White pine weevil attack on white spruce: A survival time analysis

The survival time of a white spruce tree (Picea glauca (Moench) Voss) with respect to the attack by the white pine weevil (Pissodes strobi (Peck)) was defined as the number of years until an attack occurred. In this context, resistant trees are those capable of delaying attacks rather than preventing attacks. This study investigated the patterns of survival times of resistant and susceptible trees in a progeny trial of white spruce in the interior of British Columbia, Canada. By doing so, we demonstrated that survival time analysis, a technique specifically developed for dealing with clinical medicine and industrial reliability tests, was a very useful approach in analyzing resistance of hosts to herbivore attack. The results suggested that survivorship of resistant trees was significantly different from that of susceptible trees, as expected. The median survival time of susceptible trees was ~12 yr after seeding, while it was 21 yr for resistant trees. The survival times of white spruce trees were identified adequately following a lognormal distribution. Based on the estimated hazard functions of the lognormal distribution, the most severe weevil infestation was predicted to occur at 19 yr for susceptible trees, and at 26 yr for resistant trees. Infestation level was affected by several factors, such as tree height, seasonal temperature, and precipitation. An accelerated failure time model was used to evaluate the effect of these factors on survivorship. The identification of resistant or susceptible trees by survival times is to be incorporated into an integrated pest management program for the white pine weevil in British Columbia.