An international team of scientists has identified substances that make up the aggregation pheromone of the bark beetle Polygraphus proximus, which is dangerous for fir forests. Based on the discovered compounds, the researchers propose to design traps that will help reduce the activity and spread of the pest beetle, thus, reducing its detrimental effect on fir forests. The results of the study are published in the journal Chemoecology.

The bark beetle Polygraphus proximus is an alien bark beetle from the Far East which annually causes significant damage to the fir forests of Siberia. Now it has already spread to the Volga region and the Moscow region. Such activity of the pest can lead to serious environmental and economic consequences. Insect pheromone traps can help slow down its dispersal and will allow one to detect pests at an early stage of its spreading. However, the pheromones produced by this bark beetle had been unknown.

Scientists of the Federal Research Center "KSC SB RAS" together with colleagues from the University of Central Sweden identified the components of the pheromone of the bark beetle Polygraphus proximus. The detected substances can be used as pheromone baits.

Bark beetles produce special volatile substances - aggregation pheromones to communicate with their relatives and attract them to a suitable food object. To find out the composition of the pheromones of the bark beetle, the researchers grew insects in the laboratory and collected their volatile substances. After analysis, the scientist identified several specific compounds characteristic of the bark beetle Polygraphus proximus: twelve for males and one for females.

To assess their attractiveness to beetles, the scientists conducted field experiments for three seasons in a coniferous forest near Krasnoyarsk. There have been breeding grounds for the bark beetle for a long time. In this area, about 60% of fir trees died due to beetle activity. The researchers found that two of the thirteen compounds found could be used as bait - (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol and 3-methyl-2-buten-1-ol. The largest number of insects were caught in traps with the first compound. However, it also attracted bark beetles of another species: Polygraphus subopacus . There were almost three times more of them in traps than the desired beetle, despite the fact that this species was found in these places much less frequently. The researchers hypothesized that this compound is present in the pheromones of both species. But the second compound can be used as a bait for catching only Polygraphus proximus, since the other beetle Polygraphus subopacus is not interested in it.

Candidate of Biological Sciences, Head of the Laboratory of the V.N. Sukachev Institute of Forest SB RAS Yury Baranchikov  “The bark beetle Polygraphus proximus , first discovered in Siberia 13 years ago, is now considered the most aggressive bark beetle ever found on Siberian fir trees. At the moment, he damaged more than half a million hectares of fir forests in the Krasnoyarsk Region only. Pheromone traps would at least facilitate early detection of this pest. This study made it possible to identify specific components of the bark beetle aggregation pheromone that can be used as bait for trapping pests.

The pheromone of P. proximus should also contain other compounds that will increase the number of caught insects, make the pheromone mixture even more species-specific, and significantly increase the efficiency of such traps. Therefore, the full composition of the polygraph aggregation pheromone has yet to be determined. Traps with these pheromones can be used to detect P. proximus in the forest stand, to determine the boundary of its distribution, and also to infect bark beetles with entomopathogenic fungi. If they are used together with the sanitary felling of affected trees, this will help reduce the population and restrain the spread of the pest,” explained the results of the study, Candidate of Biological Sciences, Head of the Laboratory at the V.N. Sukachev Institute of Forest SB RAS, Yuri Baranchikov.