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Eucalyptus essential oil as a natural pesticide
Daizy R. Batish
a,
*, Harminder Pal Singh
b
, Ravinder Kumar Kohli
a,b
, Shalinder Kaur
a
a
Department of Botany, Panjab University, Chandigarh 160014, India
b
Centre for Environment and Vocational Studies, Panjab University, Chandigarh 160014, India
1. Introduction: rationale and objectives
Since antiquity humans have been dependent upon natural
ecosystems for marketable commodities such as food, fodder,
fuelwood, timber and medicines. However, until recently, very
little significance was given to the natural, hidden, life-supporting
services of the natural ecosystems. It is only when the disruption/
loss of these natural resources poses/results in a severe threat to
the very existence of human civilization, these intrinsic values
have been highlighted. In fact, these services are ignored largely
due to their non-marketable potential and a negligible role in
modern trade-based economy. Nevertheless, during the last
decade the importance of these natural benefits has been
highlighted and the perils linked to their loss realized. The phrase
‘ecosystem services’ has been widely used for these underpinned
natural environmental benefits (Ehrlich and Ehrlich, 1981) and
considered as ‘world’s natural capital’(Costanza et al., 1997).
Majority of the ecosystems services’, particularly intangible,
provided by nature are complex, interwoven and intricately
related. However, some of the ecosystem services include simple
products such as fodder, fuelwood, oil, and resins that are
commercially marketed. Ecosystem services have been recognized
since ancient times. For example, Plato (ca. 400
B
.
C
.) based on his
direct observation concluded that deforestation leads to soil
erosion and results in drying up of springs. Ecosystem services
have been grouped into five categories—provisioning (food, fuel,
fodder, essential oil), regulating (carbon sequestration, nutrient
cycling), supporting (purification, cleansing, pest control), cultural
(spiritual, recreational and aesthetic) and preserving (biodiversity
protection) services (Millennium Ecosystem Assessment, 2005). Of
late, these intrinsic services of nature have been recognized as an
important tool for conservation and resource management (Reid,
2006). As per report of the World Bank (2006), more than one
billion people are directly dependent upon ecosystem services. It is
very difficult and more so debatable to assess the ecosystem
services in monetary terms or market-economy; however, some
estimates have been made. Costanza et al. (1997) opined that
monetary value of global ecosystem services is in the range of US$
16–54 trillion (10
12
) per year with an average value of US$ 33
trillion per year. Looking at the importance of ecosystem services
to mankind, it is worthwhile to explore environmental benefits of
the natural products to mankind.
Among the variety of nature’s ecosystem services, the natural
pest control is an important aspect. DeBach (1974) reported that
99% of the crop pests are controlled by natural enemies such as
birds, spiders, parasitic wasps, viral diseases and other organisms.
In fact, natural pest control not only minimizes the use of synthetic
chemicals, protects crops, but also saves huge amount of money
spent on chemical compounds (Naylor and Ehrlich, 1997). It is thus
pertinent to explore the pesticidal activity of natural products.
Forest Ecology and Management 256 (2008) 2166–2174
ARTICLE INFO
Article history:
Received 16 February 2008
Received in revised form 25 June 2008
Accepted 4 August 2008
Keywords:
Antimicrobial activity
Eucalyptus species
Essential oils
Environment friendly pest control
Herbicidal activity
Insecticidal/insect-repellent activity
ABSTRACT
Eucalyptus (family Myrtaceae), an Australian native, represented by around 700 species is a genus of tall,
evergreen and magnificent trees cultivated world over for its oil, gum, pulp, timber, medicine and
aesthetic value. Among the various wood and non-wood products, essential oil found in its foliage is the
most important one and finds extensive use in food, perfumery and pharmaceutical industry. In addition,
the oil possesses a wide spectrum of biological activity including anti-microbial, fungicidal, insecticidal/
insect repellent, herbicidal, acaricidal and nematicidal. The present paper discusses this environmentally
benign pest control using eucalyptus oils against bacteria, fungi, insects, nematodes, weeds and mites.
The use of eucalyptus oil as a natural pesticide is of immense significance in view of the environmental
and toxicological implications of the indiscriminate use of synthetic pesticides and overcoming/reducing
the problem of increasing pest resistance.
ß2008 Elsevier B.V. All rights reserved.
* Corresponding author. Tel.: +91 172 2534005.
E-mail address: daizybatish@yahoo.com (D.R. Batish).
Contents lists available at ScienceDirect
Forest Ecology and Management
journal homepage: www.elsevier.com/locate/foreco
0378-1127/$ – see front matter ß2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2008.08.008
World over, pests (especially weeds, pathogens and insects) are
the largest competitor of agricultural crops and severely reduce the
crop production in the range of 25–50% (Pimentel et al., 1991;
Oerke, 2006). Among the pests, weeds alone are held responsible
for nearly 34% reduction in crop yield (Oerke, 2006). To protect
agricultural crops enormous amount of synthetic pesticides are
used world over. As per Agrow (2007) report, the total value of
world’s agrochemical market was between US$31–35 billion and
among the products herbicides accounted for 48% followed by
insecticides (25%) and fungicides (22%).
