Medicinal and Aromatic Plants—Industrial Profiles


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part of The Gordon and Breach Publishing Group.

INSECT PESTS OF TEA TREE
105
a dull body with cream and green longitudinal stripes and a pointed tail that they raise in
defence when disturbed. Larval pupation occurs within the thick soft bark of mature trees,
in residual stumps or in fallen debris.
In plantations with short cutting cycles and complete removal of the above ground
biomass, sawflies are unlikely to become established. Plantations next to native stands should
be checked in late summer and autumn when adults could fly in and lay eggs that could lead
to larval defoliation. Neglected plantations could become a breeding site for sawflies in
time.
Moth Larvae
The larvae of loopers, leafrollers, leaftiers, etc. cause some defoliation. However, moth
larvae are often controlled when spraying for other pests such as P. tigrina, psyllids etc.
Loopers feed on exposed leaves and may be 30–40mm when fully grown. They arch up the
middle of the body into an inverted U-shape when moving. When disturbed they remain
attached at the rear and wave the front part of the body around.
The leaf-roller and tiers shelter during the day and emerge in the evening to feed.
Disturbance of the leaf shelters often causes the larvae to drop down on a silk thread.
Adult moths can have a wing span of up to 50mm and depending on species vary from
dark brown to creamy white, often with patterned fore and hind wings. They fly near dusk
and deposit eggs singly on leaves or stems.
Predatory bugs, e.g. Oechalia schellenbergi (Guérin-Méneville), exert significant control
on these moths, particularly the looper caterpillars. These bugs also prey upon the larvae of
P. tigrina, particularly late in the season. The potential of this bug is being investigated on a
large plantation producing oil to organic certification. Insectary produced bugs will augment
natural field populations.
INSECTS FEEDING ON WOOD AND BARK
Cerambycidae (Longicorn Beetles)
Too few beetles have been collected from plantations to form an opinion of the pest status
of this group. Longicorns feed on wood. In plantations the harvest schedule and the size of
the woody components are not conducive for these pests. Never-the-less plantations near
remnant native stands may find occasional beetles on plant stems. In the future the old cut
stems near ground level could act as an entry point for some cerambycids.
Weevils
A range of adult weevils, including Aades sp. and Amnemus quadrituberculatus (Boheman),
have been collected feeding on the bark of stems within plantations. Depending on the
density of adults and the extent of their feeding, stems can be ringbarked and die. The
incidence of weevil damage is increasing and these feeding sites may allow entry of spores
of Dothionella ribis, which can kill whole plants causing significant gaps within a plantation.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

A.J.CAMPBELL AND C.D.A.MADDOX
106
Successful control of weevils will depend on understanding the biology and ecology of
the pests. The significance of weevil damage is currently an unknown quantity. Since the
weevils feed on the plant stems, application of chemicals using current plantation technology
will be inadequate.
Termites
Termites occur along the east coast, but they are not a problem in tea tree plantations.
However, plantations not protected by a high water table are at risk. At West Wyalong,
inland New South Wales, termites are a significant pest causing the death of trees
(Gumming 1997). This probably indicates the trees are growing on a poor-quality site
outside their natural geographical range. The termites enter the plant through the root
system and then continue to feed within the stems. Control of termites will be both difficult
and costly.
Stem-boring Lepidoptera
An unidentified stem borer is causing concern for some growers in northern New South
Wales. The moth lays its egg within 30cm of the apex of the dominant leader and just above
a leaf base. On hatching the new larva enters the center of the shoot and chews its way either
up or down before pupation. Before pupation the larva chews the wood in the shoot down to
the cambial layer. Over time the shoot desiccates before snapping off in the wind and releasing
the moth. The extent of damage only becomes obvious once the shoots desiccate and become
a straw colour. Despite its apparent increase in some plantations, for reasons unknown, the
damage caused by the moth is probably not significant.
VALUE OF PARASITES AND PREDATORS
With the push for producers to achieve organic status, the use of predators and parasites to
control pests is an attractive management option. However, despite the existence of many
beneficial insects attacking all stages of the pests in tea tree they are a relatively ineffective
form of pest control and cannot be relied upon. The main problem is the lag in the
development of the pests and the beneficial species. Beneficial insects usually become
effective towards the end of a cycle of pest activity. They are at their greatest abundance
after most of the damage has occurred. Current management practises on plantations do not
allow for refugia in which beneficial insects can shelter or over-winter. The development of
beneficial insect populations recommences each season within the plantation and depends
on migration. The parasites and predators found are generalists and attack most pests found
within tea tree.
PROBLEMS ASSOCIATED WITH CHEMICAL USAGE FOR PEST CONTROL
When P. tigrina or other pests invade a plantation, and the foliage practically disappears
over night, the incentive to use an insecticide is high. This practice is safe if only
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

