Individual Variation and Sexual Dimorphism in Thamnoecha Uniformis (Butler 1875), Lepidoptera: Sphingidae

4 Pages·2002·2.3 MB·

by  Peter Smetacek

INDIVIDUAL VARIATION AND SEXUAL DIMORPHISM
IN THAMNOECHA UNIFORMIS (BUTLER 1875),
LEPIDOPTERA: SPHINGIDAE
1
Peter Smetacek2
Key words: Lepidoptera, Sphingidae, hawkmoths, Thamnoecha uniformis
Existing information about Thamnoecha uniformis (Butler 1875) is examined and the range of
individual variation and sexual dimorphism in the species discussed.
Introduction This larva was subsequently parasitised
and no moth developed out of Since no Indian
it.
The hawkmoth Thamnoecha uniformis hawkmoth was known to feed on conifers and
(Butler 1875) is a Himalayan endemic. The uniformis was, at the time, the only known
genus is monobasic and little is known about representative of this group in the area, and
the species. Since the original description by lastly, a male uniformis was found by Dierl (op.
Butler in 1875, only males of the species were cit.) in the daytime settled on a chir pine trunk
known until Dierl (1970) described a single in Nagarjong, it was assumed that the larva was
female from Narkanda (Himachal Pradesh). that of uniformis. This has, however, not been
Although Dierl (op. cit.) observed some confirmed by actual breeding experiments.
differences between the sexes, he did not appear Although there is little reason to doubt that chir
to have more than a single pair to hand on which pine is the larval food plant of uniformis it is
,
he based his observations. The present study pertinent that Sphinx ligustri L. has been
developed out of the need to place the sexes recently reported from Kumaon (Smetacek
correctly without resorting to genitalic 1994). While ligustri is not known to feed on
examination, a task that has caused some conifers, the point is that uniformis is not the
confusion in the past. The confusion was caused only representative of the group in the western
by the relatively great individual variation in Himalaya.
such a sparingly marked species. In the present study, T. uniformis has been
This moth has been recorded from Sabathu recorded in every month from March through
near Shimla, which is the type locality, and August. It is always extremely scarce, no more
Narkanda in Himachal Pradesh; Katarmal and than one individual appearing at a time. The
Bhimtal in Kumaon and Nagarjong and southwest monsoon, which dictates the flying
m
Godaveri in Nepal. It ascends to 2,700 period ofmost hawkmoths in this area, does not
(Narkanda) and has been recorded from as low perceptibly affect the emergence pattern of
m
as 1 ,280 (Katarmal). It will probably be found uniformis. Nor has this moth been found to be
even lower in suitable localities, i.e. chir pine affected by climatic anomalies such as drought
(Pinus roxburghii Sarg.) forests. or unusually warm winters. It has always been
The larval food plant of Thamnoecha very scarce, even though its presumed larval food
uniformis is thought to be chir pine by a process plant, chir pine, covers vast tracts in Kumaon.
ofelimination. Dierl (op. cit.) found a larva with It may be added that the assessment ofits scarcity
the characteristic form and stripe of a conifer- is based on its attendance at artificial light,
feeding hawkmoth close to the Sphinx L. genus rather than actual examination of chir pine
on chir pine in Nepal. forests at appropriate times.
The only factor which seems to affect
'Accepted March, 2000
populations of this moth, besides larval
2Jones Estate, Bhimtal,Nainital, Uttaranchal 263 136, India.
26 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 99(1), APR. 2002
;
INDIVIDUAL VARIATIONANDSEXUAL DIMORPHISMINTHAMNOECHAUNIFORMIS
parasites, is forest fire, which is an almost Diagnosis: Palpi, vertex of head, thorax
regular phenomenon in chir pine forests. None and abdomen brownish-grey. The sides of head
were recorded after major fires. However, the black. Vertex of thorax cinereous grey. Collar
same can be said for all other hawkmoths and and tegulae proximally fringed with black.
insects that happen to live in or near chir pine Antennae fasciculate, terminally swollen into a
forests. club and narrow at base. Antennae more than
Both sexes are attracted to mercury vapour half the length of the forewing.
