Abstract
Sirex noctilio, a European woodwasp, occasionally shares resources with the native S. nitobei and other colonizers in northeast China. The impact of its coexistence on individual species remains unclear. Random sampling was conducted to assess the patterns and extent of insect co-colonization across various spatial scales. Additionally, we analyzed wood sections to determine the density, adult size, and distribution of the two Sirex species. Spatial scales revealed negative associations (Asemum striatum and Phaenops sp.) and neutral ones (Ips acuminatus) between woodwasps and other co-colonizers. Clustering of woodwasps and Phaenops sp. occurred at a small scale (0-7.3 m). Regression analysis showed a positive correlation between the chance of woodwasp attacks and past attacks on the same host, with little impact from other colonization factors. The distribution and body size of S. noctilio within the tree appeared unaffected by S. nitobei's presence. In the presence of S. noctilio, S. nitobei tended to lay eggs in damaged sections. At the stand level, the overall impact of S. noctilio on S. nitobei population density is likely positive because S. nitobei prefer weaker trees, a preference potentially influenced by initial attacks from S. noctilio on healthier hosts.