Eucalyptus Oil: Extraction, Analysis, and Properties for Use in Pest Control

Authored by: Hamir Singh Rathore , Leo M.L. Nollet

Green Pesticides Handbook

Print publication date:  May  2017
Online publication date:  July  2017

Print ISBN: 9781498759380
eBook ISBN: 9781315153131
Adobe ISBN:




Eucalyptus is a diverse genus of trees (rarely shrubs). It is native of Australia. There are more than 800 species of Eucalyptus, mostly native to Australia. A few native species are found in parts of adjacent New Guinea and Indonesia. A very small number of native species are also found in a distant country, the Philippines. The Eucalyptus genus is a part of the myrtle family (Myrtaceae), which is a family of dicotyledon plants, that is, flowering plants. The seed of this family of plants typically contains two embryonic leaves or cotyledons.

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Eucalyptus Oil: Extraction, Analysis, and Properties for Use in Pest Control

3.1  Introduction

Eucalyptus is a diverse genus of trees (rarely shrubs). It is native of Australia. There are more than 800 species of Eucalyptus, mostly native to Australia. A few native species are found in parts of adjacent New Guinea and Indonesia. A very small number of native species are also found in a distant country, the Philippines. The Eucalyptus genus is a part of the myrtle family (Myrtaceae), which is a family of dicotyledon plants, that is, flowering plants. The seed of this family of plants typically contains two embryonic leaves or cotyledons.

Eucalyptus is also known as gum tree [1]. The Myrtaceae is a family of evergreen trees and shrubs. Eucalyptus plants vary in size from shrub to tree. Commonly, most eucalyptus shrubs grow to heights of 6–25 feet, with a spread of between 5 and 10 feet. Eucalyptus shrubs grow upright with an open shape. The foliage is paired, with apposite blue-green leaves. Some species of eucalyptus shrubs, such as E. globulus, commonly known as Tasmanian blue gum, are invasive plants that are not ideal for garden landscapes.

The Tasmanian blue gum, southern blue gum, or blue gum (E. globulus) typically grows from 30 to 55 m (98–180 feet) tall. The tallest currently known specimen in Tasmania is 90.7 m (297 feet) tall. It has also been reported that even taller trees are known (101 m or 330 feet). The natural distribution of the species includes Tasmania and southern Victoria (particularly the Otway Ranges and southern Gippsland). The species also occurs rarely on King Island and Flinders Island in Bass Strait and on the summit of You Yangs near Geelong. There are naturalized nonnative occurrences in Spain, Portugal, Akmas, and other parts of southern Europe, southern Africa, New Zealand, western United States (California), Hawaii, Micronesia, Caucasus (western Georgia), and Asia (India).

The d’Entrecasteaux expedition made immediate use of the species when they discovered it. Its timber was used to improve their oared boats. The Tasmanian blue gum was proclaimed as the floral emblem of Tasmania on November 27, 1962. The species name is from the Latin globulus, “a little button,” referring to the shape of the opercula.

Eucalyptus trees are used primarily for their wood, and they also provide other products, including oil, which is used for a variety of industrial and pharmaceutical purposes. Most species of eucalyptus trees produce some essential oil, but only about 20 have commercially viable concentrations of oil in their leaves. Several hundred species of Eucalyptus have been found to contain volatile oil. The following species are utilized currently in different countries:

  • E. globulus Labill (Tasmanian blue gum) in the People’s Republic of China, Portugal, Spain, India, Brazil, Chile, Bolivia, Uruguay, and Paraguay
  • E. smithii R. Baker (gully gum) in South Africa, Swaziland, and Zimbabwe
  • E. polybractea R. Baker (syn. E. fruticetorum F. Muell. ex Miq.) (blumallee) in Australia
  • E. exserta F. Muell (Queensland peppermint) in the People’s Republic of China
  • E. radiate Sieber ex DC (syn. E. australiana and E. radiata var. australiana) (narrow-leaved peppermint) in South Africa and Australia
  • E. dives Schauer (cineole variant) (broad-leaved peppermint) in Australia
  • E. camaldulensis Dehnh (syn. E. rostrate Schdl.) (river red gum) in Nepal

Other species, such as E. cinerea and E. cineorifolia, has also been used for medical purposes, while E. macarthurtii has been used in perfumery in the past. E. citrodora Hook (lemon-scented gum) and E. staigeriana F. Muell. ex Bailey (lemon-scented ironbark) are being used currently in perfumery in the People’s Republic of China, Brazil, and India.

The deliberate introduction of eucalyptus to other parts of the word, as an invasive species, has sometimes resulted in unintended consequences, including deadly wild fires, reduced habitat for native plants and animals, and reduction of valuable wetland.

