Citation: Zhang A, Klun, Jerome A, Wang S Carroll JF, Debbou M (2009). Isolongifolenone: A Novel Sesquiterpene Repellent of Ticks and Mosquitoes . Journal of Medical Entomology; 46(1)100-106.

More than 700 million cases of mosquito-transmitted disease are reported annually, some of which are cases of deadly diseases such as malaria or serious ones like dengue.

The most widely used mosquito repellent has been N,N-diethyl-3-methyl benzamide (DEET), commonly known as DEET. However, the product has raised some environmental concerns, as it can contaminate water sources and interfere with wild life. Additionally, some studies have suggested that DEET may cause neurological damage in humans. Thus, DEET needs to be replaced with some less damaging alternative.

In a short article recently published in the Journal of Medical Entomology, a group of researchers presents a natural alternative to DEET. Isolongifolenone is a natural product found in Humiria balsamifera, a plant common in South America and widely used in many perfumes, fragrances, and cosmetics, due to its woody smell. In this study, it was successfully tested against blood-feeding arthropods that are important disease vectors, including Aedes aegypti and Anopheles stephensi. Besides the mosquitoes, the group also showed that (-)-isolongifolenone also repels tricks such as Ixodes scapularis and Amblyomma americanum.

Until now, preparation of (-)-isolongifolenone has been done by a process considered to be inefficient and to generate many unwanted by-products. However, the authors of this study present an easy method that facilitates the synthesis of this compound from inexpensive turpentine oil feedstock.

To test whether (-)-isolongifolenone is indeed capable of repelling mosquitoes and tricks, the researchers compared the efficiency of (-)-isolongifolenone with DEET, using an in vitro bioassay system that has been applied to determine new candidate repellents for human use. For the thick bioassay, the group used a fingertip bioassay, in which the test solution is applied to the outer layer of a strip of cloth that is allowed to dry and then wrapped around the finger of a volunteer.

The results were measured according to proportions of not biting (for mosquitoes) or repelled (for ticks) and then compared.

The group showed that (-)-isolongifolenone effectively stops the biting of Aedes aegypti (L) and Anopheles stephensi at 25nmol compund/cm2 cloth and that the activity of both (-)-isolongifolenone and DEET against Aedes aegypti (L) was higher with increasing concentrations of the product.

The (-)-isolongifolenone was also effective in repelling I. scapularis nymphs at 78 nmol compound/cm but the nymphs remained in the finger. For A. americanum, the tricks actually dropped off the finger. The repellent activity against tricks also increased with concentration.

In general, both (-)-isolongifolenone and DEET were more efficient against Aedes aegypti than Anopheles stephensi . Between the trick species, I. scapularis was significantly more sensitive than A. americanum, which none compound was capable of complete repelling.

Many compounds have shown repellent proprieties against mosquitoes but in most cases these new compounds are expensive or their synthesis labour-intensive. This is not the case for (-)-isolongifolenone, which seems to be easily made from turpentine oil. Thus, (-)-isolongifolenone could be an excellent candidate for replacing the so far one and only DEET for the task of helping keep mosquitoes at bay.

2009 Entomological Society of America, via TropIKA.net