However, the excessive use of synthetic pesticides in the
croplands, urban environment, and water bodies to get rid of
noxious pests has resulted in an increased risk of pesticide
resistance, enhanced pest resurgence and development of resis-
tance/cross-resistance, toxicological implications to human health
and increased environmental pollution. In fact, combating of
environmental pollution and its ill-effects on the life and life-
support systems is one of the most serious challenges before the
present day world. Efforts are thus being made world over to
replace these synthetic chemicals with alternatives, which are
safer and do not cause any toxicological effects on the environ-
ment. The natural pest and disease control either directly or
indirectly using natural plant products/botanicals, including
essential oils, holds a good promise (Regnault-Roger, 1997; Isman,
2000, 2006; Bakkali et al., 2008). Among essential oils, Eucalyptus
oil, in particular, is more useful as it is easily extractable
commercially (industrial value) and possesses a wide range of
desirable properties worth exploiting for pest management
(Boland et al., 1991; FAO, 1995; Barton, 2000). We refer it as a
provisioning ecosystem service since the oil is commercially
important product of the tree. Our objective in the present context
is to review its use as a natural pesticide, which could be another
supporting ecosystem service.
2. Essential oils: their characteristics and potential
Plant essential oils are obtained from non-woody parts of the
plant, particularly foliage, through steam or hydrodistillation. They
are complex mixture of mainly terpenoids, particularly mono-
terpenes (C10) and sesquiterpenes (C15), and a variety of aromatic
phenols, oxides, ethers, alcohols, esters, aldehydes and ketones
that determine the characteristic aroma and odour of the donor
plant. Presence of volatile monoterpenes or essential oils in the
plants provides an important defense strategy to the plants,
particularly against herbivorous insect pests and pathogenic fungi
(Langenheim, 1994). These volatile terpenoids also play a vital role
in plant–plant interactions and serve as attractants for pollinators
(Tholl, 2006). They act as signaling molecules and depict
evolutionary relationship with their functional roles (Theis and
Lerdau, 2003).
Aromatic plants and their essential oils have been used since
antiquity in flavor and fragrances, as condiment or spice, in
medicines, as antimicrobial/insecticidal agents, and to repel insect
or protect stored products (Dorman and Deans, 2000; Isman and
Machial, 2006; Bakkali et al., 2008). These constitute effective
alternatives to synthetic pesticides without producing adverse
effects on the environment (Isman, 2000; Isman and Machial,
2006). However, the attempts to characterize their pest control
activity under in vitro conditions started in 1900s (Dorman and
Deans, 2000). Moreover, the interest in essential oils has regained
momentum during the last decade, primarily due to their fumigant
and contact insecticidal activities and the less stringent regulatory
approval mechanisms for their exploration due to long history of
use (Isman, 2006). Of late, the essential oils are being tried as
potential candidates for weed (Singh et al., 2003; Batish et al., 2004,
2007), and pest and disease management (Isman, 2000; Pawar and
Thaker, 2006; Abad et al., 2007). It is primarily because essential
oils are easily extractable, ecofriendly being biodegradable and get
easily catabolized in the environment (Zygadlo and Grosso, 1995),
do not persist in soil and water (Misra and Pavlostathis, 1997;
Isman, 2000, 2006), possess low or no toxicity against vertebrates—
fishes, birds and mamamals (Enan et al., 1998) and play an
important role in plant protection against pests (Isman, 2000;
Isman and Machial, 2006; Bakkali et al., 2008). All these benign
properties of essential oils permit their use even in sensitive areas
such as schools, restaurants, hospitals and homes.
3. Eucalyptus essential oils as pesticide—Why?
Among various aromatic plants, genus Eucalyptus L
0
Herit
(Family Myrtaceae and a native of Australia) represented by over
700 species distributed throughout the world (Brooker and Kleinig,
2006) is one of the most-extensively planted pulpwood species
(Zobel, 1988). It consists of tall, magnificent and evergreen trees
with fragrant foliage rich in oil glands and is an excellent source of
commercially important eucalyptus oil that finds extensive use in
pharmaceutical, perfumery and industry (Brooker and Kleinig,
2006). The common oil yielding Eucalyptus species include: lemon
or lemon-scented eucalyptus (E. citriodora), Tasmanian blue gum
(E. globulus), blue mallee (E. polybractea), and River red gum (E.
camaldulensis). As per a report, essential oil from Eucalyptus
species are among the world’s top traded oils and oil extracted
from E. citriodora is one of the world’s major oil in terms of trade
volume (Green, 2002).
