Insects physiology

1. ARTHROPODS PHYSIOLOGY

2. INTRODUCTION
EXTERNAL ANATOMY
 Exoskeleton
 head
 thorax
 abdomen
INTERNAL ANATOMY
 digestive system
 excretory system
 Reproductive system
 endocrine and nervous system
CLASS ARACHNIDA
 Morphology &structure
 Body division
 Gnathosoma
 Idiosoma

3. INTRODUCTION
 Insect physiology is the study of how insects live and
reproduce.
 Insects are arthropods meaning they have an external
skeleton that covers the internal tissues.
 The exoskeleton protects the internal tissue but also
allows for sensory systems to function.

4. EXOSKELETON
 The integument makes up the skeleton of insects
 Very strong yet flexible for movement and providing
points for muscle attachment.
 Highly variable and can be adapted for various functions.
 It can be very hard, e.g. mandibles, or very soft e.g.
integument of larvae.
 All external structures are made of cuticle, which
produces the great diversity of insect species today.
 It is the site of sensory organs and also the source of
colour.

5. Different layers of exoskeleton

6. Exoskeleton cont…..
Epicuticle
 Thinnest layer with its primary function of water protection.
 Lipids found on its surface provides protection against water
loss in terrestrial insects and water gain in aquatic insects.
 The hydrocarbons and other lipids are constantly being
transported to the surface through the `underlying cuticle in
pore canals.
 Oenocytes are a cell type usually found associated with
epidermal cells that produce the hydrocarbons.
 These are transported to epidermal cells by lipophorin, lipid
carrier protein.
 Hydrocarbons and other molecules on the surface can also be
used by insects in chemical communication with other insects
and animals.

7. Exoskeleton cont….
The exocuticle and endocuticle
 They are primarily made up of a protein and chitin complex
held tightly together with small molecular weight cross-linking
molecules called diphenols.
 Chitin is the second most abundant biopolymer on earth.
 This hydrogen bonding gives chitin some of its chemical
properties, it is resistant to swelling in water, resistant to
hydrolysis by bases and dilute acids, and to being dissolved by
organic solvents.
 Chitin microfibrils are about 2.8-5 nm in diameter and are
surrounded by a protein matrix in a helical fashion. The degree
of cross- linking with diphenols results in a hard cuticle.

8. Exoskeleton cont…..
 The exocuticle has considerably more crosslinked protein
than the endocuticle.
 The exocuticle can also be tanned resulting in a brown color.
Sclerotization and quinone tanning are processes that harden
the cuticle.
 Both use the diphenols N-acetyldopamine and N-β-
alanyldopamine as a substrate for cross-linking. A polyphenol
oxidase is the enzyme that initiates the cross-linking
pathways.

9. Exoskeleton cont…..
 Some cuticle is sclerotized, some is tanned; some have different
cross-linking diphenols in varying amounts, different proteins
and chitin content all contribute to giving cuticle its unique
properties.
 Various parts of the cuticle have different levels of diphenols
resulting in harder cuticle. N-β-alanyldopamine is found
primarily in the hardest cuticle, for example the cutting edge of
caterpillar mandibles.
 Adult leaf cutter ants have increased concentrations of zinc in
the cutting edge of the mandible.
 The thickest hardest cuticle would have a thicker exocuticle
while more pliable cuticle usually lacks the exocuticle.

10. THE MOLTING PROCESS

11. HEAD

12. Head cont….
The head of an insect is composed of a series of segments,
specialized for food gathering and manipulation, sensory perception,
and neural integration.
The head bears the eyes (compound eyes and ocelli), antennae,
and mouthparts.
The anterior part of the head is the frons.
 The anterior area below the dorsum of the head, between and
behind the eyes is the vertex.
The area below the compound eye, on the side of the head, is the
gena.
The liplike sclerite is the clypeus.

