Cajeput (Melaleuca minor syn. M. leucadendra) is a tree in the myrtle family that is native to Australia. Like its botanical cousin, tee tree (M. alternifolia), its leaves and stems yield a highly aromatic essential oil that is mildly camphorous with fruity undertones. Similarly, the oil is also antifungal and antimicrobial. It is also a natural and highly effective deterrent to mosquitoes.
In a 2006 study that compared the efficacy of 41 plant extracts and 11 oil mixtures against three species of mosquitoes using (bless them) human volunteers, researchers found that cajeput and catnip oils were among the top five oils that effectively provided 100% repellency against all three species for up to 8 hours. This sounds remarkably impressive, doesn't it? Unfortunately, the study authors conclude their evaluation with this statement: "This effect needs, however, a peculiar formulation to fix them on the human skin" without further elaboration. Fine. We're not going to let a little pharmaceutical snobbery get the best of us.
In a similar study published in the Journal of the American Mosquito Control Association (good to know there is one), scientists evaluated the essential oils of thyme, catnip, amyris, eucalyptus and cinnamon against three species of mosquitoes (Aedes albopictus, Ae. aegypti and Culex pipiens pallens). In this experiment, catnip oil came out on top as the most effective deterrent with up to 6 hours of protection.
Where does cinnamon come in? While cinnamon oil may not be quite as powerful in keeping hungry mosquitoes at bay, it has some value in that department and it also smells nice. Seriously...the addition of this oil in the following formula helps to balance the strong aromatic properties of the other oils.
Pour the vodka into a measuring cup or small bowl. Add the essential oils and stir to blend. Using a small funnel, pour the mixture into amber or cobalt blue bottles. Attach a finger mister and cap in place of the screw cap to use as a spray. Label and store in a cool, dark cabinet. Avoid getting the oil mixture near the eyes or other sensitive membranes.
"Repellency effect of forty-one essential oils against Aedes, Anopheles, and Culex mosquitoes."; Amer A, Mehlhorn H.; Parasitology Research; 2006 Sep;99(4):478-90. http://www.ncbi.nlm.nih.gov/pubmed/?term=cajeput+oil+mosquito
"Adult repellency and larvicidal activity of five plant essential oils against mosquitoes."; Zhu J, et al.; Journal of the American Mosquito Control Association; 2006 Sep;22(3):515-22. http://www.ncbi.nlm.nih.gov/pubmed/17067055