Jasmonate-inducible plant defences cause increased parasitism of herbivores

In many plants, defence systems against herbivores are induced through the octadecanoid pathway1,2, which may also be involved in recruiting natural enemies of herbivores3. This pathway can beinduced by treating plants with jasmonic acid4 or by natural herbivory, and increases resistance against herbivorous insects intomato plants5, in part by causing production of toxic and antinutritive proteinase inhibitors and oxidative enzymes6,7,8. Herbivore-infested tomato plants release increased amounts of volatiles9 and attract natural enemies of the herbivores10, as do other plants11,12,13,14,15. The octadecanoid pathway may regulate production of these volatiles, which attract host-seeking parasitic wasps16,17. However, plant resistance compounds can adversely affect parasitoids as well as herbivores18. 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.