Plant essential oils as mosquito repellent - a review

Abstract

Malaria is considered endemic in 104 countries and territories around the world nessessitating its control. Essential oils belonging to various plant species
and possessing mixtures of hydrocarbons have been seen to act as effective repellent against various pests. The monoterpenoids constituting the major component is
found to be cytotoxic to plant and animal tissue thus impairing the normal functioning of these tissues. The commercially marketed repellents basically consist of
essential oils from plants Cymbopogon nardus, Eucalyptus maculata, Cymbopogon excavatus, Mentha piperita, Azadirachta indica. The volatile nature of these
components due to their short duration of efficacy has urged for the development of novel formulations, use of fixatives such as vanillin and combination essential oil
plants as repellents. The easy availability and less adverse environmental impact have led to the increased interest in plant origin insecticides as an alternative to
chemical insecticides. The present article envisaged to review the reports of essential oils on its effectiveness as repellent.
Keywords: Repellent, pesticide, mosquito, repellent, essential oil.

Full text

©SRDE Group, All Rights Reserved. Int. J. Res. Dev. Pharm. L. Sci. 741
International Journal of Research and Development in Pharmacy and Life Sciences
Available online at http//www.ijrdpl.com
December - January, 2013, Vol. 3, No.1, pp 741-747
ISSN: 2278-0238
Review Article
PLANT ESSENTIAL OILS AS MOSQUITO REPELLENT-A REVIEW
Bhupen Kalita, 1* Somi Bora, 1 Anil Kumar Sharma2
1. Girijananda Chowdhury Institute of Pharmaceutical Science, Guwahati, Assam-781017.
2. Kemwell Biopharm Pvt. Ltd. Bangalore, Karnataka-560022.
*Corresponding Author: Email bhupenkalita7@gmail.com
(Received: September 11, 2013; Accepted: November 01, 2013)
ABSTRACT
Malaria is considered endemic in 104 countries and territories around the world nessessitating its control. Essential oils belonging to various plant species
and possessing mixtures of hydrocarbons have been seen to act as effective repellent against various pests. The monoterpenoids constituting the major component is
found to be cytotoxic to plant and animal tissue thus impairing the normal functioning of these tissues. The commercially marketed repellents basically consist of
essential oils from plants Cymbopogon nardus, Eucalyptus maculata, Cymbopogon excavatus, Mentha piperita, Azadirachta indica. The volatile nature of these
components due to their short duration of efficacy has urged for the development of novel formulations, use of fixatives such as vanillin and combination essential oil
plants as repellents. The easy availability and less adverse environmental impact have led to the increased interest in plant origin insecticides as an alternative to
chemical insecticides. The present article envisaged to review the reports of essential oils on its effectiveness as repellent.
Keywords: Repellent, pesticide, mosquito, repellent, essential oil.
INTRODUCTION
Mosquito borne diseases are major human and animal health
problem in all tropical and subtropical countries. The
diseases transmitted include malaria, filariasis, yellow fever,
Japanese encephalitis and dengue fever. There has been
exploration of various methods over the centuries to combat
threats from mosquito borne diseases. With the beginning of
the 20th century there grew an interest for use of biological
control agents but this was declined with the discovery of
insecticidal properties of DDT in 1939. However its
deleterious impact on non-target population and the
development of resistance prompted for the search of
alternative, simple and sustainable methods of mosquito
control[1, 2, and 3].
Considerable research efforts have proved that essential oil
compound and their derivatives are an effective and
alternative means of controlling nuisance mosquitoes and
their property of rapid degradation in the environment has
favoured for its increased specificity [4]. The justification of
essential oils as green pesticides lies in the fact that the
constituents of all essential oils are moderately toxic or
mostly found to be nontoxic to mammals, birds and the
aquatic ecosystem [5].