As stated above, several species of Eucalyptus are known. A good number of publications are available on each species.

3.2  Eucalyptus melliodora

E. melliodora is a species of trees. There are more than 800 species of eucalypts, and almost all of them are in Australia. Eucalyptus can be found in almost every part of Australia, and the species is adapted to many different habitats. Eucalyptus is one of three similar genera that are commonly referred to as “eucalypts,” the other being Corymbia and Angophora. They are also known as gum tree because they exude copious sap from any break in the bark. Eucalypts have many local names, like “gum trees,” “melee,” “box,” “ironbark,” “stringybark,” and “ash.”

3.2.1  Flowers and Leaves

Eucalypts have special flowers and fruits that no other trees have. When they flower, a bud cap made of petals grows around the flower until it is ready to open. Then, the bud cap falls off to reveal a flower with no petals.

The woody fruits are called gumnuts. They are roughly cone shaped and open at one end to release the seeds. Almost all eucalypts are evergreen. However, some tropical species lose their leaves at the end of summer. The leaves are covered with oil glands. The shape of the leaves of the older eucalypts differs with time. The leaves of eucalypts of a few years old become longer and spearhead or sickle shaped. Some species keep the round leaf shape throughout their life span. In most cases, their flowering starts when adult leaves begin to appear.

3.2.2  Bark

There is a different type of bark on different species of eucalyptus trees. Some trees have smooth bark at the top but rough bark lower down. In smooth-barked trees, most of the bark falls off the tree, leaving a smooth surface that is often colorfully marked. The bark dies every year. With rough-barked trees, the dead bark stays on trees and dies out. Eucalyptus trees are classified in the following groups on the basis of their kind of bark. The classification allows for easy understanding of different species of Eucalyptus for better usage.

  • Stringybark: It consists of strands that can be pulled off in long pieces. It is usually thick with a spongy texture.
  • Ironbark: It is hard, rough, and deeply furrowed. It is soaked with dried sap exuded by the tree, which gives it a dark red or even black color.
  • Tessellated: Its bark is broken up to many distinct flakes. These flakes are like cork and can flake off.
  • Box: It has short fibers.
  • Ribbon: It has the bark coming off in long thin pieces but still loosely attached in some places; can be long ribbons, firmer strips, or twisted curls.

3.2.3  Tall Timer

Currently, specimens of the Australian “mountain ash” are among the tallest trees (92 m) in the world [1] and the tallest of all flowering plants, such as coast redwood, that is, conifers.

3.2.4  Frost

A few eucalypts, the hardiest eucalyptus, which are known as snow gums, such as E. pauciflora, are capable of withstanding cold and frost (–20°C). Two subspecies (wild varieties) of this tree can survive even colder winters. However, most eucalypts cannot survive frost, or they can only survive light frost (–3°C to –5°C). Several other species, especially from the high plateau and mountains of central Tasmania, have produced extreme cold-hardy forms. The seeds of these hardy strains are planted for ornamental trees in colder parts of the world.

3.2.5  Animal Kingdom

It is known that essential oil obtained from eucalyptus leaves is a strong, natural disinfectant, so it is used in some medicines. Eucalyptus oil at high concentration is poisonous, and it is also used as a pesticide. Several marsupials, such as koalas and some possums, are partly resistant to eucalyptus oil. These animals can recognize which plants are safe to eat by their smell. Eucalypts make a lot of nectar, which provides food for many insects.

3.2.6  Dangers

All branches of eucalypts drop off as they grow, so eucalypt forests are littered with dead branches. As a result, a large number of tree-felling workers are killed by falling branches. Many deaths are caused by simple camping under eucalypts. The camping is made as trees shed whole and very large branches above the soil to save the water of this soil during droughts. Therefore, the Australian ghost gum eucalyptus is also called “widow maker.”

3.2.7  Fire

In summer or on hot days, eucalyptus oil (essential oil) vapor rises above the bush to create the well-known distant blue haze of the Australian landscape. The essential oil catches fire very easily, and bush fires can move rapidly through the oil-rich air of the tree crowns. The fallen leaves and branches and dead bark are also flammable. Most species are dependent on trees for spread and regeneration, and eucalypts are well adapted for periodic fires. They regenerate in several ways [2]: (1) by sprouting from underground tubers [3], (2) through hidden buds under their bark, and (3) from seeds sprouting from underground in the ashes after fire has opened them.

