Autumn Gum Moth –
Mnesampela privita
Number 4
Revised 2001
By Charlma Phillips, Principal Forest Health Scientist
The Autumn Gum Moth is one of the most common insects found on eucalypts. It is an
important pest in Blue Gum plantations throughout southern Australia.
The caterpillar (larval) stages feed on many species of eucalypts but prefer the juvenile
leaves of those species with blue-green foliage eg Tasmanian Blue Gum (E.globulus) and
Shining Gum (E. nitens).
Description
Eggs are oval in shape and pale green in colour when
first laid. They turn dark brown/black as they mature (the
egg itself is transparent, the dark colour is the larva
developing inside the egg). Hatched eggs are clear and
appear whitish. Eggs are laid in batches, usually on the
undersurface of juvenile leaves. Each batch may contain
up to several hundred eggs. When population numbers
are high, several batches may be laid on the same leaf.
Newly hatched larvae are approximately 2mm long.
They vary in colour from light grey-green to almost
black, with black and red markings and a tan head.
Older larvae are mottled grey-green and black with two
conspicuous large yellow or cream dots in the middle
of the back. Mature larvae are approximately 35mm in
length.
The pupal stage (the inactive, resting stage between
larval and adult stages) occurs in the soil.
Adult moths have mottled orange/ brown forewings and
pale hindwings. Moths are approximately 20mm long with a wingspan of 40mm. Male and
female moths are similar in appearance.
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Lifecycle
Eggs are laid in late summer/ autumn
through to winter. They are usually laid on
the underside of the leaf, low down on the
tree. Hatching occurs within 2-3 weeks.
Larvae go through 5 stages and at the end of
each stage shed their skin (moult). The
whole larval stage lasts for approximately 2
months, depending on temperature.
Occasionally larvae may be found throughout
the year.
Fully fed larvae drop off the tree and burrow
into the soil where they pupate. This stage
may last 6-9 months after which time the
adult moth emerges. Adults do not feed.
They mate, lay eggs and die a short time
later.
Habits
On hatching, the tiny larvae cluster together
around the empty eggshells and begin
feeding. They feed by skeletonising the leaf, i.e. by feeding on the surface layer of the leaf.
This causes the leaves to go brown. Older larvae feed on the whole leaf, often leaving only
the midrib.
Young larvae are highly gregarious but as they get older they
become more solitary.
Larvae feed mainly at night. During the day older larvae rest
inside shelters formed by webbing the leaves together, usually
at the ends of branches. At night they leave the shelters to feed
and return to them in the daytime.
If disturbed, larvae regurgitate a green fluid.
Adult moths, though rarely seen, fly during the day and at night.
Some individuals in the pupal stage will enter diapause (a state
of suspended animation – all development ceases). This state
may extend from early summer through to late autumn. These
adults will then emerge early in winter when new growth on the
eucalypts ensures a plentiful food supply for the larvae.
Damage
Autumn Gum moth can cause major damage for the first two to three years after planting.
On rare occasions it may damage older trees, even those with no juvenile foliage. In
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general, damage is most common on trees up to 5m in height. Once the tree produces
adult foliage, the impact of Autumn Gum Moth is reduced.
Most defoliation occurs in autumn and this can seriously affect tree growth. Light to
moderate damage is rarely a problem as the trees quickly recover. However if there is
>50% damage or the trees are completely defoliated, there will be considerable loss of
growth. If damage occurs over several successive seasons, some trees may die.
Over 96% of the total amount eaten by the larvae, is consumed during the 4th and 5th larval
stages. So it is very important to recognise this pest early, and decide if control is
warranted.
Damage by young larvae
Damage by older larvae
Control
Biological:
Eggs are attacked by several species of tiny wasps. Larvae are parasitised by several
species of wasps and flies. Larvae are also attacked by predators eg scorpionflies, and
predatory bugs.
Some larvae may be attacked by bacterial, viral and fungal diseases.
Chemical:
Chemical control is often necessary when small trees are attacked and are in danger of
being defoliated. No insecticides are registered specifically for use on Autumn Gum Moth
but most broad spectrum chemicals will kill larvae. However these chemicals also kill other
insects including natural enemies. For more information refer to Forest Insects No 30,
"Control of Insect Pests in Eucalypt Plantations".
Control is not difficult to achieve but large larvae are in shelters during the day and
therefore are protected from sprays until they emerge to feed at night. Spraying late in the
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day is the best way to ensure the chemical is effective. Young larvae can be sprayed at
any time.
Summary
When to Look:
Look for eggs and young larvae in early autumn and also in spring.
Mature larvae are found mainly in autumn and winter, however they
may be found at any time of the year.
Where to look:
Look on eucalypts with blue-green juvenile foliage.
Eggs: Look on the underside of juvenile leaves, may also be on the
top of the leaves.
Larvae: Look on juvenile leaves and in webbed shelters on the tips of
branches. Also look low down on the tree for evidence of young
larvae.
What to look for: Look for skeletonised leaves and for whole chewed leaves with just
the midrib left. Look for leaves webbed together at the ends of
branches.
NOTE: It is very important to look for signs of infestation early, before much damage has
occurred. In particular look for skeletonised leaves. If only the midribs are left and the
larvae are large and in shelters, most of the damage will have already been done and it
will be too late for control.
For further information contact:
PIRSA Forestry
PO Box 2124
MOUNT GAMBIER SA 5290
Phone: (08) 8724 1232
Fax: (08) 8723 1941
E-mail: [email protected]
Disclaimer: While this publication may be of assistance to you, the Government of South
Australia and its officers do not guarantee that it is without flaw of any kind or is wholly
appropriate for your particular purpose. The Government therefore disclaims all liability for
any error, loss or other consequence that may arise from you relying on any information in
this publication.
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