is the technical name for this amazing process. When we touch a hot stove, our central nervous system springs into action and our body pulls back. Since plants don't have nerves they've evolved to use scent compounds (volatiles) to rapidly send signals from one part of the plant to the other. So, say, a caterpillar starts chewing on a leaf...the plant can detect certain compounds in the caterpillar's saliva, which it produces in copious quantities as it happily masticates.
Reception/detection of caterpillar spit compounds in the plant's chewed part then sets off a biochemical chain of events in which the plant's genes are turned on to produce volatile SOS signals...So, now the leaves and plant parts above/below/near where the caterpillar is chewing then receive/detect the SOS signals. What happens next is that those plant parts turn on genes that start producing defensive compounds to make that tissue less palatable or downright nasty to the caterpillar. THat's only plant protection strategy number one.
Number two is that the predatory and parasitic bugs in the neighborhood can also smell these plant SOS scents and orient to them. IN other words, the plant sets up a scent trail for the caterpillar's natural enemies. This enables the natural enemies to rapidly find the caterpillar and then eat or parasitize it.
This process takes quite a bit of energy, and also requires activation by herbivore saliva compounds, so once a plant is harvested/picked, the system would quit after the energy reserves were depleted or input was lost.
There are 2 different defense processes: ONe for chewing bugs (like caterpillars, grubs, and grasshoppers) and pathogenic fungi (like rusts, smuts) and another for sucking bugs (like aphids) and bacterial pathogens (like citrus greening). Plant defense system #1 uses a scent compound called methyl jasomonate as a primary signal compound. IT smells like jasmine flowers as the name implies.
Plant defense system #2 uses a scent compound called methyl salicylate as a primary signal compound. WHen you use a topical analgesic like ben gay, you are smelling methyl salicylate. THIs compound is produced from salicylic acid, which is the main ingredient in aspirin. I think it got its name from the willow genus: Salix.
Googling 'herbivore induced plant compounds' provides lots of neat diagrams to explain this better than I did. Namaste.
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