The role of juvenile hormone in the density related color variation in larvae of cephonodes hylas lepidoptera sphingidae


Ikemoto, H.

Applied Entomology & Zoology 18(1): 57-61

1983


Topical application of juvenile hormone (JH) and a juvenoid (ZR 515) to the crowded larvae of C. hylas caused pale pigmentation of the solitary phase at the next instar. Thus, the role of JH in the phase control of Cephonodes larvae and Locusta hoppers appears to be similar or identical. JH I and JH II were 4-20 times more potent than JH III in their inhibition of dark pigmentation. ZR 515 was the most effective among the chemicals used.

Appl.
Ent.
Zool.
18
(1)
:
57-61
(1983)
The
Role
of
Juvenile
Hormone
in
the
Density-Related
Color
Variation
in
Larvae
of
Cephonodes
hylas
L.
(Lepidoptera
:
Sphingidae)l
Hajime
IKEMOTO
Tokyo
Prefectural
Isotope
Research
Station,
Fukasawa,
Setagaya,
Tokyo
158,
Japan
(Received
June
26,
1982)
Topical
application
of
juvenile
hormone
(
JH)
and
a
juvenoid
(ZR
515)
to
the
crowded
larvae
of
Cephonodes
hylas
caused
pale
pigmentation
of
the
solitary
phase
at
the
next
instar.
This
result
suggests
that
the
role
of
JH
in
the
phase
control
of
Cephonodes
larvae
and
Locusta
hoppers
is
similar
or
identical.
JH
I
and
JH
II
were
4-20
times
more
potent
than
JH
III
in
their
inhibi-
tion
of
dark
pigmentation.
ZR
515
was
the
most
effective
among
the
chemicals
used.
INTRODUCTION
The
density-related
color
variation
in
larvae
of
the
larger
pellucid
hawk
moth,
Cephonodes
hylas
was
reported
by
SASAKAWA
and
YAMAZAKI
(1967).
The
topical
appli-
cation
of
a
juvenoid
(ZR
515)
to
the
1st
instar
larvae
of
C.
hylas
kept
in
crowds
caused
pale
pigmentation
characteristic
of
the
solitary
phase
at
the
next
instar
(IKEMoTo,
1981).
There
are
some
differences
in
the
color
type
of
the
crowded
Cephonodes
larvae
between
the
2nd-3rd
and
4th-5th
instars.
Further
studies
on
the
role
of
juvenile
hor-
mone
(JH)
in
the
density-related
color
variation
in
larvae
of
C.
hylas
were
carried
out
by
means
of
topical
application
of
JH
and
ZR
515
to
the
2nd
and
3rd
instar
larvae
reared
in
crowds.
MATERIALS
AND
METHODS
Eggs
of
C.
hylas
were
collected
in
the
field,
as
previously
described
(IKEMoTo,
1981).
Hatchlings
were
reared
in
a
group
of
3
individuals
at
25
±1°C
under
a
16
hr
day
time
condition.
The
chemicals
used
were
JH
I,
II,
III
and
isopropyl-11-methoxy-3,
7,
11-
trimethyl-2,
4-dodecadienoate
(ZR
515).
Both
the
2nd
and
3rd
instar
lasted
2-3
days.
The
chemicals
were
applied
topically
to
the
32
hr
old
larvae
of
the
two
instars,
respec-
tively,
by
the
method
previously
described
(IKEMoTo,
1981).
As
control,
a
plot
reared
in
isolation
was
established.
For
each
experiment,
21
individuals
were
used.
1
Supported
in
part
by
a
Grant-in-Aid
(No.
56390006)
for
Scientific
Research,
from
The
Ministry
of
Education,
Science
and
Culture,
Japan.
57
58
H.
IKEMOTO
RESULTS
Application
of
chemicals
to
the
2nd
instar
crowded
larvae
JH
I
and
JH
II,
JH
III,
and
ZR
515
were
applied
to
the
2nd
instar
crowded
larvae
within
the
dose
of
0.1-2.5,
2.5-12.5
and
0.02-2.5
pg
respectively.
The
colors
of
the
2nd
and
3rd
instar
crowded
larvae
can
be
classified
into
three
types;
yellow
green,
dark
green
and
dark
brown.
By
increasing
the
dose
of
the
chemicals,
the
yellow
green
type
grew
more
numerous
and
orange
and
light
brown
types
newly
appeared,
resulting
in
a
decrease
of
the
dark
brown
type
at
the
next,
3rd
instar.
The
orange
larvae
gradually
became
pale
yellow
green
in
color,
and
the
orange
color
faded
during
the
3rd
instar
period.
The
color
tone
of
the
light
brown
larvae
did
not
change
during
the
3rd
instar.
Neither
the
orange
nor
the
light
brown
type
appeared
in
the
control
plot
(Table
1).
This
suggested
that
the
orange
and
light
brown
types
are
intermediates
in
the
process
of
light
pigmentation
by
the
application
of
the
chemicals.
JH
I
and
JH
II
were
10-20
times
more
active
than
JH
III
in
their
inhibiting
effect
on
darkening.
ZR
515
was
the
most
effective
among
the
chemicals
used.
Usually
both
the
4th
and
5th
instar
crowded
larvae
are
dark
brown
or
yellow
green
with
many
black
spots
or
a
dark
brown
dorsomedian
