Using the "smell of fear" to control garden pests

Many herbivorous insects are pests that can destroy crops and make the home gardener’s life a misery. Although pesticides may keep these pests at bay for a while, they soon become resistant and continue to wreak havoc. Researchers at Pennsylvania State University have created a new strategy to deter garden pests by using the odor emitted by a predatory insect. This encourages the pests to leave the area without ever coming into direct contact with the predator.

Dr. Sara Hermann and Dr. Jessica Kansman, both scientists in the Department of Entomology, will present the results of their research at a meeting of the American Chemical Society, ACS Fall 2021. The researchers will explain how they plan to bottle the odor of predatory ladybird beetles (commonly known as ladybugs) and release this “smell of fear” to change the behavior of common garden pests such as aphids.

“It is not uncommon to use our senses to avoid risky situations. If a building was on fire, we as humans could use our senses of sight or smell to detect the threat,” said Dr. Hermann, the project’s principal investigator. “There is evidence for such behavioral responses to risk across taxa that suggests prey organisms can detect predation threats, but the mechanisms for detection aren’t very well understood, especially with insects.”

“Insects rely on olfactory cues to find food, mates and places to live, so this is a great opportunity to investigate how to use these smells to manipulate their behavior,” said Dr. Kansman. 

The researchers chose to work on ladybugs because they are already recognized as useful predators for controlling many different types of crop and garden pests. Ladybugs prey on aphids, that are destructive to a variety of crops because of their large numbers and their tendency to transfer pathogens between their plant hosts. 

Research by Dr. Hermann has already shown that odors from ladybugs can make aphid reproduction rate decrease and can also increase the rate of wing growth in aphids, which helps them to move away and avoid the threat of being eaten. 

The experts extracted the volatile odor from live ladybugs in the laboratory and profiled it using gas chromatography-mass spectrometry. Once they had identified the individual components of the odor, they introduced these, one by one, to live aphids. The team connected the antennae of each aphid to an electroantennogram (EAG) machine to record the specific chemical compounds that the aphid detected.

The study revealed that aphids showed the strongest responses to a group of organic compounds called methoxypyrazines. These included isopropyl methoxypyrazine, isobutyl methoxypyrazine and sec-butyl methoxypyrazine. 

The researchers then made a blend of the most potent odor components to use in an essential oil diffuser to waft the predator’s scent across a field or garden.

Future work will involve the experimental use of the scent diffusers in the field to see whether aphids respond in the same way as they do in the laboratory. In addition, they wish to try the technique with different crop and garden pests and their natural predators, and to market their diffusers for use by farmers and gardeners.

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By Alison Bosman, Earth.com Staff Writer