lamps of 125-160 W. They are active at dusk Forewing grey with a proximally curved
and during the early hours of darkness, almost ferruginous medial band and two similar
never appearing after 2030 hrs in summer. Their postmedial bands. The bands are distinctly
activity at dawn has not been assessed. Unlike marked in some individuals, nearly obsolete in
most hawkmoths that are active and nervous for others. One prominent black streak in the
some time after being attracted, both sexes of interspace between veins 2 (Cu ) and 3 (Cu,)
2
uniformis settle directly upon arrival and rarely and another above it in the interspace between
change position. Usually, they select a dark veins 4 (M ) and 3 (Cu,). Rarely, there is a short
3
surface to settle upon, but will do so on a white- black streak in the interspace between veins
washed pillar if no other convenient perch is 5 (M and 4 (M as in the Nepalese specimen
2) 3)
available. They rarely settle under the glare of figured by Allen (1993). These marks are
the lamp, preferring a shady comer. At rest, they variable, one or the other might be longer or
hold their wings draped laterally over the more heavily marked or one might be altogether
abdomen, the short abdomen and blunt wings obsolete. Dark points on the cilia at the veins.
giving them the appearance ofNotodontids rather Hindwing reddish-brown, cilia grey. The verso
than hawkmoths. They closely resemble the surface is uniform grey, the cilia as on
European Sphiwc pinastri L., especially at rest. the recto surface except that on the hindwing,
Althoughpinastri is knownto visit flowers atdusk, there are faint dark points discernible at the
uniformis has never been seen visiting flowers. veins.
The following is a description ofthe sexes: In the Katarmal specimen, the medial area
ofthe forewing recto, between the rufous bands,
Thamnoecha uniformis (Butler) is darker than the rest of the wing.
mm
Female: Length of forewing: 23 - 29
1875. Hyloicus uniformis Butler. Proc. (mihi).
mm mm
zool. Soc. Lond.: 261. Expanse: 53 (Dierl op. cit.) to 66
1903. Thamnoecha uniformis Rothschild (mihi).
&
Jordan. Rev. Sphing.: 153. Forewing to antenna ratio: 2.15: 1 to 2.4:
mm
Male: Length of forewing: 23-25
1 .
(mihi). Material Examined: 6 exs.: 2.vi.l974;
mm
Expanse: 50 (Dierl op. cit 18.V.1989; 6.iv.l982; 5.vi.l998; 22.viii. 1997,
.
Hampson 1892; Bell & Scott 1937) to 54 mm all collected at Jones Estate, Bhimtal, 1,500 m,
(Hampson 1892). Coll. P. Smetacek; 7.vi.l925 Bhimtal, Maxwell
BM
Forewing to antenna ratio: 1.76: 1. Coll., 1967-553 (Coll. Natural History
Material Examined: 2 exs.: 5.vii. 1989, Museum, London) (Photograph ofrecto surface
Katarmal 1,280 m Leg. R Smetacek; 2 1 .iii. 1994, examined)
m
Jones Estate, Bhimtal, 1,500 Leg. P. Diagnosis: Palpi pale grey, sometimes
Smetacek. nearly white, contrasting with the rest of the
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 99(1), APR. 2002 27
INDIVIDUAL VARIATIONANDSEXUAL DIMORPHISMINTHAMNOECHA UMIFORMIS
head. Vertex of head, vertex of thorax and description of Protoparce uniformis Butler, he
mm
abdomen grey. Collar and tegulae brownish-grey gives an expanse of 54 for the material
and defined proximally by a narrow black fringe. examined by him. Since only males were known
Antennae simple, narrow, terminally swollen into at the time, it follows that this measurement
a prominent club, the tip tapering to a point but applies to males. In the same work, Hampson
not hooked. Antennae less than half the length described Pseudosphinx concolor for the first
ofthe forewing. time and gave a measurement of 50 mm.
Forewing uniformly grey, the inner area P. concolor turned out to be a synonym of
&
faintly ferruginous or darker grey. Traces ofone uniformis. Bell Scott (1937) used Hampson’s
medial and two postmedial ferruginous bands on (1892) description of concolor in their
the costa ofsome individuals. These bands never description of uniformis and apparently
reach below vein 4 (M The two black streaks overlooked the measurement of 54 mm given by
).
3
in the interspaces between vein 4 (M and vein Hampson (op. cit.) for Protoparce uniformis.
