the wood and feed on the woody material in both the larval and 
adult stages; and (c) ambrosia beetles which bore directly and 
deeply into the sapwood, and in some cases into the heartwood, 
and feed entirely on fungi which grow on the tunnel walls. Sev- 
eral publications dealing with eastern members of the family are 
available (41, 197, 70, 698). 
Bark beetles are typically soft and yellowish when first formed 
but soon harden and turn reddish to dark brown or black. 
They are small, cylindrical beetles, from about 0.9 to 9.5 mm. 
long. The larvae are small, white, curved, legless grubs with en- 
larged thoracic segments. The heads and mandibles are usually 
strongly sclerotized and darker in color than the remainder of 
the body. As a group, the larvae are so similar in appearance to 
larvae of the family Curculionidae that it is next to impossible to 
separate the two groups in the larval stages. 
When they attack a tree, twig, branch, or log, the adults con- 
struct entrance tunnels directly through the bark to the phloem 
or into the wood, depending on the species. The entrance tunnel 
is only long enough to reach a nuptial chamber or directly into an 
egg gallery. Pitch and sap exuding from these holes harden at the 
surface in various forms of pitch or resin tubes on conifers. In 
the case of ambrosia beetles, boring dust is pushed out through 
the holes. Egg tunnels of true bark beetles are constructed from 
the entrance tunnels along the surface of the wood, cutting 
through the inner bark and often scarring the wood. Egg tunnels 
of wood-feeding species are completely within the wood, while 
those of ambrosia beeties are deep in the sapwood. The latter may 
be simple, branched, or compound. The females of many species 
deposit their eggs in niches cut into the sides of the tunnel, cover 
them with frass, and plug the opening toward the tunnel. Others 
deposit their eggs in larger niches or in grooves or layers and 
cover them with boring dust. Still others, particularly some of 
the ambrosia beetles, place their eggs free in the tunnels. 
When bark beetle larvae hatch they feed away from the egg 
tunnel, more or less at right angles to it. The larvae of many 
species construct galleries with a specific, recognizable pattern. 
Ambrosia beetle larvae, in contrast, remain in the egg tunnel and 
feed on fungi growing on its walls. A large number of species 
pupate in cells at the ends of larval galleries, either in the 
wood, in the outer bark, or between the wood and bark. The 
adults remain in those cells until their exoskeletons harden, some- 
times even longer. When first formed, they are soft and yellowish; 
later, after hardening, they become reddish to dark brown or 
black. While there, they feed on the phloem, often consuming all 
that remains after the larvae finish feeding. When ready to 
emerge, the beetles gnaw holes through the bark to escape. The 
majority leave a given tree within a few days. The Ambrosia 
beetle adults emerge through their parent’s entrance tunnels. 
Bark beetles either fly to and attack new host trees as soon as 
they emerge or congregate under the bark of the host tree and 
hibernate or wait until sexually mature before flying. A few 
species feed on the twigs, buds, or bark of other trees before 
attacking a tree for breeding purposes. Generally speaking, the 
adults spend only enough time in flight, or outside the bark, to 
find new host material. 
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