13. THE ANTENNAE
Antennae vary greatly among insects, but all follow a basic plan:
segments 1 and 2 are termed the scape and pedicel, respectively.
The remaining antennal segments (flagellomeres) are jointly called
the flagellum.

14. Antennae cont…..
Antennae function almost exclusively in sensory perception
 Detects information as motion and orientation, odor,
sound, humidity, and a variety of chemical cues.
 Some of the most common types of insect antennae)

15. types of insect antennae

16. THORAX
 The insect thorax is divided into three parts: prothorax ,
mesothorax , and metathorax
 Each segment consists of hardened plates, or sclerites.
 Dorsal sclerites are called nota (sing. notum), lateral
sclerites are called pleura (sing. pleuron), and ventral
sclerites are called sterna (sing. sternum).

17. THORAX CONT….

18. Wings
 Insects have evolved many variations of the wing.
 Membranous wings are thin and more or less transparent,
common among the Odonata and Neuroptera.

19. Wings cont….
Haltere are an extreme modification among the order
Diptera (true flies), in which the hind wings
are reduced to mere nubs used for balance
and direction during flight. HALTERE

20. Wings cont…..
 Elytra (sing. elytron) are the hardened,
heavily sclerotized forewings of beetles
(Order Coleoptera) and are modified to
protect the hind wings when at rest.

21. Wings cont,,….
 A variation of the elytra is the hemelytra.
 Forewings of Hemipterans are said to be hemelytrous-they are
hardened throughout the proximal two-thirds while the distal
portion is membranous.
 Unlike elytra, hemelytra function primarily as flight wings.
 In both cases, the membranous hind wings (when present)
are used in flight and are folded beneath the forewings when
at rest.
 The wings of butterflies and moths are covered with scales,
and mosquitoes possess scales along wing veins

22. Wings cont…..
HEMELYTRA
Membranous
hind wing

23. LEGS
 The fore-legs are located on the prothorax, the mid-legs on
the mesothorax, and the hind legs on the metathorax.
 Each leg has six major components as shown below

24. Legs cont….
Cursorial : Used
for walking/ running.
Some textbooks
distinguish the two by
calling walking legs
ambulatory or
gressorial, but the leg
structure is basically
Raptorial: Fore legs
modified for
grasping.
These are often
associated with
Preying Mantids.
Fossorial :
Fore legs and
tibiae specialized
for digging;
common in
ground-dwelling
insects

25. Legs cont….
Saltatorial: Hind legs adapted
for jumping; characterized by an
elongated femur and tibia.
Natatorial: fore or hind legs adapted
for swimming; charachterized by
elongated setae on tarsi

26. ABDOMEN
 The dorsal and ventral abdominal segments are termed terga
(singular tergum) and sterna (singular sternum), respectively.
 Spiracles usually can be found in the conjunctive tissue
between the terga and sterna of abdominal segments 1-8.
 Reproductive structures are located on the 9th segment in
males (including the aedeagus, or penis, and often a pair of
claspers) and on the 8th and 9th abdominal segments in
females (female external genitalia copulatory openings and
ovipositor).

27. Abdomen cont….

28. MODIFICATIONS OF THE OVIPOSITOR

29. INTERNAL MORPHOLOGY OF INSECTS

30. Digestive and excretory system

31. Digestive system/alimentary canal
 long tube-like structure that runs from the mouth to the anus
 centrally located within the body cavity, or hemocoel
Foregut/ stomodeum
 The anterior-most region which includes the Buccal cavity, the
esophagus, and the crop.
 Begins the breakdown of food particles and transport them to
the next region, the midgut (or mesenteron).
The midgut is the major area of digestion and absorption.
The hindgut/ proctodeum) consists of the ileum, colon, rectum,
and (often) rectal pads. The hindgut functions in water and solute
reabsorption and waste excretion.

