Before organophosphates, before organochlorines, before carbamates, before synthetic pyrethroids, there were botanicals, the naturally occurring chemicals plants produced as their own defensive mechanism against feeding insects. Plants have had 400 million years to develop highly complex chemicals that defend against their own specific predators, and extracts from plants have been used by humans for at least 2,000 years to deter or kill insect pests. There is documentation of pyrethrum powder being used as a delouser on children in ancient Persia as far back as 400 B.C.E., and extracts from the neem tree (Azadirachta indica) were used by ancient cultures for insecticidal purposes and remain in use today. The Egyptians, Chinese, Greeks and Romans were all aware of the insecticidal properties of certain plants.
Despite their long history, botanicals are not used as insecticides on a large scale, even though they have long been in widespread use in fragrances, cosmetics and cleaning products. Moreover, many plants that supply botanical extracts that have insecticidal properties, such as rosemary and peppermint, are approved by the U.S. FDA for food use and are consumed by humans daily.
“Some of the confusion factor is how can these same plants being used in flavor and fragrance industries also be insecticidal,” says Steve Bessette, vice president of the botanicals division at Keyplex. “It’s difficult for people to comprehend given what we’ve been doing for the last 50 years. Many conventional pesticides were developed from the nerve gas research done in World War I and World War II, such as DDT. DDT was magic at the time — it was a very, very effective compound, and that led everybody away from what we were using, which had been natural compounds like rotenone, natural pyrethrum and nicotine. Nobody really knew about the persistence in the environment or the environmental exposure risk of DDT and the others. Now people are starting to go back and say, ‘What did we do before we had these?’”
The names of many insecticidal plants seem to come from a cookbook: mint, rosemary, thyme and clove, and they are proven safe for mankind and the environment. However, all-natural does not always mean safe for all. Nicotine is poisonous in concentrated form, and ricin, another deadly poison, is also from a plant, Ricinis communis. But because botanicals break down quickly, even these risky compounds have no long-term impact in the environment, and this is a key benefit to risk exposure.
Botanicals are derived from plants in several different forms: powdered seeds, roots and flowers, chemical extracts and essential oils. Purified essential oils are extracted from plants via steam distillation. Oils such as cedar, cinnamon, citronella, citrus, clove, garlic, mint and rosemary have long been used since antiquity as insect repellents, but studies in the 1990s have demonstrated they are effective as contact insecticides and fumigants as well.
“Some of these natural compounds have been present in the food system for more than 300 years,” Bessette says. “There’s a very long history of positive usage. Not only in the flavor industry, but also in cosmetics and fragrances that are applied to the skin. There’s a great deal of human exposure already — they are ubiquitous in the environment.”
Compounds Target Insect-Only Receptors
How are oils that are toxic to insects so safe for humans? Bessette says it is all in the mode of action and uses peppermint oil as an example.
“The essential oil compound targets a nerve receptor system that only insects use,” he says. “So it doesn’t have the same effect on mammals as it does on insects. When applied to an insect, the chemistry of the essential oil compound is almost identical to the chemistry of the octopamine neurotransmitter that insects use. The botanical compound binds to the octopamine receptor (instead of the actual neurotransmitter) and shuts down the signal pathway. The essential oils have broad-spectrum activity because all insects have receptors for this neurotransmitter. Our studies showed not only how the essential oils work but why they are safe for you and me — because we don’t have those same receptors in our bodies, whereas all the conventional synthetics target a nerve receptor system that humans share with insects.”
Bessette says octopamine was already known to be the most dominant neurotransmitter in insects, but no one had been able to find a molecule that would target that receptor safely.
“We went back and asked, ‘What is nature doing,’ Bessette says. “We started looking at essential oils and breaking them down and looking at the mode of action of each compound. We knew the target chemistry we needed, and that’s how we put the two together. We are the first to be able to target the octopamine receptor with a molecule that is safe for people and the environment.
“We spent about 15 million dollars over seven years applying modern science to green chemistry. We wanted to figure out how these products work and how we can use them in various applications in agriculture, turf and ornamentals.”
Safe Track Record Allows Flexibility of Use
The product Bessette and an advisory panel of natural product experts eventually developed with Keyplex is Ecotrol Plus. The active ingredients are rosemary oil, peppermint oil and geraniol, an oil derived from several species of plants, including roses and scented geraniums. Not only are these compounds USDA approved, they are also GRAS (Generally Recognized As Safe) by the FDA, meaning they can be used in food products. They also met the seven criteria for federal exemption by the U.S. EPA, which includes no history of issues using the products and no persistence in the environment. There is no re-entry interval, or pre- or postharvest interval, meaning spraying and harvesting can happen on the same day.
Because essential oils have a unique mode of action and are so effective, Bessette feels they can also be used as a valuable tool for rotating or tank mixing in with other chemistries to help combat resistance to the synthetic chemicals.
“In the history of botanicals, people have used them either as repellents or attractants, and nobody has looked at the compounds themselves: the structure/activity relationship, the mode of action, stability in the environment, will they emulsify, will they be useful in an agricultural setting as opposed to a homeowner setting,” Bessette says. “We wanted to apply the science and formulate the product in a manner it would be consistently effective in our target application.”