Predators that exploit prey pheromones may select for relatively subtl
e chemical changes that confer partial escape yet retain intraspecific
functionality. Parallel experiments conducted with a transcontinental
ly distributed bark beetle, Ips pini, demonstrated that the most abund
ant predators in California and Wisconsin were more attracted to prey
from distant sources than to those from local sources. Conversely, loc
al I. pini populations were most attractive to local conspecifics. Any
benefits to prey are probably only partial and temporary, however, be
cause all predators showed some attraction to both I. pini populations
. Responses by other insects exploiting I. pini communication systems
varied with ecological guild. A parasitic wasp that attacks adult host
s was more attracted to local than to distant I. pini populations. Sec
ondary subcortically feeding herbivores that cannot colonize living tr
ees but rather breed in trees killed by I. pini were highly attracted
to infested logs but did not consistently prefer either I. pini popula
tion source. Some possible underlying mechanisms, implications for nat
ural enemy-prey coevolution, and suggested strategies for biological c
ontrol are discussed.