Jasmonate and salicylate induce expression of herbivore cytochrome P450 genes

Jasmonate and salicylate are plant-produced signals that activate plant defence genes after herbivory1,2,3 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 proteins6,9,10 in the plants. Although the jasmonate and salicylate signal cascades activate different sets of plant defence genes10, or even act antagonistically11,12, there is substantial communication between the pathways2,3,13. 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.