Plant essential oils and their efficacy against adult mosquitoes

Infectious diseases spread by mosquitoes are significant problems in many locations throughout the world.  The yellow fever mosquito (Aedes aegypti) is the primary vector of the dengue virus, a rapidly spreading mosquito-borne virus.  Anopheles gambiae is a vector of the malarial Plasmodium parasites which are a threat to half of the world’s population.  The primary control method of mosquitoes is the use of chemical insecticides.  Mosquito control efforts have been hampered by (1) increasing insecticide resistance, and (2) increased public concern about the safety of chemical insecticides.  Use of chemical insecticides with synergists, like piperonyl butoxide (PBO), has been partially effective at overcoming resistance and reducing amounts of insecticides used.  Terpenoids in plant essential oils have been shown to be mildly effective in killing mosquitoes.  In addition, essential oils and their terpenoids have been shown to enhance the potency of natural pyrethrins.  In an effort to identify plant essential oils that could be utilized as an alternative to pyrethroids or enhance the activity of pyrethroids, 30 plant essential oils, from various plant families, were topically applied to adult female Ae. aegypti and An. gambiae; data was analyzed using Probit analysis.  In addition, mixtures of plant essentials oils and a commercially available permethrin formulation were analyzed for enhanced efficacy and compared to PBO.  Plant essential oils are not as toxic as conventional synthetic compounds; however, some appear to have similar or better efficacy as enhancers when compared to PBO.