INSECT PESTS OF TEA TREE
107
registered chemicals are used in accordance to their label. Withholding periods before
harvesting must be followed. Registered chemicals applied at inappropriate rates or
frequencies could cause residues and their presence will influence marketing
opportunities.
The unique nature of the crop, i.e. oil in oil sacks within the leaf, the solubility of
most insecticides in the oil itself and the extraction process increases the chances of
residues. Contract distillers must be aware of the possibility of residue carry over from
one job to the next and take steps to clean the still between runs. Given the potential for
tea tree oil, the industry must take responsibility for registering new chemicals after
their proper screening for efficacy and residues. The industry should not rely on
chemicals registered for use in other crops. Softer control options like Bacillus
thuringiensis (Elliot et al. 1992) and organic methods are available, but need evaluating
for use on tea tree.
CONCLUSIONS
On the evidence available P. tigrina, mites and psyllids cause the greatest damage within
plantations and P. tigrina is the best recognised pest. Understanding conditions necessary
for the development of pest outbreaks, i.e. threshold temperatures for the survival of eggs
and larvae, allows the generation of a model that accounts for field behaviour. In conjunction
with a reliable trapping method, e.g. colour trapping for P. tigrina, viable management
strategies and action thresholds can be developed. These strategies if applied will be cost
effective, minimise the use of insecticides and reduce the risk of residues in the oil.
The lack of biological data prevents the development of models for pests other than P.
tigrina and the collection of such data should be an industry priority. Without such data the
misuse of chemicals will continue to occur, increasing the possibility of oil contamination
in the marketplace.
Finally, not all insects found in plantations are pests. The full pest complex of tea tree
remains unknown, action thresholds are non-existent and the significance of any pest depends
on the weather patterns.
REFERENCES
Campbell, A.J. and Maddox, C.D.A. (1996) Insect Pest Management in Tea Tree. RIRDC Final Report
DAN-91A, NSW Agriculture Tropical Fruit Research Station Alstonville, December 1996.
Clarke, B. (1996) NSW Agriculture, Casino. Personal communication.
Colton, R.T. and Murtagh, G.J. (1991) Tea Tree Oil Plantation Production. Agfact P6.4.6 NSW
Agriculture & Fisheries.
Cumming, A. (1997) Mount Mulga Pastoral Co., West Wyalong. Personal communication.
Curtis, A. (1993) Growth and oil production of Australian M. alternifolia. M.Ag.Sc. Thesis, University
of Queensland, Agriculture Faculty.
Elliot, H.J., Bashford, R., Greener, A. and Candy, S.G. (1992) Integrated pest management of the
Tasmanian Eucalyptus leaf beetle, Chrysophtharta bimaculata (Olivier) [Col: Chrysomelidae].
Forest Ecology and Management, 53, 29–38.
Goodyer G. (1995) African Black Beetle. Agfact AE.54 NSW Agriculture.
Larsson, S. and Ohmart, C.P. (1988) Leaf age and larval performance of the leaf beetle Paropsis
atomaria. Ecological Entomology, 13, 19–24.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

A.J.CAMPBELL AND C.D.A.MADDOX
108
Maddox, C.D.A. (1996) Aspects of the biology of Paropsisterna tigrina (Chapuis) the major pest of
Melaleuca alternifolia (Cheel). M.Sc. thesis, Department of Entomology University of Queensland,
Brisbane, Australia.
Murtagh, G.J. (1994) Oil gland research techniques. Rural Industries Research and Development
Corporation Final Report, NSW Agriculture, Wollongbar, January 1994.
Ohmart, C.P., Thomas, J.R. and Stewart, L.G. (1987) Nitrogen, leaf toughness and the population
dynamics of Paropsis atomaria (Olivier) [Col.: Chrysomelidae]—a hypothesis. Journal of the
Australian Entomological Society, 26, 203–207.
Ohmart, C.P. (1991) Role of food quality in the population dynamics of chrysomelid beetles feeding
on Eucalyptus. Forest Ecology and Management, 39, 35–46.
Patterson, K.C., Clarke, A.R., Raymond, C.A. and Zalucki, M.P. (1996) Performance of first instar
Chrysophtharta bimaculata larvae (Coleoptera: Chrysomelidae) on nine families of Eucalyptus
regnans (Myrtacae). Chemoecology, 7, 1–13.
Southwell, I.A., Maddox, C.D.A. and Zalucki, M.P. (1995) Metabolism of 1,8-cineole in tea tree
(Melaleuca alternifolia and M. linariifolia) by pyrgo beetle (Paropsisterna tigrina). Journal of
Chemical Ecology, 21, 439–453.
Southwell, I.A. and Stiff, I.A. (1989) Ontogenetical changes in monoterpenoids of Melaleuca
alternifolia leaf. Photochemistry, 28, 1047–1051.
Treverrow, N.L. (1992) The insect fauna of Melaleuca alternifolia with emphasis on three known pest
species . Rural Industries Research and Development Corporation Final Report. NSW Agriculture,
Wollongbar, November 1992.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

