Present and future use of semiochemicals in pest management of bark beetles

Attractive compounds affecting the mass aggregation of bark beetle populations on host trees suitable for colonization usually consist of two obligatory components that act synergistically and species-specifically. Semiochemicals inhibiting response act on their own and seem less specific. From nearly 100 species investigated so far, mass aggregation can be simulated with commercial synthetics in about nine species of economic importance. Aspects leading to the application of attractants in monitoring and mass trapping pest populations affecting European spruce forests result from intensive coordinated research at the university, industry, and forestry level. Technology transfer was facilitated by, and adapted to, the infrastructure of European forestry; traps economically replace the trap tree methods conventionally used for centuries. Expected applications in the near future are refined monitoring methods to measure population levels and predict damages. Also, mass trapping should remain a worthwhile tool in preventing beetle damage in forests under management intensive enough to remove excessive breeding material. In the long run, response-inhibiting semiochemicals resulting in the dispersal of pest populations (Ablenkstoffe) may gain wider application. The spruce engraverIps typographus L. and its associatePityogenes chalcographus L. are used as examples to describe the feasibility of developing and applying inhibitors as new tools in the management of bark beetle pests: Applying a slow-release verbenone formulation (verbenone strip) wrapped around the trunk of spruce trees at breast height appears to protect spruces from destructive attack byIps typographus, while small polyethylene ampullae containing terpinene-4-ol counteract aggregation of P. chalcographus. Inhibitors appear applicable in both strategies, damage prevention as well as damage restriction, and consequently may accommodate also pest control in less intensively managed forests. Future application of semiochemicals in the management of bark beetle pests will rest with the availability of effective means and methods and their acceptance by the forestry interest. This acceptance is presently somewhat hampered by misconceptions about mass trapping, and by (1) "missing links" in the knowledge of the beetles' dispersal and aggregation behavior, (2) the chemosynthesis of chiral pheromone components at the industrial level, and (3) legal barriers.