The macadamia twig girdler


Ironside, D.A.

Queensland Agricultural Journal 104(5): XXIX-XXX

1978


The macadamia twig girdler (Neodrepta luteotactella (Walker)) is most prevalent on young trees where it can cause severe growth checks and even death.

The
macadamia
twig
girdler
by
D.
A.
lronside,
Entomology
Branch.
THE
macadamia
twig
girdler
(Neodrepta
luteotactella
(Walker))
is
most
prevalent
on
young
trees
where
it
can
cause
severe
growth
checks
and
even
death.
The
insect
is
active
throughout
the
year
and
the
greatest
damage
to
macadamia
occurs
during
summer
and
autumn.
The
adult
moths
which
belong
to
the
family
Xyloryctidae
are
least
active
during
winter.
Typically,
the
twigs
of
infested
trees
show
signs
of
girdling
at
the
forks
or
leaf
whorls
and
the
leaves
may
be
skeletonized
and
incor-
porated
into
larval
shelters.
Tunnelling
in
the
nuts
may
occur
on
bearing
trees
but
this
is
rarely
a
serious
problem.
Host
plants
and
distribution
As
well
as
macadamia,
the
insect
also
attacks
many
other
native
proteaceous
trees
such
as
Banksia,
Grevillea,
Hakea,
Persoonia,
Buck-
inghamia,
Stenocarpus,
and
Xylomelum.
It
occurs
in
all
macadamia
areas
in
coastal
Queensland
but
the
heaviest
infestations
are
usually
in
elevated
areas.
Life
history,
habits
and
damage
ADULT—The
adult
is
a
silvery-white
moth,
satiny
in
appearance
with
yellow
legs
and
antennae
and
with
a
wing
span
of
up
to
26
mm.
It
is
mainly
active
at
night
and
is
attracted
to
mercury
vapour
light
which
has
been
used
in
traps
to
monitor
pest
abundance.
EGG—The
egg
is
approxiately
0.7
x
0.4
mm,
yellow
when
laid
and
changing
to
red-
dish-orange.
It
is
proportioned
and
pat-
terned
in
such
a
way
as
to
resemble
corn
on
the
cob.
Eggs
are
laid
singly
at
leaf
axils
on
terminal
shoots
and
apparently
in
the
vicinity
of
old
twig
girdler
damage.
LARVA—During
development,
the
larvae
may
pass
through
6
to
9
stages;
6
to
7
being
more
common.
On
hatching,
it
is
about
1.5
mm
long
and
yellow-orange
in
colour
with
a
black
head.
Feeding
commences
in
crevices
at
leaf
axils,
in
folds
of
leaves
or
at
old
damage
sites.
The
larva
feeds
under
webbed
shelters
which
become
cluttered
with
excrement
and
damaged
foliage
as
larval
development
proceeds.
Numerous
larvae
at
various
stages
of
develop-
ment
often
occur
in
the
one
shelter.
Webbed
shelters
may
remain
on
the
tree
long
after
the
life
cycle
is
completed,
giving
it
a
ragged
appearance.
Twigs
weakened
by
girdling
readily
snap
off
and
this
tends
to
induce
a
bunched
habit
of
growth.
Tunnelling
in
the
husks
and
kernels
causes
damage
similar
to
that
of
the
maca-
damia
nut
borer.
When
fully
grown,
the
larva
may
be
up
to
23
mm
long.
It
has
a
dark
brown
to
black
head
capsule
and
its
body
is
mottled
brown
relieved
by
longitudinal
rows
of
dark
brown
dots.
The
larva,
on
reaching
its
pre-pupal
stage,
contracts
and
becomes
lighter
in
colour.
It
constructs
a
dull
brown,
silken
cocoon
(about
12
mm
in
length)
in
which
the
transformation
to
the
pupa
occurs.
DURATION
OF
THE
LIFE
CYCLE—Develop-
ment
time,
when
the
insect
is
reared
in
the
laboratory
at
26°C
on
macadamia
nut
husks,
is
from
62
to
84
days.
This
comprises
7
days
for
eggs,
39
to
69
for
larvae,
and
12
to
17
for
pupae.
During
spring
and
summer,
however,
egg
laying
to
adult
emergence
on
trees
in
the
field
can
take
from
3
to
5
months.
Natural
enemies
Over
20
natural
enemies
have
been
recorded
and
it
appears
likely
that
these
are
important
in
regulating
pest
populations.
Most
of
these
enemies
are
wasp
parasites
which
attack
the
insect
during
its
larval
stage.
An
unidentified
bethylid,
a
braconid,
Agathiella
sp.
and
the
ichneumonids
Goryphus
turneri
Cheesman
and
Stiromesostenus
albiorbitalis
Cheesman
are
among
the
more
common
parasites.
September-October
1978
Queensland
Agricultural
Journal
axis
The
macadamia
twig
girdler
f
Adult
moth
of
the
macadamia
twig
girdler
(wing
span
up
to
26
mm).
sh
Immature
larva
on
a
damaged
leaf.
Fully
grown
larva
up
to
23
mm
long
on
a
macadamia
nut.
ABOVE.
Typical
twig
girdling
damage
on
a
young
grafted
tree.
LEFT.
Webbed
shelter
of
the
larva
incorporating
insect
excrement
and
damaged
leaves.