Random acts of weevil: A spatial analysis of Hylobius warreni attack on Pinus contorta var. latifolia in the sub-boreal spruce zone of Northern British Columbia

The Warren root collar weevil (Hylobius warreni) is a native pest of lodgepole pine (Pinus contorta var. latifolia) in western North America. Damage caused by larval feeding at the root collar and roots often results in low to moderate levels of mortality in many regenerating lodgepole pine stands. We investigated the spatial distribution of lodgepole pine trees, weevil-attacked trees, and mortality due to attack. Stem maps of all lodgepole pine trees were generated in nine, 50-m × 50-m plots in six pine plantations infested by H. warreni. All trees in each plot were assessed for attack and mortality. In all plots, live-attacked trees were significantly larger than live-nonattacked trees. In each of three plantations, two contiguous plots were established to allow assessment of within-site variation and spatial structure variation at different scales. We used Ripley's univariate L(t) function to analyze the spatial distributions of all host trees, attacked host trees, and dead attacked host trees, respectively. The distribution of attacked trees generally coincided with the distribution of host trees. The distribution of attack did not change with increasing attack intensity among plots, but did so within plots. Trees killed by H. warreni were randomly distributed in all plots except one, and spatial distribution was not affected by attack intensity. Mortality increased as a function of attack. Our findings support that this insect does not aggregate, and that virtually all lodgepole pine are potentially susceptible to attack, i.e., host distribution alone largely explains distribution of both attack and mortality.