Medicinal and Aromatic Plants—Industrial Profiles


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A.J.CAMPBELL AND C.D.A.MADDOX
96
Nambiar, E.K.S. and Zed, P.G. (1980) Influence of weeds on the water potential, nutrient content and
growth of young radiata pine. Australian Forestry Research, 10, 279–288.
Nambiar, E.K.S. and Sands, R. (1993) Competition for water and nutrients in forests. Canadian Journal
of Forestry Research, 23, 1955–1968.
Putnam, A.R. and Weston, L.A. (1986) Adverse impacts of allelopathy in agricultural systems. In A.R.
Putnam and C.S.Tang (eds.), The Science of Allelopathy, Wiley, New York, U.S.A., pp. 43–56.
Sands, R. and Nambiar, E.K.S. (1984) Water relations of Pinus radiata in competition with weeds.
Canadian Journal of Forestry Research, 14, 233–237.
Smethurst, P.J., Comerford, N.B. and Neary, D.G. (1993) Weed effects on early K and P nutrition and
growth of slash pine on a Spodsol. Forest Ecology and Management, 60, 15–26.
Storrie, A., Cook, T., Virtue, J., Clarke, B. and McMillan, M. (1997) Weed management in tea tree
plantations. NSW Agriculture.
Tamasi, J. (1986) Agrotechnical factors modifying the root system. In J.Tamasi (ed.), Root Location
of Fruit-trees and its Agrotechnical Consequences, Akademiai Kiado, Budapest, Hungary, pp.
47–65.
Tisdall, J.M. and Huett, D.O. (1987) Tillage in Horticulture. In P.S.Cornish and J.E.Pratley (eds.),
Tillage: new directions in Australian agriculture, Australian Society of Agronomy, Inkata Press,
Melbourne, Australia, pp. 72–93.
Virtue, J.G. (1997) Weed interference in the annual regrowth cycle of plantation tea tree (Melaleuca
alternifolia). PhD Thesis. The University of Sydney.
Woods, P.V., Nambiar, E.K.S. and Smethurst, P.J. (1992) Effect of annual weeds on water and nitrogen
availability to Pinus radiata trees in a young plantation. Forest Ecology and Management, 48,
145–163.
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.

97
5. INSECT PESTS OF TEA TREE:
CAN PLANTATION PESTS BE MANAGED?
A.J.CAMPBELL AND C.D.A.MADDOX
NSW Agriculture, Tropical Fruit Research Station,
Alstonville, NSW, Australia
INTRODUCTION
Before 1980, the tea tree industry was largely an opportunistic cottage industry. Production
of oil followed the harvesting and distillation of leaf from natural stands of Melaleuca
alternifolia (Cheel) growing on the coastal flood plains of the Richmond and Clarence
rivers of northern New South Wales (NSW). Natural populations were sparse and closely
interspersed with Eucalyptus, Acacia and Casuarina species. Periodic defoliation by leaf
chewing insects was common and pest management was nonexistent.
Since 1980 about 3,400 ha of plantation tea tree, of limited genetic diversity, have been
established in NSW (Clarke 1996). Plantations are established with 30,000–40,000 plants
per hectare (Colton and Murtagh 1991) and are mostly harvested annually.
Within plantations the young leaf available to pests has dramatically increased. At the
same time no significant increase in the large wood or bark components observed in natural
forests has occurred. This change in the ratio of the leaf to wood and bark components and
the short cutting cycle has caused a shift in the composition of the insect fauna.
Moving to a plantation based industry has focused attention on the monitoring and control
of insects damaging foliage. With further investigation and collecting under differing seasonal
conditions, the number of pest species associated with tea tree will increase. Some currently
recognised pests (e.g. Paropsisterna tigrina (Chapuis) commonly called Pyrgo beetle) may
become less significant with improved pest control measures and monitoring strategies.
Other invertebrate groups (e.g. mites and psyllids) may increase in significance, once their
true impacts on oil yield are known.