32. Digestive system cont…..
 Gastric caecae mark the end of the foregut and beginning
of the midgut.
 The purpose of these structures is to increase surface area
for greater nutrient absorption.
 The constriction at the gastric caecae also marks the spot
of the cardiac valve.
 Malpighian tubules are creamy to yellow in color and work
in conjunction with the ileum to provide the primary site
for osmoregulation and excretion.

33. Circulatory system
 The system is open”, meaning that insects lack a complex
network of veins and arteries to help transport blood throughout
the body. Instead, insect blood (hemolymph) flows relatively
“freely” throughout the hemocoel

34. Circulatory system cont…..
 Only dorsal vessel is present in the insect circulatory system.
 Posteriorly (In the abdominal region), the dorsal vessel acts as
the heart, pumping hemolymph forward into the anterior
region (in the head and thorax), where it acts as the aorta and
dumps the hemolymph into the head.
 It flows posteriorly and is returned to the heart via ostia,

35. Nervous System
 To view the ventral nerve cord, examine the ventral
region of the roach’s body cavity for something that
resembles a railroad track running from the head
posteriorly to the abdominal region.
 The “railroad track” is made up of two nerve cords
(connectives) that run longitudinally with a series of node-
like ganglia.
 The anterior most region of the ventral nerve cord is
called the subesophageal ganglion.
 dorsal to that structure is the insect “brain” (or
supraesophageal ganglion

36. Nervous system cont…

37. Endocrine system
 Although typically produced in very small quantities, hormones
may cause profound changes in their target cells. Their effect
may be stimulatory or inhibitory.
 Categories of hormone-producing cells in an insect's body:
 Endocrine glands -- secretory structures adapted exclusively for
producing hormones and releasing them into the circulatory
system.
 Neurochemal organs -store their secretory product in a special
chamber until stimulated to release it by a signal from the
nervous system (or another hormone).
 Neurosecretory cells - respond to stimulation by producing and
secreting specific chemical messengers. They serve as a link
between the nervous system and the endocrine system
 Internal organs – includes the ovaries and testes, the fat body,
and parts of the digestive system.

38. Endocrine system cont….
 These structures form an endocrine system that helps maintain
homeostasis, coordinate behavior, and regulate grIn insects,
the largest and most obvious endocrine glands are found in the
prothorax, just behind the head.
 These prothoracic glands manufacture ecdysteroids, that
stimulate synthesis of chitin and protein in epidermal cells and
trigger a cascade of physiological events that culminates in
molting.
 Once an insect reaches the adult stage, its prothoracic glands
atrophy (wither away) and it will never molt again.
 Prothoracic glands produce and release ecdysteroids only after
they have been stimulated by prothoracicotropic hormone
(PTTH).

39. Endocrine system cont….
 The corpora allata, lie just behind the corpora cardiaca.
 They manufacture juvenile hormone (JH), that inhibits
development of adult characteristics during the immature stages
and promotes sexual maturity during the adult stage.
 Neurosecretory cells in the brain regulate activity of the corpora
allata - stimulating them to produce JH during larval or nymphal
instars, inhibiting them during the transition to adulthood, and
reactivating them once the adult is ready for reproduction.

40. Endocrine system cont….
 The neurosecretory cells produce and secrete brain hormone that
appears to be the same as PTTH
 Ovaries and testes produce gonadal hormones that coordinate
courtship and mating behaviors.
 Ventral ganglia produce eclosion hormone that helps an insect shed its
old exoskeleton and another bursicon that causes hardening and tanning
of the new one.
 There are still other hormones that control the level of sugar dissolved
in the blood, adjust salt and water balance, and regulate protein
metabolism.
 Moulting hormone stimulate a series of physiological events, apolysis,
that lead to synthesis of a new exoskeleton

41. Reproductive System
 Closely related species are often isolated from one
another via small variations in the morphology of
reproductive organs that prohibit interspecies mating.
 However, a generalized system can be constructed that
closely represents all sexually reproducing insects

