Note on a nest of
Saunders’ Embiid Oligotoma saundersii (Westwood) (Insecta: Embioptera:
Oligotomidae) from Kolkata, India
Prosenjit Dawn 1,
Kailash Chandra 2 & K.A. Subramanian 3
1,2,3 Zoological Survey of India,
M-Block, New Alipore, Kolkata, West Bengal 700053, India
1 prosenjit.dawn@gmail.com, 2 kailash611@rediffmail.com
(corresponding author), 3 subbuka.zsi@gmail.com
doi: http://dx.doi.org/10.11609/JoTT.o3741.6379-84
Editor: Alexi
Popov, National Museum of Natural History, Sofia, Bulgaria. Date
of publication: 26 September 2014 (online & print)
Manuscript details: Ms #
o3741 | Received 07 August 2013 | Final received 31 July 2014 | Finally
accepted 20 August 2014
Citation: Dawn,
P., K. Chandra & K.A. Subramanian (2014).
Note on a nest of Saunders’ Embiid Oligotoma saundersii (Westwood)
(Insecta: Embioptera: Oligotomidae) from Kolkata, India. Journal of
Threatened Taxa 6(10): 6379–6384; http://dx.doi.org/10.11609/JoTT.o3741.6379-84
Copyright: © Dawn et al. 2014. Creative Commons Attribution 4.0
International License. JoTT allows unrestricted use of this article in any
medium, reproduction and distribution by providing adequate credit to the
authors and the source of publication.
Funding: Self funded.
Competing Interest: The
authors declare no competing interests.
Acknowledgements: The authors are thankful to Dr. K.
Venkataraman, Director, Zoological Survey of India, Kolkata, for providing
necessary facilities and encouragement.
For figures, images, tables -- click here
Embioptera
is one of the less worked out ancient insect orders in India. This group is mainly distributed in the
warmer tropical region, having 31 species representatives from India (Chandra
2011). The life history, social
structure and behavioural biology are known for a very limited number of
species, such as the biology of Embia major Imms by Imms (1913), study
on Oligotoma humbertiana (Saussure) by Ananthasubramanian (1956),
biology of Embia minor Mukerji by Mukerji (1927) and a study on nymphs
and adults of Oligotoma saundersii (Westwood) by Ling (1934). This present work is an attempt to study
further the biology, early life stages and reproductive structures of the
species.
Materials and Methods: The nest containing living insects was collected from a garbage
hip (mostly Coconut husk) inside home. An attempt was made to serve the colony with food, but after two days as
a few insects died, the individuals were taken out by making a dissection in
the nest and collected in 70% ethanol. In the mean time, a few behavioural statements were noted. The specimens were first examined under
a stereoscopic binocular and the body form, dimensions, colour, number and
other characteristics studied. For the detailed study some specimens were
treated with 10% KOH (cold) for varying lengths of time according to the
sclerotization, and then cleared in distilled water. After the usual process of
neutralisation and dehydration, they were cleared in clove oil and temporary
slides were made using clove oil and studied in detail under a microscope. The species was identified following the
keys by Kapur & Kripalani (1957). An attempt was made to dissect out the reproductive structures of a male
and a female adult specimen. The
number of specimens was limited thus, it was a bit uncertain to get results as
the insects were very soft. Still a
very coarse idea about the reproductive structures we have got from the
insects. The specimens were kept in
clove oil for a few weeks; the body becomes transparent enough to see the
reproductive structures from outside. The abdominal parts of these specimens were separated and treated with
10% KOH to make the sclerites loose and then the reproductive structures were
dissected out with very fine needles. After dissection, photographs were taken
with a Leica Stereo Zoom Microscope (Leica M205A) using the software Leica
Application Suit (LAS V3.8) and the necessary editing was done using Adobe
Photoshop 7.0 software. The
specimens were deposited at the National Zoological Collections, Zoological
Survey of India, Kolkata.
Result and Discussion: The nest: The nest was collected by the
third author from his house [Dover Lane, Ballygunge, Kolkata]. Generally the representatives of
Embioptera make their nest under bark or sometime in leaf-litter, forming
silk-webs around some hard scaffold material, but in this case the nests were
made by spinning silk around rice and coconut hay, dry flowers and leaves
inside the house. The nest was
irregular in shape but to some extent roundish, with a length of 7–8 cm
and a width of 5–6 cm and it was about 1cm thick (Image 3A). The nest was kept under observation for
a few days inside a plastic cover. At night the male specimens came out of the nest and two of them died
outside the nest (Image 3B). An
attempt was made to feed the insects with a rotten flower (a Hibiscusflower was there in the nest, that’s why the attempt was made with only the Hibiscus)
but failed. Then the nest was
dissected and the insects taken out. The nest consisted of long slender tubes made of fine white silk
secreted from the silk gland in the enlarged first tarsal segment of the front
legs of the insects. All
individuals both young and adults are capable of producing the silk but most of
the construction work is done by the adult females and the few last life stages
(Ling 1934). The silk tubes are
transparent enough to see the larvae and female adults from outside. The nest was built by making several
tunnels through Hibiscus flower, straw, coconut husk and a bunch of
hair.
