ATLANTA -- The oil in an orange peel may turn out to be an environmentally safe weapon against an array of harmful insects.
Dr. Craig Sheppard of the University of Georgia's Coastal Plains Experiment Station in Tifton said in tests he conducted, the orange peel oil killed imported fire ants, house flies, stable flies, black soldier flies, cat fleas, paper wasps and house crickets.
'You can put a tiny drop of it on an ant or a house fly and it will be dead almost instantly,' said Sheppard.
Sheppard said his research, and that of others, shows that a compound called limonene is the ingredient in the citrus oil that kills certain insects. Limonene makes up 80 to 90 percent of the oil and is found not only in oranges but in other citrus fruits as well.
'It acted as a contact poison and a fumigant and was toxic to all insects tested,' he said.
Limonene also kill plants, however, and that this will restrict its use. That, plus the fact that chemists and entomologists are still investigating it may explain why no major use has yet been made of the discovery.
The citrus peels seem to be nontoxic to humans and other vertebrates and are used as flavorings in soft drinks and baking.
The finding that the limonene of citrus peel will kill certain insects is not new, according to Sheppard. Historical records mention that the 'juice of lemons' was used as a remedy for mosquitoes during Sir Francis Drake's third voyage to the New World in 1572 and 1573. Other experiments showing the toxicity of citrus peel were conducted as recently as 1979, he said.
But Sheppard's experiments were a fresh demonstration that the insecticidal properties of citrus oil, a naturally-occurring compound, could kill a host of insects.
Those experiments began when someone at a Jacksonville, Fla., firm producing a citrus oil hand cleaner threw some of the oil out the back door on a fire ant hill. All the ants died and the experiment station was asked to make some tests.
In a scientific paper outlining his experiments, Sheppard termed limonene a natural insecticide that may prove valuable for ridding pets, livestock and people of parasites and for 'fumigating food handling and storage facilities, and for pest control around households.'
One veterinary supply house already is marketing a product containing limonene, he said.
'The next step must be to determine the best sources, recovery techniques and applications for known toxicants in citrus peel oils and search for possibly unidentified toxins,' Sheppard said.
He said the experiment station has had some inquiries from chemical manufacturers about his research with limonene. 'Somebody has to go to the trouble to register it. So far, nobody has chosen to do this so they can market it.'
Sheppard predicted that a small manufacturer may be the first to market the product.