HOW CATERPILLAR-DAMAGED PLANTS PROTECT THEMSELVES BY ATTRACTING PARASITIC WASPS

Parasitic and predatory arthropods often prevent plants from being sev erely damaged by killing herbivores as they feed on the plants. Recent studies show that a variety of plants, when injured by herbivores, em it chemical signals that guide natural enemies to the herbivores, It i s unlikely that herbivore-damaged plants initiate the production of ch emicals solely to attract parasitoids and predators, The signaling rol e probably evolved secondarily from plant responses that produce toxin s and deterrents against herbivores and antibiotics against pathogens, To effectively function as signals for natural enemies, the emitted v olatiles should be clearly distinguishable from background odors, spec ific for prey or host species that feed on the plant, and emitted at t imes when the natural enemies forage, Our studies on the phenomena of herbivore-induced emissions of volatiles in corn and cotton plants and studies conducted by others indicate that (i) the clarity of the vola tile signals is high, as they are unique for herbivore damage, produce d in relatively large amounts, and easily distinguishable from backgro und odors; (ii) specificity is limited when different herbivores feed on the same plant species but high as far as odors emitted by differen t plant species and genotypes are concerned; (iii) the signals are tim ed so that they are mainly released during the daytime, when natural e nemies tend to forage, and they wane slowly after herbivory stops.