Protecting gardens and crops from insects using the 'smell of fear'
Aug 2021, phys.org
They're using methoxypyrazines, such as isopropyl methoxypyrazine, isobutyl methoxypyrazine and sec-butyl methoxypyrazine. Methoxypyrazines smell like "green, herbaceous, vegetative, green peppers, freshly cut grass, and asparagus."
But for aphids, methoxypyrazines smell like ladybugs. Aphids hate ladybugs. And farmers hate aphids.
On a related note, the smell of cut grass is a defense mechanism for grass to tell other grass that it's being attacked, and to "brace yourselves." The next time you smell it, you can think of the sound of grass screaming.
via American Chemical Society: Smell of fear: Harnessing predatory insect odor cues as a pest management tool for herbivorous insects, ACS Fall 2021.