42. Reproductive system cont….
Female rep system Male rep system

43. CLASS ARACHNIDA
Legs
Cephalothorax
Abdomen

44. Morphology and structure
 Almost all adult arachnids have eight legs ( Insects have 6 legs).
 They also have two further pairs of appendages that have become
adapted for feeding, defense, and sensory perception.
 The first pair, the chelicerae, serve in feeding and defense.
 The next pair, the pedipalps, have been adapted for feeding,
locomotion, and/or reproductive functions.
 In Solifugae, the palps are quite leg-like, so that these animals appear
to have ten legs.
 The larvae of mites and Ricinulei have only six legs; a fourth pair usually
appears when they moult into nymphs.

45. Morphology and structure
 Unlike insects, arachnids lacks antennae or wings. Their body
is organized into two ;prosoma/cephalothorax, and the
opisthosoma/abdomen.
 The cephalothorax is derived from the fusion of the cephalon
(head) and the thorax, and is usually covered by a single,
unsegmented carapace.
 The abdomen is segmented in the more primitive forms, but
varying degrees of fusion between the segments occur in
many groups.
 It is typically divided into a preabdomen and postabdomen,
although this is only clearly visible in scorpions, and in some
orders, such as the Acari, the abdominal sections are
completely fused.

46. Class Arachnida
 Extremely varied in lifestyle
 Some scavengers(feeding on dead and decaying remains oif plants &
animals)
 Pests of cultivated plants (feeds on living plants)
 Predatory( feeding on other mites)
 Mites are arthropods , there is considerable similarity to insects-
external jointed skeleton & distinct jointed legs.
 Mites like other arthropods moults at intervals as they grow

47. Mouth parts
 Either chewing or piercing form but do not correspond to
those of insects
 Formed from 2 pairs of appendages in the head region
sometimes borne on a projection refered as false
head(capitulum)
Chewing forms
 A pair of pincer-like chelicerae is present.
Piercing forms
 Stylet-like structures may be developed as part of feeding
apparatus.
 Plant feeding mites are essentially liquid feeders on plant
juices and have mouth parts adapted for this purpose.

48. Respiratory system
 A simple respiration tracheal system is present in many mites
which are one of the few group of organisms besides insects
to respire in this way.
 The no. of spiracles present (there may be only a single pair)
and their arrangements are features used in the classification
of mites.
 Many small mites do not possess a tracheal system and
respire through the general body surface

49. Gnathostoma
 Its a small anterior projection bearing the 3 structures that make up the
mouthparts: the hypostome, a pair of chelicerae, and the pedipalps
 The hypostome is medially located and ventral to the mouth; the
chelicerae are used to pierce or tear the skin
 The mouthparts of the Acari are modified for specialized feeding
 Mites have small mouthparts and often feed on lymph and other
secretions that are produced once the chelicerae bite the tissue
 The hypostome lacks teeth and therefore does not serve as an anchor

50. Gnathosoma cont….
 Mites possess 3 pairs of walking legs as larvae and 4 pairs as
nymphs and adults Each leg is usually divided into 6 segments:
coxa, trochanter, femur, tibia, pretarsus and tarsus (usually the
tarsus terminates in a claw)

51. Idiosoma
 The capitulum is the head and the idiosoma is the body. The
idiosoma is composed of the propodosoma, metapodosoma, and
opisthosoma. The segmentation that divides the propodosoma
from the hysterosoma is the hallmark of Arachnida .
 in Acari there is no division between the metapodosoma (thorax)
and the opisthosoma (abdomen). This makes the body rounded.
 Each leg is numbered starting from the head.
 The top portion of the capitulum, the gnathosoma, has two
additional pairs of short appendages (one of which are the
chelicerae) that have evolved for feeding, sensing, and
reproducing.
 Also, they don’t have antennae or wings like insects, but they do
have hair-like bristles called setae.

52. Illustration of Idiosoma and gnathososma

53. Illustration cont….

54.  END ……………………………………