Trap trees: an effective method for monitoring mountain pine beetle activities in novel habitats

Abstract

Mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) has recently expanded its range into the lodgepole pine forests in Alberta, Canada. However, it is unknown whether semiochemical tools developed in the beetle’s historical range are suitable for monitoring MPB in the new environment. Thus, we conducted a 3-year study to test new MPB monitoring tools in Alberta. A field trial selected a combination of MPB pheromones and two host volatiles. Using this combination, we baited different numbers of trees in triangular, square, or rectangular formations (spatial arrangements of trees) to determine how the densities of baited trees affect MPB attraction. Three plots, each made up of three formations, were arranged in a linear transect at various distances between formation boundaries. The proportion of baited trees mass-attacked was highest in the square formation. However, the proportion of spillover trees mass-attacked (attacks on non-baited trees) was lower when formations were 1 km apart compared with 4 or 8 km apart. In a follow-up test of the square formation alone, there was no difference in trap tree effectiveness between distances of 8 and 12 km. We suggest that four baited trees spaced 50 m apart in a square formation at a 12 km distance can be used in the field.