)
3
2 (Cu ) are usually faint and often one or both This presumption is strengthened by the fact that
2
are entirely obsolete. Cilia of forewing with Protoparce uniformis is not mentioned in the
&
prominent dark points at the veins. Hindwing synonymy by Bell Scott (op. cit.), although
uniformly brownish-grey in some individuals, Pseudosphinx concolor is included.
grey in others. Verso surface uniformly grey with It is noteworthy that in Hampson’s (op.
a fine marginal dark line to both wings. cit.) description ofProtoparce uniformis males,
there is no mention of the horizontal black
Discussion streaks on the forewing recto between vein 2
(Cu2) and vein 4 (M3). Kitching {in litt.) notes
From the above, it is evident that there are that there are three males and four females in
modest but consistent differences between the the collection of the Natural History Museum
sexes, both in the external structure as well as in in London (UK). All are somewhat worn and
the pattern. The structure and length of the faded, with the pattern difficult to distinguish.
A
antennae are the most evident external structural specimen from this collection has been figured
differences. Died (1970) noted that the antennae by D’Abrera (1986), and it is ofinterest that, on
ofthe female are thinner than those ofthe male. the basis of the characters of the antennae, the
This is due to the fascicles on the male’s antennae specimen is likely to be a female, not a male as
rather than their actual thickness, which is more stated. The specimen in the same collection from
or less the same as those of the female. Dierl Bhimtal, of which a photograph was examined,
also stated that the antennae of the female are is slightly worn, particularly on the distal half
shorter than the male, reaching only a little over of the forewing recto. It lacks the horizontal
half the length of the forewing costa. In the black streaks on the forewing recto. Rothschild
&
specimens examined in the present study, the Jordan (1903) note that in all the specimens
antennae of the female are less than half the examined by them, which are the three male
length of the forewing costa, while those of the specimens mentioned above, the tips of the
male are more than half the length of the antennae were broken off.
forewing costa. The ferruginous bands on the forewing
Contrary to Dierl’s (op. cit.) observation, recto are usually more strongly developed in
size is not a distinguishing factor between the males than in females. Besides this, only females
sexes. The usual expanse given formales by most appear to have the black marginal line on the
authors is 50 mm. However, in Hampson’s (1892) verso surface of both wings.
28 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 99(1), APR. 2002
:
INDIVIDUAL VARIATIONANDSEXUAL DIMORPHISMINTHAMNOECHAUNIFORMIS
The black streaks on the forewing are Acknowledgements
variable, but despite Hampson’s (op. cit.)
description of male Protoparce uniformis I amgrateful to Ian J. KitchingoftheNatural
mentioned above, which lacks these streaks, I History Museum, London (UK) for his kind help
am of the opinion that these streaks are which made this paper possible. I am also grateful
prominent in males, while in females, they may to J.M. Cadiou for literature and the photograph
be present, or one or more might be absent. I ofthe specimen from Bhimtal, in the collection of
have a female in good condition, which entirely the Natural History Museum, London and to the
lacks both the black streaks. anonymous referees fortheirvaluable suggestions.
Refer ENCES
Allen, M. (1993): Marvellous Moths of Nepal. Know HimalErgebn. Forsch.-Unt. Nep. Him. 3/3: 319-320.
Nepal Series, No. 6. RohitKumar, Lashkar, Madhya Hampson, G.F. (1892): TheFaunaofBritishIndia including
Pradesh. Pp. 13; pi. 10. Ceylon and Burma, Moths Vol. I. Taylor & Francis,
Bell, T.R.D. & F.B. Scott (1937): The Fauna of British London. Pp. xxiii + 527.
India including Ceylon and Burma. Moths Vol. V, Rothschild, W. & K. Jordan (1903): A Revision ofthe
Sphingidae. Taylor & Francis, London. Pp. xviii + Lepidopterous Family Sphingidae. Nov. Zool. 9
537; xv pi.; 1 map. (Supp.): 972 pp., 67 pis.
D’Abrera, B. (1986): Sphingidae Mundi. E.W. Classey, Smetacek, P. (1994): AnAnnotatedListofthe Hawkmoths
Faringdon, U.K. Pp. 8 + 226. (Lepidoptera: Sphingidae) ofKumaon, N. India: A
Dierl, W. (1970): Grundzuge Einer Okologischen Probable Case ofFaunal Drift. Rec. zool. Surv. Ind.,
TiergeographiederSchwaermerOstenepals. Khumbu Occ. Paper 156 1-55.
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 99(1), APR. 2002 29