This chapter contains basic information on the pests of tea tree in Australia based on the
limited available knowledge. The pests vary seasonally, annually, and from plantation to
plantation. The response of the NSW growers to a survey on pests and industry issues is
summarised. Some producers have a poor knowledge of the pests and their control options.
This poor knowledge base when combined with the inappropriate use of chemicals has led
to the occasional residue in oil in the market place. The potential for residues will determine
the direction of future plantation management practises for pest control. Tea tree pests are
discussed according to the stage of growth and the plant component that they damage. A
successful monitoring technique for P. tigrina is outlined and its value to the industry in
terms of better pest management and more effective pesticide use is discussed.
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
98
INSECT FAUNA OF PLANTATIONS AND NATURAL STANDS
The initial entomological study by Treverrow (1992) on the north coast of NSW identified
66 phytophagous species, or species groups, found in tea tree. Of these, 35 were restricted
to plantations, 21 were recovered from native areas and an additional 10 were common to
both. The number of phytophagous species is now over 100 based on the collections made
by the authors. Leaf beetles of the family Chrysomelidae (12 species each from a different
genus) dominate. The Chrysomelidae, including P. tigrina, cause rapid defoliation and
have the greatest obvious impact on oil recovery. All growers considered P. tigrina to be the
most significant pest.
INDUSTRY PERSPECTIVES ON PESTS
A survey of 30 producers, accounting for 60% of the estimated NSW plantation area,
was conducted in 1996. The plantations ranged from 0.5–1,200 ha in size, with a
median of 12 ha. Small producers dominate the industry. Ten plantations were less
than 5 ha in size while an additional 5 were from 5–10 ha. Only 10 plantations were
greater than 20 ha in size, of which 4 claimed organic status. For holdings of less
than 10 ha, 14 claimed to be organic. Smaller producers have the poorest
understanding of the pests present and the available control options. All growers,
irrespective of size and production philosophy, had experienced losses due to insects
at some time.
Most growers, whilst not stating exactly how they control insect pests, were generally
happy with their current pest management strategies. Nevertheless, identification of the
smaller sap-sucking groups (mites and psyllids) was a recurring problem. All producers
were acutely aware of the difficulties in presenting a product with a “clean green” image in
the market place. For the ease of marketing, growers are now seeking organic production
status. This shift towards organic production, if closely adhered to, should insure residue-
free oil in the market place.
Insecticidal residues were detected in oil in 1995. However, the industry as a whole does
not consider insects to be a major issue. Only 12% of producers now regarded them as a
major problem when they occurred. Producers consider Pyrgo beetle, psyllids and mites as
the worst pests (
Table 1
). More than 82% of the growers believed marketing of oil was the
largest single issue facing the industry.
INSECTS DAMAGING NEW SEEDLINGS
African Black Beetles, Mole Crickets and Cut Worms
The introduced African Black Beetles (Heteronychus arator) periodically damages newly
set transplants in the field. Transplants are ringbarked at or below ground level, which
causes desiccation and death. Adult beetles attracted into plantations from the surrounding
pastures cause the damage. It is unlikely the beetle or its larvae could survive the soil
preparation work associated with plantation establishment. Damage is most severe in spring
and late summer-autumn on light, well-drained soils.
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
99
No evidence exists to indicate Black Beetles are a pest in established plantations. The
main effect of damage is the loss of plants within an area that may warrant replanting if
severe. Since the adult beetles seldom fly (Goodyer 1995), maintenance of a clear uncultivated
buffer may reduce the potential for damage. The worst damage is likely to occur in areas
previously cropped with, or near, sugarcane.
Mole Crickets
Gryllotalpa spp. are easily recognised by their powerful forelegs used for digging. Mole
crickets can cause significant damage to newly set tea tree transplants by severing their
roots. Crickets usually forage in horizontal tunnels in the top 5 cm of soil but may feed on
the soil surface during periods of high humidity following rain or irrigation. Damage relates
to soil type and is worst in sandy loams near rivers or creeks.
Cutworms
Agrotis caterpillars occasionally attack newly set transplants, cutting through their stems
near ground level and feeding on the felled plants. Both Agrotis ipsilon (black cutworm)
and A. munda (brown or pink cutworm) occur in spring through autumn along the coast.
