Integrated Approaches to the Prevention of Damage by Xylophagous Insects
Csóka, GY., and Kovács, T. 1999. Xylophagous insects. Forest Research Institute. Erdészeti Turományos Intézet. Agroinform Kiadó, Budapest. 189 pp.
In this chapter we will give a few very short examples to emphasise the fact that in the fight against harmful xylophagous insects prevention of initial attack must have priority. As mentioned earlier, the most devastating outbreaks of xylophagous insects (such as bark beetles and some longhorn species) most frequently occur in (or at least start from) large scale monocultures (for example, conifer and hybrid poplar plantations), particularly if these stands were planted on poor sites not satisfying the demands of the given tree species. Knowing this fact, it is most important to choose suitable sites for a particular tree species. In addition it is also extremely important to create conditions in the forests which are close to natural conditions (mixed stands, diverse structure and age distribution). It is similarly important to know that some forms of abiotic damage, such as snowbreak and windthrow, can also provide perfect conditions for the insects. Therefore it is very important to remove dead, dying and damaged trees from the forest after these abiotic damage. A typical problem is that the cut wood is kept in huge piles in the forest for a long time. In the case of pine logs this provides extremely good conditions for several bark beetle species.
The most serious damage by pine weevil, Hylobius abietis, usually occurs where, after felling conifers, the area is planted again with conifer seedlings without removing the stumps. These conditions are optimal for the weevil because its larvae develop in the stumps and the adults feed on the bark of the seedlings. It is therefore best to avoid planting conifers after cutting coniferous forests. If it is necessary to replant with conifers, there are several ways to reduce the damage. Adult insects can be lured and trapped efficiently using artificial substrates producing an odour similar to that of their wounded foodplant (eg. freshly cut stumps). It is also possible to treat the stumps with fungal suspensions (eg. Peniophora gigantea) causing rapid decay of the wood and making the stump unsuitable for the larval development of the weevil.
Pheromones and traps baited with them are already available for many important bark beetle species. Both aggregation and anti-aggregation pheromones can be used in selective and environmentally friendly control. The first kind of pheromone is used in mass trapping of the animals, and the second can keep the beetles away from the place protected by them. Aggregation pheromones can also be useful in monitoring the population density of bark beetles. In a similar way, some specific trap trees can be used and then removed from the forest after the insects have oviposited on them but before the new generation emerges.