Forest Pests: Insects, Diseases & Other Damage Agents

Ips typographus

Translation of French document (Jean-Pierre Renaud)

The european spruce bark beetle belong to the scolytidae family. The adult is from 4.5 to 6 mm long and characterised by its excavated elytral declivity laterally armed with four spines on each side.

Life cycle

Norway spruce (Picea abies) is the preferred host of the European spruce bark beetle, but it can also be found on fir, pine, larch,and other spruces species.

The initial adult flight occurs in spring with the first warm days (a few consecutive days with temperature higher than 18-20°C are needed). Male starts the breeding process and one to two females join him (it is a polygamous species). Once fecundated, females bore through the bark and construct egg galleries that are parallel to the wood grain. Eggs are laid by groups alternatively along opposite sides of the galleries. Newly hatched larvae mine outward and perpendicularly to the main gallery. These secondary galleries are sinuous and are widening out, ending by a pupal chamber.

Young adults become sexually mature only after they have spent some time under the bark.

Over wintering in galleries occurs either at the larvae, pupae, or young immature stages. Mature adults over winter in the litter.

The annual life cycle largely depends on local climate: there are usually two generations per year in the plain locations of France, whereas in the mountains only one generation is realized. Flights take place almost any time from the initial spring flight until October, as long as weather conditions remain favourable (no rain and temperature warmer than 20°C). Beetles of different generations can be flying at a given time.

Damages

Once a tree has been attacked, and larvae have bored galleries underneath its bark, fungi settle and occasionally destroy the sap conducting tissues. The settlement of the bark beetles is always a massive process, since they are producing aggregative pheromone. For an infested tree, it takes from a few weeks to a few months to die after that the beetles have completed their development under the bark.

The European spruce bark beetle is a secondary parasite that mainly attacks weaken, injured, or freshly harvested trees. Under certain circumstances (e.g. storms…), when beetle populations build up rapidly, it becomes a primary epidemic parasite, being even able to attack successfully healthy trees.

The fungi, carried by beetles, are responsible of a blue wood staining process (Ophiostoma spp.)which causes wood depreciation, even for trees that are rapidly harvested.

External evidence of infestation

1st picture: Typical galleries underneath the bark: double long egg gallery (length = 20 cm; width = 3 mm)

2nd picture: recent attack: when tree colonization begins, one can see entrance holes and reddish sawdust on the stem and at the lower part of the tree; then bark loosen and tree needles start to discolor from yellow to red.

3rd picture: old attack: dispersed dead trees showing loose bark.