Eucalytpus species not only provide fuel biomass and reduce
atmospheric carbon dioxide levels directly (Barton, 2000; Martin,
2002), but also perform a variety of indirect services through their
essential oil used as insect/pest repellent and as a pesticidal agent
(Barton, 2000). In fact, eucalyptus oil has been known for hundreds
of years as antibacterial, antifungicidal and antiseptic in nature
(Brooker and Kleinig, 2006). Eucalyptus oil ranks superior in
quality and has advantages over essential oil from other tree crops,
since it has multipurpose uses in perfumery, pharmaceutical and
other industries (Boland et al., 1991; FAO, 1995).
Under naturalconditions, essentialoil of Eucalyptus is also known
to provide allelopathic property to the tree (Kohli, 1990; Liu et al.,
2008). Essential oil emanated from its foliage has been demon-
strated to retard the growth of associated vegetation (del Moral and
Muller, 1969; Kohli, 1990; May and Ash, 1990; Liu et al., 2008).
Additionally, the presence of essential oil also provides defense
advantage to Eucalytpus leaves against herbivory and attack by
harmful insects (Brooker and Kleinig, 2006). In general, the plant
secondary metabolites including phenolics, tannins and even
monoterpenes are considered to have co-evolved with herbivory
(Vourc’h et al., 2002; Bailey et al., 2004; Foley and Moore, 2005).
However, whether herbivory and presence of essential oil in
Eucalyptus species has any evolutionary relationship is not clearly
understood. Anyhow, a strong genetic basis has been established for
the resistance of E. globulus to marsupial herbivory largely due to
presence of sideroxylonal (O’Reilly-Wapstra et al., 2004).
Eucalyptus oil has been placed under GRAS (Generally Regarded
as Safe) category by Food and Drug Authority of USA and classified
as non-toxic (USEPA, 1993). Even the Council of Europe has
approved use of eucalyptus oil as a flavouring agent in foods
(5 mg/kg) and candies and confectionery items (15 mg/kg)
(Council of Europe, 1992). At low concentrations, it is also used
extensively in soaps, detergents and perfumes (Furia and Bellanca,
1971). Currently, three to five thousand tonnes of Eucalyptus oil
are traded every year in international markets and around two-
third of this is produced by Australia (Barton, undated).
D.R. Batish et al. / Forest Ecology and Management 256 (2008) 2166–2174
2167
4. Nature and composition of eucalyptus essential oils
The eucalyptus oil is a complex mixture of a variety of
monoterpenes and sesquiterpenes, and aromatic phenols, oxides,
ethers, alcohols, esters, aldehydes and ketones; however, the exact
composition and proportion of which varies with species (Brooker
and Kleinig, 2006). The pesticidal activity of eucalyptus oils has
been due to the components such as 1,8-cineole, citronellal,
citronellol, citronellyl acetate, p-cymene, eucamalol, limonene,
linalool,
a
-pinene,
g
-terpinene,
a
-terpineol, alloocimene, and
aromadendrene (Watanabe et al., 1993; Li et al., 1995, 1996;
Cimanga et al., 2002; Duke, 2004; Batish et al., 2006; Su et al., 2006;
Liu et al., 2008). The major components identified in essential oil
with pesticidal activity extracted from various Eucalyptus species
are given in Table 1. However, the bioactivity of the essential oil
depends upon the type and nature of the constituents and their
individual concentration. It further varies with species, season,
location, climate, soil type, age of the leaves, fertility regime, the
method used for drying the plant material, and the method of oil
extraction (Brooker and Kleinig, 2006).
The various components of eucalyptus essential oil act
synergistically (and not additively) to bring the overall pesticidal
activity (Cimanga et al., 2002). Among the various components of
eucalyptus oil, 1,8-cineole is the most important one and, in fact, a
characteristic compound of the genus Eucalyptus, and is largely
responsible for a variety of its pesticidal properties (Duke, 2004).