Although there exist several advancements in the field of
synthetic drug chemistry and antibiotics but plants still
continue to be one of the major raw materials for drugs
treating various ailments of human. In fact Clinical and
Pharmaceutical investigations have helped in elevating the
status of various medicinal plants by identifying the role of
active principles present in them and exploring their mode of
action in human and animal systems [6]. However essential
oils due to their volatile nature demand for frequent re-
application to maintain its potency. They evaporate

©SRDE Group, All Rights Reserved. Int. J. Res. Dev. Pharm. L. Sci. 742
completely and thereby their effectiveness is short lived and
so complete protection cannot be achieved [7]. The review
tries to compile the health scenario affected by mosquitoes
and discusses the available methods of mosquito control with
special focus on essential oils as alternative of synthetic
chemicals.
Mosquito borne diseases:
Since ancient times, mosquitoes have been reported as the
source of various ailments affecting human. Comprising
approximately 3500 species, mosquitoes are found beyond
the tropical and subtropical regions of the world. The chief
genera which vector human disease causing pathogens are
Anopheles (malaria, filariasis), Aedes (yellow fever, dengue,
chikungunya) and Culex (West Nile, Japanese encephalitis,
filariasis). Over its life span a female mosquito repeatedly
takes a blood meal as protein source to complete egg
development. By injecting the saliva which may contain
pathogens into the host animal, the pathogens thus complete
an obligatory life cycle phase and multiply in the mosquito’s
salivary glands. This thereby makes female mosquito an
ideal transmitter of diverse blood borne pathogens and
agents of devastating human diseases [8, 9]. Over the years
malaria have been considered as one of the leading cause
of death in India (Table: 1).History reveals that the highest
incidence of malaria in India occurred in the 1950s with an
estimated 75 million cases and 0.8 million deaths per year
[10]. Malaria is caused by the protozoal parasites
Plasmodium vivax Grassi and Feletti, Plasmodium malariae
Feletti and Grassi, Plasmodium ovale Stephens, and
Plasmodium falciparum Welch, which are transmitted by
Anopheles mosquitoes. Studies suggest that for any form of
malaria to be endemic in a certain area a number of
requirements must be fulfilled, it needs the presence of a
large number of competent anopheline mosquitoes with a
sufficient preference for human blood and an exposed
human population with enough number of malaria carriers
and susceptible individuals for the chain of infection to persist
[11].
Reports signify that annually 100 million cases of dengue
fever and half a million cases of dengue hemorrhagic fever
(DHF) occur globally (Table: 2), with an average case of
fatality rate around 5%. Potential reasons for the global
resurgence and spread of dengue fever and DHF epidemics
(million)
Death due to malaria
(thousand)
1995 2.93 1151
1996 3.04 1010
1997 2.66 879
1998 2.22 664
1999 2.28 1048
2000 2.03 932
2001 2.09 1005
2002 1.84 973
2003 1.87 1006
2004 1.92 949
2005 1.82 963
2006 1.79 1707
2007 1.51 1310
2008 1.52 924
Table 2: Severe outbreaks of DF/DHF across India.
Year Number of
DF/DHF
cases
Number of
death
Region
1996 10252 423 Delhi
2006 12317 184 21 states/Union
Territories
2007 5534 69 18 states
Control of Mosquitoes:
are assumed due to population growth, uncontrolled
urbanization in tropical and subtropical countries,
proliferation of breeding sites for Aedes mosquitoes and the
lack of effective mosquito control [12].
One of the leading causes of acute encephalopathy is
encephalitis affecting children and adolescents particularly in
the tropics. Mosquitoes proliferate in close association with
pigs & other animal reservoirs and are found to spread virus
of Japanese encephalitis basically in malnourished children
of poor families from rural area [13].
Table 1: Countrywide malaria surveillance data (1995-
2008)
Year Total malaria cases
Kalita B. et. al., December-January, 2013, 3(1), 741-747

©SRDE Group, All Rights Reserved. Int. J. Res. Dev. Pharm. L. Sci. 743
The efficient way to control these diseases is to control
mosquito vector populations and prevent mosquito bites
(Table: 3). Studies reflect that insect repellents play an
important role in preventing the mosquito vector, deterring
an insect from flying to, landing on or biting human and
animal skin. Generally the widely used compounds as insect
repellents are synthetic chemical repellents but they bear the
disadvantage of being not safe for human, especially
children, domestic animals because they may cause skin
irritation, hot sensation, rashes or allergy [14].
