Many predatory insects that prey on herbivores also feed on the plant, but it
is unknown whether plants affect the performance of herbivores by responding
to this phytophagy with defence induction. We investigate whether the prior
presence of the omnivorous predator Macrolophus pygmaeus (Rambur) on tomato
plants affects plant resistance against two different herbivore species.
Besides plant-mediated effects of M. pygmaeus on herbivore performance, we
examined whether a plant defence trait that is known to be inducible by
herbivory, proteinase inhibitors (PI), may also be activated in response to
the interactions of this predator with the tomato plant. We show that exposing
tomato plants to the omnivorous predator M. pygmaeus reduced performance of a
subsequently infesting herbivore, the two-spotted spider mite Tetranychus
urticae Koch, but not of the greenhouse whitefly Trialeurodes vaporariorum
(Westwood). The spider-mite infested tomato plants experience a lower
herbivore load, i.e., number of eggs deposited and individuals present, when
previously exposed to the zoophytophagous predator. This effect is not
restricted to the exposed leaf and persists on exposed plants for at least two
weeks after the removal of the predators. The decreased performance of spider
mites as a result of prior exposure of the plant to M. pygmaeus is accompanied
by a locally and systemically increased accumulation of transcripts and
activity of proteinase inhibitors that are known to be involved in plant
defence. Our results demonstrate that zoophytophagous predators can induce
plant defence responses and reduce herbivore performance. Hence, the
suppression of populations of certain herbivores via consumption may be
strengthened by the induction of plant defences by zoophytophagous predators