Objective In the eastern Tianshan Mountains, natural Picea schrenkiana forests are progressively declining as a result of persistent damage by Ips hauseri and Pityogenes spessivtsevi. Removing infested source trees during the overwintering period is an important control measure, but winter operations are largely confined to aboveground damaged trees. To enable the precise removal of these beetle sources, this study clarified the distribution patterns of the two bark beetle species in the trunks and branches of P. schrenkiana at different damage stages during the overwintering period. The findings provide a basis for developing scientific and precise overwintering control strategies.

Method In the early overwintering period, P. schrenkiana trees were assigned to five damage stages according to the degree of crown needle discoloration (from fully green to fully gray), and 15 sample trees were selected in total. After felling, the trunk was divided into sections and dissected, and lateral branches were collected from the upper, middle, and lower crown layers. The abundance, developmental stage, and distribution of the two bark beetle species were then systematically surveyed and recorded.

Result In the early overwintering period, live I. hauseri and P. spessivtsevi occurred only in early-, mid-, and late-stage damaged trees, whereas none were found in healthy or standing dead trees. Early-stage damaged trees were the principal reservoir of overwintering beetles within the forest. The two species showed marked niche differentiation on infested trees. I. hauseri was concentrated in the middle and lower trunk (4−5 m) and consisted almost entirely of adults. In contrast, P. spessivtsevi mainly occupied the middle and upper trunk and the lateral branches of the crown. On the trunk, it was concentrated at two height intervals, 4−5 m and 10−11 m. Larvae dominated at 4−5 m, whereas adults dominated at 10−11 m and in the lateral branches.

Conclusion In the early overwintering period, I. hauseri and P. spessivtsevi were concentrated on damaged trees with pronounced crown discoloration, and the two species showed marked niche differentiation. For managing bark beetle damage during the overwintering period, we recommend using crown discoloration as an indicator and prioritizing the graded, precise removal of early- to late-stage damaged trees. Treatments should be differentiated according to the spatial distribution of the different developmental stages on the trunk and branches, so as to minimize the beetle population base in the following year.