Table 3: Methods of mosquito control
Chemical
methods
Non-chemical
methods
Biological
methods
Synthetic
repellents:
DEET,
Permethrin
Natural
repellents:
Neem oil,
Citronella
oil
Physical method:
Medicated net, Non-
medicated net,
Mosquito traps
Mechanical methods:
Electric mosquito
zapper, Mosquito
magnet
By growing some
fish species that
feeds on
mosquito larvae
in water bodies
Fogging is a temporary method of controlling mosquitoes
and such other pests but is particularly necessary in the
context of health threats from severe bug populations and
for an outdoor activity where these pests are unwanted. The
method employs a thermal fogger which produces a
pesticide fog or smoke by heating the fogging solution with a
coil inside the unit. It is ready-to-use fogging solution and
each gallon contains 0.5% Pyrethrins and 5.0% Piperonyl
Butoxide. Another revolutionary approach is the
transdermaltechnology to deliver a natural mosquito
repellent nutrient directly into the blood stream for a
complete 24-hour mosquito protection. The active ingredient
in the patch is Vitamin B1 or Thiamine as it is known to be the
most effective natural mosquito repellent discovered to date.
It was found that female mosquitoes are repulsive to the
scent of Thiamine, therefore the patch works by inducing a
controlled amount of Vitamin B1 into the blood stream [7].
Many synthetic chemicals as mosquito repellent are available
in the market in various form like mosquito repellent cream,
mosquito repellent patch, coils, spray, mosquito repellent
wipe and mosquito repellent liquid that evaporate on
heating. But most of the products are irritant to the users and
environment.
Essential oils as green pesticide:
Essential oils are volatile naturally occurring, complex
compounds characterized by a strong odour and are formed
by aromatic plants as secondary metabolites. They are
liquid, volatile, rarely coloured, lipid soluble and soluble in
organic solvents with a density generally lower than that of
water. There are 17,500 aromatic plant species among
higher plants and approximately 3,000 essential oils are
known out of which 300 are commercially important for
pharmaceuticals, cosmetics and perfume industries apart
from pesticidal potential. In nature essential oils play an
important role in the protection of the plants as antibacterial,
antiviral, antifungal, insecticides and also against herbivores
by reducing their appetite for such plants. They also may
attract some insects to favour the dispersion of pollens and
seeds or to repel the undesirable. Owing to the attraction for
natural products like essential oils, despite their wide use and
being familiar to us as fragrances, it is important to develop
a better understanding of their mode of biological action for
new applications in human health, agriculture and the
environment. Some of them constitute effective alternatives or
complements to synthetic compounds of the chemical industry
without showing the same secondary effects [15].
Literature cited indicates that certain natural products
Zanthoxylum armatum (Rutaceae); Azadirachta indica
(Maliaceae) and Curcuma aromatica (Zingiberaceae) have
been investigated for repellent activity against mosquitoes.
Callistemon rigidus (bottle brush), A. indica (neem) and Z.
armatum (timur) have been reported to have repellent
activity against land leeches also. Repellent action of neem
oil in the form of mats and neem cream has been evaluated
against mosquitoes. Benzene and methanol extracts of
Artemisia vulgaris have been reported to have repellent
activity against Aedes aegypti. Quelling, an insect repellent
produced in China, derived from the extract of the lemon
grass and eucalyptus plants were evaluated against
mosquitoes. Essential oil obtained from Vitex negundo was
used as repellent against Aedes aegypti. Repellent
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©SRDE Group, All Rights Reserved. Int. J. Res. Dev. Pharm. L. Sci. 744
properties of Lantana camara (Vervanaceae) flowers against
Aedes mosquitoes have also been reported [16]. Most of the
plant based insect repellents currently on the market contain
essential oils from one or more of the following plants:
citronella (Cymbopogon nardus), cedar (Juniper virginiana),
eucalyptus (Eucalyptus maculata), geranium (Pelargonium
reniforme), lemon-grass (Cymbopogon excavatus), peppermint
(Mentha piperita), neem (Azadirachta indica) and soybean
(Neonotonia wightii) [17].
