Inventory of Polygraphus beetles in Småland and evaluation of a pheromone trap monitoring method

Abstract

Four-eyed bark beetles (Polygraphus spp.) have been involved in bark beetle outbreaks in Sweden together with the European spruce bark beetle (Ips typographus). The four-eyed bark beetles (in particular Polygraphus poligraphus) seemingly contribute to the death of spruce trees. The species of four-eyed bark beetles found in Sweden; Polygraphus poligraphus (L), P. punctifrons (Thomson, 1886) and P. subopacus (Thomson, 1871) are difficult to distinguish without specialist knowledge. Pheromone substances used by the three species have been identified, making it possible to attract these insects to traps, to monitor their distribution and estimate the population size. The purpose of this project was to investigate the presence of the above-mentioned species in Småland using modified pheromone baits and traps. Traps with three different pheromone-containing baits (for the three Swedish Polygraphus species) were set out in 11 locations in Småland. 3804 Polygraphus poligraphus beetles were caught across the 11 field sites, with P. punctifrons and P. subopacus being undetected. The study has provided enhanced knowledge about monitoring P. poligraphus populations in Småland by pheromone traps. This in turn will help to understand the role of four-eyed bark beetles as a pest and aid in counteracting damage to Swedish forestlands.