The immature stages: As we were unable to rear the
insects, it was difficult to designate the life stages as proper instars. From the nest we have got three
different immature stages of the insect with different body lengths and
different body structures. The
immature stages of insects with incomplete metamorphosis are generally termed
as nymphs, but according to some workers, use of the word nymph should be
restricted only to the stages where wing buds or wing rudiments have developed
(Ananthasubramanian 1956). So, here
stages with wing pads are mentioned as nymph and all other earlier stages are
mentioned as larvae. Though the
female does not develop wing pads, individuals similar to male nymphs in size
and shape but lacking wing pads are considered as female nymphs here.
(i) Larvae: Size smaller, body length is from 4.034–5.008 mm and width
is from 0.608–0.643 mm (mesothorax). The body colour of this stage larva is very pale, only the mouthparts
are brownish-black due to chitinization. The gut has black spots that are the remnants of food materials (Image
1E & F).
Head:
Head is ovoid, larger in comparison with the body. Head length is from 0.667–0.708 mm
and width, which is most in the eye region is from 0.516–0.542 mm. The eyes are small.
Mouthparts:
Mandibles short, well built with numerous denticles, bases with strong
articulation. The dark colour of
the apical teeth and the cutting edge represents chitinization and a biting and
chewing type of feeding habit very well. Labrum fully covers the mandibles. Maxillary palps well developed and well visible from the dorsal
side. The tip of the lacinia is
partly chitinized.
Antennae:
Stout, short, with 15 segments. The
third and the last segments are a little elongated; other segments are ovoid
and encircled by small hairs.
Thorax:
Thoracic segments are well developed; prothorax smaller; meso- and metathorax
broader than the first one as well as their length. Legs are elongated, very similar to the
legs of adults. Fore tarsi are
swollen and modified for silk production. Middle legs are feeble.
Abdomen:
Ten abdominal segments visible, of which the first one continued with the
metathorax. Tenth abdominal segment
is triangular, not modified into any abdominal appendages. The end of the abdomen is very simple,
symmetrical, two anal cerci present.
(ii) Male Nymph: Five male nymphs were
collected from the nest. Body
whitish, only except the chitinized part of the mouthparts which was dark brown
to black. Body size was slightly
bigger than the adult male, length 7.183mm; width 0.9mm. Gut is externally visible due to presence
of remnants of food materials in the alimentary canal (Image 1G).
Head:
Head ovoid, length 0.948mm and width 0.741mm. A slight increase in the length of the
head is visible than the previous larvae. Eyes small. Antennae short,
with 19 segments of which the 3rd segment is distinctly bigger than
the others. Broad mandibles with
numerous well chitinized denticles remains covered dorsally with the labrum.
Thorax:
Thorax distinctly divided into three parts. Prothorax small, having a pair of fore
legs on the ventral side. Fore
tibiae are developed for silk production. Meso- and metathorax well built each with a pair of legs on the ventral
side and a pair of wing buds on the dorsal side. The middle legs are very weak, but the
hind legs are well built with musculature. A pointed claw is present at the end of all the legs. The wing bud is
dumbbell-shaped, whitish in colour, about 1.4mm in length, and remains covered
in wing sac (Image 2A). The line of
hairs and their follicles present on the wing bud appears as a brownish line on
it. In the earlier stages wing
venation is not clear, but in older nymph venation and tracheation are quite
clear, future vein formation can be assumed from the bud.
Abdominal
appendages: The tip of the abdomen is simple, very minute modifications towards
differentiation of the abdominal appendages are visible. The tenth tergum is not clearly divided,
but the 10th sternum is divided into two lateral plates (Image 2B).
(iii) Female Nymph: The female nymph is very
similar to the adult female in appearance, except the lighter colour due to
less sclerotization and the smaller size (Image 1H).
Head:
Similar to the male nymph, but the mandibles are a little elongated and the
antennae have about 16 segments.
Thorax:
Prothorax smaller, but fore tibiae a little more developed than in the male
nymph, seems to be more active. The
rest of the thorax is almost the same but a little wider than in the male,
except the presence of two pairs of wing buds in the male.
Abdominal
appendages: Abdominal appendages in the female nymph to some extent resemble
the adult female. The 10th tergum is triangular, undivided but the
10th sternum is divided longitudinally into two equal lateral plates
(Image 2D).
Adult Male: From the nest a few adult males escaped, and six adult male
specimens were collected. The adult
males are slightly smaller than the male nymphs, with a length from
5.96–6.5 mm and width from 0.83–0.9 mm. The general body colour is brown; head,
mouthparts and abdominal appendages are very dark due to chitinization (Image
1A).