Typically these oils are liquid at room temperature and get
easily transformed from liquid to gaseous state at room or
slightly higher temperature without undergoing
decomposition. The aromatic characteristics of essential oils
provide various functions for the plants including attracting or
repelling insects, protecting themselves from heat or cold and
utilizing chemical constituents in the oil as defence materials.
The concept of “Green Pesticides” refers to all types of
nature-oriented and beneficial pest control materials that
can contribute to reduce the pest population. They are safe,
ecofriendly and are more compatible with the environmental
components than synthetic pesticides. The purified terpenoid
constituents of essential oils are moderately toxic to mammals
but with few exceptions, the oils themselves or products
based on oils are mostly nontoxic to mammals, birds and fish
thereby, justifying their placement under “green pesticides”
[5].
Table 4: Mammalian toxicity of some essential oil compounds
Compound Animal
tested
Route LD50
(mg/kg)
1,8 Cineole Rat Oral 2480
Cinnamaldehyde Guinea
pig Oral 1160
Citral Rat Oral 4960
Eugenol Rat Oral 2680
d-limonene Rat Oral 4600
Linalool Rat Oral >1000
Myrcene Rat Oral 5000
Thujone Mice Subcutaneous 87.5
Thymol Rat,
Mice Oral 980,1800
(+) Carvone Rat Oral 1640
The promising herbal medicines should be subjected to
phytochemical analysis and identification of active
ingredients and clinical trials to confirm their efficacy and
safety (Table: 4), and also to determine the recommended
doses in line with WHO guidelines [18].
Mode of action of essential oils:
Essential oils being complex mixtures of volatile organic
compounds are generally produced as secondary
metabolites in plants. They are constituted by hydrocarbons
(terpenes and sesquiterpenes) and oxygenated compounds
(alcohols, esters, ethers, aldehydes, ketones, lactones and
phenols). Essential oils extracted from different families have
shown high repellency against arthropod species. Literature
has documented that essential oils and extracts from genus
Eucalyptus and Cymbopogan have been traditionally used
as effective repellents. The metabolites like the
monoterpenes such as α-pinene, cineole, eugenol, limonene,
terpinolene, citronellol, citronellal, camphor and thymol are
the common constituents in a number of essential oils
presenting mosquito repellent activity. Generally the
monoterpenoids and sesquiterpenes are associated with
repellent properties of several essential oils [19]. Amongst
the monoterpenes, a majority of them are cytotoxic to plants
and animal tissue causing a dramatic reduction in the number
of intact mitochondria and golgi bodies thereby impairing
respiration, photosynthesis and decreasing the cell
membrane permeability. Being volatile in nature so they also
act as chemical messengers for insects and other animals,
serving as a signal of relatively short duration and alarm the
pheromones. Literature cites that hairs on the mosquito
antennae are temperature and moisturesensitive. The
repellent molecules thus interacts with the female mosquito
olfactory receptors thereby blocking the sense of smell
which therefore comes as an hurdle in the recognition of host
by the mosquitoes (Fig:1) [4].
