Bothe, M. and N. McPherson Donahue. 2010. Organic aerosol formation in citronella candle plumes. Air Qual Atmos Health. 3, 3: 131–137.

Abstract: Citronella candles are widely used as insect repellants, especially outdoors in the evening. Because these essential oils are unsaturated, they have a unique potential to form secondary organic aerosol (SOA) via reaction with ozone, which is also commonly elevated on summer evenings when the candles are often in use. We investigated this process, along with primary aerosol emissions, by briefly placing a citronella tealight candle in a smog chamber and then adding ozone to the chamber. In repeated experiments, we observed rapid and substantial SOA formation after ozone addition; this process must therefore be considered when assessing the risks and benefits of using citronella candle to repel insects.

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Susy Tjahjani. 2008. Efficacy of Several Essential Oils as Culex and Aedes Repellents. Proc ASEAN Congr Trop Med Parasitol. 3: 33-37.

Abstract: DEET (N,N-diethyl-m-toluamide) is an effective repellent. However, it may be toxic to some users, so that an effective DEET substitute needs to be found. Essential oils, eg, eucalyptus, clove, and citronella oils,are safer. This study aimed to compare which of these oils was most effective, to determine whether these oils (as DEET substitutes) might be acceptable as standard repellents against Culex and Aedes, and to determine how long these oils were efficacious as repellents, and how frequently they need to be reapplied. A laboratory study, based on the method described by Fradin and Day, was conducted. Repeated tests were conducted simultaneously in 5 cages using the repellent-treated forearms of volunteers. The time in minutes, between application of the repellent and first mosquito bite, was recorded. Data were analyzed using one-way ANOVA,followed by Duncan analysis using α = 0.01. Statistical analysis showed that, against Culex, the repellency duration of eucalyptus oil was less than clove oil or citronella oil, while those of clove oil and citronella oil were less than DEET. For Aedes, the repellency duration of eucalyptus oil was less than citronella oil, while citronella oil was less than clove oil, and clove oil less than DEET. From this study, it may be concluded that against Culex, the repellency effect of clove oil/citronella oil was greater than for eucalyptus oil. These essential oils can be regarded as standard repellents. Eucalyptus oil must be re-applied every 123 minutes, while clove oil and citronella oil must be re-applied every 287 minutes. Against Aedes, the repellency effect of clove oil was greater than citronella oil; these oils may be used as standard repellents against Aedes, but not eucalyptus oil.Citronella oil must be re-applied every 40 minutes, while clove oil must be re-applied every 131 minutes.

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WONG, K. K. Y., F. A. SIGNAL, S. H. CAMPION, AND R. L. MOTION. 2005. Citronella as an Insect Repellent in Food Packaging. J. Agric. Food Chem.  53: 4633-4636.

Abstract: Of five commercial plant extracts (citronella, garlic oil, neem extract, pine oil, and pyrethrum), citronella was found to be effective in deterring the infestation of cartons containing muesli and wheat germ by red flour beetles. The chemical components were applied as part of a coating on the carton board. In an experimental set up that accelerates infestation over a 2 weekperiod, citronella-treated cartons (0.2 g/m² of carton board) reduced beetle infestation to approximately 50% of the level observed in control cartons. Evidence was provided to indicate that an insect repellent effect persists for at least 16 weeks. Additional work on the controlled release of the insect repellent would be required to prolong the effect.

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Thavara, U., A. Tawatsin and J. Chompoosri. 2002. Phytochemicals as Repellents against Mosquitoes in Thailand. Proceedings International Conference on Biopesticide. 3: 244-250.

Abstract: Repellents are commonly used for personal protection against mosquitoes worldwide. They are one of the most effective products used in prevention and control of mosquito-borne tropical diseases. Although there are a number of effective repellents containing chemical active ingredients, such as deet, KBR 3023 and IR3535 there is in concern with regard to chemical toxicity. To overcome this concern phytochemicals extracted from various plants have been formulated as mosquito repellents to be sold in Thailand in recent years. Since the year 2000, 44 formulations of mosquito repellents containing plant extractsas active ingredients were evaluated for repellency against Ae. aegypti underlaboratory conditions at the National Institute of Health (NIH), Thailand. These extracts included citronella oil, eucalyptus oil, tea tree oil, turmeric oil, bergamot oil, lavender extract, tobacco-leaves extract, clove extract and neem-leaves extract. The protection offered by these products was up to 6.3 hours. However, only 12 products were qualified for registration to be sold in the market since minimum protection time of 2 hours is the minimum in requirement. These qualified repellent products were formulated as lotion, spray, cream and balm, where citronella oil, eucalyptus oil and tea tree oil were the main active ingredients. On the other hand, the NIH also formulated a mosquito repellent containing turmeric oil and eucalyptus oil as active ingredients. It was found that this repellent provided protection time for 7 hours against Ae. aegypti, and at least 8 hours against Culex quinquefasciatus and Anopheles dirus under laboratory conditions. This study demonstrated and encouraged the development of alternative active ingredients derived from plants to be formulated as effective mosquito repellents.

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Tawatsin, A., S. D. Wratten, R. R. Scott, U. Thavara and Y. Techadamrongsin. 2001. Repellency of Volatile Oils from Plants against Three Mosquito Vectors. Journal of Vector Ecology 26, 1: 76-82.

Abstract: Volatile oils extracted by steam distillation from four plant species turmeric (Curcuma longa), kaffir lime (Citrus hystrix), citronella grass (Cymbopogon winterianus) and hairy basil (Ocimum americanum)), were evaluated in mosquito cages and in a large room for their repellency effects against three mosquito vectors, Aedes aegypti, Anopheles dirus and Culex quinquefasciatus. The oils from turmeric, citronella grass and hairy basil, especially with the addition of 5% vanillin, repelled the three species under cage conditions for up to eight hours. The oil from kaffir lime alone, as well as with 5% vanillin added, was effective for up to three hours. With regard to the standard repellent, deet alone provided protection for at least eight hours against Ae. aegypti and Cx. quinquefasciatus, but for six hours against An. dirus. However, deet with the addition of 5% vanillin gave protection against the three mosquito species for at least eight hours. The results of large room evaluations confirmed the responses for each repellent treatment obtained under cage conditions. This study demonstrates the potential of volatile oils extracted from turmeric, citronella grass and hairy basil as topical repellents against both day-and night-biting mosquitoes. The three volatile oils can be formulated with vanillin as mosquito repellents in various forms to replace deet (N,N-diethyl-3-methylbenzamide), the most common chemical repellent currently available.