stripe.
The
4th
instar
crowded
larvae
in
the
treatment
plot
also
showed
the
same
coloration,
but
their
darken-
ing
was
somewhat
paler
than
that
of
the
crowded
larvae
in
the
control
plot.
Larval
coloration
in
the
treatment
plot
did
not
differ
from
that
of
the
crowded
control
plot
at
the
5th
instar
(results
not
shown).
Table
1.
Color
types
of
3rd
instar
larvae
caused
by
topical
application
of
chemicals
to
the
preceding
2nd
instara
Chemicals
Dose
No.
of
3rd
instar
larvae
showing
these
color
types
(jig)
Yellow
green
Orange
Dark
green
Light
brown
Dark
brown
ZR
515
2.5
14
7
0.5
8
12
1
0.1
16
4
1
0.02
9
1
1
10
JH
I
2.5
11
6
2
2
0.5
8
3
4
6
0.1
7
1
6
7
JH
II
2.5
16
1
3
1
0.5
10
5
3
3
0.1
7
2
5
1
6
JH
III
12.5
6
6
3
6
2.5
4
3
2
12
Control
Crowded
4
6
11
Isolated
17
2
2
a
Hatchlings
were
reared
at
the
density
of
3
individuals
per
container
except
for
the
isolated
larvae.
Chemicals
dissolved
in
acetone
or
only
acetone
for
control
were
applied
to
the
dorsal
surface
of
abdomens.
Role
of
JH
in
Color
Variation
in
Cephonodes
hylas
Larvae
59
Table
2.
Color
types
of
4th
instar
larvae
caused
by
topical
application
of
chemicals
to
the
preceding
3rd
instara
Chemicals
Dose
(leg)
No.
of
4th
instar
larvae
showing
these
color
typesb
Yellow
green
P-1
P-2
P-3
Orange
P-1
P-2
P-3
Light
brown
P-1
P-2
P-3
Dark
brown
ZR
515
2.5
7
2
6
6
0.5
1
2
4
9
5
0.1
2
1
6
1
2
3
1
5
JH
I
12.5
5
3
2
6
1
4
2.5
5
4
1
2
3
2
2
2
0.5
3
2
6
3
7
JH
II
12.5
5
5
1
2
5
1
2
2.5
4 4
2
3
5
2
1
0.5
8
1
6
1
1
4
JH
III
25.0
4
5
3
4
2
2
1
12.5
2
7
3
3
2
4
2.5
1
3
10
2
5
Control
Crowded
3 3
9
6
Isolated
16
1
1
3
a
See
Table
1
for
rearing
densities
and
the
method
of
topical
application
of
chemicals.
b
See
the
text
for
color
grades
Application
of
chemicals
to
the
3rd
instar
crowded
larvae
JH
I
and
JH
II,
JH
III,
and
ZR
515
were
applied
to
the
3rd
instar
crowded
larvae
within
the
dose
of
0.5-12.5,
2.5-25.0
and
0.1-2.5
pg
respectively.
By
the
application
of
the
chemicals,
orange
and
light
brown
larvae
with
many
black
spots
or
a
dark
brown
dorsomedian
stripe
appeared
at
the
4th
instar
in
addition
to
the
colors
described
above
(Table
2).
These
larvae
are,
firstly,
classified
into
four
types
of
yellow
green,
orange,
light
brown
and
dark
brown
(grayish
brown—dark
brown),
respectively,
according
to
the
ground
color.
The
former
three
types
are
then
classified
further
into
three
sub-
types,
based
on
the
black
spot
pattern
and
on
the
presence
or
absence
of
a
dark
brown
dorsomedian
stripe
:
Subtype
P-1
has
a
minute
black
spot
on
the
5th
annulet
of
meso-
and
metathoracic
segments,
the
6th
annulet
from
the
1st
to
the
7th
abdominal
segments
and
the
2nd
annulet
of
the
8th
abdominal
segment.
Subtype
P-2
has
4-6
black
spots
on
the
subdorsal
line,
8-9
black
spots
contin-
uously
appearing
on
the
supraspiracular
line
and
one
large
black
spot
below
the
spiracle.
Subtype
P-3
has
a
broad,
dark
brown
stripe
on
the
dorsomedian
line
from
the
metathoracic
segment
to
the
base
of
the
caudal
horn,
in
addition
to
the
pattern
of
subtype
P-2.
Dark brown
larvae
show
a
spot
pattern
similar
to
subtype
P-2.
The
criterion
for
this
classification
is
that
previously
adopted
by
SASAKAWA
and
YAMAZAKI
(1967)
.
With
the
application
of
the
chemicals,
orange
and
light
brown
larvae
appeared,
60
H.
IKEMOTO
accompanied
by
a
decrease
in
the
dark
brown
larvae
at
the
4th
instar.
As
the
dose
increased,
subtype
P-1
increased
with
a
decrease
of
subtype
P-3.
Orange
larvae
turned
gradually
to
pale
yellow
green
during
the
4th
instar.
The
inhibiting
effect
of
ZR
515
on
dark
pigmentation
was
the
most
effective
among
the
chemicals
used.
JH
I
and
JH
II
were
only
4-5
times
more
active
than
JH
III
(Table
2).
No
differences
were
found
in
the
color
type
of
the
5th
instar
larvae
between
the
control
reared
in
crowds
and
the
treated
larvae
at
any
chemical
dosage
(results
not
shown).
Further,
no
clear
result
was
obtained
as
to
whether
or
not
larval
duration
might
be
prolonged
by
the
application
of
the
chemicals
used
in
the
present
experiment
(results
not
shown).
DISCUSSION
The
results
stated
demonstrate
that
JH
participates
in
the
pale
pigmentation
characteristic
of
the
solitary
