Influence of Ponderosa Pine Resin Volatiles on the Response of Dendroctonus ponderosae1 to Synthetic trans -Verbenol 2 , 3

Abstract

The synergistic effect of various host factors on the response of in-flight populations of Dendroctonus ponderosae Hopkins emerging from Pinus ponderosa Laws. to the aggregation pheromone trans -verbenol was quantified in a series of replicated field bioassays. Synthetic formulations of trans -verbenol, although largely inactive alone, attracted beetles when deployed with certain host terpenes, particularly myrcene and terpinolene. Freshly extracted ponderosa pine oleoresin in combination with trans -verbenol was significantly more attractive to beetle populations, particularly to females, than were pheromone complexes containing single monoterpenes or the composite monoterpene fraction of oleoresin (distilled oil), When tested with trans -verbenol on traps without replacement, fresh resin samples lost their superior attractiveness within 1 day; the numbers and sex ratios of beetle catches on exposed resin- trans -verbenol treatments paralleled those on pheromone traps baited with distilled oils. The qualitative monoterpene composition of fresh resin, however, did not appear to change with short term exposure or during the steam distillation process. In combination, these findings suggested the presence of host-produced chemical messengers other than monoterpenes in oleoresin which are disproportionately attractive to ♀ D. ponderosae , the host selecting sex. Analysis of resin samples by gas chromatography and mass spectrometry led to the constituent which may contribute to the superior field attractiveness of fresh resin. The need to further investigate the role of non-terpene host volatiles in bark beetle host selection is stressed.