Fall 2009

[ BACK ]

Repellents with the Right Stuff

Terpie's first flee shampoo inspired her owner Joel Coats to investigate natural insect repellents.

When Joel Coats washed his dog with an orange-based shampoo, he was amazed when fleas jumped off and expired. He immediately wanted to know why.

That was 20 years ago. Since that moment, Coats, an entomology professor, and several graduate students have studied the natural repellents found in oranges, catnip and hedge apples. Following a trail based in folklore, Coats says they have investigated more than 50 essential oils produced by plants as repellents.

Five patents later, Coats says he's on the cusp of investigating the molecular basis for these natural repellents and insecticides.

"I've been waiting to get the right people and the funding and it's finally coming together," Coats says.

What's coming together is a microscopic view at the molecular make up of certain compounds called terpenes. Molecular-level research is easier than it would have been 20 years ago, but it's still an intricate investigation. Molecules of the terpenes are so small that more than 6 sextillion (6 with 21 zeros after it) could fit inside a pea.

Building on data from scientists throughout the world and using computers makes it easier to study the molecular characteristics today. The software can analyze more than 100 characteristics, such as topography, shape, polarity and solubility.

"It's very arduous to separate and do testing at the molecular level," Coats says. "We've separated the individual terpenes out of the oils that are the best repellents and best insecticides and now we are looking at the molecular structures and those relationships and how the structure is related to potency."

It's the same type of research pharmaceutical companies use to determine the best analgesics for pain relief or other prescriptions. Coats is searching for the mechanism of action - how compounds affect insects.

Entomology Professor Joel Coats investigates the molecular basis for natural repellents and insecticides like those in Vietnamese pemou wood and hedge apples.

Several of the insecticidal compounds he's studying over stimulate the central nervous systems of insects, which literally stops them in their tracks. Coats says bugs that are sprayed with this compound, freeze within five seconds and one minute later they're history.

"Green chemistry is definitely the future in insect control," Coats says.

An advantage of using natural compounds is that there is no residue. Since the product is plant-based, it readily decomposes and disappears. Currently, there are a handful of companies marketing the essential oils, but few are researching the molecular structure of the compounds.

Looking for the right stuff means comparing the essential oils of several plants. Gretchen Paluch, a graduate student in entomology, is using molecular modeling to isolate the most potent repellents and predicting the effectiveness of the next ones to pursue.

To test the molecular reactions for toxicity to the insects, another graduate student grinds up flies' heads and extracts the gamma amino butyric acid (GABA) in a centrifuge. GABA is the mechanism that controls part of the nervous system in flies. The GABA overstimulation is the key to freezing insects in their tracks.

Coats says they are just beginning to understand the molecular structures that have protected plants for eons. From Vietnamese pemou wood to hedge apples, the molecular clues are there, it just takes time and minute detective work to discover the answers.

Coats' dog Terpie, which is short for Terthiophene , a chemical found in marigolds, died in 2004. She enjoyed a flea-free life.