Sexual dimorphism, sex ratio and size variation in adult Cephonodes hylas (L.) (Lepidoptera: Sphingidae) infesting coffee in Nigeria


Okelana, F.A.

Cafe, Cacao, The 31(2): 135-140

1987


Cephonodes hylas is a major defoliator of coffee in Nigeria. Study of the adults showed that males and females had distinct morphological characters that can be used with considerable accuracy to separate the sexes; these relate to the antenna, the 7th tergum, the 7th sternite and the dorsal and ventral aspects of the tail hairs. Body size was not a reliable criterion for sexing adults, but the fore- and hind wings of the female were significantly longer, and the forewings also wider, than those of the male. The sex ratio was 1 male: 0.9 female.

SEXUAL
DIMORPHISM,
SEX
RATIO
AND
SIZE
VARIATION
IN
ADULT
CEPHONODES
HYLAS
(L.)
(LEPIDOPTERA
:
SPHINGIDAE)
INFESTING
COFFEE
IN
NIGERIA
F.
A.
OKELANA
*
Introduction
The
Oriental
bee-hawk
moth
Cephonodes
hylas
(L.)
(Lepidoptera
:
Sphingidae)
is
a
major
defo-
liator
pest
of
the
Robusta
coffee
Coffea
cane-
phora
(Pierre)
in
Nigeria.
As
a
preliminary
to
investigations
on
the
bio-ecology
of
this
pest,
investigations
were
carried
out
to
assess
the
extent
of
morphological
and
size
variations
as
well
as
sex
ratio
within
the
population.
According
to
Pienkowski
et
al.,
1969,
bio-ecological
research
often
necessitates
the
adoption
of
a
reliable
method
of
sexing
individuals.
Although
from
this
study,
adult
male
and
female
of
C.
hylas
can
be
separated
with
accuracy
on
the
basis
of
external
characters,
the
relative
suitability
of
body
measu-
rements
as
indices
of
size
was
also
appraised
in
each
sex.
External
sexual
and
morphometric
cha-
racteristics
differentiating
males
from
females
of
many
insect
species
have
been
studied
by
a
num-
ber
of
investigators
viz
:
Halstead,
1963
;
Glas-
gow,
1963
;
Murdie,
1969
;
Eguagie,
1970
;
Tay-
lor,
1971
and
Daramola,
1975.
Entomology
Division,
Cocoa
Research
institute
of
Nigeria,
P.M.B.
5244,
Ibadan,
Nigeria.
Materials
and
methods
Sex
differentiation
Eggs
of
C.
hylas
were
collected
from
plots
of
Robusta
coffee
at
the
Cocoa
Research
Institute
of
Nigeria,
Headquarters,
Ibadan
and
reared
to
adults
in
the
laboratory.
Twenty
0-72
h
old
labo-
ratory-reared
adults
of
the
moth
were
then
obser-
ved
closely
in
order
to
detect
morphological
diffe-
rences.
Thus
the
adults
were
separated
into
two
groups
based
on
morphological
similarities.
In
order
to
ascertain
the
sex
of
each
group,
four
insects
from
each
were
dissected
and
their
ana-
tomy
studied.
As
the
gonads
of
the
laboratory-
reared
insects
were
observed
to
be
very
immature,
matured
adults
were
caught
from
the
coffee
plots
with
sweep
net
on
sunny
afternoons
and
their
anatomy
was
studied
too.
Hence
the
sex
of
the
insects
with
similar
external
characters
was
deter-
mined.
Sex
ratio
On
the
basis
of
results
of
the
morphological
studies,
a
total
of
two
hundred
and
thirty-six
laboratory-reared
adults
of
C.
hylas
were
separa-
ted
into
males
and
females.
Cafe
Cacao
The,
vol.
XXXI,
2,
avril-juin
1987
135
Size
variation
The
body
length
(from
the
snout
to
the
tip
of
the
«
tail
»)
and
width,
fore
wing
length
and
width,
hind
wing
length
and
the
antennal
length
of
forty
male
and
forty
female
adults
of
C.
hylas
were
measured
in
situ
to
the
nearest
millimetre
using
a
strip
of
millimetre
graph
paper.
Results
and
discussion
Sex
differentiation
Comparative
drawings
indicating
sexual
diffe-
rences
found
in
various
parts
of
the
male
and
female
of
C.
hylas
are
shown
in
figures
1
A
and
B,
2
M
and
F
and
3
M
and
F.
The
antenna
The
antenna
of
C.
hylas
is
black
and
it
is
the
clavate
type.
It
affords
an
important
secondary
sexual
character.
In
the
male
(fig.
