340 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
as long as wide, the surface very smooth with fine punctures. The gal- 
leries in the sapwood are of the compound ambrosial type, similar. to, 
but considerably smaller in diameter than those of 7rypodendron. 
With the exception of a single western species the genus in this coun- 
try is confined to coniferous trees. Decadent or dying trees and the 
stumps and trunks of felled trees are the favorite breeding places. 
Gnathotrichus do not injure living trees, but may do considerable 
damage to logs left unsawed too long. Ina beetle-killed tree the trunk 
is usually attacked soon after the bark beetles have overcome the tree’s 
resistance. Blackman (42) published on a revisional study of this 
genus. 
Gnathotrichus materiarivs is almost exactly 3 mm. long. The 
species is widely distributed over eastern Canada and in the United 
States is known from Maine to Minnesota and Nebraska and south 
to Florida and Texas. Its hosts include various species of pine, 
spruce, larch, balsam fir, and arborvitae. Other conifers used in 
plantations or as ornamentals are also subject to attack. G. aciculatus 
is really a western form, being common in New Mexico and Ari- 
zona, but is found as far east as Colorado and South Dakota in 
ponderosa pine. It is larger than @. materiarius, being 3.5 mm. long. 
The genus X y/eborus Eichh. is distributed around the world in the 
tropical and temperate zones. It probably contains more species than 
any other genus of the family, but in the United States the species of 
Pityoph thorus outnumbered those of X7 yleborus. Many of the species 
of Xyleborus are very closely related and difficult to identify, and as 
it is probable that a number of species reported from our territory 
have been incorrectly named, only those of which the authors feel 
reasonably certain will be included here. 
The galleries made by different species of Xyleborus illustrate all 
three of the general types of ambrosial burrows. Those of XY. saxeseni 
and A. pecanis are of the simple ambrosial type; those made by X. 
celsus are of the branched type; while several species. exemplified by 
A. fuscatus, make compound ambrosial burrows. Some species of 
A yleborus are rather more aggressive than most ambrosia beetles in 
that they attack decadent, but still living, tissue and sometimes ap- 
parently contribute to the death of the tree. Most species, however, 
prefer dying or freshly broken or cut material, thus affecting only the 
timber value of the tree. A few species, especially in the tropics and 
subtropics, cause considerable damage to casks containing water, wine, 
or liquor. 
Ayleborus saxeseni 1s common to both Europe and the Eastern 
States, being found in a large number of hardwood species. XY. pecanis 
was described from Mississippi in pecan, but also breeds in various 
hardwoods in the Southeastern States. It is very closely related to 
X. saxeseni and might better be considered as a variety of that species. 
XA. affinis, originally described from Cuba. breeds from New Jersey 
southward to Florida and Mississippi. It has been taken from hickory 
ae other hardwoods. XY. xylographus 1s similar to. but distinct from 
X. afinis. It breeds in various hardwoods from New York to Minne- 
sota and southward to Florida, and apparently authentic specimens 
have also been taken from pine. 2X. fitchz was described from Long 
Island and was also found in southern Pennsylvania in pitch pine. 
X. fuscatus, described from South Carolina, breeds in oaks and other 
