The influence of continuous contact on larval colour in the larger pellucid hawk moth, Cephonodes hylas L. (Lepidoptera: Sphingidae)


Sasakawa, M.

Applied Entomology and Zoology 8(3): 198

1973


In further studies in Japan on the factors influencing larval coloration in Cephonodes hylas (L.), larvae were confined singly in such a way that the body surface was continually in contact with plastic strips and they could move only forwards and backwards. Leaves of cape jasmine [Gardenia jasminoides] were provided as food. All larvae that survived to the fourth or fifth instar were dark in colour, and it is suggested that the darkening obtained when rearing is carried out under crowded conditions [cf. loc. cit.] is a result of continual contact between the larvae.

SHORT
COMMUNICATIONS
The
Influence
of
Continuous
Contact
on
Larval
Colour
in
the
Larger
Pellucid
Hawk
Moth,
Cephonodes
hylas
L.
(Lepidoptera
:
Sphingidae)
l
'
2
It
has
been
reported
that
darkening
of
larval
colour
in
the
larger
pellucid
hawk
moth,
Cephonodes
hylas,
is
mainly
determined
by
the
density
during
the
earlier
larval
instars
as
well
as
by
temperature
(SASAKAWA
and
YAMAZAKI,
1967;
SASAKAWA,
1967).
The
following
experiment
was
undertaken
to
determine
whether
darkening
could
be
induced
by
subjecting
larvae
to
continuous
contact
during
all
instars.
Single
larvae
were
held
in
a
walkway
between
adjustable
plastic
strips
(0.2
cm
in
thickness,
15
cm
in
length)
and
supplied
daily
with
fresh
leaves
of
the
food
plant,
Cape
Jasmine,
spread
on
the
lower
side
of
walkway.
The
design
of
this
con-
tainer
enabled
changes
to
be
made
in
its
internal
dimensions
as
the
larval
size
increased.
The
body
surface
of
larva
was
always
in
contact
with
the
internal
surfaces
of
strips,
and
larva
could
move
only
forward
and
backward.
The
ends
of
the
container
were
sealed
with
cotton
mesh.
Of
52
newly-emerged
larvae
tested
at
constant
temperature
of
28°C,
29,
6
and
4
died
during
the
first,
second
and
third
instar,
respectively.
The
remainder
attained
the
fifth
and
final
instar.
As
well
as
causing
high
mortality
the
restrictive
rearing
conditions
also
slowed
down
the
rate
of
larval
development.
The
mean
duration
of
the
first
instar
was
7.5
days
and
of
succeeding
instars
6.0,
6.8,
8.6
and
10.3
days,
respectively.
The
total
duration
was
more
than
twice
that
of
darker
larvae
reared
under
normal
conditions.
In-
stances
of
additional
moults
following
the
fourth
were
also
observed.
Table
1.
PERCENTAGE
DISTRIBUTION
OF
COLOUR
RATINGS
FROM
2ND
TO
5TH
INSTAR
OF
LARVAE
SUBJECTED
TO
CONTINUOUS
CONTACT
Colour
ratings
2nd
3rd
4th
5th
A-1
A
-
2
A
-
3
100
100
P
-
1
P
-
2
7
.
7
P-
3
15.4
23.
1
P
-
4
84.6
69.2
During
rearing,
larval
colour
was
assessed
on
the
basis
of
the
colour
ratings
described
by
the
author,
that
is,
A-1:
pale
yellowish-green,
A-2:
dark
green,
A-3:
brown;
P-1:
pale
green
and
each
segment
with
minute
black
spot
on
the
supraspiracular
line,
P-2:
with
more
spots,
P-3:
with
brown
dorsal
stripe,
P-4:
entirely
dark
brown.
Colour
of
all
second-
and
third-
instar
larvae
corresponded
to
the
brown
rating
and
a
further
darkening
occurred
during
later
instars
(Table 1).
These
results
suggest
that
the
darkening
of
larval
colour
noted
in
high
density
situations
is
caused
by
continuous
contact
between
larvae.
REFERENCES
SASAKAWA,
M.
(1967)
Sci.
Rep.
Kyoto
Pref.
Univ.,
Agric.
19
:
29-36.
SASAKAWA,
M.
(1969)
Sci.
Rep.
Kyoto
Pref.
Univ.,
Agric.
21
:
42-45.
SASAKAWA,
M.
and
S.
YAMAZAKI
(1967)
Jap.
J.
appl.
Ent.
Zool.
11
:
157-163.
Mitsuhiro
SASAKAWA
3
Laboratory
of
Entomology,
Faculty
of
Agriculture,
Kyoto
Prefectural
University,
Shimogarno,
Kyoto,
606
Japan.
Received
November
6,
1972
Instar
1
Appl.
Ent.
Zool.
8
(3)
:
198
(1973).
2
Contribution
from
Lab.
Entomol.,
Kyoto
Pref.
Univ.,
No.
130.
3
I
am
indebted
to
Mr.
N.
SHIMAOKA
for
his
assistance
during
the
course
of
this
experiment,
and
also
to
Dr.
G.
H.
L.
ROTHSCHILD,
Division
of
Entomology,
CSIRO,
Canberra,
Australia,
for
his
critical
reading
of
this
paper.
198
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