New Insights into the Composition of Aggregation Pheromones in Polygraphus poligraphus, Polygraphus punctifrons, Polygraphus subopacus and Polygraphus proximus

Four-eyed bark beetles of the genus Polygraphus have been involved in large bark beetle outbreaks in different parts of the world, resulting in major economic losses. A striking example is the invasive species Polygraphus proximus which is a pest on Abies sibirica in Russia. In Sweden, Polygraphus poligraphus has been involved in bark beetle outbreaks on Norway spruce, Picea abies, together with the European spruce bark beetle Ips typographus. Two related species, Polygraphus punctifrons and Polygraphus subopacus are also present in Sweden. Recently, aggregation pheromones or pheromone components have been identified for these four Polygraphus species. However, questions remain regarding the complete composition of their pheromones, particularly for P. subopacus and P. proximus, whose aggregation pheromones appear to be very similar. In an attempt to better understand the chemical communication of these species, additional studies were conducted on P. poligraphus, P. punctifrons and P. subopacus using solid phase microextraction coupled with gas chromatography and mass spectrometry (SPME–GC–MS), electroantennography (EAG) as well as SPME–GC–MS and GC–MS with electroantennographic detection (EAD). Field experiments were also conducted. In P. punctifrons, some male-specific compounds were found in addition to those previously identified. In EAG and SPME–GC–MS/EAD studies, all three Polygraphus species responded strongly to grandisol. Using a chiral column, GC–MS/EAD revealed that they were able to detect both enantiomers of grandisol. In summary, this work presents our current understanding of the aggregation pheromones in four Polygraphus species and the challenges we have met in identifying species-specific pheromone blends for some of these species.