1
A),
the
antenna
is
extremely
rough
and
slightly
stouter
than
in
the
female
(fig.
1
B),
besides,
the
upper
and
lower
surfaces
of
the
flagellum
have
a
middle
white
line
(which
consists
of
aggregation
of
white
scales)
running
throughout
its
entire
length
(fig.
I
A).
On
the
other
hand,
the
female
antenna
is
smooth,
slender
and
only
the
lower
surface
of
the
flagellum
bears
the
middle
white
line
(fig.
1
B).
The
white
scales
are
easily
rubbed
off.
The
abdomen
In
dorsal
view,
the
seventh
abdominal
tergum
in
the
male
bears
a
tergite
with
a
sub-marginal
transverse
black
line
posteriorly
(fig.
2
M)
while
in
the
female,
the
seventh
tergum
lacks
a
tergite
(fig.
2
F)
and
this
possibly
allows
for
flexibility
of
the
abdominal
tip
during
oviposition.
Conse-
quently,
in
the
female,
the
abdominal
tip
merges
smoothly
into
the
tail
whereas
in
the
male
the
tail
emerges
from
below
the
seventh
abdominal
ter-
gite
(fig.
2
M
and
2
F).
Ventrally,
in
both
sexes,
there
is
a
reddish-
brown
portion
in
the
middle
of
the
sixth
and
seventh
abdominal
sternites.
The
shape
of
this
region
on
the
sixth
sternite
is
similar
in
both
sexes
while
that
on
the
seventh
sternite
varies
in
the
two
sexes
(fig.
3
M
and
3
F).
In
the
male
the
shape
of
the
portion
on
the
seventh
sternite
is
similar
to
that
of
the
sixth
sternite
but
with
a
middle
indentation
on
its
wider
posterior
end.
However
in
the
female
this
portion
on
the
seventh
sternite
is
longer
than
that
on
the
sixth
sternite
;
also,
it
is
rectangular
in
shape
with
its
posterior
part
ending
in
a
thickened
black
plate
(the
genital
plate)
furnished
with
black,
stiff
short
hairs
cove-
ring
the
anus
and
the
genital
opening
(fig.
3
F).
The
tail
The
tail
at
the
end
of
the
abdomen
is
provided
with
an
expansile
truncated
tufts
of
hairs.
Dorsal
and
ventral
colorations
and
arrangement
of
the
colours
of
the
tail
hairs
when
the
moth
is
at
rest
allows
for
easy
differentiation
of
the
sexes
with
intact
tails.
WHITE
LINE
A
II•omm
B
Fig.
1.
Dorsal
view
of
(A)
male
antenna,
(B)
female
antenna
of
Cephonodes
hylas
(L.)
136
-
-
7
1
h
ABDOMINAL
TERGITE
_
Greenish
yellow
toll
hoirs„
.
-
-
-TAIL-
- -
--
Block
tail
hairs-
-
""
--7
th
ABDOMINAL
TERGUM
(NO
TERGITE
)
13.0mm
13.0mm
11161,,.
Fig.
2.
Dorsal
view
of
the
posterior
portion
of
the
abdomen
of
a
male
(M)
and
female
(F)
Cephonodes
hybris
(L.)
showing
the
diagnostic
characters
for
separating
the
sexes
M
Reddish
brown
portionk
White
hg
hairs-
- -
-.
7
t
h
Sternite
Reddish--
brown
\\\
denitol
plate
hairs
\XIV
-
—Block
hairs_
_
_
Short
stiff
hairs
Fig.
3.
Ventral
view
of
the
posterior
portion
of
the
abdomen
of
a
male
(M)
and
female
(F)
Cephonodes
hylas
(L.)
showing
the
diagnostic
characters
for
separating
the
sexes
A
dorsal
view
of
the
tail
in
the
male
shows
that
the
sides
and
about
one-third
of
its
tip
is
black
while
the
middle
part
consists
of
tuft
of
greenish
yellow
hairs
running
downwards
from
below
the
seventh
tergite
(fig.
2
M).
In
the
female
however,
about
one-third
of
the
tip
is
also
black
but
the
black
side
coloration
encroaches
in
about
one-
third
way
on
the
left
and
right
sides
just
below
the
seventh
tergum
while
the
middle
tuft
of
gree-
nish
yellow
hairs
extends
from
the
middle
part
of
the
abdominal
tip
but
fans
out
to
the
sides
(fig.
2
F).
Ventrally,
in
the
male,
the
hairs
around
the
anus
which
originate
from
below
the
middle
part
of
the
seventh
sternite
are
slightly
whitish
and
are
bordered
by
reddish
brown
ones
while
those
at
the
sides
and
tip
of
the
tail
are
black
(fig.