Table 1
Major constituents of the essential oil with pesticidal activity extracted from Eucalyptus species
Eucalyptus sp. Major constituents Reference
E. camaldulensis Eucamalol Watanabe et al. (1993)
E. citriodora Citronellal Ramezani et al. (2002b),Batish et al. (2006),Su etal. (2006)
E. globulus 1,8-Cineole Yang etal. (2004)
E. grandis
a
-Pinene, 1,8-cineole Lucia etal. (2007)
E. robusta
a
-Pinene Sartorelli et al. (2007)
E. saligna
a
-Pinene (during blossoming),
p-cymene (at vegetative phase)
Ceferino et al. (2006),Sartorelli et al. (2007)
E. urophylla
g
-Terpinene, Su et al. (2006)
E. camaldulensis,E. grandis 1,8-Cineole Su et al. (2006)
E. cinerea,E. viminalis 1,8-Cineole Ceferino et al. (2006)
E. grandis E. urophylla Alloocimene,
a
-pinene Liu etal. (2008)
E. alba,E. camaldulensis,
E. citriodora,E. deglupta,
E. globulus,E. robusta,
E. saligna,E. tereticornis
Cineole,
a
-pinene, p-cymene Cimanga et al. (2002)
Eucalyptus sp. p-Menthane-3,8-diol (PMD) Trigg (1996a,b),Trigg and Hill (1996)
Eucalyptus sp. 1,8-Cineole Saad et al. (2006)
Table 2
Insecticidal activity of essential oil from some Eucalyptus species
Eucalyptus sp. Tested organism Reference
E. camaldulensis Repels adult females of Culex pipiens Erler et al. (2006)
E. camaldulensis Egg mortality in Tribolium confusum and Ephestia kuehniella Tunc¸et al. (2000)
E. citriodora Toxicity against Sitophilus zeamais Tinkeu et al. (2004)
E. globulus Repellent in action, reduced fecundity, decreased egg hatchability,
increased neonate larval mortality and adversely influenced
offspring emergence in Acanthoscelides obtectus
Papachristos and Stamopoulos (2002, 2004)
E. globulus Kills pupae of Musca domestica Abdel Halim and Morsy (2005)
E. globulus Ovicidal and adulticidal against female Pediculus humanus
capitis De (human body lice)
Yang et al. (2004)
E. globulus Toxic to Aedes aegypti larvae Lucia et al. (2007)
E. intertexta,
E. sargentii and
E. camaldulensis
Kills 1–7 days adults of Callosobruchus maculatus,Sitophilus
oryzae and Tribolium castaneum
Negahban and Moharramipour (2007)
E. nicholii,
E. codonocarpa,
E. blakelyi
Sitophilus oryzae,Tribolium castaneum and Rhyzopertha dominica Lee et al. (2004)
E. saligna Repellent activity against Sitophilus zeamais and Tribolium confusum Tapondjou et al. (2005)
E. tereticornis Larvicidal, pupicidal and adulticidal activity towards Anopheles stephensi Nathan (2007)
Eucalyptus sp. Rice weevil Sitophilus oryzae Lee et al. (2001)
Eucalyptus sp. Toxic to larvae of pine processionary moth Thaumetopoea pityocampa Kanat and Alma (2003)
Eucalyptus sp. Mushroom fly Lycoriella mali Choi et al. (2006)
Eucalyptus sp. Larvicidal activity against 4th instar stage larvae of Aedes
albopictus,A. aegypti and Culex pipiens pallens
Zhu et al. (2006)
Eucalyptus sp. Tribolium castaneum,Rhyzopertha dominica,Sitophilus oryzae and
Sitophilus zeamais,Corcyra cephalonica and Sitotroga cerealella
Rajendran and Sriranjini (2008)
D.R. Batish et al. / Forest Ecology and Management 256 (2008) 2166–2174
2168
5. Insecticidal/insect-repellent activity of eucalyptus oils
Eucalyptus oil can directly act as a natural insect repellent to
provide protection against mosquitoes and other harmful arthro-
pods or serves antifeedant activity against herbivores. Some of the
examples of use of eucalyptus oil for insecticidal activity are listed
in Table 2.
Yang et al. (2004) reported that essential oils from E. globulus
and its major monoterpene 1,8-cineole showed toxicity against
human head lice, Pediculus humanus capitis. The pediculicidal
activity of essential oil and its major component 1,8-cineole was
more than that of commercially used pediculides—delta-pheno-
thrin or pyrethrum. The LT
50
value of essential oil was 0.125 mg/
cm
2
compared to 0.25 mg/cm
2
of commercial pediculides (Yang
et al., 2004). Of late, Ceferino et al. (2006) demonstrated the
fumigant toxicity/repellent activity of essential oil from E. cinerea,
E. viminalis and E. saligna, against permethrin-resistant human
head lice with KT
50
(time for 50% knockdown) values of 12.0, 14.9
and 17.4 min, respectively. Based on the study, these workers
concluded that these essential oils could be used for the
development of new products for control of human head lice
(Ceferino et al., 2006).
Eucalyptus oil has also been used as an antifeedant, particularly
against biting insects (Trigg, 1996a,b; Trigg and Hill, 1996; Chou
et al., 1997; Thorsell et al., 1998). Trigg (1996a,b) reported that
eucalyptus based products used on humans as insect repellent can
protect from biting insects up to 8 h depending upon the
concentration of the essential oil. Further, the insect-repellent
activity could be extended up to 8-days, when eucalyptus essential
oils are applied on the clothes (Mumcuoglu et al., 1996). Later,
Fradin and Day (2002) reported that 30% eucalyptus oil can prevent
mosquito bite for 2 h; however, the oil must have at least 70%
cineole content. Lucia et al. (2007) demonstrated that essential oil
from E. globulus are toxic to Aedes aegypti larvae and showed LC
50
of
32.4 ppm. Seyoum et al. (2003) reported that burning of leaves of E.
citriodora provides a cost-effective method of household protec-
tion against mosquitoes in Africa. It is particularly significant for
providing protection against mosquito bites during the evenings
before going to bed (Seyoum et al., 2003). Of late, CDC (Center for
Disease Control and Prevention, USA) recommended the use of
lemon eucalyptus oil (with p-menthane-3,8-diol, PMD, as active
ingredient) for protection against West Nile virus that causes
neurological disease or even death and is spread by mosquitoes
(Kuehn, 2005).
