Insect Repellent plants; a potential source to mitigate insect borne diseases
Plants play a key role in maintaining and cleaning the micro environment of the vicinity. Over population and urbanization results in deforestation that leads to increase in pollution in the air and one of the possible sources of disease spread in and around the cities locality.
Mainly this type of disease spread is due to insect that is the most ignored area for peoples and also for researchers & academia. Recently, some plants have been identified and used as insect repellent especially for mosquitoes that are the main cause of several serious diseases including malaria and dengue.
These diseases are not only causing a great mortality in human beings but also act as a consequential barrier to socio-economic growth of the countries all round the world. Under the changing scenario of climate change, this type of disease spread is more as compared to earlier.
Insects are common vectors of diseases and compete for food, fiber, and other natural resources, which causes direct or in direct impact on agricultural crop production and human health. For example, malaria is serious global public health problem transmitted by mosquito, which causes illness to 3.3 billion people in 106 countries.
In Pakistan, common insect borne diseases like malaria and dengue has widely spread especially in developed and crowded areas like Lahore, Rawalpindi, Peshawar and Karachi etc. Such diseases have also caused serious health issues like illness and ultimately death in various tropical and subtropical areas around the globe.
Insect repellent plants are considered as first line of defense against these insect borne diseases as they possess certain compounds that repel them from that specific area. Major groups of these compounds are nitrogenous compounds, terpenoids, phenolics, proteinase inhibitors and hormones, which are effective against repellence of phytophagous insects especially mosquitoes and members of Diptera.
These insects have specialized odorant receptor proteins/neurons that received signals from the outer environment through antennae and maxillary palps. These antennae can detect volatile compounds, which can cause toxicity to insects and ultimately repel them from that specific area. For that reason, the scientist/researchers are interested to enhance the use of low cost effective insect repellent plants instead of using high cost health effective pesticides that also have some hazardous effects on human health.
As according to an estimate every year, 29 billion mosquito coils are sold internationally, 95% of them only in Asia. Kenya annually produces 1200 tons of pyrethrum in the market for making household insecticides. People throughout the world spend reasonable part of their income on buying such household insecticides, according to an estimate; people spent almost 0.63% of per capita income to control insects in India.
Variety of easily and commonly grown insect repellent plants can be used at various suitable places (at front door, around open sitting place, at window boxes, row of plant around the home, near pond and other water sources etc.) of our home, office or any other place.
Previously, in ancient times plants having insect repellent properties were used to protect from insect bites. In recent times poor rural communities of developing countries are still using insect repellent plants to protect their homes from insects. People of developed countries like Europe, America also prefer insect repellent plants over synthetic chemicals due heath hazardous and safety issues.
Following are important insect repellent plant;
Lemongrass (Citronella citratus) is native to India and known as world famous insect repellent plant due to its unique aromatic foliage. It belongs to family Poaceae having 140 species which traditionally growing throughout the tropical and subtropical areas of Asia, Africa, and America for its essential oils and insect repellent properties. It contains number of effective insect repellent volatile organic compounds, which varies greatly with environmental conditions.
These compounds are alpha pinene, camphene, camphor, geraniol, terpenen-4-ol, most abundant ones are citronellal, citronellol, geraniol and citral. Recent reports have identified the insect avoidance role of lemon grass due to presence of various volatile compounds. It can be used at any suitable place to repel insects for example a row of plant in front of house or building, single pot plant at the side of front door, around water tank or other water course.
Niaz-boo and tulsi
Niaz-boo (Ocimum basilicum) and Tulsi (Ocimum sanctum) are known plants of family lamiaceae. These are commonly grown in Pakistan and everyone is familiar with their fragrance, which is due to the presence of essential oils like linalool, linalol, linoleic acid, p-cymene, estragosl, eucalyptol, eugenol, citral, thujone, ocimene, camphor, methyl chavicol, and oleic acid. It is a hardy plant and well known for its strong antioxidants and insect repellent activities from ancient times.
Lantana camara widely distributed plant of family Verbenaceae, having number of cultivars and hybrids. Many authors has declared it as efficient insect repellent plant to house hold protection because it is cheap, easily available, self-sustaining and has number of terpenes and alkaloids with higher ratio of caryophylene (effective repellent against Anopheles gambiae) and eucalyptol, α-humulene, and germacrene (highly toxic to mosquitoes).
It can easily protect our houses from mosquitoes entered from any side like eaves, windows, and cracks in walls throughout the year with limited available resources after attaining sufficient height. Lantana has greater magnitude of volatile organic compounds like α-pinene which is emitted in higher amount than eucalyptus, which make it extremely valuable insect repellent plant.
French marigold (Tagetes patula) is a valuable flowering plant that belongs to family Compositae and extensively used in variety of religious and social functions due to its aesthetic, medicinal and insect repellent properties. It is commonly grown plant due to its easy culture and wide adaptability and previously used by the Egyptians, Greeks and Indian as an herb, in foods and as crown of kings. It is effective insect repellent plant used in houses, gardens etc. due to presence of monoterpenoid esters.
Neem (Azadirachta indica) belongs to family Meliaceae native to Pakistan, India, Bangladesh, Myanmar, Malaysia, and parts of the African continent and traditionally using throughout the globe due to its variety of functions like insect control, firewood, shade, fodder.
It is also called as the “wonder tree” which is using to control number of disease vectors like mosquitoes, ticks, head lice, bed bugs, cockroaches, mites, and sand flies from thousands of years. It contains 35 active ingredients most importantly azadirachtin, which is most effective and well researched found in different plant parts e.g. seed, leaves, and bark, used as tree’s main agent for battle against insects in the form of repellence, fecundity suppression oviposition repellency or attraction, changes in biological fitness etc.
Garlic (Allium sativum) is a perennial bulbous herb like onion, belongs to family Alliaceae. People of different parts of the world used it in different ways to repellent insects e.g. in South America people hang it around neck, Chinease think eating garlic effective to repellent insects and some authors claimed the protection from tick after garlic consumption. It has extremely unpleasant smell due to the presence of ‘allyl-propyl-disulphide (C6-H12-S2) ingredient, which is very effective to repellent the mosquito.
Mint (Mentha piperita) is well known aromatic perennial member of family Lamiaceae, produced purple, white flower and shiny leaves with fruity aromatic taste. A good quality and quantity of essential oil is present in its leaves, which has been reported effective to repellent dangue (Aedes aegypti).
Lavender (Lavandula latifolia) is a perennial, bushy shrub belongs to family Lamiaceae and produces evergreen aromatic foliage with blue color fragrant flower on short spikes, used to extract essential oils, which is highly beneficial for medicine, perfumery and to repel insects like mosquito and moths. It is originated in Mediterranean basin and had been used by Romans and Greeks and now extensively growing in Europe, Africa, and India etc.
Nasturtium (Tropaeolum majus) is an excellent herbaceous annual cheerful flowering plant that belongs to family Tropaeolaceae and native to South America but now distributed through the world due to adaptation with variety of climates and easy to grow. It is famous for its both aesthetic and medicinal properties because it adds cheerful colors to flower beds, fences in landscape, it’s all plant parts are used as food and presence of essential oils make it suitable to repel insects.
Dr. Gulzar Akhtar, Dr. Ishtiaq A. Rajwana and Dr. Kashif Razzaq
Department of Horticulture,
Muhammad Nawaz Shareef University of Agriculture, Multan, Pakistan
Cell: +92 321 6211912