Essential oils of four wild plants inhibit the blood seeking behaviour of female Aedes aegytpi

Mosquitoes belong to the family Culicidae and are found throughout the tropical, subtropical, and temperate regions of the world. Over 3500 mosquito species have been discovered, belonging to 113 genera (Annoymous 2020). Most of the mosquito species inhabit freshwater and are known as biting and irritating pests. In addition to biting, they transmit diseases to humans and animals (Rueda 2008). Hence, mosquitoes are considered the deadliest living organism in the world (Synhorst 2020). Aedes aegypti is an important vector of many disease-causing pathogens and is commonly known as the dengue or yellow fever mosquito (Jentes et al., 2011). Ae. aegypti mosquitoes are abundant in humid, semi-tropic, and hot urbanized areas due to the availability of favourable breeding sites such as flower pots, wash basins, discarded old tyres, stagnant water, tree holes, and empty shells (Rey et al., 2006; Philbert and Ijumba, 2013). Since there is currently no approved vaccine against dengue virus infection, the most effective management strategies to reduce dengue infection are the reduction of mosquito larval habitat (Gubler and Clark, 1996), insecticidal sprays, insecticides treated nets (ITNs), and approved mosquito repellents. However, due to the imprudent use of chemical insecticides, mosquitoes have developed resistance against the pyrethroid group of insecticides (Bisset et al., 2013). In addition, excessive use of chemical insecticides has had negative effects on non-target insects (Yadav et al., 2015).

N, N-diethyl-3-methyl benzamide (DEET) is one of the best-known mosquito repellents that provides long-lasting protection against many biting insects and being used throughout the world. In Pakistan, DEET based products are mainly developed by Abbott Laboratories and marketed with a trade name of Mospel in the form of lotion, cream, and spray (Annoymous 2021). DEET is also being used against some other insect species including ticks, biting flies, and fleas (EPA 1980). In addition to being expensive, the excessive use of DEET causes toxicity to humans such as skin irritation in adults and a brain disease (encephalopathy) in children (Robbins and Cherniack, 1986; Briassoulis et al., 2001). Moreover, since the last decade, people are more inclined towards the use of natural products for personal protection against blood seeking insects, thus there is a great need to explore plant-based natural repellents.

A number of studies showed that plant essential oils have the ability to repel mosquitoes (Ansari et al., 2000; Cheng et al., 2003; Choochote et al., 2007). For example, Amomum xanthioides Wall, Curcuma zedoaria Roscoe, Kaempferia galanga (L.), Anethum graveolens (L.), Apium graveolens (L.), Carum carvi (L.), and Foeniculum vulgare Mill have been tested against Ae. aegypti (Choochote et al., 2007). Likewise, Origanum vulgare (L.) essential oil has been tested as a larvicide against Culex and Anopheles (Govindarajan et al., 2016), Mentha piperita (L.) against Aedes (Kumar et al., 2011), while Mentha longifolia (L.) essential oil has been proved as an adulticide against Culex (Al-Sarar 2014). To date, a few plant-based mosquito repellents have been identified and commercialised, however, the synthetic mosquito repellent DEET is still the strongest among the available repellents. Hence, more work is required to identify mosquito repellents from plant essential oils with repellency equivalent to DEET. In this study we have determined the repellent potential of the essential oils of four wild plants against females of Ae. aegypti and also analysed them on GC-MS to determine their chemical composition.

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