Adults become active during May and June in Indiana and West Virginia (648). 
They tend to reattack the tree in which they develop, but some dispersal occurs 
(933). The wood is entered through bark crevices, usually on the main trunk near 
the base. In oak, a tunnel is bored straight into the sapwood until it nears the 
heartwood, then it turns right or left (fig. 171B), whereas in diffuse porous wood 
such as maple and yellow-poplar, the tunnel branches but then extends toward the 
pith. Entrance holes are clean-cut and about 2 mm in diameter, with boring dust and 
sap exuding from them. Short tunnels or chambers leading from the upper and 
lower surfaces of the main tunnels are excavated at intervals. Eggs are laid in the 
chambers and the larvae live and develop in them. The larval food is a yeast of the 
genus Pichia (649) and another fungus, Ambrosiella xylebori Brader (68). Food is 
stored and transmitted by prothoracic mycetangia possessed by the male beetle 
(450). Winter is spent in the adult stage in short tunnels under bark scales or vines 
at the base of the tree (932). There are two to three generations per year. 
The Columbian timber beetle seems to prefer vigorous trees, and it attacks trees 
of practically all sizes. Damage is conspicuous in cross sections of the trunk of 
infested trees. Streaks of stain originating from the tunnels extend, often for 
considerable distances, above and below them. These and the black-stained tunnels 
cause defects known variously as “‘grease spots,” “‘steamboats,”’ “spot worm,” 
‘“flag-worms,”’ and “black holes.’ Damaged wood is rendered unfit for such uses 
as face veneer, cooperage, or furniture. In southern Indiana, red and silver maple 
woods, which are highly valued in the furniture industry, are reduced in value by 38 
percent (SOQ). 
Corthylus punctatissimus (Zimmermann), the pitted ambrosia beetle, occurs 
from southern Canada to Georgia and westward to Colorado. It breeds in a variety 
of trees and shrubs, such as maple, dogwood, American hornbeam, eastern 
hophornbeam, sassafras, rhododendron, and azalea. Young sugar maples are es- 
pecially subject to damage, and destructive infestations in them have been reported 
both in North Carolina and southern Canada. Cultivated rhododendrons and azaleas 
are also frequently attacked and killed. The adult is rather stout, cylindrical, dark 
brown or black, and 3.0 to 3.3 mm long. The antennae and legs are rusty red- 
brown. The prothorax is longer than wide, roughly tuberculate in front, finely and 
sparsely punctured, shiny behind, and extends hoodlike over the head. The elytra 
are strongly punctured but not in rows, are rounded behind, and are without furrows 
or teeth. 
The adult bores into its host near the ground line, then excavates a tunnel which 
may encircle the stem one or more times, girdling it. Small stems, from 3 to 12 mm 
in diameter, are usually attacked. Nearly all attacked stems die and annual mortality 
of 8 percent has been recorded in southeastern Canada (4/9). 
Two species of the genus Monarthrum, M. fasciatum (Say) and M. mali (Fitch), 
occur in eastern North America. Adults of M. fasciatum are yellowish brown with 
the anterior half of the prothorax and the posterior third of the elytra usually dark 
brown, and are about 2.3 to 2.8 mm long. In this species, mycetangia are possessed 
by the female (753). This species is most common in the South but occurs as far 
north as Massachusetts and Wisconsin. It breeds in many species of hardwoods, 
and has also been observed in pine. Adults of M. mali resemble those of M. 
fasciatum except for their slightly smaller size and their uniform yellowish to light 
reddish-brown color. This species breeds in injured and dying trees or recently cut 
logs and stumps of many species of hardwoods throughout the Eastern States. The 
galleries of both species of Monarthrum are branched with larval chambers extend- 
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