Nature's Answer to Insect Repellent

By: Katie Schaefer, Cosmetics & Toiletries magazine

Posted: May 29, 2009, from the June 2009 issue of Cosmetics & Toiletries.

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Zhang currently is seeking a pine oil with a high enough isolongifolene content to synthesize isolongifolenone for commercial use. “If it contained 50% isolongifolene, I could easily make the compound,” said Zhang. In the meantime, he is testing pine oil from the Humiria balsamifera (tauroniro) tree to determine the material’s efficacy.

Efficacy Testing
If evidence of the efficacy of isolongifolenone as an insect repellent could be shown, Zhang reasoned he could synthesize isolongifolenone from isolongifolene. Tests were thus conducted against two species each of ticks and mosquitoes. First, a mosquito bioassay involved maintaining mosquitoes on skin with sucrose and water before applying the test compound to the skin. After application, if the mosquitoes fed, the repellent was deemed ineffective.

The researchers also conducted the Klun and Debboun assay. “This method included a module of six small wells containing warmed red blood cells covered with a collagen membrane,” explained Zhang. Researchers placed a cloth on top of the membrane treated partially with the compound and partially with a control. The experiment was repeated with DEET. In both tests, the researchers found the isolongifolenone compound effectively deterred the mosquitoes from biting, almost 10% more than DEET.

“The average feeding deterrent of DEET is about 80% for Aedes aegypti [the yellow fever mosquito], whereas the test compound averaged about 90% for that mosquito. For Anopheles stephensi [the malaria mosquito], nearly 65% were deterred by DEET, compared with 75% by isolongifolenone.”

In addition to mosquito assays, the team conducted a tick bioassay with Ixodes scapularis, the deer tick. In this assay, a human finger is treated with either a repellent or a control and ticks either bite or drop off. The results showed that isolongifolenone effectively deterred ticks from biting.