A cry for help: Crops under attack emit cues for hungry birds

We humans are simple creatures — we find ourselves in trouble, we cry out for help. Science has known for a while that plants do something similar by letting out “sensory volatile cues,” like scents, when they’re under attack by hungry insects. The result is that birds will often pick up the cue, swoop down, and eat whatever insect is attacking. Now, for the first time, this has been studied in an agricultural setting.

It’s well understood that plants let out sensory volatile cues when being, for example, eaten by insects. This also happens in other situations, like when plants are torn or trampled. This is actually what’s happening when you catch that “freshly-mowed grass” scent on the wind — your neighbor’s lawn is calling for assistance after being chopped up by a mower.

Researchers from the University of Delaware set out to better understand the plant/bird aspect of this phenomenon in order to benefit farmers looking to supplement their pest control programs, said the research leads.

“Improving our understanding of how birds prey on insects would open new avenues in sustainable pest control,” said study lead Ivan Hiltpold.

The research team created “insect larvae” using small orange pins and Play-Doh, and planted their artificial bug babies on corn plants. Before that, they set up each corn stalk with an odor dispenser that either emitted an artificial scent meant to replicate the sensory volatile cues or an organic solvent that served as a control measure. They then measured the bird attacks/pecks around the fake larvae.

The team found that the larvae located close to the odor dispensers were attacked by birds way more often than those located near the control dispensers.

“It is a cry for help,” said Hiltpold. “It seems that birds are using that as a cue to locate a plant or a group of plants. Then, what we think, is that they use their visual acuity to locate the larvae when they’re in the vicinity of the plant emitting the volatiles.”

Another scientific conundrum touched on by the research: it provides evidence suggesting birds can smell, something science is unsure of from bird species to species. Further research is planned to learn more about what types of birds are responding to the sensory cues.

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