How does humble concern escape a devastating pest of tomato

Scientists have revealed for the first time the natural weapon used by marigolds to protect tomato plants against destructive whiteflies.

Researchers from Newcastle University's Faculty of Natural Sciences and the Environment have conducted a study to prove what gardeners around the world have known for generations: the worries repel whiteflies from the tomato.

Publish their findings today in the journal PLOS ONE, experts identified limonene – released by marigolds – as the main component responsible for the control of tomato whiteflies. Insects find the smell of limonene repellent and are slowed down by the powerful chemical.

Large scale application

The findings of the study could potentially pave the way for the development of safer and cheaper alternatives to pesticides.

Since limonene repels whiteflies without killing them, the use of the chemical should not lead to resistance, and the study showed that this did not affect the quality of the product. All that is needed to deter white flies is to interpose marigolds in tomato plots or to suspend small pots of limonene among the tomato plants so that the odor can disperse into the foliage. the tomato.

In fact, the research team, led by Drs. Colin Tosh and Niall Conboy, showed that it was possible to develop a product similar to an air freshener containing pure limonene, which could to hang in greenhouses to confuse whiteflies. exposing them to an explosion of limonene.

University of Newcastle Ph.D. Student Niall said, "We talked to many gardeners who knew that marigolds effectively protected tomatoes from whiteflies, but this has never been scientifically tested.

"We found that limonene was the most abundant chemical released by marigolds, which is exciting because limonene is cheap, not harmful, and is much less risky than pesticides, especially when you do not apply it to culture and it's just a faint perfume in the air.

"Most pesticides are sprayed on crops, not only killing the targeted parasite, it kills absolutely everything, including the parasite's natural enemies."

Limonene accounts for approximately 90% of the oil contained in citrus zest and is commonly found in domestic air fresheners and anti-mosquito products.

Dr. Tosh said, "There is great potential for using limonene indoors and outdoors, planting marigolds near tomatoes or using pure limonene pods. Another important benefit of using limonene is that it is not only safe for bees, but also for bees, providing the nectar for bees that are essential for pollination.

"All alternative methods of controlling whiteflies that can reduce the use of pesticides and introduce a greater diversity of plants and animals into agricultural and horticultural systems should be welcomed."

The researchers conducted two major greenhouse trials. Working with French concerns during the first experiment, they established that the repellent effect worked and that the concerns were an effective accompaniment to ward off white flies and tomatoes.

For the second experiment, the team used a machine that allowed it to analyze the gaseous and volatile chemicals released by the factories. Thanks to this, they could identify the chemical released by the worries. They also determined that interleaving marigolds with other companion plants, which whiteflowers do not like, does not increase or decrease the repellent effect. This means that non-host plants of whiteflies can repel them, not just worries.

A notorious pest

Adult white flies are tiny, moth-like insects that feed on the sap of plants. They cause severe losses of products to a range of crops by transmitting several plant viruses and encourage the growth of molds on the plant.

Dr. Tosh said, "Direct feeding of adults and larvae results in very high secretion of honeydew, and the secretion of honeydew that covers the leaves reduces the photosynthetic capacity of the plant and makes the fruit unmarketable. "

Other studies will focus on the development of a blend of three companion plants that will repel three major pests of tomato: whiteflies, spider mites and thrips.

In the longer term, the goal of the researchers is to publish a guide to companion plants as an alternative to pesticides that would be suitable for a range of horticultural problems.

Explore further:
The white fly confused by the cacophony of smells

More information:
Niall J.A. Conboy, Thomas McDaniel, Adam Ormerod, David George, Angharad M.R. Gatehouse1, Ellie Wharton, Paul Donohoe, Rhiannon Curtis and Colin R. Tosh

PLOS ONE. DOI: 10.1371 / journal.pone.0213071