Global Challenges/Chemistry Solutions

Providing safe foods: “Killer spices” provide eco-friendly pesticides
for organic fruits and veggies

November 11, 2009

Mention rosemary, thyme, clove, and mint and most people think of a delicious meal. But think bigger…acres bigger than what fits on a dinner table. These well-known spices are emerging as organic agriculture’s key weapons against insect pests.

Scientists in Canada are reporting new research on these so-called “essential oil pesticides” or “killer spices.” Here’s study leader Dr. Murray Isman of the University of British Columbia, who says the spices represent a newer, safer class of insecticides:

“Well, I think everybody’s interested in pesticides that have much reduced environmental
and human health impacts… Now there are a very select number of botanical insecticides
that are in fact fast-acting toxins against insects. Surprisingly a very common source of
culinary herbs that most people have in their kitchen or you can find in aromatherapy shops
are a recent edition to that arsenal. It turns out that plant essential oils, by that we mean
materials that can be steam-distilled out of certain aromatic plants, do prove to have
insecticidal properties and deterrent and repellant properties as well. These include such
things as rosemary oil, thyme oil, cinnamon oil, peppermint oils.”

Over the past decade, Dr. Isman and colleagues tested essential oils of plants and found they have a range of insecticidal activity against pests. Indeed, some spiced-based products are now being used by farmers and have succeeded in protecting organic crops, including lettuce, strawberries and onions, against destructive aphids and mites.

So, just what is it exactly about these spices that allow them to work their magic outside the kitchen? Here’s Dr. Isman again:

“It turns out that some of these oils and some of the chemical constituents in the oils are neurotoxic to many types of insects. At least one of their actions, and we’re not certain about all of their actions, one of their actions is they interfere with a neuromodulator in insects called octopamine. It’s sort of an internal valium for insects, it sort of calms them down so their nervous systems
don’t get overstimulated by external stimuli. If you remove that octopamine, which is what
some of these oils do, they get hyperexcited and eventually die.”

These pesticides, usually a combination of spices diluted with water, have added to the crop-preserving arsenal of organic growers and offer several advantages over their counterparts. First, they are readily available and don’t require lots of regulatory approval. Also, insects exposed to the spices are less likely to evolve resistance to the toxins. And, they’re safer for farm workers, who are at high risk for pesticide exposure. For more on their benefits, here’s Dr. Isman:

“Some of these oils, as some other people have mentioned, are very good antimicrobials,
so they could be very useful against food spoilage organisms, for example. They are useful
against certain plant pathogenic fungi and bacteria, and they do have this phytotoxic effect
on plants, so at high concentrations they can be used as natural herbicides.”

One more note. These “killer spices” aren’t just limited to agricultural use. Some show promise in the home as eco-friendly repellents against mosquitoes, flies and roaches. And, perhaps as an unexpected bonus, these natural pesticides can have a pleasant, spicy aroma. Some in fact contain the same oils used in aromatherapy products, including cinnamon and peppermint.

Smart Chemists/Innovative Thinking
Smart chemists. Innovative thinking. That’s the key to solving global challenges of the 21st Century. Please check our other podcasts on safe foods [Providing Safe Food and Reducing “Grapefruit/Drug” Interactions]. Today’s podcast was written by John Simpson. I’m Adam Dylewski at the American Chemical Society in Washington.

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