Moths breed locally in pasture or weedy areas, or are blown in (often over considerable
distances) on the wind associated with storm fronts. Cool, wet conditions in spring through
autumn favour outbreaks of black cutworms. The brown cutworm prefers a mild dry
winter to give good survival of over-wintering pupae. Early emergence of moths and
rapid population development occurs with good growing conditions in spring through
autumn.
Cutworms are more likely to infest new plantations next to pasture or weed areas.
Transplants held near lights at night, that attract Agrotis moths, may become infested before
Table 1 Industry survey—insect pests causing problems
for growers and warranting control
Source: Campbell and Maddox (1996).
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
100
field planting. Feeding damage if severe can kill or stunt plant growth and replanting may
be necessary. Cutworms are only a problem after the transplanting stage and before the
onset of rapid plant growth.
INSECTS DAMAGING FOLIAGE OF ESTABLISHED PLANTS
Chrysomelids
Paropsisterna tigrina has emerged as the most significant pest of plantation tea tree. The
beetles over-winter in sheltered crevices within poorly managed plantations or in the
surrounding wooded areas. Adults begin feeding and egg production in spring on expanding
flush growth. Soil temperatures above 15°C (Curtis 1993) and adequate soil moisture triggers
plant growth. The larvae are initially gregarious. On consumption of the young flush growth
near the oviposition site the larvae spread out over the plant. Both larval and adult stages
feed on young foliage produced in spring and autumn.
Like most paropsines on their respective myrtaceous hosts, P. tigrina is a specialist
feeder and has adapted to its host’s chemical defences. It is strictiy a flush growth feeder
although it will excise mature leaves when high population densities (>50 per plant)
occur.
The rate at which new foliage matures on the plant is the key factor when assessing the
resistance of a particular plant to P. tigrina attack. Many changes occur in the leaves as they
age. The oil constituents change from precursor to end product forms (Southwell and Stiff
1989) and volatile emissions decrease (Murtagh 1994). Leaves become harder and their
colour changes dramatically (Maddox 1996). Leaf colour changes from yellow to dark
green. This occurs anywhere from near the bud to below the 10th pair of leaves, depending
on their growth rate. Young regrowth is more vivid with a higher leaf colour chroma and
value (based on Munsell notation), and this is the basis for the use of glossy yellow plates as
a monitoring tool.
Changes in leaf oil are more rapid and occur in the first green leaf below the terminal
bud (Southwell and Stiff 1989). In spring and autumn when flush growth occurs, P.
tigrina females detect (either physically or chemically) these oil changes in the foliage
and this stimulates oviposition after feeding. The preferred oviposition site is on the
first “mature” leaves back along a twig from the terminal bud. On hatching the first
instar larvae move to the terminal foliage to feed. Their survival, like other paropsine
beetles, is dependent on the presence of young soft foliage (Ohmart et al. 1987; Larsson
and Ohmart 1988; Ohmart 1991; Maddox 1996; Patterson et al. 1996). Trees must be
actively growing to support a larval population. Once a tree has had the flush growth
removed it is no longer suitable for P. tigrina oviposition. The probability of forecasting
an outbreak is high if colonising adults can be monitored because oviposition is locally
synchronised.
The number of P. tigrina generations within a plantation depends on temperature and
soil moisture levels. The maximum daily rate of egg production is 13 eggs/female/day, at
29°C and 85% humidity. Exposure of eggs for 2–6 hours at 38–40°C reduces hatching to
less than 15%; while exposure of 1st and 2nd instar larva to 35°C for 4–6 hours killed more
than 75%. Exposure of small larvae at 40°C for 4 hours causes 100% mortality. Field
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 101
temperatures were corrected for solar radiation affects, otherwise body temperatures are
underestimated by 8°C for larvae and 3–4°C for eggs (Maddox 1996).
