A female Anopheles mosquito transmits microparasitic Plasmodium sporozoan, which causes malaria disease in humans. Out of 229 million malaria cases worldwide, 409,000 deaths have been reported in 2019. Interestingly, more than 90% of fatalities were observed in sub-Saharan Africa. In the case of Ghana in SSA, malaria accounts for 39% of outpatient attendance, 25% of all admissions, and 4% of all death cases. Some strategies to reduce malaria in Ghana have largely been vector control methods e.g., use of insecticide-treated nets and indoor sprays. However, a decline in the use of insecticide-treated nets due to skin irritation and/or demand for sufficient indoor air-flow requires research into safer vector control approach. Moreover, considerations for environmental impact, health implications, and insecticide resistance development in mosquitoes to synthetic sprays suggest the need for study on environmentally-friendly vector management approaches. Naturally occurring semiochemicals derivable from plants have either significantly reduced host-seeking behaviour of pests. In this case, use of plant-based semiochemicals may be an alternative. Therefore, objectives of the current study were to examine mosquito repellency potential of Ocimum gratissimum, O. tenuiflorum and O. basilicum against a selected Anopheles mosquito species and characterised the headspace volatile composition of the plants. For the volatile repellency activities against Anopheles gambiae, an arm-in-cage method was used. Gas Chromatography coupled Mass spectrometry was used for the structure elucidation of the volatile compounds from the Ocimum plants. Repeated tests revealed that headspace volatiles from the three Ocimum species could repel A. gambiae adults over a long period of time. However, only the headspace volatile from O. tenuiflorum achieved the longest repellency time-length (110 ± 10.0 min) similar to that of Odormos, a synthetic repellent. The GC-MS analysis confirmed numerous volatile compounds present in the headspace volatiles from each Ocimum plant similar to those reported in literature. To the best of our knowledge, this is the first report of (E)-4,8-Dimethyl-1,3,7-nonatriene in O. tenuiflorum headspace volatiles. future study on mosquito repellency potential of individual volatile compounds from Ocimum species against mosquitoes may change people’s perceived choice to use O. tenuiflorum.

Mosquito repellency potential of plants’ volatiles: can people’s preferences demand future research need on volatile compounds from Ocimum tenuiflorum?

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