Agriculture Reference
In-Depth Information
Beetles damaging non-timber items
dried below fi bre saturation point so that re-
infestation is prevented. The old workings
of ambrosia beetles are typically identifi ed
in fi nished timbers and furniture from the
band of fungal staining around their small,
round tunnels, which tend to pass straight
across the grain.
Also detected by their damage in sawn
timbers, but with slightly larger holes, are
the longicorn beetles (Cerambycidae) with
oval holes to approximately 12 mm long
and augur beetles (Bostrychidae) with clean
circular holes to about 8 mm diameter. As
their tunnels tend to meander, the observed
surface hole shape can be quite variable.
Adult beetles emerging from their host
timbers can damage non-food items such as
plasterboard and items sitting on timbers.
Unexpected exit hole patterns can create
confusion, for example where beetle exit
holes of hardwood-feeding lyctids appear
in softwood timbers or run across fl oor-
boards rather than along them. Similarly,
bostrichid beetles have been recorded dam-
aging electrical insulation (Barnes, 1946),
although this form of damage is relatively
uncommon. Products made of wood-like
materials such as bamboo (Graminae:
Bambusoidae) may contain high levels
of starch and so are at risk from beetle
attack, particularly by
Dinoderus minutus
(Lyctidae) (Plank, 1950; Garcia and Morrell,
2008).
Beetles damaging green timber framing
Some structures are built from framing
timber that is still green (not dried before
use). This means that beetles that were
present in the original tree may complete
their life cycle after the timber has been
concealed in the building fabric. In
Australia, up until the mid-1980s, it was
common for houses to be built of green
Eucalyptus
timber, which permitted longi-
corns to complete their development and
cause great alarm as the large adult beetles
emerged several years later. Management
actions are not required because these
beetles cannot re-infest. It is suffi cient to
patch the large oval exit holes (Creffi eld,
1996). Most beetles that infest green timber
are generally killed by the drying and
handling processes involved in the prepar-
ation of the timber.
Types of Beetle Damage
The type of damage varies greatly with
beetle type. The damage ranges from cos-
metic damage where the surface is holed, to
structural damage where the timber loses
the ability to carry the required loads. The
most severe structural damage occurs where
the beetles are capable of re-infesting so that
they consume the timbers until complete
destruction. Some species, such as the
ambrosia beetles, leave a few holes and tend
not to damage structural capacity. Others
such as powder post beetles literally reduce
much of the timber to powder, leaving it
entirely unserviceable.
Factors Contributing to Infestation
Beetles infesting dried timbers
Timber quality
Borers cannot live in totally dry wood but
can infest when dry wood gains suffi cient
moisture. The acceptable moisture range
varies between beetle types but a moisture
content of more than 10% and sometimes as
high as 40% is required. Consequently the
risks from beetle infestation are greater
where timber is subjected to high humidity,
which invariably affects population distri-
butions (French, 1968).
Timbers vary greatly in quality. Dense
timbers carry large deposits of resins that
render them inedible. Borers attacking fresh
(un-aged) timber often have a strong
requirement for starch and are restricted to
the sapwood where starch has been stored,
rarely damaging heartwood. Beetles also
tend to specialize between hardwood
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