The leaves of some plants protect from pests because as they are chewed, they release a chemical combination of acids and alcohols that attract pest-eating insects.

One way plants protect themselves from pest damage is by using a highly-evolved chemical language. This chemical language communicates detailed information regarding what specific kind of insect pest is causing damage to the plant, and thus attracts the appropriate pest-eating insect to “rescue” it by killing off the pest.

Damage from insect feeding elicits the release of signaling molecules systemically within the plant. These signaling molecules turn on genes for the production of volatile compounds, acids and alcohols which evaporate into the surrounding air to communicate the presence of the pest insect to pest-eating insects. Plants can recognize various insect pests by proteins in their oral secretions, as well as by the type of damage they cause. For example, piercing and sucking insects (such as whiteflies and aphids) elicit different signaling molecules than chewing insects (such as caterpillars). Because the signaling molecules elicited by different insect pests vary, the genes activated for volatile compound production are unique to that pest species, alone. The result is that the plant produces a specific volatile blend that attracts the most appropriate pest-eating insect to rescue the plant from the threat at hand.

The release of plant volatiles can be stimulated by an attack from a wide range of insect species, from mountain pine beetles to aphids. Furthermore, the type of pest-eating insect that is attracted to the plant’s volatiles can vary from parasite to predator. In fact, plant volatiles can be perceived by any insect or plant in the surrounding area that stands to benefit from knowing the status of the plant. A community benefit of this volatile chemical communication strategy is that, because the chemicals are airborne, plants in close proximity to the affected plant receive a warning of the impending danger.

This summary was contributed by Melissa Moore Friedman.

References

“Since the blends of HIPVs [herbivore induced plant volatiles] may vary with the attacking herbivore... various components and cross-talk between the involved signaling pathways are thought to be responsible for the characteristic terpenoid blend ... Several oxylipin compounds (JA) [jasmonic acid], its precursors, and related compounds] very probably act as master switches for herbivore stimulated plant responses, activating distinct sets of defense genes leading to terpenoid formation … Moreover, synergistic and antagonistic cross-talk among the signaling pathways (Ca 2+ [calcium ion], JA [jasmonic acid] and ethylene signaling) is involved in terpenoid biosynthesis, and this integrated signaling is responsible for volatile terpenoid formation in plants...” (Arimura et al. 2009:913).

 “...chewing arthropods increase endogenous JA levels but do not significantly induce SA [salicylic acid] levels, whereas sucking arthropods induce both JA and SA in wildtype plants...” (Arimura et al. 2009:913). 

Book
The Secret Garden: Dawn to Dusk in the Astonishing Hidden World of the GardenJanuary 11, 1992
David Bodanis

Book
Ecology of Predator-Prey InteractionsNovember 8, 2005

Journal article
Chemical and Molecular Ecology of Herbivore-Induced Plant Volatiles: Proximate Factors and Their Ultimate FunctionsPlant and Cell PhysiologyFebruary 25, 2017
G.-i. Arimura, K. Matsui, J. Takabayashi