Temperature influences beetle activity and egg production. Outside the temperature range
of 15–35°C egg production is negligible. Females resume oviposition after feeding on new
flush growth for 5–7 days at 25°C and 80% relative humidity. Field temperatures outside
the threshold range of 11.5 and 35°C, in spring and autumn, cause the bimodal distribution
pattern of P. tigrina. On the north coast of NSW 5 generations of beetles are theoretically
possible, but a maximum of 3 generations is more likely (
Figure 1
).
Yellow sticky traps located above the plants and throughout a plantation to survey adults
maybe of more benefit than counting beetles on plants (Campbell and Maddox 1996). The
traps intercepted beetles up to 2 weeks before finding beetles on the plants. Trap counts
give managers a warning of the location and likely time of damage by the beetles and their
larvae.
Trap colour was determined by comparing counts of P. tigrina on different coloured
plates in the field. A high gloss yellow consistently gave the highest counts. Given the
variability within plantations and the size of P. tigrina aggregations, traps on a 50m grid
allow accurate detection and plotting of activity. Placing traps in the field before the flights
of the over-wintering adults can significantly reduce the use of insecticide. Traps allow site
specific spraying to minimise foliar damage, reduce follow up insecticide use and restrict
the expansion of the pest within the plantation.
Detection of the invading over-wintering population of P. tigrina is the crux of successful
monitoring and control strategy in managed plantations.
In managed plantations, colour traps located around the perimeter indicate migratory
activity. Within a plantation, P. tigrina populations establish in spring then leave and return
to the same areas in autumn. The mechanism responsible for this behaviour is unclear and
understanding this process could allow refinements to the monitoring technique. Evaluation
and field testing of potential tree marking compounds (namely thujanes or cineole
metabolites) identified by Southwell et al. (1995) are required.
Significant P. tigrina outbreaks have occurred at most plantations in NSW. The outbreaks
monitored were at Wyrallah in February and November 1991, Grafton in February 1992
and Cudgen in February 1996. These outbreaks were linked to the occurrence of major
rainfall events (150–250mm in 48 hours) followed by rapid plant growth. At these times
because of wet: conditions, growers were unable to adequately protect the foliage during
the build up phase of P. tigrina. Favourable weather patterns with no hot dry periods and
maximum temperatures less than 32°C for 5–6 weeks lead to the development of 2 or 3
generations of P. tigrina. Leaf cutting occurred when the adults swarm, and little or no flush
growth remained on the trees. Management of P. tigrina under these conditions depends on
access to the plantations, otherwise losses will remain high. Such weather patterns are not
uncommon during autumn on the north coast of NSW.
Scarabaeids (Pasture Scarabs)
Diphucephala lineata, the small green pasture scarab causes extensive localised
defoliation of tea tree in early to mid summer on some plantations. The beetles feed
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
102
Figure 1 The use of temperature and insect development data to describe the field activity of
Paropsisterna tigrina on M. alternifolia at Ballina during the 1995–96 growing season. Chart A plots
the incidence of adults on yellow flight traps (n=44) within the plantation, and the larval and adult
activity on the plants (10 plants neighbouring each trap) over 31 weeks. Chart B shows the theoretical
insect development possible over the same time scale based on available heat (291 Degree Days for
each adult). If the threshold temperatures (11.5 and 32°C) are considered lethal then predicted adult
emergence (*) matches field trap catch patterns in chart A. Chart C contains the daily weather information
gathered from an automatic station scanning hourly.
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
103
and mate on the trees then return to the soil to lay their eggs. Trees at the edge of
plantations bordering remnant forest or pasture are at the greatest risk and the worst
damage occurs in plantations near lighter sandy soils. The larvae are subterranean pests
of pasture and grass species.
Nectar Scarabs (Phyllotocus spp.)
Nectar scarabs are small light brown beetles with a dark brown tip to each wing cover and
long hind legs. These beetles can swarm, particularly on plants in flower but cause no
damage. Oviposition occurs in the soil, and on hatching the larvae feed on decaying organic
matter and pasture roots. When plantation managers see large numbers of beetles they
occasionally panic and want to spray.
