western cedar borer.  In general the adults of both species are a shiny bronzy blue-green on top and coppery-golden underneath (1-2 cm in length).  The mature grub is white with brown mouth parts (3-4 cm long). 

Golden Buprestid: range is essentially the southern half of the province; preferred host is Fd; and damage is usually restricted to the sapwood.

Western Cedar Borer: range is restricted to southern Vancouver Island and adjacent coast at low elevations and most often on exposed south facing slopes; preferred host is Cw; fresh cut logs will have bore holes at the knot faces; and damage is mostly in the heartwood in the upper crown. 

HYMENOPTERA

Two groups of hymenopterans will be discussed:

Carpenter Ants

This is a social insect that lives in colonies.  There are 3 castes of adults: workers, winged females and winged males.  A mating flight occurs in late spring/early summer.  Males die soon after mating.  Females mate only once but lay eggs throughout her 2-15 year life span.  She may be taken in by an existing colony to replace a queen or start her own colony.  Carpenter ants belong to the genus Camponotus – there are 1,000’s of different species.  In nature they infest stumps, logs, snags and dead portions of trees.  They however can be attracted to wood structures.  They are attracted to damp and decaying wood – they can however extend a nest into sound wood.  They don’t eat wood; they simply excavate to make a home.  The colonies are clean as the wood shavings are taken out of the home.  In fact it is the wood shavings at an entrance that can serve as a first clue as to their presence.  They are omnivores (fruit, insects, foliage, etc.) and often prefer honeydew.  They are also good scavengers, and if in the home will collect food scraps and crumbs to bring back to the nest.  Management tactics include:

Wood wasps (Horntails)

These are large wasps (2.5 cm) with a thick waist and a “horn tail”.  They are metallic blue-black with some yellow/orange markings.  Adults emerge in spring and typically infest fresh killed trees and logs.  Trees suffering recent fire damage are very attractive.  The female uses her ovipositor to lay eggs in solid wood (i.e. through the bark).  Larva tunnel in the wood (tunnel is about the diameter of a pencil).  Pupate in phloem.  Life cycle is 1-2 years.  This is not a serious pest of trees or structures – but can be found in firewood.

ISOPTERA

Termites are social insects with a structured caste system, consisting of the king & queen, soldiers, workers and winged reproductives (they may also have “kings & queens in waiting”).  Unlike carpenter ants, termites do in fact feed on wood (and other cellulose products like pulp & paper).  Another difference is that termites seal off their nest and thus the tunnels contain frass (whereas the ant nests are clean).  They are usually found in windfalls, stumps and logs in contact with the ground.  Termites play a major role in the breakdown of wood (recycling).  They can however, also infest wooden structures and cause significant damage – in the US the estimated cost of damage and control is close to a billion dollars per year.  Termites are often divided into three groups:

Pacific Dampwood Termites are found in southern BC.  They require wood that has high moisture content, but is not necessarily in direct contact with the ground.  These termites are usually found in rotting logs but can also damage poles, pilings and buildings.  These termites have a major swarm (flight) in late summer.  The wings fall of after mating.  The predation rate is very high and usually only a few of the mated pairs survive to start a new colony.

Western Subterranean Termites are also found in southern BC.  However, subterranean termites typically infest ‘buried wood’ (including rotting stumps).  This is due to the fact that these termites require higher moisture content than dampwood termites.  However, they do often extend their colony by building earthen tubes.  It is by the connection of these tubes that these termites infest wooden structures.  Aside from the earthen tubes, there are no external signs of infestation as a veneer of outer wood is always left in tact.  However, the entire inner core of a beam of wood can be colonized.

Drywood termites do not occur in BC – they are found in warmer climes such as the southern US.

Management for termite damage in BC can be (over) simplified to keeping wood structures dry and, in the case of the subterranean termite – keep a look out for earthen tunnels at the base of buildings.