Studies have indicated that terpenoids containing
two functional groups are biologically active as mosquito
repellents. The repellent activities of 20 synthesized
terpenoids with two functional groups, one being negatively
charged end containing either ester/ether bonds or an
ethanol hydroxyl group and the other positively charged end
containing alkane groups were assessed. It was revealed
that the positive end is more favorable for receptor
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©SRDE Group, All Rights Reserved. Int. J. Res. Dev. Pharm. L. Sci. 745
interactions and its magnitude characterizes the electrophilic
nature of the group, consequently the repellent-receptor
interactions are most likely to be related to electrophilic
interactions. Also it was shown that molecular descriptors such
as dipole moment and boiling point are closely related to
repellent activity. Generally the dipole moment is related to
lipophilicity or specific electrostatic interactions with receptor
whereas boiling point/vapor pressure might determine
duration of contact with olfactory chemosensilla of
mosquitoes [20].Although repellent activity of essential oils
are generally attributed to some particular compounds but if
a synergistic phenomenon is established among these
metabolites then it may result in an increased bioactivity
compared to isolated components. Also this synergistic effect
is showed with mixture of oils. The minor constituents found in
low percentages may also act as synergists enhancing the
effectiveness of the major constituents through a variety of
mechanisms [21]. Essential oils act at a vapor phase and are
generally effective when freshly applied as they usually
dissipate quickly within a short period of time due to their
high volatility. However this property can be improved
through the development of formulations that would keep the
active ingredients onto the skin for a longer period of time.
The product composition basically determines the increase in
repellency property of essential oils [22].
Formulation based on creams, polymer mixtures or
microcapsules results in increase in repellency duration
through controlled release. An example is the successful
microencapsulation of Zanthoxylum limonella oil in
glutaraldehyde crosslinked gelatin in order to improve
mosquito repellent properties. Development of new
formulations, fixative additives and the production of
combined repellents are the possibilities that add up for the
effectiveness and greater economic value to repellents
obtained from essential oils [23].
CONCLUSION
Plants as alternative source of repellent agent reported in
numerous ethnobotanical evaluation. They have been used
traditionally in many parts of the world. The repellent
properties of plant essential oils to mosquitoes andinsects
were well known before the advent of synthetic chemicals.
Plant-derived repellents usuallydo not pose hazards of
toxicity to humans and domestic animalsand are easily
biodegraded. Compared to synthetic compounds,
naturalproducts are presumed to be safer for human use.
Moreover, in contrast withsynthetic repellents which pose
environmental threat, lethal effects on nontarget organisms
and the resistance of mosquitoes to insecticides have
increased during the last five decades, the natural products
Fig 1:Target sites in insects as possible neurotransmitter mediated action of essential oils.
Kalita B. et. al., December-January, 2013, 3(1), 741-747

©SRDE Group, All Rights Reserved. Int. J. Res. Dev. Pharm. L. Sci. 746
are usually simple, cost effectiveand accessible to
communities with minimal external input. These problems have
demanded the necessity for developing alternative
strategies. Due to the easy availability, low budget and less
adverse environmental impact the interest in developing
plant origin insecticides as an alternative to chemical
insecticides has attracted great attention. Although there is
widespread use of plants as repellents, scientific
understanding of these plants is, however, largely
unexplored and therefore there is a need to collect
ethnobotanicalinformation on these plants as a first step prior
to evaluationof their efficacy and safety as repellents.
Novel drug delivery system of plant based active substances
are need of the time. Recent technological developments in
isolation and standardization of herbal drugs motivating
research in novel sustained and controlled delivery device
taking phytoconstituents. But pharmaceutical research in
mosquito repellent products yet to gear up. Novel mosquito
repellent device of essential oils have greater scope in lieu
of the fact that in twenty first century also mosquito borne
diseases are affecting a large population worldwide.
Essential oils because of their volatility act for a short
duration. Polymeric slow release device containing essential
oils can be one option for making them long acting. Also
multiple emulsion with essential oil core may be a smart
delivery system. Such topically applicable formulations will
be convenient for people to apply and terminate. Essential
oils abundant in nature and apart from its medicinal and
flavor value, its use in repelling mosquito can be considered
as sustainable and biocompatible delivery device as green
alternative.
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How to cite this article:
Kalita B., Somi Bora S., Sharma A.K., “Plant essential oils as mosquito repellent-A Review” Int. J. Res. Dev. Pharm. L. Sci.,
2013, 3(1), pp. 741-747.
Kalita B. et. al., December-January, 2013, 3(1), 741-747