Byers, J.A., Birgersson, G., Löfqvist, J., & Bergström, G. 1988. Synergistic pheromones and monoterpenes enable aggregation and host recognition by a bark beetle, Pityogenes chalcographus. Naturwissenschaften 75:153-155.

Abstract-- We report the strong synergism between two pheromone components in causing the attraction of the six-spined spruce bark beetle or "Kupferstecher", Pityogenes chalcographus L. (Coleoptera: Scolytidae), in the field. Our field results also suggest that several monoterpenes of Norway spruce, Picea abies (L.) Karst, when presented with the pheromone components, play a role in host recognition and colonization by the beetle because they caused relatively more beetles to enter holes in artificial hosts. Furthermore, sexual differences in strategies of host resource competition are indicated because of the lower proportions of males than females that entered the holes as well as were attracted to higher release rates of pheromone.
entire paper Chemical Ecology
Chemical Ecology