DIFFERENTIAL RESPONSES AMONG NATURAL ENEMIES AND PREY TO BARK BEETLE PHEROMONES

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.