The enemy of my enemy is...( When plants are dam...)

When plants are damaged by herbivorous insects, they release a plume of volatile chemicals. In the laboratory, these can function as a "call for help", since they attract enemies of the herbivores (predators and parasitoids). Kessler and Baldwin from the Max-Planck-Institute for Chemical Ecology in Jena now (March 16, 2001, Science) demonstrate for the first time that: 1) this "indirect defense" also functions in nature and; 2) that only specific constituents of the volatile plume are required. Specifically, the study demonstrates that herbivore-induced volatiles from wild tobacco in the Great Basin Desert of SW USA attract predatory bugs to the larvae and eggs of the plant's dominant herbivore, the five-spotted hawkmoth. Moreover, these same volatile signals deter egg-laying moths. Plants solve their pest problems by recruiting backup forces among members of their ecology community with volatile alarm signals.

Plants are not passive in the face of attack (enemies include pathogens, herbivorous insects, grazing mammals, etc). In response, they rapidly increase the production of a suite of chemical defenses that poison, repel or slow the growth of their attackers (see Karban and Baldwin, 1997 for examples). Many of these direct defenses, which can be very effective, serve as models for pest control strategies in agriculture. However, these direct defenses also create problems for plants: 1) herbivorous insects rapidly evolve resistance to these defenses, which 2) allows the insects to
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Contact: Andre Kessler and Ian T. Baldwin
kessler@ice.mpg.de
49-3641-643660
Max-Planck-Gesellschaft
13-Mar-2001