'These products expand the limited arsenal of organic growers to combat pests. They're still only a small piece of the insecticide market, but they're growing and gaining momentum,' he said.

The natural pesticides have several advantages. Unlike conventional pesticides, these 'killer spices' do not require extensive regulatory approval and are readily available.

An additional advantage is that insects are less likely to evolve resistance -- the ability to shrug off once-effective toxins. They're also safer for farm workers, who are at high risk for pesticide exposure, he noted.

But the new pesticides also have shortcomings. Since essential oils tend to evaporate quickly and degrade rapidly in sunlight, farmers need to apply the spice-based pesticides to crops more frequently than conventional pesticides.

Researchers are now seeking ways of making the natural pesticides longer-lasting and more potent, he noted.

These findings were presented at the American Chemical Society's 238th National Meeting.