One thing we can agree with establishment malaria researchers is that mosquito bites are not desirable. We don’t believe that disease is transmitted but mosquito bites are uncomfortable and itchy. Before travelling to Botswana a few years ago I prepared my own homemade natural mosquito repellent by dissolving 1% peppermint oil in coconut oil!
And today in MalariaWorld there is an interesting paper comparing natural and synthetic mosquito repellents. In ‘Do natural or synthetic excito-repellents work better? A study on coastal malaria vector Anopheles epiroticus in Ko Chang, Thailand’, Sukkanon et al compared the effectiveness of four synthetic and two natural mosquito repellents with field and laboratory strains of Anopheles epiroticus.
An insecticide-susceptible laboratory strain of An. Epiroticus and field strain of An. epiroticus derived from fed females collected using an entomological mount aspirator around the buffalo pen were used in the trial. Four synthetic and two natural repellent agents were used in the study. Three pyrethroids (deltamethrin, permethrin, alpha-cypermethrin) and DEET (N,N-diethyl-meta-toluamide) were the synthetics. Vetiver oil (extracted from the roots of the Vetiveria zizanioides plant) and citronella oil (extracted from lemongrass) were the natural repellents. They were dissolved in alcohol and soaked in paper in the studies.
Mosquitos were exposed to treated paper in contact studies, where mosquitos could contact the paper, and non-contact studies (paper behind a net). The chamber had an escape to another chamber and effectiveness of the repellent was measured by the number that escaped.
For the laboratory strain, 5% citronella oil was the most effective repellent for in both the non-contact (59.26%) and contact (52.73%) studies. Vetiver oil 5% achieved 40.38% in contact study. The best synthetic was deltamethrin at 42.11% in contact study. For the contact study with the field strain the synthetics were more effective – DEET 5%, 64.15% and deltamethrin 5%, 60.00%. The natural material were also effective at 5% in contact study – vetiver oil 48.14% and citronella oil 40.74%. High mortality rates were also observed for the mosquitos that did not escape in non-contact citronella oil study.
The authors concluded that pyrethroids, particularly deltamethrin and permethrin, along with DEET, showed enhanced efficacy against field populations as contact irritants, while natural repellents like citronella oil were more effective against laboratory strains as non-contact repellents.