3.2.8  Fire and the Growth of Eucalypts

As stated above, eucalypts grow back quickly after fire. When the first humans arrived about 50,000 years ago, fires became much more frequent and the fire-loving eucalypts increased many times, for roughly 70% of the Australian forest. On the other hand, valuable timber trees, such as alpine ash and mountain ash, are decreased drastically as they are killed by fire and only grow back from fresh seeds.

3.3  Uses and Abuses of Eucalypts

  • Eucalypts are important because of their fast growth, especially for providing wood that is a dire need of people.
  • They are also planted in parks and gardens to provide timber, firewood, and pulpwood.
  • Eucalypts take a very large quantity of water from the soil. Therefore, they are planted in some areas to lower the water table and reduce the salt concentration in the soil.
  • Eucalypts have also been used in malaria eradication by draining the soil in places such as Algeria, Sicily [3], and California [4]. Drainage removes swamps, which provide a habitat for mosquito larvae. But such drainage may also destroy harmless habitats.
  • Eucalyptus oil is used for many purposes [5,69]—for cleaning and deodorizing, as in traces in food supplements such as sweets, cough syrups, and decongestants. It is also used as an insect repellent [5]. The oil also has therapeutic, perfumery, flavoring, antimicrobial, and biopesticide properties [69].
  • Tasmanian blue gum leaves are used as a therapeutic herbal tea. In India, it is part of green tea [10].
  • E. globulus bark contains various phenolics, such as guinic, dihydroxyphenylacetic, and caffeic acids; methylellagic acid (MEA)–pentose conjugate, and so forth [11].
  • The nectar of eucalyptus produces a high-quality honey that is known for its buttery taste. In fact, eucalyptus flowers in late January, before the flowering of other nut and fruit trees in the United States.
  • The ghost gum’s leaves were used by Aborigines to catch fish. Aqueous extract of eucalyptus leaves are a mild tranquilizer that stuns fish, making them easy to catch.
  • Eucalyptus is also used to fabricate the didgeridoo, a musical wind instrument. It was popularized by Aborigines.
  • Eucalypts are grown on plantations in many parts of the world, including the United States, Brazil, Morocco, Portugal, South Africa, Israel, and Spain, to obtain pulpwood for the production of paper and eucalyptus oil.
  • Eucalyptus wood for energy is considered to hold great potential as a renewable energy source [12].
  • Most species have been found to be invasive (spreading out of the area they are planted in), and they are developing hazards for local flora and fauna (wildlife).

3.4  Worldwide Cultivation of Eucalyptus

A botanist, Sir Joseph Banks, was the first to introduce eucalyptus to other parts of the world on the Cook expedition in 1770. It has since been planted in several parts of the world.

3.4.1  Spain

Eucalypts are planted in pulpwood plantations in place of the native oak woodland in Spain. The native woodland was supportive to native animal life, while the eucalypt groves are totally unfavorable to local wildlife. Therefore, there is a decline of wildlife population that is leading to silent forests. Eucalyptus helps some industries, such as sawmilling, pulp, and charcoal producing.

3.4.2  California

In the 1850s, many Australians reached California to participate in the California gold rush. The climate of a great part of California is similar to that of most areas of Australia. So, some people planned to introduce eucalyptus in California. By the early 1900s, eucalyptus was planted in thousands of hectares with the encouragement of the state government, which was hopeful to have a renewable source of timber for construction and furniture purposes. However, it was not possible for two reasons: (1) the trees were cut when they were too long, and (2) the Americans were untrained in processing trees to prevent the wood from twisting and splitting [13]. Mainly the blue gum, a kind of eucalyptus, was found useful in providing windbreaks for highways, orange groves, and other farms in the treeless central part of the state. In many cities and gardens, eucalyptus was admired as ornamental trees and used for shade.

Eucalyptus forests in California have been discarded due to the fact that they drive out the native plants and do not support native animals. They also create fire problems. For example, in 1991 a firestorm destroyed about 3000 homes and killed 25 people in Oakland Hills [14]. As a result, in some parts of California, eucalyptus forests are being replaced by native trees and plants. In order to save the flora and fauna, some eucalypts are being destroyed by insects managed from Australia [15].

3.4.3  Brazil

In 1910, eucalyptus was introduced in Brazil in order to fulfill the requirement of the timber and charcoal industry. Unfortunately, the aftereffects of high consumption of water by eucalyptus were not studied. It causes the soil to dry out, killing many local native plants on which the fauna survive.

