Short Communication
Stomatogastric nervous system in the larva of Oryctes
rhinoceros
(Coleoptera: Scarabaeidae)
O. Veena,1 Susha Dayandan2 and S. Sreekumar 2
1Department of Biotechnology, Kariyavattom Campus, University of Kerala, 2Department of Zoology,
University College, University of Kerala, Thiruvananthapuram, Kerala, India
Corresponding Author: O. Veena, E-mail: veenamanojkumar@gmail.com
Received: 10/08/2024; Revised: 05/10/2024; Accepted: 13/10/2024; Published: 29/01/2025
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Abstract
The larvae of Oryctes rhinoceros possess a well-developed stomatogastric nervous system. It consists of a
median frontal ganglion placed in front of the brain on the dorsal side of the oesophagus and is connected to the
brain by a pair of frontal connectives. It also gives out a single recurrent nerve to the hypocerebral ganglion. The
hypocerebral ganglion, in turn, is connected to the ingluvial ganglion located at the posterior part of the
oesophagus. The nerves associated with the stomatogastric nervous system innervates the mouth parts,
oesophagus and the anterior part of the pharyngeal musculature and plays an important role in the regulation of
feeding.
Keywords: Oryctes rhinoceros, stomatogastric nervous system, frontal ganglion, ingluvial ganglion,
hypocerebral ganglion.
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Introduction
The sensory system in insects has been evolved to numerous specialisations to permit them to detect the features
of external environment and to monitor constantly the internal state of an organism. Food selection and
gustation are of primary importance to sustain growth and development in voracious immature stages of
insects.[1] In most insects, among the external organs associated with feeding, the maxilla is the primary organ
of sensory system with virtual tasting capability. This property of maxilla is due to the presence of variously
modified integumentary sensory processes with rich nerve supply known as sensilla. In Oryctes rhinoceros two
types of sensilla are predominantly present in the maxilla viz, trichoid and basiconic sensilla.[2] The trichoid
sensilla are further recognised into pointed and blunt types. The basiconic sensilla are associated with gustatory
reception. Among the trichoid sensilla, the blunt types may be chemosensory while the pointed ones may have a
chemo-mechanosensory function. All the chemoreceptors appear to respond to phagostimulants, and deterrents
and the system appears to be both complex and plastic. [3,4] Several studies have reported changes in the number
of chemosensory sensilla on mouth parts and antennae of grasshoppers with variation in the complexity of
chemosensory environment. In insects the mouth parts including sensory structures, foregut and the anterior part
of the midgut are associated with a network of neurons and ganglia and this part of the nervous system is
referred to as stomatogastric nervous system (SGNS). It controls feeding as well as the movement of food
through the foregut and midgut. SGNS is also a centre of neuroendocrine activity due to the presence of
neurosecretory cells in one of its components, the frontal ganglion. The present report describes the
stomatogastric nerve system in the larvae of Oryctes rhinoceros.
Materials and Methods
Actively feeding larvae were ether anaesthetized and pinned dorsal side up on a wax layered petri dish flooded
with insect saline. The cuticle and head capsule of the larvae were cut open at mid dorsal line to expose the
stomatogastric nervous system (SGNS). The fat body and muscles adhering to the SGNS were removed
carefully using a pair of forceps and the parts of SGNS were observed under stereoscopic dissection microscope.
Results
Stomatogastric nervous system in the final instar larvae of Oryctes rhinoceros is well developed and found
associated with brain lying on the dorsal side of oesophagus (Figure 1). The stomatogastric nervous system
innervates the anterior parts of the alimentary canal. The integral part of the system is the median frontal
ganglion. The frontal ganglion is visible as an intact pear-shaped structure with apex pointing posteriorly, just in
front of the brain lying above the oesophagus. The frontal ganglion gives out a single frontal nerve, which
passes to clypeus and also innervates the mouthparts. The frontal ganglion is connected to the tritocerebrum by a
pair of frontal connectives which arises from the antero-lateral portions of the frontal ganglion and runs through
the sides of oesophagus to join the brain. On its way, it receives labral nerves. The labral nerves pass into the
pharyngeal musculature and to the labrum. The frontal ganglion gives out a single median recurrent nerve which
passes backward along the mid dorsal line of the oesophagus and just behind the brain it passes through the
hypocerebral ganglion to get connected to the single median ingluvial ganglion. The recurrent nerve also
innervates pharynx. The hypocerebral ganglion is connected to brain via two connectives. The ingluvial
ganglion innervates the posterior as well as the anterior midgut.
