European spruce bark beetle

Appearance

Adults are usually 4.0–5.5 millimetres long, cylindrical and robust, black or brownish-black. Elytral declivity is slightly shiny, with 4 teeth on each margin side. The third tooth is the biggest and club like on its top. The egg is yellowish-white. The larva is white and legless. The pupa is also white.

Status

Interventions for beetle outbreaks are controversial in locations such as the Šumava National Park in the Bohemian Forest of the Czech Republic. Some authorities suggest that outbreaks be allowed to run their course, even at the expense of most of the forest. Others, including the lumber industry, request intervention. Some experts argue that salvage logging tends to have a greater negative effect on the vegetation than the bark beetle outbreak alone. A study of the effects of forestry interventions on the herb and moss layers of infested mountain spruce forests suggest that without intervention the forests do eventually recover. Salvage logging also had negative effects on the composition of species, delaying recovery.

Behavior

Bark beetles are so named because they reproduce in the inner bark, living and dead phloem tissues, of trees. Adult beetles hibernate in forest litter and host trees when environmental conditions are not favorable for reproduction. When conditions are right, they travel up to half a mile in search of a vulnerable host. Once the host is located, the adult burrows through the weakened bark in order to build tunnels where they can mate and lay eggs. They release pheromones to attract more individuals to the host tree. Two to five weeks after contamination, they may migrate to another host and repeat the process. Once the larvae hatch, they feed and pupate under the bark. Up to three generations are produced per year.

Bark beetles communicate with one another using semiochemicals, compounds or mixtures that carry messages. Some electrophysiological and behavioral statistics show that bark beetles can not only sense olfactory signals directly from other bark beetles, but also some compounds from trees.

It is also possible that beetles are attracted to the pheromone ipslure. They are also thought to be attracted to ethanol, one of the byproducts of microbial growth in dead woody tissues.

Bark beetles can form a symbiotic relationship with certain Ophiostomatales fungi. These phloem-feeding bark beetles use phloem-infesting fungi as an addition to their diet.