Spatial colonization patterns of the European woodwasp, Sirex noctilio, at a pine plantation in the Adirondacks

Spatial colonization patterns can be an important component of understanding an insect’s life history. Aggregation can play a key role in population biology by allowing insect herbivores to escape regulation by predators or overcome host defenses. Here, we analyze spatial colonization patterns of the European woodwasp, Sirex noctilio, at a pine plantation in New York State. Sirex noctilio is a recently-introduced invasive pest that has caused considerable economic loss in commercial pine plantation in the Southern Hemisphere and attacks and kills Pinus resinosa and P. syslvestris in North America.  We used Kulldorff’s spatial scan statistic to assess whether tree mortality from S. noctilio was spatially aggregated more or less than expected given the a priori assumption of complete spatial randomness of events. We tested patterns of aggregation using four spatial scan windows sizes (5, 10, 20, and 30 m) to assess consistency in the model from a fine to coarse analysis. We found mortality attributed to S. noctilio was significantly clustered at each scanning window extent. However, patterns of mortality may not be attributed to the same underlying processes for each model. Further analysis should incorporate the role of site and stand level variables in aggregation of S. noctilio mortality.