| | 17. Barkbeetles are small, cylindrical beetles which excavate
galleries under the bark of many kinds of trees. |
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18. Barkbeetles are rarely the primary cause of death of a tree,
but they may be an important contributing factor. The European
and native elm barkbeetles transmit the fungus which causes Dutch
elm disease. |
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19. The two beetles were of little concern until the disease
arrived in America. Since that unfortunate introduction, the
disease and the barkbeetles have worked as a deadly team. the
barkbeetles carry disease spores as they disperse and provide
suitable points of infestation with their galleries. In return,
the dying trees provide an excellent habitat for large colonies
of barkbeetles. |
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20. The European elm barkbeetle, slightly larger than the native
species prefers to build its galleries with the central egg
tunnel running with the wood s grain. Smaller side tunnels made
by the newly hatched larvae radiate out from the central one. |
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21. Galleries of the native elm bark beetle are oriented across
the grain and are usually forked. |
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22. Pines are subject to attack by several species of bark
beetles. Some infest only the smaller branches, others only the
trunk. The beetles are very similar in appearance, but each
species vary considerably in size and each has a distinctive
gallery. As with borers, bark beetle control is mainly
preventative. Maintaining trees in good condition is very
important since bark beetles prefer weak, unthrifty trees. Once
infested, treatment is impractical. Trees rarely recover;
however, insecticides are of some value in protecting as yet
uninfested trees nearby. |