phase
of
Cephonodes
larvae.
It
is
well
known
that
JH
causes
a
loss
of
dark
pigments
and
thus
induces
the
light
pigmentation
of
the
solitary
phase
of
the
locust
(
JoLY
and
MEYER,
1970;
L.
and
P.
JoLY,
1974).
JoLY
et
al.
(1977)
have
also
observed
higher
haemolymph
titers
of
JH
in
isolated
nymphs
and
adults
of
Locusta
migratoria
than
in
their
crowded
counterparts.
These
authors
suggest
that
higher
JH
titer
may
be
a
factor
involved
in
the
determination
of
the
solitary
phase.
However,
PENER
(1976)
suggests
that
a
key
factor
in
the
development
of
body
color
depends
on
the
susceptibility
of
a
target
tissue
to
JH
rather
than
on
the
titer
of
JH
itself.
Taking
these
factors
into
account,
it
will
be
necessary
to
elucidate
whether
the
same
target
responds
differently
to
JH
in
isolated
and
crowded
larvae
of
C.
hylas.
It
is
established
that
epidermal
ommochromes
are
frequently
associated
with
melanin
localized
on
the
overlying
cuticle
(LINZEN,
1974).
In
the
dark
brown
type
of
the
Cephonodes
larvae,
the
integument
covered
completely
with
a
black
cuticle
also
contains
ommochrome
granules;
a
similar
linkage
is
also
observed
in
the
dorsomedian
stripe
of
subtype
P-3
larvae
(IxEmorro,
unpublished
data).
In
the
armyworm,
Leu-
cania
separata,
larval
black
coloration
with
density
is
dependent
only
on
the
production
of
melanin
in
the
cuticle
(IwAo,
1962;
IxEmorro,
1968).
It
seems
likely
that
JH
is
not
responsible
for
the
pigmentation
of
the
armyworm
with
density
(OGURA,
1975).
The
author
has
suggested
that
JH
affects
light
pigmentation
by
inhibiting
the
formation
of
cuticle
melanin
and
epidermal
ommochromes
when
both
melanin
and
ommochromes
are
responsible
for
dark
coloration
in
the
larval
integuments,
as
in
the
case
of
Cephonodes
larvae
(IKEMOTO,
1981).
The
mechanisms
by
which
JH
acts
to
prevent
darkening
is
unknown.
In
the
tobacco
hornworm,
Manduca
sexta,
JH
I
and
JH
II
were
200-300
times
more
potent
than
JH
III
in
morphogenetic,
gonadotropic
and
black
mutant
larval
pigmentation
assays
(RIDDIFORD
and
AJAMI,
1973;
NIJHOUT
and
RIDDIFORD,
1974;
FAIN
and
RIDDIFORD,
1975).
In
Cephonodes
larvae,
JH
I
and
JH
II
were
only
4-20
times
more
active
than
JH
III
in
their
inhibition
of
dark
pigmentation.
Role
of
JH
in
Color
Variation
in
Cephonodes
hylas
Larvae
61
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M.
J.
and
L.
M.
RIDDIFORD
(1975)
Juvenile
hormone
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in
the
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during
late
larval
development
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the
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sexta
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H.
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H.
(1981)
Effect
of
a
juvenoid
on
the
larval
body
colour
change
depending
on
population
density
in
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hylas
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77-80.
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S.
(1962)
Studies
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L.
and
P.
JoLY
(1974)
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gregaire
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solitaire
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P.
and
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MEYER
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M.
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M.
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N.
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M.
P.
(1976)
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allata
on
yellow
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M.
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YAMAZAKI
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density
on
the
larval
coloration
and
develop-
ment
of
larva
and
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in
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hylas
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Sphingidae).
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