All hardwood trees in the eastern half of the United States are subject
to attack by the Columbian timber beetle, but oaks, maples, birch,
basswood, yellow-poplar, and elm are the preferred hosts in the South.
The beetle causes two major types of damage: 1) physical damage caused
by the 1/32″ to 1/16″ hole excavated by the adult into the sapwood, and
2) degrade caused by stain which may extend for a considerable distance
above and below the gallery. Large diameter trees are preferred as
hosts, but trees as small as one and one-fourth inches in diameter may
be attacked.
[Illustration: Callow adult and pupae of the Columbian timber
beetle.]
There are two and sometimes three generations of this insect each year.
Adults from the first generation emerge from late May through June and
those from the second in October. The first evidence of attack is the
white dust which collects at the entrance hole. Later, depending on the
tree’s physiological condition, a sap-soaked area may develop around the
entrance hole. The adult bores a horizontal hole into the sapwood of a
healthy tree for a few inches and later constructs two or three shorter
lateral branches. “Cradles” (or egg chambers) are then constructed for a
short distance perpendicular to these galleries. The female deposits a
single egg in each chamber. The offspring spend their entire
developmental period within the cradles feeding on fungi which grow on
the sapwood. It is this fungus which causes the extensive staining
characteristic of Columbian timber beetle attack. Winter is spent in
both the pupal and adult stages in the brood galleries.
[Illustration: Columbian timber beetle entrance holes in
yellow-poplar.]
Chemical control is not practical for forest trees.