Custom Search
|
|
|
||
 the country. They do not cause any serious structural damage to wood in use, but since they can be
present in both hardwood and softwood products with some bark on, they should be recognized.
The beetles may survive in sawed lumber for a year or more, or until the wood is dry.
The female lays eggs in a gallery constructed in the cambium. The larvae tunnel away from the egg
gallery. The galleries increase in size and become tightly packed with frass. Only the surface of the
wood is slightly etched by these tunnels (Figure 4-27). Bark beetles pupate at the ends of the tun-
nels. The adults emerge from the pupal stage and tunnel straight out through the bark. The surface
of the bark is sometimes riddled with round exit holes 1/16 to 1/8 inch in diameter. The beetles are
brown, reddish-brown, or black, no more than 1/8 inch long, cylindrical, robust, and the head is par-
tially or completely concealed from above. Bark beetles cannot live in seasoned wood, so there is
no reinfestation.
Ambrosia beetles do not attack dry wood, but their damage can be seen as
small tunnels, surrounded by stained wood in both hardwood and softwood lumber. The damage
usually does not affect the strength of the wood.
The adult beetles bore 1/50 to 1/8 inch-diameter tunnels straight for several inches into the wood of
trees or green logs and throw out all of the frass. Once inside the sapwood, the tunnel may branch
and follow the curvature of one or more annual rings, or it may be unbranched and relatively
straight. There also may be short side tunnels of the same diameter that follow the grain and where
larvae feed and later pupate.
As the tunnels are constructed, the walls are inoculated with a fungus by the adult beetles. The fun-
gus stains the gallery walls black, blue, or brown (Figure 4-28). The staining often spreads through
the surrounding wood and is particularly obvious in lighter-colored species. The beetles will con-
tinue to infest the wood as long as it remains moist, but attack ceases when the wood dries out.
Upon drying, the wood can be used without further deterioration.
4.3.5.2 Prevention and Control. Control procedures are based on three ap-
proaches. These are 1.) eliminate or reduce the beetle population, 2.) use naturally durable wood, or
use a chemical treatment to protect susceptible wood, and 3.) control environmental conditions in
the wood to retard development of the beetles or larvae.
For the beetles that begin their attack under the bark, the removal of any bark edges is a good
preventive measure. Many of the round-headed and flat-headed borers feed under the bark for ex-
tended periods before they enter the wood. The bark beetles confine their attack to the inner bark,
and are thus eliminated by bark removal.
Before sawn wood is purchased or placed into service, it should be inspected. If an active infesta-
tion is suspected, the wood should be heat sterilized before leaving the manufacturing plant. Table
4-5 gives the times and temperatures required to kill lyctid beetles and most other borers. For
bostrichid beetles higher temperatures should be used.
|
 
|
|
|
||