3.4.4  India

E. tereticornis and Eucalyptus hybrid are the two most widely planted eucalypts in India. The species have spread to most parts of the country. Gujarat took the lead in this direction and was followed by Karnataka, Punjab, Haryana, Uttar Pradesh, and other states. Further, farmers went ahead in states such as Gujarat, Haryana, and Punjab in raising irrigated plantations, and the concept of high-density plantations evolved as a suitable alternative to agricultural crops. Unfortunately, this has not had much success. This futile approach was tested because of the versatile nature and amenability of eucalyptus for harvesting in short rotations. Because of the green revolution, India is self-sufficient in food grains, but there is an acute shortage of fuel. In India, despite the unclear situation regarding water requirements, particularly in semiarid areas, eucalyptus has commercial acceptability and is being grown for various purposes, namely, paper and pulp, honey and oil, rural small-scale industries, timber, poles (eucalyptus poles are good for transmission purposes and are also used in the construction of dwelling houses), charcoal, and fuel. Eucalyptus is a versatile, fast-growing, and strongly coppicing tree possessing a wide range of soil and climatic adaptability. Basically, a light demander, the growth of the species is very much reduced under shade. Eucalyptus is known for its drought hardiness. The species is also moderately salt tolerant and relatively fire resistant. Eucalyptus is generally regarded as frost sensitive. There is an impression that eucalypts and wildlife do not go together. While it is true that the natural forest is a better habitat for wildlife, eucalyptus plantation also supports wildlife in places where there is acute deforestation due to a low water table and shortage of rain.

In India, eucalyptus was first planted around 1790 by Tippu Sultan, in his garden on Nandi Hills near Bangalore. The sultan obtained seed from Australia and grew about 16 species of eucalyptus [16]. Subsequently, eucalyptus was planted in Nilgiri Hills, Tamil Nadu, in 1843, and then from 1856, the regular plantation of E. globulus was raised to meet the demand for firewood [17]. There were several other attempts to introduce eucalypts in different parts of the country. Today, in fertile land eucalypts have been ignored due to their excessive water absorption tendency and unfriendly nature to native flora and fauna.

About 170 species, varieties, and provenances of eucalypt were tried in India; out of this number, the most sustainable and favorable has been E. hybrid, a form of E. tereticornis that is known as Mysore gum. In India, it has been found to be fast growing, capable of overtopping weeds, fire hardy, and browse resistant; it coppices well; and it has adaptability to a wide range of edaphoclimatic conditions [11 , 18]. Other species that are grown on a plantation scale are E. grandis, E. citriodora, E. globulus, and E. camaldulensis.

3.5  Eucalyptus Oil

3.5.1  Methods of Extraction

Many techniques are available for the extraction of essential oil. One technique may produce nicer-smelling oil, while another gives oil with greater aromatherapeutic value. It turns out that essential oil production, like wine making, is an art form as well as a science. Therefore, the procedure applied for oil extraction from plants is important because some processes use solvents that can destroy the therapeutic properties. Some plants, especially flowers, do not lend themselves to steam distillation. Their fragrance and therapeutic essences cannot be completely released by water. For example, jasmine oil and rose oil are often found in “absolute” form. Thus, selection of the method is based on the experience of the user, as well as the application of the product. Therefore, each method has its own merit and importance in the processing of aromatherapy-grade essential oil. For a description of the techniques (maceration, expression method, cold pressing, distillation, hydrodistillation, steam distillation, turbo distillation, extraction with volatile solvent, and supercritical carbon dioxide extraction), the reader is directed to Chapter 1.

3.6  Extraction of Eucalyptus Oil

Generally, the fresh or partially dried leaves and young twigs are steam distilled to extract eucalyptus oil. E. globulus is the primary source of global eucalyptus oil production. China is the largest commercial producer of this oil [19,20]. The oil yield ranges from 1.0% to 2.4% (fresh weight). It contains cineol as its major part. It is virtually phellandrene-free, a necessary characteristic for internal pharmaceutical use [21]. In 1870, Cloez identified and ascribed the name eucalyptol; now it is more often called cineole. It is the dominant portion of E. globulus oil [21]. Eucalyptus oil is a complex product. It is made up of many, sometimes hundreds, distinct molecules that come together to form the oil’s aroma and therapeutic properties. Most of these molecules are fairly delicate, so their structure may be altered or they may be converted into simple molecules. Therefore, a given method of extraction may give more complete oil, or it may lead to the accumulation of more artifacts than normal. Several papers are published in the literature on methods used for the extraction of eucalyptus oil. A few selected publications are summarized in the following paragraphs.

