The natural fatty acids present in coconut oil are more effective at repelling biting flies, ticks, and other pest arthropods than the harsh chemical DEET, according to a new study headed by the US Department of Agriculture.
Writing in the journal Scientific Reports, the researchers explain that they were motivated to look into new plant-based insect repellents by the increasing safety regulations and public concern over DEET (N,N-Diethyl-meta-toluamide). Developed in 1944, DEET has been the most widely used repellent in the decades since. However, DEET-based products can lead to skin irritation and have been linked to seizures and toxicity in children and pregnant women.
As to the plant-based repellent products already available, many are quite effective – after all, they are composed of extracts or synthetic versions of extracts from plants that people all over the world have been using, in less high-tech preparations, as repellents for thousands of years. But unfortunately, most of these work for less than 2-4 hours after application.
After characterizing all the different fatty acids present in coconut oil, the team grouped the molecules according to the length of their carbon chains. In a series of laboratory-based tests, medium-chain-length fatty acids with eight to 12 carbons were found to be potent against two types of biting flies – stable flies and horn flies – and bed bugs. At least 90 percent of these bugs were deterred for a full two weeks after application to cloth or paper elements put inside the insect enclosures. In contrast, a 10 percent DEET product began to lose its effect against bed bugs by day three.
The compounds also repelled lone star and brown dog ticks for at least one week. Tests with yellow fever Aedes aegypti mosquitos also showed an impressive rate of deterrence (93 percent), but the fatty acids needed to be applied at a higher concentration than for the other arthropods. Overall, preparations of medium-chain fatty acids were better than DEET preparations of the same concentration for both types of flies and bed bugs, and were equally effective for ticks. They were also matched at high concentrations for mosquitos.