Jasmonate-mediated induced plant resistance affects a community of herbivores.
The negative effect of induced plant resistance on the preference and performance of herbivores is a well-documented ecological phenomenon that is thought to be important for both plants and herbivores. This study links the well-developed mechanistic understanding of the biochemistry of induced plant resistance in the tomato system with an examination of how these mechanisms affect the community of herbivores in the field. Several proteins that are induced in tomato foliage following herbivore damage have been linked causally to reductions in herbivore performance under laboratory conditions. Application of jasmonic acid, a natural elicitor of these defensive proteins, to tomato foliage stimulates induced responses to herbivory. Jasmonic acid was sprayed on plants in three doses to generate plants with varying levels of induced responses, which were measured as increases in the activities of proteinase inhibitors and polyphenol oxidase [catechol oxidase]. Field experiments conducted in Davis, California, USA, over 3 years (summers of 1995-97) indicated that induction of these defensive proteins is associated with decreases in the abundance of all four naturally abundant herbivores, including insects in three feeding guilds, caterpillars (Spodoptera exigua), flea beetles (Epitrix hirtipennis), aphids (Macrosiphum euphorbiae, Myzus persicae) and thrips (Frankliniella occidentalis). Induced resistance killed early instars of noctuid caterpillars (S. exigua and Trichoplusia ni). Adult flea beetles strongly preferred control plants over induced plants, and this effect on host plant preference probably contributed to differences in the natural abundance of flea beetles. The general nature of the effects observed in this study suggests that induced resistance will suppress many members of the herbivore community. By linking plant biochemistry, insect preference, performance, and abundance, tools can be developed to manipulate plant resistance sensibly and to predict its outcome under field conditions.