Herbivorous insects use diverse feeding strategies to obtain nutrients
from their host plants. Rather than acting as passive victims in these
interactions, plants respond to herbivory with the production of
toxins and defensive proteins that target physiological processes in
the insect. Herbivore-challenged plants also emit volatiles that attract
insect predators and bolster resistance to future threats. This
highly dynamic form of immunity is initiated by the recognition
of insect oral secretions and signals from injured plant cells. These
initial cues are transmitted within the plant by signal transduction
pathways that include calcium ion fluxes, phosphorylation cascades,
and, in particular, the jasmonate pathway, which plays a central and
conserved role in promoting resistance to a broad spectrum of insects.
A detailed understanding of plant immunity to arthropod herbivores
will provide new insights into basic mechanisms of chemical
communication and plant-animal coevolution and may also facilitate
new approaches to crop protection and improvement.