Jasmonate-inducible plant defences cause increased parasitism of herbivores

In many plants, defence systems against herbivores are induced through the octadecanoid pathway(1,2), which may also be involved in recruiting natural enemies of herbivores(3). This pathway can be induced by treating plants with jasmonic acid(4) or by natural herbivory, and increases resistance against herbivorous insects in tomato plants(5), in part by causing production of toxic and antinutritive proteinase inhibitors and oxidative enzymes(6-8). Herbivore-infested tomato plants release increased amounts of volatiles(9) and attract natural enemies of the herbivores(10), as do other plants(11-15). The octadecanoid pathway may regulate production of these volatiles, which attract host-seeking parasitic wasps(16,17). However, plant resistance compounds can adversely affect parasitoids as well as herbivores(18). It is unclear whether the combination of increased retention and/or attractiveness of parasitic wasps to induced plants and the adverse effects of plant defence compounds on both caterpillars and parasitoids results in a net increase in parasitization of herbivores feeding on induced plants. Here I show that inducing plants with jasmonic acid increases parasitism of caterpillar pests in an agricultural field twofold. Thus, elicitors of plant resistance may become useful in agriculture.