Trypodendron scabricollis (LeC.) occurs from New York to 
North Carolina and Mississippi and breeds in various species of 
pine and hemlock. The trunks (fig. 99) and larger limbs of 
weakened and dying pines are preferred, but freshly cut lumber 
is also subject to attack and serious damage. Adults are reddish- 
brown and from 3 to 3.5 mm. long. The elytra are smooth and 
finely striate. 
COURTESY OF DUKE UNIV. SCH. OF FOREST. 
FIGURE 99.—Tunnels of the ambrosia beetle, Trypodendron scabricollis, in 
wood of the lower bole of a loblolly pine. 
Trypodendron retusum (LeC.), the largest of the eastern 
species, attacks poplars and paper birch throughout the Northern 
States and southern Canada. It has also been recorded from West 
Virginia and several Western States. Adults are from 3.8 to 4.6 
mm. long; the pronotum is broadly emarginate in front; and 
there is a broad, smoky yellow stripe on each elytron. T. betulae 
Swaine occurs throughout the Northern States and eastern Can- 
ada and breeds in birch. Adults are black and from 8 to 3.5 mm. 
long. There is a faint yellow band toward the rear of the pro- 
notum and a broad yellow stripe on each elytron. T. bivittatum 
Kirby, the spruce timber beetle, occurs in eastern United States 
and eastern Canada and breeds in pines, spruces, fir, arborvitae, 
larch, and hemlock. Its color is similar to that of T. betulae, and 
it is about 3 mm. long. 
The genus Gnathotrichus Eichh. contains several species of 
true ambrosia beetles. The adults are small, cylindrical, and dark 
brown or black. The head is invisible from above, and the body 
surface is finely punctured, smooth, and sparsely covered with 
hairs near the elytral declivity. Blackman (73) revised the genus. 
Gnathotrichus materiarius (Fitch) occurs from eastern Canada 
south to Florida and westward to Nebraska and Texas. It breeds 
in the lower portions of the trunks of dead and dying pines, 
spruce, balsam fir, larch, arborvitae, and other conifers. Adults 
are dark brown to black and about 2.7 to 3.1 mm. long. The pro- 
thorax is asperate in front; the disc is much longer than broad; 
the elytra taper slightly at the rear end, and the declivity is 
slightly grooved at the suture and covered with short, sparse 
hairs. 
268 
