Protection of gardens and crops from insects with the “smell of fear”

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For home gardeners and farmers, herbivorous insects pose a great threat to their hard work and crop yields. The predatory insects that feed on these bugs give off odors that pests can detect, which changes the behavior of the pests and even their physiology not to be eaten. As beetles become more resistant to traditional pesticides, researchers now report that they have developed a way to bottle up the “scent smell” produced by predators to naturally repel and destroy destructive insects without the need for harsh substances.

The researchers will present their results today at the autumn meeting of the American Chemical Society (ACS).

“It is not uncommon to use our senses to avoid risky situations. If a building is on fire, we as humans could use our sense of sight or smell to recognize the threat, ”says Sara Hermann, Ph.D., project manager for investigators. “There is evidence of such behavioral responses to risk in all taxa, suggesting that prey organisms can detect predatory threats, but the mechanisms by which they can be detected are not very well understood, especially in insects.”

“Insects rely on olfactory cues to find food, partners, and places to live, so this is a great opportunity to explore how to use those smells to manipulate their behavior,” says Jessica Kansman, Ph.D. , a postdoc who will work in the meeting. Hermann and Kansman are from Pennsylvania State University.

Aphids are an extremely destructive pest to a number of crops, and their large numbers, their ability to transmit plant pathogens, and their increased resistance to insecticides make them a persistent problem for growers. They are also a favorite of the ladybirds, which gardeners applaud as a source for sustainable pest control. Hermann’s research has shown that aphids and other herbivorous insects avoid fields and gardens when they can smell nearby predators. In addition, exposure to the olfactory stimuli emanating from ladybugs can also cause aphids to slow their reproductive rate and increase their ability to grow wings, both behaviors aimed at avoiding threats.

With these observations in mind, the research team set out to determine whether the olfactory signals emitted by ladybirds alone could control pests. They began by identifying and extracting the volatile odor profile of live ladybugs using gas chromatography – mass spectrometry, which separates and identifies the individual components of the ladybird odor. To see what compounds the aphids would respond to, they hooked the antennae of live aphids to an electrical antenna device (EAG) and exposed them to every single smell the predator emitted to see what compounds they detected. The strength of their reactions was measured using the signal picked up by the EAG machine. Of the many compounds emitted by ladybirds, aphids were the most responsive to methoxypyrazines, such as isopropyl methoxypyrazine, isobutyl methoxypyrazine, and sec-butyl methoxypyrazine. Once the compounds were identified, Hermann and his team set out to develop a special scent blend that can be used in an essential oil diffuser that diffuses the scent over time in a garden or field.

Next, the team plans to field test their scented diffusers to see if the effects on aphids and ladybugs are similar to what they saw in the laboratory. Hermann and Kansman also want to determine the distribution area of ​​the diffusers and whether they can be applied to other pests and predators as well as different plant species. They are also working with a manufacturing company to develop special diffusers for later commercial use by farmers and gardeners.

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More information:
Smell of fear: Using odor signals from predatory insects as pesticides for herbivorous insects, ACS Fall 2021.

Provided by the American Chemical Society

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