Fadel et al. have studied [22] the effect of extraction techniques such as hydrodistillation and supercritical fluid extraction (SFE) on the composition of eucalyptus oil. They found that the oil obtained by SFE possesses higher antioxidative activity than the HD extract. Two compounds, p-cymen-7-ol and thymol blue, present in eucalyptus oil are responsible for the antioxidative activity. A newly identified compound, p-cymen-7-ol, in the leaves of eucalyptus species exhibited superior antioxidative activity compared with butylated hydroxyanisol.

The hydrodistillation described in the European Pharmacopoeia [23] has been applied for the isolation of essential oils from eucalyptus leaves collected in Australia and two species, E. cinerea and E. globulus, obtained from a botanical garden in Jena, Germany.

Robinson [24] has suggested the following procedure for the extraction of eucalyptus oil: Load about 8 tons of fresh, uncompressed eucalyptus leaves in a large vat with a series of steam pipes that run along its bottom. Secure the lid tightly to the vat with locking clamps. Turn the boiler on and begin feeding steam through the pipes at the bottom of the vat. This will cause steam to pass through the leaves, which will vaporize the essential oils in the leaves. This vaporization process requires 3–4 hours and will leave black liquor, which will drain through a hole in the bottom of the vat. Collect the eucalyptus vapor through outlets at the top of the vat. The vapor will collect in a central pipe that is surrounded by pipes that contain cold water. The water circulates through this condenser and cools the vapor back to a liquid state. Drain the condensed distillate into a collection vessel. The distillate contains a water and oil component that will eventually separate. The oil may then be skimmed off the surface. Pour the oil into drums for further refinement. Rectify the unrefined eucalyptus oil. This is a more specific type of distillation that includes the use of chemical reagents that remove the impurities in the eucalyptus oil.

3.7  Mechanisms of Steam Distillation of Eucalyptus Oil

It is known that steam distillation may provide a temperature that is substantially below that of the boiling point of the individual constituent. This is a basic requirement when dealing with temperature-sensitive material like essential oil, which is insoluble in water and may decompose at its own boiling point. Eucalyptus oil contains compounds possessing boiling points up to 200°C or higher. In the presence of the aqueous phase (either water or steam), these compounds volatilize at a temperature close to 100°C at atmospheric pressure. Hence, it seems that there is still a need to carry on more research work in order to develop advanced techniques, such as hydrodiffusion, a sort of inverse steam distillation, in which steam is introduced at the top of the organic material–packed chamber, and oil and condensate are obtained from the bottom. The product obtained contains higher ester contents due to less thermally induced hydrolysis.

Therefore, fresh or dried eucalyptus leaves are placed in the plant chamber of the still, and the steam is allowed to pass through the leaves under pressure. The steam treatment softens the cells and allows the oil to escape in vapor form. The steam temperature is regulated to a temperature that is high enough to vaporize the oil, but not too high to burn the leaves or oil. The steam carries the vapors of essential oil through the condenser. Ultimately, the essential oil layer floats on the water surface, which may be separated by decantation or skimmed off.

Thus, a number of factors (including the quality of the leaves, the quality of the equipment, and most important, time, temperature, and pressure) determine the final quality of steam-distilled oil. The color, odor, and therapeutic effects of the oil obtained depend on the technology of the distillation process.

3.8  By-Products of Eucalyptus Oil

The water obtained after decantation of oil, a by-product of distillation, is called floral water, distillate, or hydrosol. It possesses many therapeutic properties, so it is valuable in skin care for facial mists and toners. The chemical reactions that occur during steam distillation result in the formation of some artificial chemicals, which are called artifacts. The artifacts have been found to be useful in massage, as they possess mild antiseptic and soothing properties, as well as a pleasing floral aroma.

3.9  Physical Properties

Eucalyptus oil has a clear, sharp, pungent, and cooling taste, and a fresh and very distinctive smell (camphoraceous odor). It is a pale yellow liquid and is watery in viscosity. It is insoluble in water, miscible in alcohol having a high concentration or in anhydrous alcohol, and also miscible in oil, fats, paraffins, ether, chloroform, and glacial acetic acid. The boiling point of its major compound, cineole (eucalyptol), is 176°C–177°C.

3.10  Methods of Analysis of Eucalyptus Oil

Gas chromatography with fused-silica capillary columns is the routinely used technique in analyzing the essential oils. It can easily analyze major components of essential oil, which can be used to estimate the quality and quantity of the sample. The resolution of gas chromatography can be improved by using the chiral phase (cyclodextrin derivatives) in the column. Several new columns and detectors have been developed to make gas chromatography a commercial technique for the detection and estimation of the quality of eucalyptus oil on the spot; that is, the market value of the oil is decided on the basis of the chromatograph. A few recently reported papers on essential oils are summarized in the following.

