Scientists have found a cheap and alternative way to repel insects with a natural weapon only marigolds emit.

Gardeners have long known that marigolds protect tomato plants from whiteflies. Researchers from Newcastle University's School of Natural and Environmental Sciences identified that it emits a chemical called limonene to repel the insects away.

Limonene has a strong odor that slows down whiteflies and repels them from hosting on tomato plants.

Companion Planting

To protect the plants, gardeners do a companion planting where marigolds are interspersed around the tomato foliage. Limonene is also safe not only to the environment but also to pollinators like bees.

"Another important benefit of using limonene is that it's not only safe to bees, but the marigolds provide nectar for the bees which are vital for pollination," lead author Dr. Colin Tosh said.

Limonene is inexpensive and less risky than pesticides. Unlike limonene, pesticides kill everything that it is sprayed upon including organisms that are beneficial to the plant.

Future Of Pesticides

The researchers saw that the limonene in marigold could be a natural alternative to synthetic pesticides. The chemical only has a repelling and not killing effect; thus, the researchers said there will be no resistance once the whiteflies are exposed to it.

"This indicates that repellent volatile organic compounds from marigold are the probable cause of the reduction in whitefly performance on tomato intercropped with marigold," the authors wrote.

Limonene makes up about 90 percent of the oil component in citrus peel. It is a common ingredient in mosquito repellent and household air freshener.

Researchers also determined that other non-host plants that whiteflies do not like, not just marigolds, can repel them. Tosh said that any natural alternatives to pesticides like limonene should be welcomed to improve plant and animal diversity.

Whiteflies are notorious pests that feed on the plant sap. It can be destructive as it encourages mold growth on the plant.

The group is planning to experiment on three companion plants repellent against major tomato pests: whiteflies, thrips, and spider mites.