Interactions between components of the aggregation pheromone during chemotaxis by the bark beetleIps paraconfusus

The male-produced aggregation pheromone inIps paraconfusus is composed of three compounds. Female bark beetles were exposed to combinations of these compounds, presented as point sources in an enclosed, circular arena. By itself,cis-verbenol (cV) had no effect on the number of beetles that reached the source. Either ipsenol (Ip) alone or ipsdienol (Id) alone strongly increased the number that reached the source, with Id producing a dose-response curve with a much steeper slope. cV moved the onset of the response to Id to higher doses of Id, but the response rose more rapidly after onset than when cV was absent. Overall, cV inhibited the effect of Id except at the highest dose. cV affected the onset of the response to Ip little or none, but strongly increased the slope of the response, synergizing the effect of Ip. The responses to combinations of Id and Ip were related to the log of a linear combination of their doses. The results are consistent with a model where Id and Ip act at a single site of action, but with different potencies, while cV appears to modify the effects of Id and Ip, rather than affecting the site of action directly.