Root Deformation Reduces Tolerance of Lodgepole Pine to Attack by Warren Root Collar Weevil

Surveys were conducted on regenerating stands of lodgepole pine to determine the relationship between root deformation and susceptibility to attack by the Warren root collar weevil, Hylobius warreni Wood. The total number of trees attacked by H. warreni did not differ between planted and natural trees. A matched case-control logistic regression suggested that root cross-sectional area was more important in predicting weevil attack for naturally regenerated trees than for planted trees, but weevils were associated with a larger reduction in height-to-diameter ratios for trees with planted root characteristics than for trees with natural root form. Neither the stability of attacked versus unattacked trees differed significantly and there was no significant interaction of weevil attack and tree type, but weevil-killed trees had different root characteristics than alive, attacked trees. Lateral distribution and root cross-sectional area were significant predictors of alive attacked trees versus weevil-killed trees, suggesting that trees with poor lateral spread or poor root cross-sectional area are more likely to die from weevil attack. We conclude that root deformation does not necessarily increase susceptibility to attack but may increase the likelihood of mortality. Thus, measures to facilitate good root form are needed when planting pine in areas with high risk of Warren root collar weevil attack.