The Role of Plant Essential Oils in Mosquito (Diptera: Culicidae) Control

Approximately half of the world’s population is at risk of malaria, and about 250 million deaths are reported annually. There are two strategic approaches to malaria management: prevention (vector control, drug prophylaxis and potential use of vaccines) and treatment (drugs, blood transfusion, etc). The use of botanicals, specifically essential oils is an alternative to the current use of synthetics and pyrethroids. Essential oils can be used as larvicides and repellents. The major constituents of those that have been used in mosquitoes are mainly terpenoids (Acyclic Monoterpenoids, Monocyclic Monoterpenoids, Sesquiterpenoids, Bicyclic Monoterpenoids, Diterpenoid). Earlier, in vitro physicochemical assays characterized most of them as antioxidants. However, recent studies suggest that at least in part, the encountered beneficial effects of essential oils are due to pro-oxidant effects at the cellular level. Approximately 40 plant species in about 10 families dominated by Labiateae (Lamiaceae) and Asteraceae, have provided essential oils for experimental studies as larvicides and repellents to mosquitoes. Results from both studies have been very promising. LC50s varied across plant and mosquito species and across geographical locations within plant species. In repellency tests, RD50 also varied across plant and mosquito species. Some of these essential oils are promising candidates as larvicides in Integrated Vector Management (IVM) in Malaria Management that combines: Indoor Residual Spraying (IRS), use of Insecticide-Treated Net (ITN) and larviciding. As repellents, they will contribute to the reduction in human-mosquito contact, an important component of protection, a strategic approach to malaria management.