In southern oaks and chestnut 
Platypus quadridentatus 
Flatheaded beetles making compound, ambrosial bur- 
rows in southern conifers, especially in pines; more 
than So Mm slONS = 24 2e0 Platypus flavicornis 
The genus Scolytus Geoff. is represented in eastern North 
America by a number of species of true bark beetles, several of 
which are of economic importance, all except one that breeds in 
deciduous trees. The adults differ from other bark beetles in 
having short, thick, brown or black bodies, in having the outer 
angle of the fore tibia produced into a curved hook, and in having 
the ventral surface of the abdomen ascend abruptly to the rear. 
In some cases declivity is concave or excavated and ornamented 
by spines, tubercles, ete. Blackman (74) revised the genus. 
The smaller European elm bark beetle, Scolytus multistriatus 
(Marsh.), the principal vector of the Dutch elm disease fungus, 
Ceratocystis ulmi (Buisman) C. Moreau, in the United States, is 
an introduced species, having been first observed in North 
America at Boston, Mass., in 1909 (132). Since then, it has 
spread over most of the United States and into southern Canada. 
Its hosts include all native and introduced species of elms and the 
related species, Zelkova serata. Adults are small, dark reddish- 
brown, shiny beetles about 3 mm. long. The under-side of the 
posterior is concave and armed with a noticeable projection or 
spine on the undersurface of the abdomen (fig. 84 A). The larvae 
are typical, legless grubs, and about 3 mm. long. 
Winter is spent in the larval stage under the bark, and pupation 
and transformation to adults occurs in the spring. The adults 
begin to appear about mid-May through holes made in the bark. 
On heavily infested trees or cut material the bark may be liter- 
ally peppered with these small “shot-holes.”’ Soon after emergence 
and before entering other dead, dying, or recently cut elms for 
breeding purposes, they ordinarily fly to the smaller twigs of 
nearby living, healthy elm trees to feed. Feeding occurs in the. 
crotches of twigs, usually in the outer perimeter of the crown, 
but also occasionally in its center. It is while the beetles are feed- 
ing in these twig crotches that healthy trees are inoculated with 
the Dutch elm disease fungus. Beetles emerging from trees killed 
by the disease or from fungus-infected logs carry the spores of 
the fungus on their bodies. When some of these spores rub off and 
become lodged in the feeding wounds, infection can occur. 
Chances of innoculation of a healthy elm are greatest in the spring 
and early summer when the long vessels of the tree are open and 
functioning and are near enough to the surface for the beetles to 
cut them while feeding. 
After having fed on healthy elms, the beetles seek out suitable 
places for breeding purposes. Preferred breeding material con- 
sists of living elms severely weakened by drought, trees rapidly 
dying from disease or injury, broken limbs, firewood, or any 
recently cut elm wood. None of this material is ever attacked, 
however, if the bark has been removed or if it has dried to the 
point of cracking. The beetles bore through the bark and con- 
struct egg galleries 1 or 2 inches or more in length in the inner 
235 
