Variations in the attack pattern of Dendroctonus micans and the colonization rate of Rhizophagus grandis in Picea orientalis stands

Abstract

The great spruce bark beetle, Dendroctonus micans, is an invasive pest that has spread to almost all of the Picea orientalis forests in Turkey, affecting many trees and causing active damage. The species-specific predator Rhizophagus grandis plays an important role in suppressing populations of this pest because it is only found in D. micans galleries. In this study, the attack pattern of D. micans and the colonization rate of R. grandis were investigated according to some stand characteristics, such as aspect, developmental stage, crown closure, and stand type. It was determined that 20.5% of the 2025 sample trees evaluated in 83 sample plots were attacked by the beetle and that active damage from the beetle was currently continuing in 5.8% of the trees. There was no difference in the attack pattern of D. micans between shady and sunny aspects. However, trees showed significant differences in terms of susceptibility to beetle attacks based on developmental stage, crown closure, and stand type. The damage rates of the beetle were 19.8% and 29.6% for the mature and overmature stages, respectively; 28.5%, 18.8%, and 16.4% for low, medium, and full coverage stands, respectively; and 10.5–32.3% for different stand types. The colonization rate of R. grandis was 18.2%. This rate was not affected by the aspect, developmental stage, crown closure, or stand type. However, the rate was higher in the stands heavily infested by D. micans. In addition, there was a moderate correlation between the total number of D. micans individuals in active galleries and the total number of R. grandis individuals in these galleries.