3
M).
In
the
female
on
the
other
hand,
the
ventral
tail
hairs
are
completely
black
(fig.
3
F).
Sexing
of
C.
hylas
based
on
the
morphological
differences
discussed
above
was
always
correct.
Sex
ratio
Table
I
(p.
138)
shows
the
sex
ratios
of
samples
of
adults
of
C.
hylas
reared
in
the
laboratory.
The
ratios
ranged
from
I
:
0.5
to
I
:
1.5
males
to
females
in
individual
samples.
In
the
samples
of
adults
combined,
the
sex
ratio
was
one
hundred
and
twenty-six
males
to
one
hundred
and
ten.
females
which
was
approximately
1
:
0.9.
This
means
that
for
mass
rearing
of
the
moth
in
the
laboratory
one
should
expect
ten
males
to
every
nine
females.
In
the
field,
the
situation
is
likely
to
be
similar
due
to
the
fact
that
the
eggs
which
were
reared
to
adults
were
collected
from
the
field.
It
is
noteworthy
to
mention
that
over
90
%
of
the
adults
caught
with
sweep
net
on
sunny
afternoons
in
the
coffee
plots
were
females
that
have
come
to
oviposit
on
the
host
plant.
The
adult
moth
is
known
to
feed
on
the
liquid
exuda-
tes
from
coffee
flowers
(Corbett
et
al.,
1932)
but
in
Nigeria
when
the
immature
stages
of
the
pest
137
TABLE
I
Sex
ratio
in
laboratory
reared
adults
of
Cephonodes
hylas
(L.)
Number
of
Sex
ratio
Adults
Males
Females
40
24
16
1
:
0.7
18
10
8
1
:
0.8
10
5
5
1
:
1
8
5
3
1
:
0.6
23
15
8
1
:
0.5
50
24
26
1
:
1.1
56
26
30
1
:
1.3
16
11
5
1
:
0.5
15
6
9
1
:
1.5
Total
236
126
110
Sex
ratio
of
adults
combined
1
:
0.9
are
prevalent
in
the
plots,
coffee
is
either
in
the
flushing
or
fruiting
stage.
Perhaps
if
other
alter-
native
host
plants
on
which
the
adults
feed
during
its
reproductive
cycle
on
coffee
are
discovered
the
sex
ratio
of
the
moth
on
such
plant(s)
might
be
similar
to
the
obtained
1
:
0.9
males
to
females
of
the
laboratory
rearing.
Size
variation
A
number
of
factors
ranging
from
genetic
to
environmental
factors
are
known
to
be
responsi-
ble
for
inter-
and
intra-sex
variations
of
some
insects
(Murdie,
1969
;
Howe
and
Currie,
1964
;
Anderson,
1956
;
Eguagie,
1970
;
Okelana
and
Osuji,
1985).
Despite
the
fact
that
the
populations
of
C.
hylas
under
study
were
reared
in
the
labora-
tory,
males
and
females
of
the
moth
still
overlap.
ped
considerably
in
body
measurements
like
body
length
and
width,
antennal
length
;
and
wing
length
and
width.
There
was
no
significant
diffe-
rence
in
the
body
length
and
width
;
and
antennal
length
of
the
male
and
the
female.
However
the
fore-
and
hind-wing
lengths
in
the
female
were
significantly
longer
than
in
the
male.
Also
the
width
of
the
fore
wing
of
the
female
was
signifi-
cantly
wider
than
in
the
male
(table
II).
From
this
study
it
is
evident
that
size
is
only
a
suggestive
and
not
a
reliable
criterion
for
sexing
individuals
of
many
insect
species
(Eguagie,
1970)
including
C.
hylas.
TABLE
II
Morphometrics
(mm)
of
adult
Cephonodes
hylas
(L.)
Physical
character
No.
measured
Sex
Mean
±
S.E.
Range
40
M
33.0
1
.72
29.0-38.0
Body
length
40
F
33.7
1
.90
29.0-38.0
40
M
9.9
1
.20
8.0-12.0
Body
width
40
F
10.3
1
.20
8.0-12.0
40
25.9
1
.48
23.0-29.0
Fore-wing
length
40
F
27.7
1
.61
23.0-31.0
40
M
8.7
1
.06
8.0-10.0
Fore-wing
width
40
F
9.3
1
.10
8.0-10.0
Hind-wing
length
40
12.7
1
.12
10.0-14.0
40
F
13.1
1
.18
11.0-15.0
Antennal
length
40
13.3
1
.13
12.0-15.0
40
F
13.2
1
.16
11.0-15.0
M
=
male,
F
=
female
I
am
grateful
to
the
Director
of
the
Cocoa
Research
Institute
of
Nigeria
for
granting
the
permission
to
publish
this
paper.
