Outbreak of Pityogenes chalcographus and Pityophthorus pityographus on Spruce Seedlings Resulting from Inappropriate Management in a Forest Nursery

Abstract

In this report, we describe a local outbreak of small bark beetles on 4-year-old seedlings of Picea abies in a forest nursery in Central Europe in 2021. In March 2022, 10–50% of the seedlings were “dry” (i.e., with dry and easily broken twigs and with easily peeled bark) in each 4-row bed in the nursery. Half of the dry plants were completely covered by galleries of bark beetles and another 35% of the seedlings were with one or two bark beetle galleries. Almost 90% of the beetles found on the affected seedlings were Pityogenes chalcographus, and only 10% were Pityophthorus pityographus (we studied 100 seedlings in the second bed). The chipping of Picea pungens in previous years had left many felled trunks, branches, and other logging residues in the area. These residues are covered by galleries of both bark beetles. We suggest that, after multiplying on the logging residues, the beetles could not find suitable material for reproduction and were lured to the nursery seedlings, which had been weakened by location (a location that provided inadequate shade and no wind protection) and by repeated replanting.