109
6. BIOMASS AND OIL PRODUCTION OF TEA TREE
G.JOHN MURTAGH
Agricultural Water Management, Goonellabah, NSW, Australia
INTRODUCTION
The economic viability of the production of tea tree oil is heavily dependent on the oil yield
from a plantation (Reilly 1991). Whilst other factors such as operating costs and the price of
oil also affect profitability, the oil yield can vary considerably making it a key variable in
any analysis of plantation profitability.
Tea tree oil is an essential oil that consists of a complex mixture of secondary plant
products. The synthesis and accumulation of such products is typically complex and can be
endogenously controlled, dependent on development processes that are related to cell
differentiation, and sometimes regulated by exogenous factors including light, temperature
and wounding (Wiermann 1981). This chapter explores the range of factors that appear to
affect the production of tea tree oil, and indicates similarities and differences to other essential
oil crops. With tea tree, the major components of oil yield are the oil concentration in leaves
and the leaf yield. Both are affected, but in different ways, by a number of factors including
the environment, plantation management and genetics (Murtagh 1991).
Most tea tree oil that is used in commerce is sourced from selected chemotypes of
Melaleuca alternifolia (Murtagh 1998). Suitable oil can also be obtained from chemotypes
of M. linariifolia (Williams 1995), M. dissitiflora (Brophy and Lassak 1983) and M. uncinata
(Brophy and Lassak 1992), but as most experimental and commercial experience is with M.
alternifolia the discussion will refer to this species unless indicated otherwise.
Terminology and Plant Parts
In this chapter, the term oil concentration is used to describe the amount of oil in a unit
weight of the plant, or part of the plant such as the leaf. The standard unit is milligrams of
oil per gram of dried leaf (mg/g). When the amount of oil was given as a volume in the
referenced publications, it was converted to a weight by multiplying by the average oil
density of 0.9 (Penfold and Morrison 1950). Another common unit of concentration expresses
the weight of oil as a percentage of the plant weight. This can be converted to mg/g by
multiplying by ten. To provide consistency, all published results were converted to the
standard unit in this chapter.
When the weight of the plant or oil is referenced to a unit area where it grew, it is referred
to as a yield with units of kg/ha or g/m
2
. Some authors use the term oil yield to describe the
concentration as defined above, but in this chapter such use was altered to maintain
consistency.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

G.J.MURTAGH
110
Much agronomic work refers to the yield of above-ground parts and does not include the
weight of roots. The above-ground growth is referred to as biomass. As tea tree oil is found
only in leaves, it is useful to subdivide the total biomass into three components; leaves, fine
stems and main stems. Fine stems are defined as stems of less than 2.5mm diameter (Murtagh
1988), and main stems are the remainder. Fine stems carry virtually all the leaves. The total
of leaf plus fine stems are called twigs. Such measurements are expressed on a dry-weight
basis using separate estimates of the moisture content in each fraction to make the conversion.
When twigs were distilled and the oil concentration was expressed per unit weight of twig,
it was converted to a concentration per unit leaf weight by dividing by the measured ratio of
leaf in twig. If this was unavailable and the measurements being compared were taken over
a short interval, a typical ratio of 0.68 (Murtagh 1996) was used.
OIL CONCENTRATION
Tea tree oil is stored in subepidermal glands that are adjacent to the epidermis and equally
distributed on both sides of a leaf (list et al. 1995). Oil glands are first apparent in immature
leaves, with the number per leaf increasing as the leaf expands, to reach a maximum just
before the leaf is fully expanded. The oil gland density appears to be under some degree of
genetic control (List et al. 1995).
Analytical Methods
Two principal methods are available to determine the oil concentration: steam distillation or
solvent extraction. A specific case of steam distillation that has the biomass immersed in the
boiling water is sometimes termed hydrodistillation. More specialised methods such as
head space analysis are usually confined to detailed experiments. Each of the two methods
has its own advantages. Steam distillation can accommodate the larger samples that arise
when all positions on a single plant or a number of plants in an agronomically sized plot are
sampled. The method mimics the commercial process and gives oil of a similar chemical
composition. It is important that the system incorporates a cohobation or reflux return to
obtain complete recovery of the alcohol components of the oil (Kawakami et al. 1990;
Murtagh 1991a).
On the other hand, solvent extraction followed by quantitative gas chromatographic
analysis can use much smaller samples that can vary from a single leaf up to at least 5 g.
Solvent extraction also avoids the conversion of precursor compounds in young leaves to
the major constituent, terpinen-4-ol, as occurs with steam distillation (Southwell and Stiff
1989; Cornwell et al. 1995), and thereby suits biochemical investigations. It is the system
of choice when there are a large number of samples, as in plant breeding programs, and in
such sampling the issue of extracts having a different oil composition to the commercial
product, which is distilled, can be avoided by not using young growth (Baker 1995). Tea
tree has a sufficiently high oil concentration to enable a direct chromatographic analysis of
the solvent extract without the need to concentrate the extract by evaporation, thus avoiding
the accompanying losses that can be a drawback of the solvent extraction method (Charles
and Simon 1990).
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