Figure 1 Stomatogastric nervous system in larvae of Oryctes rhinoceros
B : Brain SG : Suboesophageal
Ganglion
CA : Corpus allatum CC : Corpus Cardiacum
DB : Dorsal Blood Vessel FC : Frontal
FGN : Frontal ganglion FG : Frontal Ganglion
HG : Hypocerebral Ganglion IG : Ingluvial Ganglion
MG : Midgut RN : Recurrent Nerve
LN : Labral Nerves
Discussion
The present study reveals that the final instar larva of Oryctes rhinoceros has a well-developed stomatogastric
nervous system. It includes a median frontal ganglion on the dorsal surface of the oesophagus and in close
proximity with the brain.[5] This is in accordance with the earlier observations of Orlov (1924) in Oryctes
nasicornis and for other insect orders.[6] It is observed in the present study that in the larvae of Oryctes
rhinoceros, the frontal ganglion is seen as a pear-shaped intact structure with apex pointing posterior. From the
antero-lateral sides of frontal ganglion, a pair of frontal connectives arises and they run through sides of
oesophagus to the brain. Ayali (2004) has described that in Schistocera gregaria and Manduca sexta, frontal
connectives emerging from the frontal ganglion remain connected to the tritocerebrum of the brain.[7] The
frontal connectives of Oryctes larvae are found to have innervations in the pharyngeal musculature. The frontal
ganglion gives out a frontal nerve which innervates the clypeus and mandibles. In Manduca sexta, an anteriorly
directed frontal nerve innervates buccal musculature.[7] The frontal ganglion posteriorly gives out a recurrent
nerve which passes underneath the brain and enters into hypocerebral ganglion. The recurrent nerve on its way
receives innervations from the anterior part of the oesophagus as in Calliphora and Drosophila [8] and larval
Manduca sexta.[9] The recurrent nerve ends in the single ingluvial or stomachic ganglion. It innervates the
posterior part of the foregut and anterior part of the midgut. These findings are in accordance with the earlier
reports by Orlov (1924) in Oryctes nasicornis and Oryctes rhinoceros and others.[10] Variable degree of
modification from this basic Pterygota plan may be seen in other insect groups described so far by these authors.
Thomsen (1951) has described varying degree of fusion in between hypocerebral ganglion, corpora cardiaca and
corpora allata to form Weisman’s ring in Cyclorrampha (Diptera) [11]. In Ephemeroptera, Odonata, Blattoidea,
Megaloptera and Isoptera, the frontal ganglion is connected with brain at pars intercerebralis or medialis
region by a median connective. In Dictyoptera the hypocerebral ganglion gives out a median recurrent nerve
which runs back to the crop and terminates in a single ventricular ganglion, whereas hypocerebral ganglion of
Orthoptera sends out paired lateral nerves which end in ingluvial ganglion. [7,12] Apterygota represents an under
developed stomato-gastric nervous system .[13]
It is reported that the frontal ganglion innervates foregut muscles and is necessary for producing motor patterns
of foregut in Manduca sexta and adult locust.[7,9,12] Miles and booker (1994) have found that in the adult
Manduca sexta, the frontal ganglion is essential for the action of the cibarial pump during feeding.[9] Cessation
of feeding is observed in frontal ganglionectomised larvae of Oryctes rhinoceros[5], probably by exerting effects
on movement of mandibles and foregut peristalsis. From these studies it can be deduced that, in insects, frontal
ganglion is instrumental in passing food through foregut and crop emptying.[7] The regulatory action of gut
muscles can be attributed to the sensory component of the stomatogastric nervous system. Sensory information
mediated via the gut wall has shown to be instrumental in controlling feeding.[14] The volumetric feedback
from the gut influences regulation of meal size in crickets and locusts.[15,16] Clark and Langley (1963) have
reported that in Locusta migratoria the frontal ganglion forms a link in the conduction of nervous impulses
originating from the stretch receptors of pharynx passing via posterior pharyngeal nerve and frontal connectives
to the brain.[17] The present observations also agree well with these earlier reports.
