208 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
KEY TO INSECT INJURIES BY SCOLYTIDAE AND PLATYPODIDAE—Continued 
30. In rather narrow compound ambrosial burrows in the wood of 
decadent or felled conifers: 
In pine; Pennsylvania and New York 
Xyleborus fitcht Hopk., p. 340. 
‘In pine; South Dakota 
Gnathotrichus aciculatus Blkm., p. 340. 
In pine, spruce, larch, balsam, etc.; in Eastern and South- 
eastern States____Gnathotrichus materiarius Fitch, p. 340. 
In notably coarser compound ambrosial burrows in decadent and 
felled conifers; beetles stout, dark brown to black, marked with 
lighter brown or yellow: 
Known from pine, wing covers often with indistinct stripe of 
smoky brown on black 
Trypodendron scabricollis Lec., p. 339. 
Common in pine, spruce, larch, hemlock, balsam, arborvitae; 
wing covers of beetles with distinct yellow stripes 
Trypodendron bivittatum Kby., p. 339. 
36. Flatheaded ambrosia beetles making compound ambrosial burrows 
in southern hardwoods; beetles less than 5 mm. long: 
Beetles in hickories, oaks, gums, cypress, etc. 
Platypus compositus Say, p. 342. 
In southern oaks and chestnut 
Platypus quadridentatus Oliv., p. 343. 
Flatheaded ambrosial beetles making compound ambrosial burrows 
in southern conifers, especially in pines; larger, more than 5.5 
110 0 Yee) (0) 0 ae ie ee ee ep ee Platypus flavicornis F., p. 342. 
DISCUSSION OF THE SPECIES OF SCOLYTUS 
The genus Scolytus Geoff. is readily distinguished from other bark 
beetles by the short, thick, brown or black body, by the outer an- 
gle of the fore tibia being produced into a curved hook, and by the 
contour of the abdomen—the ventral surface ascending abruptly be- 
hind, and in some cases being concave or excavated and ornamented 
by spines, tubercles, etc. 
Blackman (43) considered all the species of Scolytus as true bark 
beetles, all but one of the eastern species breeding in deciduous trees. 
Most of the species are monogamic, the egg galleries being of the 
simple longitudinal variety, but a few produce burrows of the forked 
or the radiate type. The genus contains several species of well-known 
economic importance, one of these, the hickory bark beetle (Scolytus 
guadrispinosus) being decidely injurious on its own account; snes 
another, the smaller Eur opean elm bark beetle (S. multistriatus), 
important as the chief insect vector of the destructive Dutch ae 
disease. Several species of importance in the Western States are 
treated by Keen (262). 
The hickory bark beetle (Scolytus quadrispinosus) is black, 
3 to 5 mm. in length, and about twice as long as wide, with the upper 
surface nearly devoid of hairs. In the female the ventral surface of 
the abdomen is strongly ascending and is only slightly concave, 
whereas in that of the male the second segment is very deeply exca- 
vated with the anterior margin strongly extended, the third segment 
bears three large spines, and the fourth segment a single spine. The 
armature on the male is likely to be more str ongly developed in speci- 
mens from the South, and some specimens have additional spines, 
This scolytid breeds in all species of hickory, including native and 
cultivated pecans, and has been observed constructing burrows in 
butternut. It is found from Quebec to Georgia, Alabama, and Mis- 