BIOMASS AND OIL PRODUCTION 111
In a comparative study with tea tree (Baker et al. 1995), the two methods gave a similar
recovery of monoterpenes, but more sesquiterpenes with solvent extraction. A major problem
in doing the comparison was to obtain equivalent samples of very different size.
Either fresh or air dried samples can be distilled without affecting the result (Murtagh
and Curtis 1991). Although dried samples distill more slowly, distillation is virtually
complete within two hours (Murtagh and Smith 1993). Similar delays occur with solvent
extraction (Doran et al. 1996). Because of oil losses, samples should not be oven dried
before distilling. Losses increase with the drying temperature, and also vary between
samples (Curtis and Murtagh 1989). The widest variation they measured between samples
ranged from no oil loss at 45°C and 50% loss at 125°C in samples from one tree, to 33%
loss at 45°C and 93% loss at 125°C from another tree. Points of note in these results were
the consistent pattern of relatively high or low losses across all temperatures within a
batch, and the lack of a relation between the relative batch loss and the moisture content
of the samples before drying.
Variation in Oil Concentration
From first experience, the oil concentration was observed to vary over time (Penfold et
al. 1948) and this gave rise to a number of studies that attempted to document and
explain the variation (
Table 1
). Of the 12 studies that measured variation over time, five
recorded a variation of more than 100% above the lowest value in the study, six had a
variation between 15–57%, and only one recorded no variation. Similar variation is
often found with other essential oils or secondary metabolites, as instanced in reviews
by Flück (1963), Wiermann (1981), Harborne and Turner (1984), Lawrence (1986),
Gershenzon and Croteau (1991).
Seasonal Variation
The oil concentration is generally highest in summer and lowest in late winter/early spring.
Figure 1A
 shows the average seasonal variation in repeated tests on two plantations (Murtagh
1992; Murtagh and Smith 1996) in the humid subtropical environment of northern New
South Wales (NSW). Although insufficient samples were taken during June-August to
complete part of the trend line on the plantation that experienced winter frosts, the seasonal
range was greater where winters were cooler. The trends shown in Figure 1A are means
over a number of years, and while all years have a seasonal trend it can vary both in absolute
magnitude and extent of variation (Murtagh and Smith 1996).
Tea tree is also grown in the dry tropics of north Queensland. Here there was almost no
seasonal variation in a stand of a low concentration type, but more than 50% variation in a
high concentration type (Figure 1B) (Drinnan 1997). Seasonal variation in oil concentration
of more than 50% has also been observed in young leaves of Eucalyptus camaldulensis,
another myrtaceous species with subepidermal oil glands (Doran et al. 1995).
The upper leaves on a tea tree plant often have a higher oil concentration than lower
leaves (Curtis 1996), leading to the suggestion that the seasonal trend in concentration
reflects oil losses during autumn-winter, followed by the production of new leaves with
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

G.J.MURTAGH
112
Table 1 A literature survey of the variation in oil concentration in tea tree
*Factors used to convert units used in published data to mg/g DW; 
a
Oil density of 0.9g/ml, 
b
Leaf : twig
ratio of 0.68, 
c
Leaf dry weight=36% wet weight, 
d
Assumed published values were %w/w,
e
Range taken from greatest variation measured within a day.

Range expressed as a percentage of the lowest value.
a high concentration during the following spring. In other words, the whole-plant oil
concentration increases during spring because of the increasing proportion of young leaves
rather than an increase in oil concentration in older leaves. List et al. (1995) obtained two
pieces of evidence that support this view, that they termed the one-way development path.
Their anatomical study suggested that immature glands were lined with metabolically active
cells, whereas mature glands were lined with highly vacuolate cells that are unlikely to be
involved in oil synthesis. Secondly, they found no variation in oil concentration over 48
hours.
However, not all data supports the one-way development hypothesis. Penfold et al. (1948)
found that the oil concentration increased rapidly from the lowest to near the highest value
for the year between October and November. This rate of increase was too rapid to be
explained by the production of new leaves. A similar result was reported by Murtagh (1988)
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,

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