Impact of Ocimum Basilicum Leaf Essential Oil on The Survival and Behaviour of An Indian Strain of Dengue Vector, Aedes aegypti (L.)

Objective: Aedes aegypti (L.) is a well-known widely spread disease vector transmitting several diseases of concern. Current investigations were undertaken to discover the larvicidal and repellent potential of essential oil from the basil plant, Ocimum basilicum leaves against Ae. aegypti as a suitable and eco-safe alternate to chemical insecticides.

Methods: The larvicidal potential of basil oil was evaluated against Ae. aegypti early fourth instars using WHO protocol and LC50 and LC90 values were calculated. The efficacy of basil oil as mosquito repellent was assessed using the human-bait technique for 3 hours and the percent protection was calculated.

Results: Exposure of early fourth instars of Ae. aegypti with various concentrations of O. basilicum essential oil for 24 h revealed a moderate LC50 and LC90 value of 141.95 ppm and 100.82 ppm, respectively. The investigations also showed that oil did not have any hormono-mimetic effects as it did not result in the formation of any larval-pupal intermediates. However, the basil essential oil exhibited significant effective repellency against adult Ae. aegypti. Introduction of the arms of human volunteers applied with basil oil in the cages of dengue vector resulted in 100% protection till 120 min as compared to control arm which experienced 3 to 8 bites. Remarkably, the experimental arm was bitten just once in every 15 minutes in next 45 minutes after which only 2 bites were recorded until 180 min of exposure.

Conclusion: Our results recommended the efficient use of basil leaf essential oil as an efficient repellent and as a moderate larvicide agent against Ae. aegypti. Identification of bioactive components in the oil, their individual mode of action and synergistic effects, along with investigations on their impact on the environment and nontarget organisms would help in formulating strategies for mosquito management.