During a walk I found drawings on the trunks of a number of blown down trees. They were originally hidden under the bark. According to another walker, these come from worms, and given their nature, this does not seem impossible to me. The thick stripes in the middle of the fanned-out drawing are always nice and vertical on the trunk (i.e. parallel to the tree trunk). Can you explain this? My nine-year-old son and I are already curious!
Answer
Dear Lawrence,
the damage picture on your beautiful photo is the typical damage picture of bark beetles and their larvae (family Scolytidae). The family of bark or bark beetles is a very extensive family of fairly small beetles (3 to 5 mm) that are often attracted to diseased, languishing and dead trees.
The males of the bark beetles search the bark of weakened trees for a suitable place to crawl into the bark. After working through the bark, almost drilling, they first dig a kind of “mating chamber”, which is a cavity under the bark.
The male then secretes a certain chemical that lures the females to the tree from a great distance. After mating, the females start to make a corridor up to 15 cm from the mating chamber, this is called the “mother corridor”, in which dozens of eggs are laid by the female.
Small larvae hatch from those eggs and they begin to feed on the wood; and this is very typical, often in corridors more or less perpendicular to and on either side of the mother corridor. This is how the characteristic feeding pattern is caused. Both the mother duct (the thick stripes), the mating chamber (cavity at the end of the “thick stripes”) and the larval ducts are clearly visible on your photo.
The larvae feed on the wood, and once fully grown they transition to a pupal stage at the end of the feeding cycle. A new bark beetle then emerges from that pupal stage.
This beetle then burrows out through the bark through a small round “exit opening” and looks for new dying trees in the area. Those small exit openings in the bark are sometimes so massive that they are reminiscent of the shot from a shotgun. If you can still find bark, you will certainly notice the small exit openings or holes.
Because the feeding of the larvae prevents the transport of nutrients and water in the tree, the weakened trees can die further. In the absence of weakened trees or in the event of a massive outbreak of the beetles, healthy trees can also be affected.
Kind regards,
Hans
Answered by
Hans Castels
identification of insect pests in agriculture and horticulture, stock goods and homes
Burg. van Gansberghelaan 96 box 1 9820 Merelbeke
http://www.ilvo.vlaanderen.be
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