Plant Compounds that Smell like Cut Grass Attract Parasitic Wasps for Protection
The smell of cut grass in recent years has been identified as the plant’s way of signalling distress, but the aroma also summons beneficial insects to the rescue.
“When there is need for protection, the plant signals the environment via the emission of volatile organic compounds, which are recognized as a feeding queue for parasitic wasps to come to the plant that is being eaten and lay eggs in the pest insect,” said Dr. Michael Kolomiets, Texas A&M AgriLife Research plant pathologist in College Station.
Plants “communicate” when attacked by producing defensive proteins and secondary metabolites, either to repel insect pests or to make themselves less appetizing. One such group of signalling compounds are known as green leaf volatiles.
To test how this functions in plants during insect attacks, Kolomiets and his team used a mutant corn plant that cannot produce green leaf volatiles, which smell like mown grass. That’s when they observed that the parasitic wasps didn’t pay attention to plants without the green leaf volatiles.
“This molecule, since it is a volatile, attracts parasitic wasps,” Dr. Kolomiets said. “They come to the plant that is being chewed up by insect herbivores and lay eggs in the caterpillar’s body. We have proven that when you delete these volatiles, parasitic wasps are no longer attracted to that plant, even when an insect chews on the leaf. So this volatile is required to attract parasitoids. We have provided genetic evidence that green leafy volatiles have this dual function — in the plant they activate production of insecticidal compounds, but also they have indirect defense capability because they send an SOS-type signal that results in attraction of parasitic wasps.”
Kolomiets tested the phenomena both in the lab and in the field, and he hopes to continue the research by testing other grassy crops such as sorghum.
“This is just a tip of the iceberg. We have found that this gene is required for many, many different physiological processes, such as drought tolerance,” he said. “We observed that mutant plants are drought susceptible as well as susceptible to insect feeding. We are trying to identify the exact function of green leafy volatiles in drought tolerance and how it works.”
Such findings may help plant breeders know how to develop new varieties that are more resistant to insects and drought, he noted.
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