Conclusion
The frontal ganglion of Oryctes rhinoceros has a critical role in feeding and moulting as reported in other insect
orders.[7] Most of the previous studies and the present study on Oryctes rhinoceros indicate that the frontal
ganglion plays an important role in growth, feeding and metamorphosis. Information on feeding and
metamorphosis can be of great value in designing alternative insect pest management strategies.[7]
Financial support and sponsorship
Nil
Conflict of interest
There are no conflicts of interest.
References
1. Zacharuk RY, Shields VD. Sensilla of immature insects. Annu Rev Entomol. 1991; 36:331-54.
2. Veena O, Susha Dayanandan, S Sreekumar. Studies on the influence of frontal ganglionectomy on feeding
and maxillar morphology of the final instar larvae of Oryctes rhinoceros (Coleoptera: Scarabaeidae).
Entomon. 2011; 36:231-6.
3. Blaney VM. Behavioural and electrophysiological studies of taste discrimination by the maxillary palps of
Locusta migratoria (L). J Exp Biol. 1975; 62:555-69.
4. Haskell PT, Schoohoven LM. The function of certain mouthpart receptors in relation to feeding in
Schistocerca gregaria (Forsk) and Locusta migratorioides (R and F). Entomol Exp Appl. 1969; 12:423-40.
5. Veena O. Regulation of feeding in coconut pest Oryctes rhinoceros (Coleoptera: Scarabaeidae).
[Dissertation]. Trivandrum: University of Kerala; 2013.
6. Orlov J. Die Innervation des Darmes der in section (Larvden Von Lamelicorneiern). Z Wiss Zool. 1924;
122:425-502.
7. Ayali A. The insect frontal ganglion and stomatogastric pattern generator networks. Neurosignals. 2004;
13:20-36.
8. Roland Spie B, Andreas Schools, Heinzel HG. Anatomy of the stomatogastric nervous system associated
with the foregut in Drosophila melanogaster and Calliphora vicina. Third instar larvae. J Morphol. 2007;
269: 272-282.
9. Miles CI, Booker R. The role of the frontal ganglion in foregut movements of the moth Manduca sexta. J
Comp Physiol. 1994;174A:755-67.
10. Kirby P, Beck R, Clarke KU. The stomatogastric nervous system of the house cricket Acheta domesticus L.
I. The anatomy of the system and the innervation of the gut. J Morphol. 1984; 180:81-103.
11. Thomsen M. Weismann’s ring and related organs in larvae of Diptera. Dan Biol Skr. 1951;6(5):32.
12. Ayali A, Zilberstein Y, Cohen N. The locust frontal ganglion: a central pattern generator network
controlling foregut rhythmic motor patterns. J Exp Biol. 2002; 205:2825-32.
13. Tembhare DB. The nervous system. In: Modern Entomology. New Delhi: Himalaya Publishers; 1997. p.
165.
14. Gelperin A. Neural control systems underlying insect feeding behaviour. Am Zool. 1972; 12:489-96.
15. Möhl B. The control of foregut movements by the stomatogastric nervous system in the European house
cricket Acheta domesticus L. J Comp Physiol. 1972; 80:1-28.
16. Simpson SJ. The role of volumetric feedback from the hindgut in the regulation of meal size in fifth-instar
Locusta migratoria nymphs. Physiol Entomol. 1983; 8:451-67.
17. Clarke KU, Langley PA. Studies on the initiation of growth and moulting in Locusta migratoria
migratorioides. J Insect Physiol. 1963; 9:363-73.