Eucalyptus essential oil was extracted from E. globulus. It is also known as Tasmanian blue gum, southern blue gum, or blue gum. Gas chromatographic analysis shows [25] that the main components of eucalyptus oil are α-pinene (13.85%), β-pinene (0.78%), sabinene (—), limonene (4.31%), 1,8-cineole (67.67%), p-cymene (13.13), linalool L (—), terpinen-4-ol (—), α-terpineol (45.68%), α-terpinenyleacetate (—), d-carvone (—), α-phellandrene (—), aromadendrene (—), epiglobulol (—), piperitone (—), and globulol (—).

E. camaldulensis var. brevirostris leaves were extracted by hydrodistillation and supercritical fluid extraction. Both extracts were analyzed by gas chromatography with mass spectrometry (GC-MS), and 90 compounds were identified [22]. In both extracts, the main compounds were found to be β-phellandrene (8.94% and 4.09%), p-cymene (24.01% and 10.61%), cryptone (12.71% and 9.82%), and spathulenol (14.43%, 13.43%, and 13.14%). The yield of the monoterpene hydrocarbons in HD extract (0.288 g/100 g fresh leaves) was slightly higher than that in SFE extract (0.242 g/100 g fresh leaves). The SFE extract possessed a higher concentration of the sesquiterpenes, light oxygenated compounds, and heavy oxygenated compounds than the HD extracts.

A literature survey [26] shows that efforts have been made to analyze in situ the main components of eucalyptus oil by means of Raman spectroscopy. The two-dimensional Raman maps obtained by this method demonstrate a unique possibility to study the essential oil distribution in the intact plant tissue. Fourier transform (FT)–Raman and attenuated total reflection infrared (ATR-IR) spectra are recorded for essential oils isolated from several eucalyptus species by hydrodistillation. The density functional theory (DFT) calculations were made in order to interpret the spectra of the essential oils. It has been shown that the main components of essential oils can be recognized by both techniques by comparison of spectra obtained with the spectra of pure terpenoids. It has been found that the vibrational spectroscopic data are very comparable to those obtained by gas chromatography. Both complementary spectroscopic techniques have the potential to replace the existing standard procedures available for quality control purposes. It has also been claimed that both methods can be used in the flavor and fragrance industries, as well as in the pharmaceutical industry, in order to monitor fast quality checks of incoming raw materials and regular control of distillation processes. The in situ Raman procedure also provides the possibility of nondestructive analysis of essential oil cells in the intact plant tissue without sample preparation.

Krock et al. [27] have evaluated parallel cryogenic trapping multidimensional gas chromatography coupled with Fourier transform infrared spectrometry and mass spectrometry (MDGC-FT-IR-MS) for the analysis of essential oils. It has been found that MDGC-FT-IR-MS is a good tool to differentiate essential oils, and it can be used as a general method for the analysis of complex mixtures. The data obtained for an authentic sample and for known adulterated eucalyptus Australian oil can be used as the standard for analyzing the unknown samples, as well as for the samples from an unknown source. It has also been claimed that the presence of camphor or a combination of α-thujene, decane, sabinene, β-phellandrene, and γ-terpinene indicates the adulteration of eucalyptus oil.

Maciel et al. estimated the chemical composition of essential oils [28] from three species of plants belonging to the Eucalyptus genus [28]. GC and GC-MS were used to analyze E. staigeriana (I), E. citrodora (II), and E. globulus (III). Their percent composition obtained is given in the parentheses in places I, II, and III: α-pinene (3.27, 1.1, 4.15), o-cymene (1.75, —, 2.93), (+) limonene (28.82, —, 8.16), 1,8-cineole (5.39, 0.8, and 83.89), α-terpinolene (9.4, —, —), (–) isopulegol (—, 7.3, —), β-citronellal (0.8, 71.77, —), isopulegol (—, 4.3, —), Z-citral (—, 2.9, —), trans-geraniol (10.77, —, —), E-citral (4.2, —, —), methyl gernate (14.16, —, —), and geraniol acetate (3.66, —, —).

3.11  Composition of Eucalyptus Oil for Pharmaceutical Use

The properties and uses of the major constituents [25] of pharmaceutical British Pharmacopoeia (BP)-grade eucalyptus oil are discussed in the following. The required percentage of the constituent is given in parentheses.

