Mosquito Repellency of Mugwort

Burning mugwort (Artemisia argyi) to repel mosquitoes has long been practiced as a traditional pest-control method. Whether this practice represents mere folk wisdom or has genuine biological effectiveness was addressed in a study published in Scientific Reports.

Artemisia argyi（Image source：竹围墙， CC BY-SA 3.0 ）

Researchers collected mugwort samples from seven provinces of China—Gansu, Shandong, Sichuan, Henan, Hubei, Chongqing, and Yunnan. Essential oils were extracted from these plants through steam distillation, and their chemical compositions were analyzed using gas chromatography–mass spectrometry (GC-MS). The results showed substantial variation in chemical composition among essential oils originating from different regions. Each oil contained between 56 and 87 identifiable chemical constituents, indicating considerable diversity. Despite this variability, four compounds appeared consistently in all samples regardless of geographic origin: β-caryophyllene, caryophyllene oxide, eucalyptol, and phytol. Their relative proportions, however, differed among the samples.

The study evaluated the biological activity of these oils against the mosquito Anopheles sinensis through three experimental approaches:

1. Larvicidal assay – Different concentrations of mugwort essential oil were added to water containing twenty fourth-instar mosquito larvae, and mortality rates were recorded.

2. Fumigant toxicity assay – A fixed dose of mugwort essential oil was allowed to volatilize inside a sealed container of 250 mL, and the time required to immobilize twenty adult mosquitoes was measured.

3. Repellency assay – Human forearm skin treated with mugwort essential oil was inserted into a mesh cage containing one hundred starved Anopheles sinensis for a period of sixty-five minutes. The number of mosquitoes landing on the treated skin was counted to determine the repellent effect.

Anopheles sinensis（Image source：James Gathany，CC0 1.0 ）

In the larvicidal experiments, the mugwort sample collected from Hubei province showed the strongest effect. A concentration of only 40.23 µg/mL was sufficient to kill half of the fourth-instar larvae. This potency may be related to the relatively high proportion of phytol in that oil, which accounted for 16.28% of its composition. Previous studies have also indicated that phytol possesses notable insecticidal properties.

In contrast, the fumigant toxicity and repellency assays showed the best performance for mugwort samples from Gansu province. In fumigation tests using a 2 µL dose, half of the adult mosquitoes lost mobility within only 4.71 minutes. In the repellency experiment, treated skin still provided 65.68% protection after sixty-five minutes. This effect is likely associated with the high concentration of eucalyptol in the Gansu sample, which reached 21.89%. Eucalyptol is already known to function as an effective mosquito repellent in several plant species.

Overall, the findings demonstrate that mugwort indeed possesses measurable mosquito-repelling properties. However, even though essential oils are derived from natural plant sources, it cannot be assumed that all their components are harmless to humans. If mugwort essential oil is to be developed into commercial products in the future, careful evaluation of toxicological safety and appropriate dosage will be necessary.

Author: Shui Ye-You

Reference:

Luo DY et al. (2022). Repellency and insecticidal activity of seven Mugwort (Artemisia argyi) essential oils against the malaria vector Anopheles sinensis. Sci Rep.