In response to herbivore damage, several plant species emit volatiles that
attract natural predators of the attacking herbivores(1-5). Using spider mi
tes (Tetranychus urticae) and predatory mites (Phytoseiulus persimilis)(1-4
), it has been shown that not only the attacked plant but also neighbouring
plants are affected, becoming more attractive to predatory mites(3,6) and
less susceptible to spider mites(6). The mechanism involved in such interac
tions, however, remains elusive. Here we show that uninfested lima bean lea
ves activate five separate defence genes when exposed to volatiles from con
specific leaves infested with T. urticae, but not when exposed to volatiles
from artificially wounded leaves. The expression pattern of these genes is
similar to that produced by exposure to jasmonic acid. At least three terp
enoids in the volatiles are responsible for this gene activation; they are
released in response to herbivory but not artificial wounding. Expression o
f these genes requires calcium influx and protein phosphorylation/dephospho
rylation.