Killer Spices Can "Season" Pests to Death

August 16, 2009

Herbs and spices used to flavor food are also green alternatives to synthetic pesticides, scientists say.

Oils from thyme, rosemary, mint, and other herbs and "killer spices" are gaining favor among farmers as alternatives to synthetic pesticides, according to Murray Isman, an entomologist at the University of British Columbia in Canada. (Also see "Killer Bugs Made Welcome on Green Farms.")

Sprayed onto crops like any garden-variety pesticide, the plant oils repel insects, similar to how chili peppers can repel elephants. Other oils kill pests outright, the study says.

Originally intended for the perfume and food-flavoring industries, the killer-spice oils are already available wholesale and may be headed to retail shelves if the new use catches on, the researchers say.

The all-natural pesticides should be inexpensive too, Isman reasons, since they're already in widespread use as wholesale perfume ingredients and flavorings for food. Companies are already working to bring the spice oils to retail shelves for farmers, he said.

Killer Spices Cause Fatal Spasms

Research suggests the oils interfere with the insect nervous system, making the muscles so hyperactive that bugs essentially spasm to death.

The oils also can disrupt an insect's cellular membranes, causing fatal leakages of essential fluids.

The plant oils are most effective against small, soft-bodied bugs that suck on plant juices, such as aphids, whiteflies, and spider mites.

"Small, soft-bodied insects are more vulnerable to having their membranes melted or smothered by the oils," Isman said.

Small insects also have large surface areas relative to their internal volume, so more of the bug is likely to come into contact with the oil, he added.

Since "killer spices" are natural, you might think insects would have evolved defenses against the seasonings. But scientists think insects may be less likely develop resistances to plant-based pesticides, because they tend to be complex chemical mixtures and therefore more complicated to defend against.

"With most conventional pesticides, you have one chemical that's the poison," Isman said.

Killer Spices Not Necessarily Killer Apps?

The prognosis isn't entirely rosy for killer spices, though.

The oil-based pesticides evaporate quickly and degrade rapidly in sunlight. As a result, they have to be reapplied every few days, compared to every few weeks for conventional pesticides.

"At the end of the day, what matters is how much it costs and the health and environmental impacts," Isman said. "And there the plant-based pesticides have an advantage."

Findings presented today at an American Chemical Society meeting in Washington, D.C.

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