Table 3
Antimicrobial (against fungi and bacteria) activity of essential oils from some Eucalyptus species
Oil source Microbe (s) Reference
E. camaldulensis Penicillium digitatum causing fruit rot of mandarin cv. Kinnow under both in
vitro and in vivo conditions
Dhaliwal et al. (2004)
E. camaldulensis Dermatophytes—Microsporum canis,Microsporum gypseum,Trichophyton rubrum,
Trichophyton schoenleinii,Trichophyton mentagrophytes and Epidermophyton floccosum
Falahati et al. (2005)
E. camaldulensis Seed-borne fungi – Colletotrichum graminicola,Phoma sorghina, and Fusarium
moniliforme – of sorghum without any negative effect on Sorghum
Somda et al. (2007)
E. citriodora Human pathogens Microsporum nanum,Trichophyton mentagrophytes and T. rubrum Shahi et al. (1999)
E. citriodora Mycelial growth and germination of spores of Didymella bryoniae Fiori et al. (2000)
E. citriodora Radial growth and dry weight of rice pathogens, Helminthosporium oryzae and
Rhizoctonia solani DC
Ramezani et al. (2002a,b)
E. citriodora Aspergillus sp., Penicillium sp., Fusarium sp. and Mucor sp. Alfazairy (2004)
E. citriodora Phytopathogenic fungi, postharvest pathogenic fungi, Botrytis cinerea and
three soil-borne pathogenic fungi, Fusarium oxysporum,Pythium ultimum
and Rhizoctonia solani
Lee et al. (2007)
E. citriodora Candida sp. Dutta et al. (2007)
E. citriodora Phytophthora cactorum,Cryphonectria parasitica and Fusarium circinatum Lee et al. (2008)
E. citriodora Botrytis cinerea Tripathi et al. (2008)
E. dives Gram-positive and Gram-negative bacteria and Saccharomyces cerevisiae Delaquis et al. (2002)
E. globulus Spore germination and radial growth of Pythium aphanidermatum Edson Oluma and Garba (2004)
E. globulus Escherichia coli O157:H7 Moreira et al. (2005)
E. globulus,E. maculata and E. viminalis Fungus Trichophyton mentagrophytes Takahashi et al. (2004)
E. robusta and E. saligna Staphylococcus aureus,Escherichia coli and Candida albicans Sartorelli et al. (2007)
E. tereticornis Staphylococcus aureus,Bacillus cereus,Escherichia coli,Micrococcus luteus,
Proteus mirabilis and Alcaligenes faecalis
Singh and Sharma (2005)
Eucalyptus grandis E. urophylla Pathogenic fungi Fusarium oxysporum,Pyricularia grisea,Gloeosporium
musarum and Phytophthora capsici
Liu et al. (2008)
Eucalyptus sp. Dermatophytes—Candida spp. and Pityrosporum orbiculare Kothavade et al. (1997)
Eucalyptus sp. Mycelial dry weight of Penicillium aurantiogriseum and P. viridicatum Khaddor et al. (2006)
Eucalyptus sp. Spores of bacteria Clostridium botulinum 62A and Bacillus cereus TChaibi et al. (1997)
Eucalyptus sp. Colony forming units of Staphylococcus aureus ATCC-25923 Donoyama and Ichiman (2006)
Eucalyptus sp. Gram-positive and Gram-negative bacteria and fungi Pattnaik et al. (1996)
D.R. Batish et al. / Forest Ecology and Management 256 (2008) 2166–2174
2169
6. Antifungal and antimicrobial activity of eucalyptus oils
Eucalyptus essential oils and their major constituents possess
toxicity against a wide range of microbes including bacteria and
fungi, both soil-borne and post-harvest pathogens. They have been
found to reduce mycelial growth (Fiori et al., 2000), and inhibit
spore production and germination (Fiori et al., 2000; Oluma and
Garba, 2004). Some of the studies of antimicrobial effects of
eucalyptus oils are listed in Table 3.
