Green Leaf Volatiles

How do plants defend themselves from herbivores? Thorns, spines, and perhaps toxic or poisonous chemicals come to mind. But when an uninvited insect starts enjoying a free meal of leaf cells, the plant may just trick the insect into helping them call the cops!
Scientists have known for some time now, that when plant tissues are damaged, chemical compounds may be released into the air. These “green leaf volatiles” produce the smells of freshly cut lawns and alfalfa fields. Scientists have learned that these chemicals may play an important role in plant defense, and they are gaining greater insight into how they work.
A study in the journal Science recently reported that when caterpillars of the tobacco hornworm started chewing on the leaves of wild tobacco, the saliva of the caterpillar reacted with green leaf volatiles in the plant to produce compounds that functioned to attract predatory insects. The predatory insects followed the “scent trail” to the leaves and proceeded to eat the caterpillars and nearby eggs. This study was particularly informative in discovering that it was the caterpillar’s saliva that actually contributed to the formation of the compounds that attracted the caterpillar’s predators.

This is a relatively new area of study for ecologists, and research on green leaf volatiles will certainly help ecologists better understand this interesting aspect of plant defense. Research may also provide insight into more effective pest control as well as the development of more pest resistant crop varieties.

There is another aspect of green leaf volatiles that you might find intriguing. As some of you know, the orchid family is known for having some unusual and interesting pollination mechanisms. Some orchid flowers have been found to produce green leaf volatiles, not to attract predators of insects chewing their leaves, but for pollination. Those orchids are some crafty little gems!

I hope this gives you a little more to consider the next time you smell cut plants, see a caterpillar chewing on a leaf, or happen upon some orchid in the prairies or woods of our region. There is a lot more going on out there than most of can imagine!

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.