The Western View: Insects Repelled by Unfamiliar Odors

Dan Pest Update, Western View

Susan Ellis, USDA APHIS PPQ,

Plants have been naturally defending against insect pests for millions of years.  Could odor be a weapon against bugs?

Scientists from the University of Vermont have discovered that not only do insects follow familiar scents to find their favorite foods, they are repelled by odors from plants they don’t know.  The study shows that there is some sort of logic to this, and it puts researchers on the path to figuring out which unfamiliar plant odors can affect insect behavior.

The team went looking for something to repel swede midge, a tiny fly that is becoming a major problem for Northeastern growers of cabbage-family crops.  They found that particular essential oils – garlic, spearmint, thyme, eucalyptus, lemon and cinnamon bark – were most effective at repelling the midge. The findings come as good news to organic farmers who don’t have an effective solution for managing the pest.

The researchers said that the more aromatic plant oils, like mint, basil and lavender, do a good job of repelling insects, but why and how are not known.  While essential oils have been used in pest management, figuring which oil is most effective has been by trial and error.  The reason that insects are repelled by odors has long been a mystery.  Just as mysterious is, which particular smells work, and specifically which smell works best – and why do some work better than others.

It turns out that odors from plants that are more distantly related to the host plant work better – they are generally more repellent. They also found that odors that were more chemically different were more likely to be repellent.   It’s logical because similar odors would be confusing to the insects; they could misinterpret the plants as hosts.

It’s an interesting that is ripe with possibilities.   It suggests a new approach to sustainable solutions for invasive pests.  It will be interesting to see if new pest management strategies come out of this work. 

The Western View: Insects Repelled by Unfamiliar Odors

I’m Len Wilcox and that’s the Western View from AgNet West and Citrus Industry Magazine.  Visit us on the web at

About the Author

Len Wilcox

Len Wilcox is a retired scientist who also ran a newspaper and has written for agricultural publications since the 1980s. He was a regular contributor to California Farmer Magazine. His commentary “The Western View” is a regular feature on Farm City Newsday and AgNet West.