Ramezani et al. (2002a,b) showed that volatile oil from lemon-
scented eucalyptus and its major constituent monoterpene
citronellal possessed a wide spectrum of fungicidal activity and
inhibited the radial growth and dry weight of six phytopathogenic
fungi. Recently, Lee et al. (2007) demonstrated that lemon-scented
eucalyptus oil (at 10
m
ll
1
air) controlled the apple gray mold by
70%. Cermelli et al. (2008) screened E. globulus oil against 120
isolates of Streptococcus pyogenes, 20 isolates of S. pneumoniae,40
isolates of S.agalactiae, 20 isolates of Staphylococcus aureus,40
isolates of Haemophilus influenzae, 30 isolates of H. parainfluenzae,
10 isolates of Klebsiella pneumoniae, 10 isolates of Stenotropho-
monas maltophilia and a strain each of adenovirus and mumps virus
and reported that H. influenzae,H. parainfluenzae, and Stenotro-
phomonas maltophilia and Streptococcus pneumoniae are very
susceptible. The study concluded that eucalyptus oil could be
used for the control of respiratory tract bacteria.
Su et al. (2006) demonstrated the antifungal activity of essential
oils from Eucalyptusgrandis,E. camaldulensis,andE. citriodoraagainst
the mildew and wood rot fungi viz. Aspergillus clavatus,A. niger,
Chaetomium globosum,Cladosporium cladosporioides,Myrothecium
verrucaria,Penicillium citrinum,Trichoderma viride,Trametes versi-
color,Phanerochaete chrysosporium,Phaeolus schweinitzii and Lenzites
sulphureus. Based on the study, the authors opined that essential oil
from E. citriodoracould be an excellent choice as a wood preservative
and preservation of leather goods and wood artifacts.
Cimanga et al. (2002) demonstrated the antibacterial activity of
essential oil extracted from Eucalyptus camaldulensis,E. tereticornis,
E. alba,E. citriodora,E. deglupta,E. globulus,E. saligna, and E. robusta
against Pseudomonas aeruginosa. They concluded that composite
essential oils were more effective than the additive activity of their
major constituents such as 1,8-cineole,
a
-pinene, and p-cymene.
Recently, Tzortzakis (2007) demonstrated that essential oil
vapours from E. globulus offer a good choice for maintaining
postharvest freshness and firmness of strawberry and tomato
during storage and transit. Further, no change was observed in
sweetness, and organic acid and total phenolic content upon
exposure to oil vapours (Tzortzakis, 2007).
Further, studies have also documented that eucalyptus
essential oils are effective even against resistant strains of
microbes. For example, Sherry et al. (2001) demonstrated that a
topical application of eucalyptus oil can effectively remove the
methicillin resistant Staphylococcus aureus infection. Trivedi and
Hotchandani (2004) showed that strains of Klebsiella spp., Proteus
spp., Pseudomonas spp., Escherichia coli, and Staphylococcus aureus
resistant to conventional antimicrobials (tobramycin, gentamicin,
amikacin, ciprofloxacin, chloramphenicol and cefotaxime) were
inhibited by the commercially available eucalyptus oil containing
63% 1,8-cineole. Eucalyptus oils not only show toxicity against a
wide range of fungi and bacteria but also possess antiviral activity.
For example, Schnitzler et al. (2001) reported that eucalyptus oil
exhibits in vitro anti-herpes virus activity.
7. Herbicidal activity of eucalyptus oils
Essential oil extracted from Eucalyptus species exhibit phyto-
toxicity against weeds and have a great potential for weed
management (Kohli et al., 1998; Singh et al., 2005; Batish et al.,
2007; Setia et al., 2007).
Kohli et al. (1998) reported that essential oil from E. tereticornis
and E. citriodora when applied in vapour form significantly
decrease the germination of noxious weed Parthenium hyster-
ophorus. Further, fumigation of mature plants with eucalyptus oil
vapours reduced growth, chlorophyll and water content, and
decreased cellular respiration. The inhibitory activity of oil was
time-dependent and gradual decline in weed growth was observed
with increasing period of oil exposure. Fifteen days after
fumigation, plants showed various levels of visible injury in terms
of chlorosis, necrosis, and tissue damage, and even complete
wilting that varied with source of oil and period of exposure (Kohli
et al., 1998). The essential oil from E. citriodora was more toxic than
that of E. tereticornis and it was attributed to the variability in their
chemical constitution. The study concluded that eucalyptus oil is
promising for weed management provided the economics of their
extraction and application are thoroughly worked out (Kohli et al.,
1998). However, they did not evaluate the toxicity against other
associated plants and non-target organisms.
Further studies were conducted to determine the impact of
essential oil extracted from E. citriodora against several crops such
as Triticum aestivum,Zea mays,Raphanus sativus, and weed plants
Cassia occidentalis,Amaranthus viridis and Echinochloa crus-galli
(Batish et al., 2004). It was demonstrated that eucalyptus oil
exhibit a species-specific toxicity and the toxic effect was more on
small-seeded crops like A. viridis compared to large-seeded R.
sativus. Further, when the toxicity of oil was evaluated against 4-
week-old weeds under greenhouse conditions, it was observed
that growth reduction was more in broad-leaved C. occidentalis
than in grassy weed—E. crus-galli. A higher toxicity of eucalyptus
oil from E. citriodora was not surprising since citronellal (a major
component of E. citriodora essential oil; Batish et al., 2006) is more
toxic against broad-leaved (dicot) weeds than towards grassy
(monocot) weeds (Singh et al., 2002, 2006).
