1. Department of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China
2. Department of Entomology, University of Illinois, Urbana, Illinois 61801, USA
3. Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801, USA

Correspondence to: Xianchun Li^1,2May R. Berenbaum² Correspondence and requests for materials should be addressed to M.R.B. (e-mail: Email: maybe@uiuc.edu) or X.L. (e-mail: Email: lxc@life.uiuc.edu).

Abstract

Jasmonate and salicylate are plant-produced signals that activate plant defence genes after herbivory^{1, 2, 3} or pathogen⁴ attack. Amplification of these signals, evoked by either enemy attack or experimental manipulation, leads to an increase in the synthesis of toxic compounds (allelochemicals)^{5, 6, 7, 8} and defence proteins^{6, 9, 10} in the plants. Although the jasmonate and salicylate signal cascades activate different sets of plant defence genes¹⁰, or even act antagonistically^{11, 12}, there is substantial communication between the pathways^{2, 3, 13}. Jasmonate and salicylate also contribute to protecting plants against herbivores by causing plants that experience insect damage to increase their production of volatile molecules that attract natural enemies of herbivorous insects¹⁴. In response to plant defences, herbivores increase their production of enzymes that detoxify allelochemicals, including cytochrome P450s (refs 15, 16). But herbivores are potentially vulnerable to toxic allelochemicals in the duration between ingesting toxins and induction of detoxification systems. Here we show that the corn earworm Helicoverpa zea uses jasmonate and salicylate to activate four of its cytochrome P450 genes that are associated with detoxification either before or concomitantly with the biosynthesis of allelochemicals. This ability to 'eavesdrop' on plant defence signals protects H. zea against toxins produced by host plants.