Spatial Exposure Responses of Malaria Vectors to Eucalyptus grandis (W. Hill ex Maiden) and Cymbopogon citratus (DC.) Stapf Essential Oils.

Background

Recently, the use of volatile compounds as spatial repellents have received special attention as a promising strategy for adult An. gambiae s.l control. Anopheles gambiae s.l is a primary vector of malaria, an arthropod-borne disease of global significance. Current strategies for controlling mosquitoes heavily rely on vector control methods. Understanding the responses of these vectors to volatile compounds will be helpful in the formulation of repellants or attractants for control vector populations. This study was conducted in Nwoya district, Uganda, one of the high-malaria-transmission areas in the northern part of Uganda, as one of the ways of reducing contact between the parasite, vector, and malaria outbreak. Materials and

Methods

In this study, a laboratory-reared female An. gambiae Kisumu strain from Uganda Virus Research Institute (UVRI) insectaries were used to examine spatial behavior responses of An. gambiae to selected EOs of Eucalyptus grandis and Cymbopogon citratus. Spatial activity responses were measured using a Y-tube olfactometer under controlled conditions using three replicates in various concentrations of the tested EOs. These oils were extracted by steam distillation and the main constituents identified using gas chromatography-mass spectrometry.

Results

Mosquito response curves indicating effective repellency concentrations are reported, as well as the gas chromatography-mass spectrophotometry analysis results. For Eucalyptus grandis, the two components with the highest composition were L-α terpineol and Eucalyptol, while those for Cymbopogon citratus were Lavandulol, methyl ether, and citral. Other components had a percentage composition less than five but they might play a big role in repellent activity against mosquito species.

Conclusions

The mosquito repellency results in this study indicate that Eucalyptus grandis and Cymbopogon citratus EOs could be used as mosquito repellents, providing more evidence that natural products have promising lead compounds for further development of botanical spatial repellents. Further characterization of EOs and testing on mosquito behavior related to the prevention of malaria and other vector-borne diseases will promote innovation in vector control and provide new vector control tools that are needed in this era of insecticide resistance.