Tomato plants are primed by Helicoverpa zea (tomato fruitworm) oviposition for impending neonate feeding

Plants initiate antiherbivore mechanisms when they are attacked by insects. Most of the studies on the induction of plant defenses by insect herbivory have been carried out with simulated herbivory (e.g. mechanical wounding combined with application of insect regurgitant) or by ‘real’ herbivory (e.g. allowing herbivores to feed on host plants). However, considering that in many cases herbivory starts by newly hatched larvae around where eggs are deposited, it would be plausible to speculate that plants may sense oviposition, initiate antiherbivory defenses and get ready for impending herbivory by neonates. Here we demonstrate that tomato plants, Lycopersicon esculentum (Solanales: Solanaceae), upregulate various antiherbivory genes only upon the oviposition by adults of tomato fruitworm, Helicoverpa zea (Lepidoptera: Noctuidae). More interestingly, tomato plants where H. zea adults laid eggs showed faster, stronger and longer levels of proteinase inhibitor gene 2 (pin2) induction upon simulated herbivory than control plants. The growth rate and survival of neonates of H. zea significantly decreased when they were allowed to feed on the tomato leaves that had been exposed to H. zea oviposition. The survival of H. zea neonates was negatively correlated with the number of eggs deposited on tomato leaves. This study shows that tomato plants sense H. zea oviposition and prime themselves for the feeding by emerging neonates. As far as we know, this is the first report of priming of host plants by herbivore oviposition.