F-519939-40 
FIGURE 93.—The native elm 
bark beetle, Hylurgopinus 
rufipes: top, adult; bottom, 
gallery pattern. 
Winter is spent in the bark of elm trees in either the larval or 
adult stages. Overwintering adults emerge during May and fly 
to living trees and feed in the bark. Later they fly to dead and 
dying trees, broken limbs, or recently cut logs or limbs to breed. 
Usually, dying or fairly moist dead limbs at least 2 inches in 
diameter are selected. Entrance holes are made in bark crevices 
or under overhanging bark flakes and they penetrate directly 
to the surface of the wood. A biramous egg gallery is constructed ~ 
with the arms extending away from the entrance hole at various 
angles (fig. 98). The gallery may be constructed horizontally, 
but is most often inclined from the horizontal. Galleries may be 
constructed entirely in the bark, or they may scar the wood 
slightly. Eggs are laid on both sides of the gallery, sometimes 
very close together. Young larvae feed away from the gallery, 
usually following the grain. Pupation occurs in cells at the end 
of the larval tunnels in the bark. There appears to be two gen- 
erations per year in the southern portions of the insect’s range. 
In the northern portions there may be only one or one and a 
partial second (410). 
When the adults emerge from elms dying from Dutch elm dis- 
ease, they often carry spores of the disease-causing fungus on 
their bodies. When they bore into the bark of healthy elms to 
feed or hibernate, some of the spores rub off onto the walls of 
their tunnels, inoculating the tree with the disease. In most parts 
of the United States, the spread of the disease by the native elm 
bark beetle is secondary to its spread by the much more abundant 
smaller European elm bark beetle. Farther north in Canada, 
251 