Psyllids
The taxonomy of tea tree psyllids is poorly understood. The commonly occurring Trioza
sp. prefers young flush growth and occur within plantations all year. However, population
explosions occur in late summer through spring, when plants may be under water stress.
Feeding by the mature and immature psyllids causes pitting and some distortion of the
leaves and shoots. Psyllids deposited their characteristic yellow eggs that are easily visible
at low magnification along the leaf margins. During dry periods in summer drops of sugary
exudate can leak from the feeding sites, crystallise and fall to the ground. As with the other
sap-suckers, ants often indicate the presence of psyllids.
Psyllids can be introduced into clean areas on the planting material. Poor nursery hygiene
and failing to insure pest-free transplants is the source of the problem. The impact of psyllids
on oil production needs quantifying and their control measures investigated.
Eriophyid Mites
Like the psyllids, the eriophyid mite complex associated with M. alternifolia is unknown
and no species are described. However, eriophyids occur all year but the damage is more
apparent in the winter and spring.
The eriophyids distort new foliage and cause the leaf margins on the ventral surface to
bend; cells on the leaf surface within the distorted area bubble and become hairy. The mites
live within the distorted areas. Eriophyids prefer new growth but also occur on basal growth
near the ground. Removal of foliage from the residual stems after harvesting, for example
with a flame weeder, may delay the colonisation of new growth with mites. The value of
flame weeders in this role needs confirming. Growers can check for the presence of mites
by gently heating the distorted foliage and examining it with a hand lens. Heat causes the
mites to become active and move about within the distorted foliage.
Work by the authors indicates varietal differences in susceptibility of monoclonal plants
to the eriophyids. Current work by D.Knihinicki (NSW Agriculture, Orange) should resolve
the taxonomy and ecology of mites associated with M. alternifolia.
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
104
Leaf Galls
Distortion and stunting of buds on new growth due to the gall fly Dasineura sp. are common
from November to March. Individual buds become brown, fail to expand then die and a
shoot below the damage then assumes apical dominance. Multiple larvae can develop within
a shoot after female flies place their eggs at the base of the bracts. Because of the ability of
the adults to fly, edge effects are not obvious and superficial damage occurs across plantations.
Despite the obvious damage in the field, gall fly is not a major pest. Variations in the
susceptibility of individual plants to the gall fly are apparent in the field.
Aphids
As with most crops, aphids occur in tea tree. Aphis gossypii Glover (cotton or melon aphid)
occurs particularly from October to May. Aphids prefer the terminal shoots of new flush
and are often attended to by ants that collect the honeydew. Black sooty mould grows on the
honeydew and indicates aphid or other sap-sucker activity.
Scale Insects
A number of scale species, including lac and nigra scales, which are major pests on other
tree crops has been identified. Plants growing on marginal sites, or already weakened by
defoliating or sap-sucking insects, appear the most prone to scale infestation. Scales are not
a major problem within plantations as the cutting cycle does not favour the development or
spread of this pest. Predators including coccinellids (generalist predators) and wasp parasites
exert some control.
Leaf Hopper
Both the adult and immature stages suck sap from the expanding shoots on flush growth.
Feeding causes the wilting of the shoots, that can then develop a distinct purple colouration.
As with other sap-sucking groups leaf hoppers are tended by ants. Black sooty mould
commonly grows on the exudate produced. Leaf hoppers occur all year, but appear most
active when the host plant has new growth in spring and autumn.
Characteristically, adult leaf hoppers are less than 10mm long, however the dominant
species on tea tree (including Erythroneura sp.) are less than 5mm long. Adults hold their
wings tent-like when at rest. The wing colour varies from being transparent to pale green,
grey or yellow depending on the species. Immature stages hop when disturbed, while the
adults either hop or fly, making them difficult to collect.
Sawflies
The tea tree sawfly larvae (Pterygophorus sp.) causes major defoliation in native stands
resulting in significant economic losses for bush cutters. In late summer wasps insert eggs
in rows into the leaf tissue of young foliage. Hatching occurs within 10–15 days and once
emerged the larvae begin feeding on the leaf. The larvae have an orange-brown head capsule,
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