Mid Sweden University

Some bark beetle species can cause considerable damage and mortality in their host trees, resulting in major economic and environmental losses. Beetles of the genus Polygraphus, four-eyed bark beetles, have been involved in large bark beetle outbreaks in Sweden together with the European spruce bark beetle Ips typographus. Three species of Polygraphus are present in Swedish spruce forests: P. poligraphus, P. punctifrons and P. subopacus. Polygraphus poligraphus has been associated with tree mortality whereas little is known about the two other species. In other parts of the world, other Polygraphus species are well-known pest insects; these include Polygraphus rufipennis, which attacks black spruce in North America, and Polygraphus proximus, which is an invasive pest in Russia where it has killed large volumes of Siberian fir. Polygraphus proximus is spreading westwards towards the European Union. Bark beetles use aggregation pheromones to coordinate mass attacks on their host trees as well as for the males to attract females. Traps baited with aggregation pheromones offer a promising way of monitoring pest species and may, in combination with other measures, contribute to pest control. Aggregation pheromones of P. rufipennis and P. poligraphus were identified over 30 years ago, but for the other Polygraphus species, no aggregation pheromones were known. The aim of this work was to investigate the chemical communication of P. poligraphus, P. subopacus, P. punctifrons and P. proximus. Beetles were allowed to bore into the bark of their host trees at the laboratory, and the emitted volatiles were sampled with SPME and analysed with GC-MS. Several sex-specific compounds were identified in all four species. Electroantennographic studies as well as field experiments were conducted in order to evaluate the biological role of these compounds. Attractive compounds which werevipresumed to be parts of the aggregation pheromones produced by the males were found for all four species, as well as some repellant compounds. Species-specific pheromone lures were developed for P. punctifrons and optimised for P. poligraphus. In P. subopacus and P. proximus, the composition of their aggregation pheromones turned out to be surprisingly similar. Both species appear to use the same main compound in their pheromones, and when this compound was used as a bait in traps, both species were caught as well as P. poligraphus. Several other compounds were also found in the emissions of volatiles collected from boring males of P. proximus and P. subopacus, but despite several field studies which were conducted in Russia and Sweden, no species-specific formulation was identified for P. subopacus. For P. proximus, one compound which was collected from the males in minor amounts appeared to be attractive to P. proximus specifically, but this effect should be confirmed in future studies. The presented work should be a good starting point for anyone who wishes to study the chemical communication of these species.