Later, the herbicidal potential of eucalyptus oil (0–100
m
lml
1
)
used as a spray treatment was evaluated against P. hysterophorus
(Singh et al., 2005) and Phalaris minor (Batish et al., 2007) under
screenhouse studies. It was observed that at lower concentrations
(50
m
lml
1
) the toxic effect was less and reversible, whereas at
higher concentrations (50
m
lml
1
) it was irreversible especially
at concentrations 100
m
lml
1
. The plants visibly looked wilted
initially and exhibited complete mortality with passage of time.
The oil treated plants showed a significantly higher degree of ion
leakage indicating a loss of membrane permeability and leading to
severe plant damage. The authors concluded that eucalyptus
essential oil possess herbicidal potential and could be incorporated
as a bioherbicide under Integrated Weed Management Pro-
grammes (IWMPs).
Though studies described above have evaluated phytotoxic/
herbicidal potential of eucalyptus oil against weeds, yet much
needs to be done as far as commercialization of this oil is
concerned. There are many constraints such as: inconsistency in
the amount of oil that varies with season, changing climate, species
and even with age (Batish et al., 2006), volatililty of the oil and its
components, lipophilicity, difficulty in plant uptake, effectivity
under field conditions and toxicity towards non-target plants.
Nevertheless, the oil could be a viable option to replace synthetic
herbicides under sustainable organic farming practices.
8. Acaricidal activity of eucalyptus oils
Essential oils and their components can be effectively used to
dispel ticks and mites, both parasitic and free-living (Yatagai,
1977; Saad et al., 2006). Eucalyptus oils rich in cineole have been
D.R. Batish et al. / Forest Ecology and Management 256 (2008) 2166–2174
2170
shown to be effective against varroa mite, Varroa jacobsoni—an
important parasite of honeybee (Calderone and Spivak, 1995),
Tetranychus urticae and Phytoseiulus persimilis (Choi et al., 2004)
and Dermatophagoides pteronyssinus (Saad et al., 2006). Based on
their study, Choi et al. (2004) concluded that eucalyptus essential
oils could be used as a natural acaricide for the control of T. urticae.
Chagas et al. (2002) evaluated the biocidal activity of essential oils
from Eucalyptus citriodora,E. globulus and E. staigeriana against the
tick—Boophilus microplus and concluded that eucalyptus oils could
be used as an ecologically and environmentally safer acaricide.
Gardulf et al. (2004) demonstrated the Citriodiol
1
, a Eucalyptus
essential oil based commercially available product, significantly
reduced the number of tick bites in humans and concluded that it
could be used to reduce tick-borne infections.
9. Nematicidal activity of eucalyptus oils
Plant-parasitic nematodes are another major group of plant
pests and infest all the food crops including vegetables and cause
huge economic loss due to reduced yield and unmarketable
produce. As per an estimate, the annual global crop loss due to
parasitic nematodes is in the order of US$ 78 billion. Eucalyptus
oils have also been shown to possess nematicidal activity. Pandey
et al. (2000) demonstrated that essential oil (at 250 ppm) from E.
citriodora and E. hybrida was highly toxic to Meloidogyne incognita
and inhibited the growth of root-knot nematode at 250 ppm.
Salgado et al. (2003) showed that essential oils from Eucalyptus
camaldulensis,E. saligma,E. urophylla cause mortality and hatching
of second stage-juveniles (J2) of Meloidogyne exigua of coffee and
concluded that essential oil contain nematicidal compounds.
Recently, Ibrahim et al. (2006) reported that eucalyptus essential
oil is toxic to the second-stage juveniles (J2s) of root-knot
nematode Meloidogyne incognita.
10. Toxicological and commercialization concerns
As regards the toxicity of eucalyptus oils, not much is known;
however, they have been categorized as GRAS by USEPA. Further,
the oral and acute LD
50
of eucalyptus oil and 1,8-cineole to rat is
4440 mg/kg bodyweight (BW) and 2480 mg/kg BW (Regnault-
Roger, 1997), respectively, making it much less toxic than
pyrethrins (LD
50
values 350–500 mg/kg BW; USEPA, 1993) and
even technical grade pyrethrum (LD
50
values 1500 mg/kg BW)
(Casida and Quistad, 1995).
Since eucalyptus oils possess a wide spectrum of biological
activity and are regarded as safer compounds, there have been
attempts to commercialize and market the insecticides/repellent
products containing eucalyptus oil as such or based upon them.
