Climatic conditions in Europe over recent years have created favourable conditions for outbreaks of the European spruce bark beetle in many European countries. As part of the National Forest Monitoring carried out by the Latvian State Forest Research Institute “Silava”, special attention has been paid this year to monitoring the flight activity of the first generation of bark beetles in Latvia. In the summer of the previous year (2019), a rapid population increase was observed in Latvia – compared to 2018, the population more than doubled.

The cool, windy spring of 2020 delayed the emergence of the bark beetles, and overall flight activity decreased significantly. Figure 1 shows that bark beetle flight activity has decreased significantly compared to 2019. Similar to 2019, the highest bark beetle activity this year was observed in the north-eastern regions of Vidzeme.

Figure 1. European spruce bark beetle flight activity in May 2020.
The figure shows the average number of beetles caught in one trap in the monitoring plots.
In the bottom right corner, bark beetle flight activity for May 2019 is shown for comparison.

The results of the previous year's monitoring indicated a high risk of bark beetle damage in Latvian forests. Consequently, in 2020, pheromone traps are being widely used in fresh coniferous clear-cuts to control bark beetles. Pheromone traps for bark beetle control are used by A/S “Latvijas valsts meži”, SIA “Rīgas meži”, the Forest Research Station, as well as some private forest owners. With the support of SIA “Latvijas valsts meži”, the State Forest Service, the Forest Department of the Ministry of Agriculture, and the Latvian State Forest Research Institute “Silava”, the use of pheromone traps was also offered to private forest owners free of charge. Planned use of traps, combined with correct forestry practices, is a highly effective method of controlling bark beetles.

Stands where the bark beetle has proliferated cannot be “cured”. Such stands can be used to protect healthy stands by felling trees and placing pheromone traps in the clear-cut areas. Therefore, every forest owner who owns or manages spruce stands older than 50 years should inspect these stands several times during the summer. If fresh bark beetle damage is noticed, it must be reported to the State Forest Service. A fresh infestation of bark beetles is indicated by entry holes about 1 mm in diameter, as well as brown bark “dust” accumulating in branch forks and at the root collar. If there are many holes, it is likely that the insects have already left the spruce, even though the needles are still green and the bark has not fallen off. After the bark beetles have emerged, the needles remain bright green for some time, even if the bark has fallen off the trunk.

Latvian State Forest Research Institute “Silava” www.silava.lv
Leading Researcher, Dr.biol. Agnis Šmits, agnis.smits@silava.lv