Further studies on the role of juvenile hormone in the density-related color variation in larvae of Cephonodes hylas L. (Lepidoptera: Sphingidae)


Ikemoto, H.

Applied Entomology and Zoology 18(3): 438-439

1983


Studies in Japan with larvae of Cephonodes hylas (L.) involving cervical ligation before the moult to the 5th instar and topical application of the juvenile hormone analogue methoprene (ZR-515) demonstrated that the dark pigmentation in crowded larvae is induced by reductions in the level of juvenile hormone.

438
Short
Communications
Further
Studies
on
the
Role
of
Juvenile
Hormone
in
the
Density-Related
Color
Variation
in
Larvae
of
Cephonodes
hylas
L.
(Lepidoptera
:
Sphingidae)
1
'
2
Hajime
IKEMOTO
Tokyo
Prefectural
Isotope
Research
Station,
Fukasawa,
Setagaya,
Tokyo
158,
Japan
(Received
February
5,
1983)
Cephonodes
hylas
larvae
show
body
color
change
depending
on
their
population
density
(SAsAKAwA
and
YAMAZAKI,
1967).
Three
color
patterns
can
be
discriminated
at
both
the
4th
and
5th
instar
larvae,
namely,
yellow-green
or
dark
brown
color,
presence
or
absence
of
a
dark
brown
dorsomedian
stripe,
and
a
number
of
black
spots.
Most
of
the
4th
and
5th
instar
larvae
reared
in
isolation
are
yellow-green
in
color
with
a
minute
black
spot
on
the
supraspiracular
line
in
each
segment
from
the
methothoracic
segment
to
the
8th
abdominal
seg-
ment
(black
spot
pattern
of
type
1).
When
several
larvae
are
reared
together,
many
individuals
change
to
dark
brown
or
yellow-green
with
a
dark
brown
dorsomedian
stripe.
These
darkening
larvae
are
mottled
with
many
black
spots
which
are
usually
4
to
6
in
number
on
the
subdorsal
line,
8
to
9
on
the
supraspiracular
line
and
a
large
one
lying
below
the
spiracle
in
each
segment
from
the
methothorax
to
the
end
of
the
abdomen
(black
spot
pattern
of
type
2).
Topical
application
of
juvenile
hormone
(
JH)
and
a
JH
analog,
ZR
515
(isopropyl-11-methoxy-3,
7,
11-trimethy-2,
4-dodecadienoate)
to
crowded
larvae
of
C.
hylas
caused
pale
pigmentation
of
the
solitary
phase
at
the
next
instar
(IxEmorro,
1981;
1983).
This
result
suggests
that
JH,
which
is
secreted
from
the
corpora
allata,
participates
in
pale
pigmentation
of
the
solitary
phase
of
Cepho-
nodes
larvae.
In
order
to
elucidate
whether
dark
pigmentation
in
crowded
Cephonodes
larvae
is
induced
by
lower
level
of
JH,
cervical
ligation
was
performed
on
the
isolated
larvae.
Fourth
instar
yellow-green
larvae
showing
the
black
spot
pattern
of
type
1
were
used
in
the
experiment.
When
the
ligation
was
performed
on
the
4th
Table
1.
Effect
of
ZR
515
on
coloration
in
developing
5th
instar
Cephonodes
larvae
cervically
ligatured
12
hr
before
molting
Treatments
a
No.
of
larvae
showing
these
color
typesb
Yellow-green
Yellow-green
with
a
dark
brown
dorsomedian
stripe
Dark
green
to
dark
brown
0
1
2
0
1
2
0
1
2
Ligatured
larvae
ZR
515
1.0
ttg
17
2
1
0.2
7
13
0.04
2
15
1
Control
5
1
7
3
4
Unligatured
larvae
3
17
a
Immediately
after
ligation,
ZR
515
dissolved
in
1
pl
acetone
was
topically
applied
to
each
larva.
Control
was
treated
with
acetone
alone.
For
reference,
color
types
of
the
unligatured
5th
instar
larvae
were
also
observed.
b
Upper
line
indicates
ground
color
type
and
presence
or
absence
of
a
dark
brown
dorsomedian
stripe.
Numbers
at
lower
line
indicate
black
spot
pattern.
0:
not
mottled
with
black
spots
at
all.
2:
mottled
with
many
black
spots.
1:
intermediate
between
0
and
2.
c
Ventral
region
showed
yellow-green.
1
Appl.
Ent.
Zool.
18
(3)
:
438-439
(1983)
2
Supported
in
part
by
a
Grant-in-Aid
(No.
56390006)
for
Scientific
Research,
from
the
Ministry
o
Education,
Science
and
Culture,
Japan.
NII-Electronic
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Short
Communications
439
instar
larvae
12
hr
before
molting,
many
of
them
showed
yellow-green
with
a
dark
brown
dorso-
median
stripe
or