  • 1,8-Cineole (eucalyptol), boiling point (b.p.) 174.4°C (at least 70%): This monocyclic monoterpene ether (oxide) is isomeric with α-terpineol, but contains neither a hydroxyl group nor a double bond. The oxygen atom in cineole is inert; for example, it is not attached by sodium or by usual reducing agents. The inertness suggests that the oxygen atom is of the ether type. It is colorless liquid with a light fresh eucalyptus fragrance and a spicy clean cooling taste. It is an antibacterial, cough suppressant, expectorant, nasal decongestant, and respiratory anti-inflammatory. It is also a flavor and fragrance and strong solvent and penetrating oil.
  • α-Pinene (up to 9%): This bicyclic monoterpene hydrocarbon has a dry woody, resinous-piney odor used in flavors and perfumery. It is mildly antibacterial and anti-inflammatory. It is also a disinfectant and deodorant. It is a strong natural solvent.
  • γ-Limonene (up to 12%): The monocyclic monoterpene hydrocarbon has the odor of orange–citrus. It is mildly antibacterial. It is a strong solvent used for the removal of oil and grease and in cleaning products, such as hand cleaners. Pure limonene oxidizes readily, and it is a skin and respiratory irritant. It is stable as a constituent of eucalyptus oil.
  • α-Terpineol: The monocyclic monoterpene alcohol is of lilac odor and strongly antibacterial. It is a common ingredient in perfumes, cosmetics, and flavors.
  • p-Cymene: The monocyclic monoterpene aromatic hydrocarbon has a strong aromatic hydrocarbon odor. It possesses good antibacterial activity and is used in soaps and preparations to help overcome undesirable odors.
  • Terpinen-4-ol: It is a tricyclic monoterpene alcohol that is colorless or with a pale yellow color, herbaceous peppery and woody odor.
  • Cuminal aldehyde: It is a colorless to yellowish oil liquid that possesses a strong persistent odor, acrid burning taste, and antibacterial activities.
  • Globulol: It is a tricyclic sesquiterpene alcohol with a sweet rose-like odor, and it is antibacterial.
  • p-Isoproplyphenol (australol): It is a phenol, and it is a very strong antibacterial.
  • Eudesmol: It is a bicyclic sesquiterpene alcohol that possesses mild antibacterial activity. It exists in α, β, and γ forms.
  • Aromadendrene: It is a tricyclic sesquiterpene hydrocarbon of a woody odor, and it possesses antibacterial as well as antifungal activity.

3.12  Common Uses of Eucalyptus Oil

  • Pharmaceutical-grade eucalyptus oil contains a wide range of natural compounds with a broad spectrum of antibacterial activity. Therefore, it is used in antiseptics, arthritis and sports muscular rubs, liniments, cough mixtures, and many other products.
  • Eucalyptus oil for commercial use is a lower-cost alternative to pharmaceutical-grade eucalyptus oil. It is a natural cleaner, freshener, disinfectant, sensitizer, and deodorizer. A water-soluble version is also available.
  • Eucalyptus oil for industrial use is an economical blend with a strong eucalyptus fragrance, especially for manufacturers to incorporate into their own formulations.
  • Special blends of aqueous solutions of eucalyptus are also available for specific purposes, such as body lotions and massage.
  • This oil possesses impressive therapeutic, perfumery properties. E. globulus oil has established itself internationally because it is virtually phellandrene-free, a necessary characteristic for internal pharmaceutical use [19]. In 1870, Cloez identified it and gave it the name EUCALYPTOL; now, it is commonly known as 1,8-cineole—the major portion of E. globulus [21].
  • The therapeutic properties of eucalyptus oil are analgesic, antibacterial, anti-inflammatory, antineuralgic, antirheumatic, antiseptic, antispasmodic, antiviral, astringent, balsamic, cicatrisant, decongestant, deodorant, depurative, diuretic, expectorant, febrifuge, hypoglycemic, rubefacient, stimulant, vermifuge, and vulnerary.

3.13  Pesticidal Properties and Uses of Eucalyptus Oil

  • It is formulated with other ingredients and applied locally to cattle horn stumps following dehorning [29].
  • E. cintrodora showed the highest mortality of the larval population of the root knot nematode, Meloidogyne incognita, at 100 ppm concentration after 48 hours [30].
  • As a nematicide, E. rudis showed significant activity at all dilutions (1:0, 1:1, and 1:2), while E. globulus showed activity at a lower concentration (1:2) for inhibition in the hatching of eggs of Meloidogyne javanica in vitro and in vivo and reduction of the number of knots.
  • The oral LD50 (mg/kg) for rat of 1,8-cineole is 2480, of eugenol for rat 2680, of thymol for mice 1800, and of menthol for rat 3180.
  • Eucalyptus oil (3%) can be used to control both hoppers and aphids with the least damage to natural enemies [31].
  • Eucalyptus oil possesses antimicrobial and biopesticide properties [21].

