Sylvain Mercier, M. Sc., Chemist
If you have already been interested in the anti-mosquito action of essential oils, you probably already know the potential effectiveness of citronella as a repellent against these insects that disturb our beautiful summer evenings.
Different insects can be vectors of serious diseases such as Aedes sp. which carries dengue or individuals of the Anopheles species that spread malaria. In addition, some insects such as the very common “horse fly” can negatively affect the yield of livestock from different farms (decreasing milk production of cows for example).
According to the recent review done by Benelli and Pavela , more than 668 scientific articles exists about repellency of mosquitoes using essential oils, but only few papers focus on repellency against other insect pests. Thus, application of essential oils as natural repellents to control the spread of diseases transmitted by this type of insects is an area in which much research still needs to be done. However, some essential oils mentioned in Benelli’s review have already demonstrated interest as a repellent for different species. Here are some of them.
Catnip (Nepeta cataria)
Black flies (Simulidae sp.) that we know very well may be vectors of river blindness in some African or Central and South American countries. In one study, catnip oil was hydrogenated to obtain an extract enriched with dihydronepetalactones. Formulated as a lotion or as a liquid preparation, this extract provides protection for more than 7.5 hours against black flies (15% active ingredients).
Tagete (Tagetes erecta)
Essential oil from Tagetes erecta (synonym of Tagetes patula) has shown a very promising insecticidal effect on bed bugs (Cimex lectularius). A dose of 100 mg/ml have killed 100% of bed bugs in tests performed by Politi et al. . Although tagete oil is toxic for bed bugs, in vivo toxicity is very low (> 4000 mg / kg), which indicates that the oil would have little or no toxic effect in humans.
Peruvian peppertree (Schinus molle)
A 100% mortality rate was achieved on the cat flea (Ctenocephalides felis) with a dose of 50 μg/cm2 of S. molle oil. This is not the first time that we talk about this species on this blog, if you are curious to learn more about it.
Thymol thyme (Thymus vulgaris ct. thymol)
Thyme ct. thymol essential oil could be an excellent tool for fighting and preventing lice infestations (Pediculus humanus). Applied for 21 minutes, different concentrations of thyme oil had an interesting knockdown effect on lice . Among three oils tested in the study (Thymus vulgaris, Aloysia polystachya and Aloysia citriodora), thyme oil is the one that had the highest egg-killing effect on lice eggs.
 Benelli, G.; Pavela, R. Beyond Mosquitoes—Essential Oil Toxicity and Repellency against Bloodsucking Insects. Ind. Crops Prod. 2018, 117 (March), 382–392.
 Politi, F. A. S.; Nascimento, J. D.; da Silva, A. A.; Moro, I. J.; Garcia, M. L.; Guido, R. V. C.; Pietro, R. C. L. R.; Godinho, A. F.; Furlan, M. Insecticidal Activity of an Essential Oil of Tagetes Patula L. (Asteraceae) on Common Bed Bug Cimex Lectularius L. and Molecular Docking of Major Compounds at the Catalytic Site of ClAChE1. Parasitol. Res. 2017, 116 (1), 415–424.
 Gutiérrez, M. M.; Werdin-González, J. O.; Stefanazzi, N.; Bras, C.; Ferrero, A. A. The Potential Application of Plant Essential Oils to Control Pediculus Humanus Capitis (Anoplura: Pediculidae). Parasitol. Res. 2016, 115 (2), 633–641.