darkening
color
(dark
green
to
dark
brown)
over
their
whole
body
after
molting
to
the
5th
instar.
Four
out
of
twenty
ligatured
larvae
showed
the
black
spot
pattern
of
type
2
(Table
1).
ZR
515
at
respective
doses
of
0.04,
0.2
and
1.0
d
ug
was
applied
to
the
dorsal
surface
of
the
abdomen
of
4th
instar
larvae
just
after
the
ligation.
Treatment
with
0.2
and
1.0
fig
of
the
chemical
caused
yellow-green
without
the
dark
brown
dorso-
median
stripe
in
all
larvae,
and
only
one
of
the
sixty
larvae
which
were
applied
with
various
doses
of
the
chemical
showed
the
spot
pattern
of
type
2.
These
results
indicate
that
dark
pigmentation
of
the
iso-
lated
larvae
induced
by
cervical
ligation
may
surely
be
due
to
a
deficiency
of
JH.
By
high
dose
of
the
chemical,
larvae
without
black
spots
(the
pattern
of
type
0)
increased
in
number.
While
few
of
type
0
were
observed
in
unligatured
larval
plot
(Table
1).
The
results
of
the
present
experiment
suggest
that
a
decrease
of
JH
favours
dark
pigmentation
in
the
crowded
Cephonodes
larvae.
The
dark
pig-
mentation
in
larvae
of
the
armyworm,
Leucania
separata
under
crowded
condition
is
induced
by
a
peptide
hormone
originating
from
the
brain
cor-
Photoperiodic
Control
of
Adult
Diapause
in
the
Bean
Bug,
Riptortus
clavatus
THUNBERG
(Heteroptera:
Coreidae)
II.
Termination
of
Diapause
Induced
under
Different
Photoperiodsl-
Hideharu
NUMATA
and
Toshitaka
HIDAKA
Department
of
Zoology,
Faculty
of
Science,
Kyoto
University,
Sakyo,
Kyoto
606,
Japan
(Received
February
14,
1983)
In
the
study
of
insect
photoperiodism,
one
sub-
ject
of
discussion
has
been
whether
insects
respond
to
the
direction
of
change
in
photoperiod
or
to
the
absolute
duration
of
photophase
(BECK,
1980).
DANILEVSKII
(1961)
concluded
that
insect
photo-
periodism
depends
on
the
absolute
duration
of
the
photophase,
either
above
or
below
a
critical
value,
1
Appl.
Ent.
Zool.
18
(3)
:
439-441
(1983)
pora
cardiaca—corpora
allata
complex
and
sub-
oesophageal
ganglion
(OGURA,
1975;
MATSUMOTO
et
al.,
1981).
JH
does
not
play
any
role
in
the
dark
pigmentation
of
the
Leucania
larvae
(OGURA,
1975).
Dark
pigmentation
in
crowded
Cephonodes
larvae
is
dependent
on
the
production
of
ommochrome
and
melanin
(IKEMoTo,
1983),
while
that
of
crowded
Leucania
larvae
is
dependent
on
the
production
of
melanin
alone
(IwAo,
1962;
IKEA/tom,
1983).
Thus,
there
are
some
biological
differences
in
the
expression
of
dark
pigmentation
depending
on
population
density
between
Cephonodes
larvae
and
Leucania
larvae.
REFERENCES
IKEMOTO,
H.
(1981)
New
Entomol.
30
:
77-80.
IKEMOTO,
H.
(1983)
Appl.
Ent.
Zool.
18:
57-61.
IwAo,
S.
(1962)
Mew.
Coll.
Agr.
Kyoto
Univ.
84:
1-80.
MATSUMOTO,
S.,
A.
IsoGAI,
A.
SUZUKI,
N.
OGURA
and
H.
SONOBE
(1981)
Insect
Biochem.
11:
725-
733.
OGURA,
N.
(1975)
J.
Insect
Physiol.
21:
559-576.
SASAKAWA,
M.
and
S.
YAMAZAKI
(1967)
Jap.
J.
appl.
Ent.
Zool.
11:
157-163
(in
Japanese
with
an
English
summary).
rather
than
the
direction
of
change
in
photoperiod,
although
the
latter
may
have
an
additional
effect.
However,
a
number
of
insects
have
been
reported
to
respond
to
the
direction
of
change
within
a
certain
range
of
photoperiod
(see
BECK,
1980
for
review).
The
bean
bug,
Riptortus
clavatus
THUNBERG,
exhibits
a
facultative
adult
diapause
which
can
be
repeatedly
induced
by
a
short-day
photoperiod
and
terminated
by
a
long-day
photoperiod.
How-
ever,
the
photoperiodic
regime
terminating
dia-
pause
was
not
quite
identical
with
that
preventing
it.
A
photoperiod
with
a
13-hr
photophase
and
an
11-hr
scotophase
(13L-11D)
at
25°C,
induced
diapause
but
terminated
it
in
some
individuals
reared
under
10L-14D
at
25°C
(NUMATA
and
HIDAKA,
1982).
In
the
present
paper,
the
effect
of
change
in
photoperiod
on
diapause
termination
was
examined
in
adults
of
R.
clavatus
reared
under
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