3.14  Mechanisms of Pesticidal Action of Eucalyptus Oil

Apart from essential oils used mainly in foods, the best-known essential oil worldwide might be eucalyptus oil, produced from the leaves of E. globulus [32]. Steam-distilled eucalyptus oil is used throughout Asia, Africa, Central and South America as a primary cleaning and disinfecting agent added to soap mop and countertop cleaning solutions; it also possesses insect and limited vermin control properties. Note that there are hundreds of species of eucalyptus, and perhaps dozens are used to various extents as sources of essential oils. Not only do the products of different species differ greatly in characteristics and effects, but also products from the very same tree can vary grossly.

The oils are generally composed [33,34] of complex mixtures of monoterpenes, biogenetically related phenols, and sesquiterpenes. Examples include 1,8-cineole, the major constituent of eucalyptus oil. They act as fumigant and contact insecticide. Their mode of action is neurological. They interfere with the neuromodulator octopamine [35] and GABA-gated chloride channels [36]. The purified terpenoid constituents of essential oils are moderately toxic to mammals, but with few exceptions, the oils themselves or products based on the oils are mostly nontoxic to mammals, birds, and fish [4]; therefore, they are called “green pesticides.” Eucalyptus oils are volatile, so they have limited persistence under field conditions. Therefore, although natural enemies are susceptible via direct contact, predators and parasitoids reinvading a treated crop 1 or more days after treatment are unlikely to be poisoned by residue contact, as often occurs with conventional insecticides.

3.15  Technology of Eucalyptus Oil as a Pesticide

In 2013, Mousa et al. [31] reported “the effect of garlic and eucalyptus oils in comparison to organophosphate insecticides against some piercing-sucking faba bean insect pest and natural enemies population.” They applied a 3% solution of dimethoate (30%), pestban (48%), garlic Allium sativa oil, and eucalyptus oil four times in each spray, and the samples were taken at the first, fifth, seventh, and tenth days after application to determine the reduction in numbers. The population of leafhoppers and plant hoppers was found to be reduced in the following order: garlic oil (68.07%) > dimethoate (67.90%) > pestban (64.02%) > eucalyptus oil (43.27%). Similarly, the efficiency for controlling aphids was found to be as follows: garlic oil (90.96%) > pestban (89.44%) > eucalyptus oil (80.66%) > dimethoate (76.14%). Garlic and eucalyptus oils were found to be superior to organophosphorus insecticides in partly maintaining the natural enemies. This suggests the possible use of eucalyptus oil in crop protection without environmental pollution.

The insecticidal effects [28] of E. straigeriana, E. citrodora, and E. globulus oils on eggs, larvae, and adults of Lutzomyia longipalpis have been assessed. In these in vitro tests, aqueous solutions of plant oils were used at concentrations of 20, 10, 5, 2.5, and 1.2 mg/ml (E. staigeriana) and 40, 20, 10, 5, and 2.5 mg/ml (E. citrodora and E. globulus). The eggs, larvae, and adults were sprayed with the oils. The hatched larvae were counted for 10 consecutive days and observed until pupation. Insect mortality was observed after 24, 48, and 72 hours. E. staigeriana oil was the most effective on all three phases of the insect, followed by E. citrodara and E. globulus oils. The major constituents of the oils were Z-citral and α-citral (E. staigeriana), citronellal (E. citrodora), and 1,8-cineole (E. globulus). This shows that eucalyptus oils may be used to control L. longipalpis—its chemical constituents are already known for their insecticidal activity—and these oils are produced on a commercial scale in Brazil.

3.16  Conclusion

Eucalyptus oil may be used as an effective green pesticide for organic food production. It might be a unique partner of future integrated pest management (IPM). The yield of eucalyptus oil ranges from 1.02% to 2.4% (fresh weight of leaves). A literature survey shows that there is a genuine interest in the harvest of eucalypts all over the world. Publications made by different countries in this area are in the following order: China > Portugal = India = South Africa > Australia > Chile = Spain = Brazil = other countries. In Asian countries, especially in India, overhasty plantation of eucalypts results in failure. The data available on the cultivation of eucalypts for wood and pulp are many folds more than that on the cultivation of eucalypts for oil production, while the market value of the latter is many times more than that of the former. This may be due to the fact that the former is easy to adopt and perform, and the latter requires skilled workers. The returns may be maximized on the eucalypts planted for the production of oil by understanding the effect of climatic and edaphic conditions, the selection of species, the application of fertilizers, the design of plantation (spacing, etc.), and the nutrient recycling. This work may be made easier by the collation of published and unpublished data that are at present scattered in the literature.


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