Spruce bark beetle numbers decline in Estonia

Spruce bark beetle numbers have fallen in Estonia over the past two years, ERR reported, with cooler, wetter summers and a growing number of natural predators contributing to the decline.

The spruce bark beetle is a small insect, growing to just 4–5 millimetres long. During mass reproduction, however, it can kill large spruce trees and spruce forests.

The Environmental Agency monitors the beetle across Estonia in cooperation with the State Forest Management Centre. The Estonian University of Life Sciences also operates monitoring stations in some counties in southern Estonia. Data from both the university and the nationwide monitoring programme show that beetle numbers have been declining for the past two years.

Merit Ehrpais, a chief specialist at the Environmental Agency, said monitoring data from the State Forest Management Centre and the agency showed that numbers were very high in 2022. They remained high in 2023, although a downward trend had already emerged in some counties. The decline became clearer in 2024, while results for 2025 were even lower than the previous year.

Kristjan Ait, a junior researcher in forest cultivation and forest ecology at the Estonian University of Life Sciences, said the available data for this year also showed relatively low trap catches.

Estonian summer weather directly affects beetle numbers. “Last year, the summer as a whole was cool and rainy, which kept numbers lower. This spring was similarly extremely unfavourable for the beetles: their flight period began relatively late, at the beginning of May,” Ait said.

The beetles’ flight period usually begins in mid-April. This year’s spring was also prolonged, cool and rainy, which further affected their numbers.

Ehrpais said pheromone trap results showed a clear link between the weather and the beetle’s spread. In weeks with cooler, wetter and windier weather, the beetle’s spread is lower, while numbers rise again during warmer periods.

The number of the beetle’s natural predators, including predatory flies, ant beetles and birds, has also increased over the years. Their populations have reached a level at which they can limit beetle numbers more effectively.

Meelis Matkamäe, chairman of the board of the Private Forest Union and chief executive of Rakvere Forest Cooperative, has also noticed that there have been fewer beetle outbreaks over the past two years.

“The situation has been quite good in managed stands over the past two years. The spruce bark beetle generally colonises weakened trees, and if a forest is managed and maintained, it is usually more difficult for the beetle to establish a colony there. In neglected stands, such as those damaged by storms or otherwise weakened, it can operate more freely and the conditions for reproduction are considerably better,” Matkamäe said.

Ait added that managed forests offer better opportunities to limit beetle numbers, while mixed stands also provide poorer conditions for reproduction.