This degrade is caused both by holes bored into the wood and by 
the presence of black stains caused by the fungus inhabiting the 
tunnels. Trees cut during the summer in the South and left for 
more than 2 weeks in the woods are often severely damaged. This 
is especially true of gum, cypress, and oak logs. 
There are three types of ambrosia beetle tunnels; simple, 
branched, and compound. Simple tunnels are unbranched, often 
penetrating deeply into the wood. Branched tunnels penetrate 
deeply into the wood and then break up into several branches, 
which extend in various directions in the same plane. Compound 
tunnels also branch off from a single entrance gallery but have egg 
niches extending from the sides of the tunnel. As these tunnels 
are excavated the beetles push the sawdust to the outside. The 
larvae of certain species live and feed in so-called cradles which 
branch off from the main galleries. Others live in the main gal- 
leries. Ambrosia beetle galleries differ from those of other wood- 
boring insects in that they are of uniform diameter throughout, 
are free of borings or other refuse, and have their walls stained 
black or brown. 
Ambrosia beetles are discussed at greater length in several 
publications (388, 698, 252, 734, 41). 
FAMILY SCOLYTIDAE 
This large family of bark beetles contains several species of 
ambrosia beetles. 
The Columbian timber beetle, Corthylus columbianus Hopk., oc- 
curs from Michigan to Massachusetts south to Georgia and Ar- 
kansas. It breeds in various living deciduous trees such as sugar, 
silver, and red maple, sycamore, yellow poplar, boxelder, bass- 
wood, beech, elm, yellow birch, and several species of oaks. Adults 
are stoutish, black, and about 4 mm. long (fig. 98 A). The front 
of the head of the female is convex and covered with short, stiff 
hairs. The pronotum is broadly rounded and asperate in front. The 
elytra are shiny, striate, and coarsely and shallowly punctured. 
The declivity is armed with small tubercles. 
Adults become active during May and June in Indiana and 
West Virginia (407). They tend to reattack the tree in which 
they develop, but some dispersal occurs. The wood is entered 
through bark crevices, usually on the main trunk near the base. 
Holes are bored straight into the sapwood until the tunnei nears 
the heartwood, then it turns right or left (fig. 97 B). Entrance 
holes are clean-cut and from 1/32 to 1/16 inch in diameter. Short 
tunnels or chambers leading from the upper and lower surfaces 
of the main tunnel 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 species Pichia (408). It is stored and trans- 
mitted by prothoracic mycetangia possessed by the male beetle 
(292). Winter is spent in both the pupal and adult stages in the 
galleries of last attacks. 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 
265 