Abdominal
terminalia, i.e., 10th abdominal tergum and sternum, modified into
species specific pattern. Process of right hemitergite (10RP1)
without a subapical spine. Process
of left hemitergite (10LP) broad spatulate, with curved sides. Left circus
basipodite (LCB) well developed, curved outwards, ending obtusely Spine of the left paraproct (LPPT)
broad, sickle-shaped. A slender,
heavily chitinized spine arises subterminally from the margin of the ninth
sternite, with two minute teeth at its base and the spine curves to the right
under the end of the sternite projecting upwards and backwards terminally
(Image 2C).
Reproductive structure: It is situated from the 5thto the last segment of the abdomen. A pair of lobular testes is suspended in the body cavity with a fine
threadlike muscle. The lower parts
of the testes are narrower and connected with thick vasa deferentia which
further downwards meets the vesicular ejaculatory duct. The ejaculatory duct opens outside in a
narrow duct through the process of hypandrium (HP). Accessory glands are present on each
side of the main reproductive structure, though their number and proper shape
and size could not be judged from the dissected specimen (Image 1C).
Adult Female: Adult females are dark brown
in colour, except the joints, which are pale in colour (Image 1B). Bigger in
size than the male adult, with a body length of 7.35mm and width of
0.913mm. The female adult differs
from the male in many aspects. Shorter antennae (2.8 mm) with 19–20
segments, second and fourth segments longer, third one smaller unlike in the
male. The mandibles are shorter with sharper teeth, dentitions more. Tibiae of fore legs well developed,
indicate the maximum ability to produce silk. Abdominal appendages are very
different from those in the male; the 10th tergum is triangular,
undivided; 8th sternum is modified to form the subgenital plate
whose posterior margin is opened for the coming out of eggs during oviposition
(Ling 1934). Female genital
aperture is visible through the middle of the 8th segment as a well
defined dark area. The cerci are symmetrical without any modification; both
basal and distal segment same in length. Tenth sternum divided in two equal lateral plates (Image 2E).
Reproductive structure: Female reproductive organ
also extends from 5th to 10th segment. Ovaries are formed of 3–4 parallel
filaments, i.e., ovarian tubules. The parallel filaments, each containing 6–7 follicles, are
supported by hard sclerotization to stick together. Filaments are connected with a thick
whitish oviduct. The ducts from
each side gradually narrow and meet together to produce a common duct
downwards. After dissection no
proper structure of accessory glands or spermatheca was visible, but their
presence is expected (Image 1D).
Behaviour: The male insects used to come out from the nest at night and they
were attracted to light. As the
nest was made around soft materials, the larvae and the females were well disguised
inside; sometime movement was visible through the transparent web wall. The larvae were far inside, and seen
only when the nest was dissected. Both the larvae and the adults were very fast in moving backward as well
as forward inside the tunnels. If
released in the open, they preferred to find a corner and made themselves
motionless; if disturbed they ran very fast. Males do not take food; their thinner
abdomen, absence of food remnants in the gut, simpler mandibles indicate
that. The eyes in the males are
well developed unlike in females, as females seldom leave the nest; on the
other hand males sometime travel good distances on wings towards light. Sometimes females with fertilized eggs
can be seen alone in the open, as they try to set a new nest.
Conclusion: These small insects are very interesting because of their typical
web building ability and social behaviour. In this study it was noticed that the insects used household waste
materials chiefly plant products such as wood, husks, dried flowers etc. to
make their nest. It indicates the
possibility for these insects to radiate globally through goods carriages,
which may be the probable cause that this species is Artificially
Cosmopolitan.. In the nest the
females are the main web builders, males are generally less in number because
they leave the nest. At a time
different life stages may be easily seen in the nest. As the insect shows hemimetabolous,
i.e., with incomplete metamorphosis, larvae do not show drastic changes in the
morphology except the measurements, development of wings and genital structures
(Table 1). It is clear that a more
detailed study and rearing of the insects will reveal some more interesting
information.
References
Ananthasubramanian, K.S. (1956). Biology of Oligotoma
humbertiana Saussure. Indian Journal of Entomology 17:
105–168.
Imms, A.D. (1913). Contribution to a Knowledge of the Structure and Biology of some
Indian Insects. II. On Embia major sp. nov., from the Himalayas. Transactions
of Linnaean Society of London 11: 167–195.
Chandra, K. (2011). Embioptera, Checklist of Indian Fauna.
http://zsi.gov.in/checklist /Indian%20 Embioptera pdf. On-line version dated 15
July 2012.
Kapur, A.P. & M.B. Kripalani (1957). Studies in Embioptera. Part
I, The Oligotomidae of India. Transactions of the Entomological Society of
London 109: 111–134.
Ling, S.W. (1934). Further notes on the biology and morphology of Oligotoma
saundersii Westwood. Peking Natural History Bulletin 9(4):
261–272.
Mukerji, S. (1927). On the morphology and bionomics of Embia minor sp. nov.
with special reference to its spinning organ. A contribution to our knowledge
of the Indian Embioptera. Records of Indian Museum 29: 253–282.