138
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3
fig.,
11
ref.
Les
males
et
les
femelles
de
Cephonodes
hylas
(L.)
(Lepidoptera
:
Sphingidae)
possedent
des
caracteres
morphologiques
distincts
qui
peuvent
etre
utilises
avec
une
grande
precision
pour
distinguer
les
sexes.
On
peut
observer
des
differences
sur
l'antenne,
le
septieme
ter-
gum
et
le
septieme
sternite
ainsi
que
sur
les
faces
ven-
trate
et
dorsale
de
la
queue
chez
les
deux
sexes.
II
existe
une
grande
imbrication
dans
les
mensurations
corporel-
les
realisees
;
en
consequence,
la
taille
n'est
pas
un
cri-
tire
auquel
on
puisse
faire
confiance
pour
reconnaitre
le
sexe
de
C.
hylas.
Cependant,
les
ailes
anterieures
et
posterieures
de
la
femelle
sont
significativement
plus
lon-
gues
que
celles
du
male
et
les
ailes
anterieures
de
la
(emetic
sont
egalement
significativement
plus
larges
que
celles
du
male.
Le
sex-ratio
de
C.
hylas
adulte
est
de
1
:
0,9
(males/femelles).
OKELANA
(F.
A.).
-
Sexueller
Dimorphismus,
Sex-
Ratio
und
Grtissenunterschiede
beim
erwachsenen
Cephonodes
hylas
(L.)
(Lepidoptera
:.Sphingidae),
einem
nigerianischen
Kaffeebaumschiidling.
Cafe
Cacao
The
(Paris),
vol.
XXXI,
2,
avril-juin
1987,
p.
135-140,
2
tabl.,
3
fig.,
11
ref.
Die
mannlichen
und
die
weiblichen
Exemplare
des
Cephonodes
hylas
(L.)
(Lepidoptera
:
Sphingidae)
haben
unterschiedliche
morphologische
Merkmale,
die
mit
hohem
Genauigkeitsgrad
zur
geschlechtlichen
Diffe-
renzierung
herangezogen
werden
konnen.
Bei
beiden
Geschlechtern
lassen
rich
Unterschiede
an
der
Antenne,
OKELANA
(F.
A.).
-
Sexual
dimorphism,
sex
ratio
and
size
variation
in
adult
Cephonodes
hylas
(L.)
(Lepidoptera
:
Sphingidae)
infesting
coffee
in
Nige-
ria.
Cafe
Cacao
The
(Paris),
vol.
XXXI,
2,
avril-
juin
1987,
p.
135-140,
2
tabl.,
3
fig.,
11
ref.
Males
and
females
of
Cephonodes
hylas
(L.)
(Lepi-
doptera
:
Sphingidae)
possess
distinct
morphological
characters
which
can
be
used
with
considerable
accu-
racy
to
separate
the
sexes.
Differences
are
to
be
found
on
the
antenna,
the
seventh
tergum
and
seventh
sternite
as
well
as
the
dorsal
and
ventral
parts
of
the
tail
in
the
two
sexes.
There
was
a
great
overlap
in
body
measure-
ments
made
hence
size
is
not
a
reliable
criterion
for
sexing
adults
of
C.
hylas.
However
the
fore-
and
hind-
wings
of
the
female
were
significantly
longer
than
the
male
while
the
fore-wing
of
the
female
was
also
signifi-
cantly
wider
than
the
male.
The
sex
ratio
of
the
adult
moth
was
1
:
0.9
(males
to
females).
OKELANA
(F.
A.).
-
Dimorfismo
sexual,
ratio
del
sexo
y
variacion
dimensional
en
el
adulto
de
Cepho-
nodes
hylas
(L.).
(Lepidoptera
:
Sphingidae)
depreda-
dador
del
cafeto
en
Nigeria.
Cafe
Cacao
The
(Paris),
vol.
XXXI,
2,
avril-juin
1987,
p.
135-140,
2
tabl.,
3
fig.,
11
ref.
Los
machos
y
hembras
de
Cephonodes
hylas
(L.)
(Lepidoptera
:
Sphingidae)
poseen
caracteristicas
morfo-
fologicas
distintas
que
se
pueden
utilizar
con
una
gran
precision
para
establecer
la
distinciOn
entre
sexos.
Se
pueden
observar,
efectivamente,
diferencias
por
to
que
respecta
a
la
antena,
el
septimo
tergum
y
el
septimo
139