142 MISC. PUBLICATION 273 U. S. DEPT. OF AGRICULTURE 
KEY TO DIAGNOSIS OF INSECT INJURY TO WOOD AND WOOD 
PRODUCTS 
A. Insects attacking green, unseasoned, or seasoning wood, living or dying 
trees, or freshly felled trees or logs, and projecting their tunnels 
directly into and through the wood... - 
1. Small, circular, open pinholes, often surrounded by dark 
stains; diameter uniform and less than one-eighth 
inch; made by small, brown, shining, cylindrical 
beetlescs 20 se i ae ee ambrosia beetles, page 148. 
2. Large, more or less circular holes in wood; diameter more than 
one-eighth inch; lightly filled with ee wood stained 
or not. 
a. Nearly circular holes of medium size in wood of broad- 
leaved trees made by caterpillers 
clear-wing moths, page 1389. 
b. Very large irregular holes one-half to 1 inch in 
diameter in broadleaved trees, usually lined with 
a silky yellowish-brown web__ carpenter moths, page 154. 
3. Circular, oval, or irregularly shaped tunnels of varying width 
gradually increasing to more than one-eighth inch in size; 
usually tightly packed with fine boring dust or coarse 
frass, except at ends occupied by larvae or pupae. 
a. Tunnels flatly oval, usually lightly packed with arc- 
like layers of sawdust-like borings and pellets of 
woody excrement, and surface of wood marked by 
fine, transverse, crescentric lines; made _ by 
slender, white, legless grubs shaped like horseshoe 
nails with very wide, flat segments back of head; 
first segment with a well developed plate on both 
upper and lower surfaces, upper plate marked 
with a central line, groove, V or Y 
flatheaded borers, page 147. 
b. Tunnels broadly oval to nearly circular, tightly packed 
with sawdustlike borings and pellets of wood ex-° 
crement; made by long, thick, white, apparently 
legless grubs, with horny plate on top of first 
thoracic segment, which is somewhat enlarged 
; roundheaded borers, page 150. 
c. Perfectly circular holes in wood, not evident in cam- 
bium, made by long, white, cylindrical grubs with 
small heads, fleshy lobes for thoracic legs, and 
the abdomen terminating rearwards with a sharp 
horny prong_-- horntails and certain Coleoptera, page 155. 
B. Insects attacking living trees and causing black checks, pitch pockets, 
pitch flecks, gum spots, or ring distortion, but not causing pinholes 
or wormhboles. 
1. Black checks showing in wood of conifers, Surrounded by 
curled or distorted wood____.__________ bark maggots, page 158. 
2. Birdseye pitch flecks in pine________________ pitch midges, page 54. 
3. Double rings, distorted rings, retarded growth’_ defoliators, page 58. 
4, Pitch pockets, gum spots, and pitch streaks in coniferous 
WV OCS 2 Sitti hie eet cms De Me eer bark beetles, page 96. 
Cas SU Seka eke 2 tance ee ce flatheaded borers, page 182. 
Se A Sail Maine Al Se Shere SUR Re pitch moths, page 139. 
IGOR Th RBIS Ae tt eeeea see ta terminal-feeding insects, page 29. 
C. Insects attacking sawed lumber, seasoned wood, or utilized wood 
products. 
1. Small wormholes in wood, tightly packed with a very fine 
powder, powder sometimes pushed out through holes in 
wood. Usually working in very dry wood. 
a. Small, nearly round tunnels in various hardwoods 
powder-post beetles, page 159. 
db. Irregulariy shaped tunnels in softwoods and hard- 
woods (see above under A, 3). 
7 Aiso from causes other than insects. 
