the Eastern States. Its hosts are recorded as birch, beech, sweet- 
gum, wild cherry, and pear. Attacks are generally confined to 
dead and dying trees, logs, and stumps. The adult female is 
reddish-brown, has a dense mat of hairs on the frons, and is from 
2.8 to 4.5 mm. long. 
Dryocoetes caryi Hopk. occurs throughout the northern conif- 
erous forests and south to North Carolina in the Eastern States. 
Its hosts are white, red, and Engelmann spruces. Infestations are 
usually confined to the trunks of small, weakened, shaded out, 
suppressed trees. The female adult is reddish-brown and from 
2.1 to 2.7 mm. long. 
Dryocoetes granicollis (LeC.), a rather rare species, breeds in 
spruce from Quebec to North Carolina. The female adult is 
reddish-brown and from 2.8 to 3 mm. long. D. piceae Hopk. is 
often very abundant in windthrown spruce. 
Polygraphus rufipennis (Kirby), the four-eyed spruce bark 
beetle, occurs in the spruce forests of the United States south in 
the Eastern States through the Appalachians. Its hosts, in addi- 
tion to the spruces, are larch, pine, and balsam fir. Infestations 
are usually found in slash and in dead and dying trees. However, 
when heavy populations develop in such material, nearby living 
trees are also subject to attack. The adult is dark brown to black 
and about 2.3 mm. long. Eggs are laid in the sides of three to five 
irregular short galleries which radiate away from a central 
nuptial chamber. The bark, but not the wood, is slightly engraved. 
The Ambrosia Beetles 
(Pin-hole Borers) 
Numerous species of beetles in the families Scolytidae and 
Platypodidae are known as ambrosia beetles because, in all cases, 
both the adults and larvae feed on a mold type of fungus, known 
as ‘ambrosia.’ The beetles introduce this fungus into tunnels 
bored into the sapwood and sometimes heartwood of trees and 
logs, where it grows on the walls and is propagated. It was dis- 
covered recently that female ambrosia beetles possess specialized 
structures called mycetangia (291). They are variously located in 
and on the body of the insect. In a few species these organs are 
found in the male and, in at least one species, Xyloterinus politus 
(Say), it is found in both sexes (1). Since the discovery that 
these specialized organs are possessed by ambrosia beetles, much 
important knowledge regarding the relationship of beetles to 
their specific microsymbiotic complexes has been gained (19, 37, 
263). 
About 36 genera of ambrosia beetles, some of which include up 
to 200 species, have been recorded throughout the world. A 
number of species breed in living trees, but decadent, dying, or 
recently cut trees, logs, pulpwood or stumps are usually preferred. 
All species require a considerable amount of moisture for de- 
velopment. In the Southern States, timber is not attacked unless 
the moisture content of the wood is at least 48 percent. Seasoned 
timber is never infested (138). 
Ambrosia beetles are important chiefly because of the degrade 
of sawn timber that results from their invasion of trees or logs. 
264 
