Citrus Flavoring Is Weaponized Against Insect-Borne Diseases

Adding a new weapon to the fight against insect-borne illnesses like Lyme disease and malaria, the Environmental Protection Agency on Monday approved a new chemical that both repels and kills ticks and mosquitoes.

The chemical, nootkatone, an oil found in cedar trees and grapefruits, is so safe that it is used by the food and perfume industries.

Nootkatone is considered nontoxic to humans and other mammals, birds, fish and bees, the E.P.A. said in a statement.

Diseases caused by the bites of ticks, mosquitoes and fleas have tripled in the United States in the last 15 years, the Centers for Disease Control and Prevention said in a 2018 report. They include Lyme disease, anaplasmosis and Rocky Mountain spotted fever from ticks; West Nile, dengue, Zika and chikungunya from mosquitoes; and plague from fleas.

“Most plant terpenes will kill bugs if you go to a high enough dose, but I haven’t seen any data that supports using it as an insecticide,” Dr. Coats said, using a term for aromatic oils exuded by many plants to repel invasive insects. “I’ve seen lots of data on it as a repellent.”

Mikkel Vestergaard-Frandsen, owner of the Vestergaard company, which makes insecticide-impregnated nets to fight malaria, said he was interested in the compound, but wanted to know more about it.

Because babies sleep under the nets, any insecticide in them must be very safe.

In many areas, mosquitoes have developed resistance to the pyrethin-based insecticides now used in nets, which are synthetic versions of a chemical found in chrysanthemum flowers.

A version of nootkatone that can linger in netting fabric for years would have to be developed, but good repellents usually dissolve too quickly for that, he said.

The C.D.C. discovered nootkatone’s repellent properties almost 25 years ago as part of a search for new tick-control compounds to fight Lyme disease, Dr. Beard said.

They investigated cedar bark and chips “because there are all these folk tales that cedar repels insects — and people keep their clothes in cedar chests,” he said.

Cedar wood itself had very little effect on ticks, he said, but Oregon State University scientists working with the agency found the terpene oil of the Alaskan yellow cedar to be powerfully repellent. The Latin name of the tree is Cupressus nootkatensis, which comes from the Nuu-Chah-Nulth people of Canada.

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