Factors that trigger population transitions of mountain pine beetle from endemic to incipient-epidemic levels are poorly understood. The population dynamics of this insect may be influenced by associations with trees colonized by other bark beetles. This study explores the spatial and temporal relationships between mountain pine beetle and non-eruptive bark beetle species in lodgepole pine stands of southern British Columbia. Increasing populations of non-eruptive bark beetles were positively correlated with each other, and with endemic mountain pine beetle. Endemic and incipient-epidemic levels of mountain pine beetle were often positively spatially associated with the bark beetles Pseudips mexicanus, Orthotomicus latidens, Ips pini, and Hylurgops species, which themselves frequently colonized the same host trees. As populations grew, mountain pine beetle shifted from attacking injured/previously colonized hosts to uncolonized hosts. Identifying these potential triggers of population phase transitions may help prevent future epidemics in areas of economic importance. --P.ii.
