Protection of lodgepole pines from mass attack by mountain pine beetle, Dendroctonus ponderosae, with nonhost angiosperm volatiles and verbenone

A number of angiosperm nonhost volatiles (NHVs) and green leaf volatiles (G LVs) were tested alone and as supplements to the antiaggregation pheromone, verbenone, for their ability to disrupt attack by the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae), on lodgep ole pine, Pinus contorta Dougl. ex Loud. var. latifolia Engel. Preliminary experiments led to a refined NHV blend [benzyl alcohol, guaiacol, benzaldeh yde, nonanal, salicylaldehyde, and conophthorin] and a refined GLV blend [( Z)-3-hexen-1-ol and (E)-2-hexen-1-ol]. In a 20-replicate experiment, NHV an d GLV groups both singly, and verbenone alone, significantly reduced MPB ma ss attack on pheromone-baited trees and on trees within 5 m of the pheromon e-baited trees. Both blends in combination with verbenone reduced the numbe r of mass attacked, baited trees to three out of 20 compared to 20 out of 2 0 of the baited controls. Each binary combination was also effective at red ucing mass attack. In these experiments, all tested repellents were release d from devices stapled to trees at the same point as the pheromone bait, su ggesting that the repellency could have been to a point source, rather than to the whole tree. Therefore, in two further experiments bands of release devices were wrapped around the treated trees and the pheromone bait was re moved from the treated trees. In one experiment, when the aggregation phero mone bait was suspended between pairs of trees treated with the NHV blend p lus GLV blend plus verbenone, only three out of 25 treated pairs had mass a ttack on at least one member of the pair. In the other 60-replicate experim ent, with no pheromone baits present, attack occurred on 13 untreated and 1 1 banded trees, all in the path of a large advancing infestation. However, the mean attack density on the banded trees was significantly reduced to a level below the 40 attacks m(-2) of bark surface required to kill a healthy lodgepole pine. As a result of these experiments, operational trials are r ecommended.