Crude eucalyptus oil was first registered as an insecticide and
miticide in US in 1948 and 29 such compounds have been
registered in US till the year 2007 for use as natural insecticide/
insect repellent/germicide (Kegley et al., 2007). Of these, only 4
products have been active and 25 have been cancelled (Kegley
et al., 2007). These include Citriodiol1, Repel essential insect
repellent lotion (2 variants), Repel essential insect repellent pump
spray and Repel insect repellent 30 by the United Industrial Corp.,
USA (Kegley et al., 2007). In the year 2005, eucalyptus oil ranked
4th (50 pounds) among the largely used insecticides for repelling
insects from beehives (Kegley et al., 2007).
Quwenling is another Eucalyptus-based product that has been
successfully marketed as an insect-repellent in China (Trigg,
1996a). It provides protection against Anopheles mosquitoes
parallel to DEET (N,N-Diethyl-meta-toluamide) and has, in fact,
replaced the widely used synthetic repelleant dimethyl phthalate.
Quwenling contains a mixture of p-menthane-3,8-diol (PMD),
citronellol and isopulegone (Trigg, 1996a). Mosiguard Natural is
another eucalyptus oil based repellent that is marketed and
contains 50% eucalyptus oil (Trigg and Hill, 1996). Buzz Away is
another commercially available repellent based on citronellal and
is marketed in China (Chou et al., 1997). MyggA1Natural is
another mosquito repellent product based on PMD from lemon
eucalyptus and is shown to repel ticks (Jaenson et al., 2006). In fact,
lemon eucalyptus oil and PMD are two plant based insect-
repellents approved by USEPA for protection against mosquitoes
(USEPA, 2007). PMD is a volatile compound naturally occurring in
lemon eucalyptus plants and now chemically synthesized. It has
been used on human clothes and skin to repel insects such as
mosquitoes, biting flies, and gnats (USEPA, 2000). It has no or very
little toxicity to the environment and poses no risks to humans and
animals. It has been developed and registered for use against
public health pests and is available as a spray and lotion (USEPA,
2000).
Though no herbicide containing eucalyptus oil has been
introduced/commercialized; yet, a natural herbicide cinmethylin
based on the chemistry of 1,8-cineole, one of the major constituent
monoterpenes, has been manufactured and marketed as Cinch1
(Grayson et al., 1987).
The lesser number of commercialized products based on
eucalyptus oil in spite of the huge scope and market for the
natural pesticides is largely due to strict market regulations
including actual toxicological evaluation against non-target
organisms, product standardizations due to variation in quality
of available plant material, intellectual property right (IPR)
concerns, and regulatory approvals that limit their commercializa-
tion (Isman, 2006). Further, registration of new products involves
highly expensive regulatory approval procedures that cannot be
met by small profits made from the use of these pesticides in
greenhouses under organic farming practices (Isman, 2006).
Additionally, the issues of product refinement and standardization
also limit the potential of essential oil based pesticides, because the
quality of the essential oils varies with season, climate, age,
geographical region, and genetic makeup of the plant (Isman, 2000,
2006).
Another drawback of these essential oils is that they volatilize
quickly in the environment and do not persist for longer duration
unlike synthetic pesticides. It results in their continuous reappli-
cations to get the desired results and thus limiting their potential
use as pesticides. Anyhow, their use is likely to be more effective
under long-term basis since insect pests have developed resistance
against synthetic pesticides. Rather, the essential oils have been
found useful against those species of pests, which are resistant
towards synthetic pesticides. Moreover, since these essential oils
are a complex mixture of components including minor constitu-
ents, in contrast to synthetic pesticides based on single products,
they act synergistically within plant as a defense strategy, it is
likely that they are more durable towards evolving pest resistance
(Feng and Isman, 1995). However, due to their largely environment
friendly nature, they can be efficiently used for pest management
in urban areas, homes and other sensitive areas such as schools,
restaurants and hospitals (Isman, 2006). More so, the real benefit of
these natural pesticides could be harnessed by the farmers in
developing countries who cannot afford costly synthetic pesticides
and those involved in organic farming and greenhouse production
systems (Isman, 2006).
11. Conclusions and way forward
From the above discussion, it is clear that eucalyptus essential
oils possess a wide spectrum of biological activity against fungi,
bacteria, insects, mites, and weeds and provides a simple,
D.R. Batish et al. / Forest Ecology and Management 256 (2008) 2166–2174
2171
inexpensive, and environment friendly (non-polluting and lesser
or no toxicological concerns) alternative pest control. Since
eucalyptus oils have a strong toxicity in the vapour form against
a wide range of microbes and insects, they could be commercially
exploited as a fumigant for stored products and also impregnated
into packaging thus preventing the insect infestation. However, the
effects on other non-target microorganisms including pollinators,
honeybees and natural predators/enemies have not been yet
evaluated. Further, experiments are needed to evaluate its
economic aspects and activity under field conditions. The volatility
and water-insolubility renders the utilization of eucalyptus oils to
control nematodes, soil-borne pathogens and weeds under field
conditions less appealing. However, it could be overcome by
emulsifying the oil with the help of surfactants or using adjuvants
for better plant adsorption and improving efficiency.
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