Change in Resistance of Lodgepole Pine to Mountain Pine Beetle Between 1965 and 1972

In 1965, 100 lodgepole pines (Pinuscontorta Dougl. var. latifolia Engelm.) in each of two areas near Radium, B.C. were graded for resistance to mountain pine beetle (Dendroctonusponderosae Hopk.) by evaluating their response to inoculation with a fungus transported by the mountain pine beetle. In 1972, mortality of these trees due to mountain pine beetle or other causes was determined, trees were inoculated and the resistance of each was again evaluated. Most trees nonresistant in 1965 had been killed by the mountain pine beetle by 1972, whereas most trees rated resistant in 1965 were still alive and were again rated resistant.