Reciprocal field tests of attraction between populations of Ips pini (Say) from California, Idaho, and New York disclosed geographic variation in pheromone systems. These differences reside both in pheromone production and reception. However, it is unknown whether variation in the pheromone bouquets is qualitative, quantitative, or both.
In New York, both sexes responded in higher numbers to their own pheromone than that produced by California or Idaho males. In California, beetles of both sexes discriminated against New York, but in Idaho only females made this distinction. In both California and Idaho, the local population showed a slight preference for the pheromone produced by Idaho males over that produced by California males.
The predator Enoclerus lecontei (Wolc.) demonstrated a four-fold preference for attractants produced by males from New York over those produced by beetles from California and Idaho. The parasitoid Tomicobia tibialis Ashmead showed the opposite trend.
There is no evidence that geographic variation in the pheromones produced by I. pini is sufficient to enforce breeding isolation between adjacent populations. However, these results dramatize the necessity of considering pheromonal variability in programs applying pheromones for the survey and control of widely distributed pests.