Insect nutrition and role of carbohydrates in the insect nutrition, Digestion, absorption, Excretion and metamorphosis

3. An inect’s ability to utilize any specific carbohydrate
depends upon a complex interrelationship including
gestation, digestive hydrolysis, absortption, and
metabolism.
The term carbohydrates is applied to polyhydroxy
aldehydes and ketones and their derivatives.
Classification of carbohydrates:
i) Pure carbohydrates.
ii) Derived carbohydrates.
iii) Conjugated carbohydrates.

4.  Pure carbohydrates: These include the simple sugars or
monosaccharides and their polymers which contain
residues of identical or different monosaccharides.
 Monosaccharides: These constitute the simpler form of
carbohydrates, which cannot be further hydrolysed.
Eg:glucose, fructose, ribose, xylose.
 Disaccharides: The bonding of two monosaccharides
form disaccharides. These two residues may be either
identical or different.

5. Xylose
Ribose

6. • Eg: maltose- 1,4 α linkage of glucose, glucose
• sucrose- 1,4 α linkage of glucose, fructose
• trehalose-1,1 α linkage of glucose, glucose
• cellobiose- β linkage of glucose, glucose
• lactose- β linkage of glucose, galactose
• Oligosaccharides: carbohydrates containing from
two to ten monosaccharide residues. The most
common oligosaccarides are di-, tri-, and tetra
saccharides.

7. maltose- 1,4 α linkage of glucose, glucose
Maltosyl trehalose

8.  Polysaccharides: These are high molecular polymers
containing many residues of monosaccharides.
 Eg: starch, glycogen, chitin,cellulose.
• Derived carbohydrates:
These include the monosaccharides which undergo
modification. These are found in large numbers in
insect cells because monosaccharides undergo
enzymatic reactions, including oxidation, reduction,
esterification and substitution.

9. • These derivatives include deoxy sugars,
phosphoric acid esters, amino sugars, alditols,
cyclitols.
 Conjugated carbohydrates: In this pure and
derived carbohydrates are combined with other
non-carbohydrate molecules.
 Insect carbohydrates and their derivatives are
found conjugative to other molecules in nucleic
acids(DNA, RNA), Nucleosides, Nucleotides,
coenzymes, and glycoproteins.

10. Carbohydrates in insect nutrition
• Carbohydrates are necessary for optimum growth,
development, reproductive activity, and survival of
individual species.
• For most species, glucose, fructose, and sucrose
are nutritionally adequate sugars
• Requirements of carbohydrates often vary
according to age, sex, and metamorphic stage.

11. • Some carbohydrates act as feeding deterrents
because they are incompletely absorbed or
hydrolyzed whereas some others are readily
absorbed but not hydrolyzed.
• At high concentrations they inhibit enzymatic
reactions involved in glycolysis and
gluconeogenesis.
• Eg. the dietary pentoses, arabinose, ribose, and
xylose inhibit larval growth of southwestern corn
borer, Diatraea grandiosella. and yellow mealworm,
Tenebrio molitor.
• The dietary hexose, galactose, is poorly utilised by
larva and adults of boll weevil, Anthonomus grandis,
even though it acts as a feeding stimulant and is
readily absorbed.

12. • The limiting factors in carbohydrate utilization
appears to be the rate of hydrolysis of
polysaccharides and oligosaccharides in the
intestinal lumen, and the rate of conversion of other
monosaccharides to glucose or fructose in the
tissues.

13. Figure illustrates how three diffrent concentrations of dietary
D-glucose affect the larval growth of D.grandoisella. when the
dietary sugar is absent

14. Carbohydrate requirements
• In larva: Insect larvae differ in the amounts of dietary
carbohydrates required for their normal growth and
development.
• This is due to difference in the rate of hydrolysis of
oligo and polysaccharides in intestinal lumen and
their conversion into glucose and fructose.

15. • Some larvae do not require carbohydrates, since
they are able to substitute dietary proteins or
lipids for carbohydrate and meet their energy
needs for growth and development from amino
acid and fatty acid oxidation.
• Eg: Tribolium castaneum, Aedes aegypti,
Musca domestica
• A high dietary starch concentration is necessary
to meet the chemical and physical feeding
requirements of larvae.

16. • Some species require moderate amount of
carbohydrates in their diet.
• For most of these species, glucose, fructose, or
sucrose comprises of 15-30% of dry weight of the
diet.
• High concentration of dietary carbohydrates are
required by the larvae which feed on starch
containing stored products. (70% dry weight)
eg: Angoumois grain moth, grain weevils.
• Larva of grain feeding insects utilise the branch
chain amylopectin portion of starch more
efficiently than the straight chain amylose portion.

17. • In adults: Adults commonly consume large
quantities of carbohydrates to meet energy
demands for flight, reproduction and longevity .
• They most commonly obtain their dietary
requirements from plant nectars and grains and
therefore consume mainly sucrose and starch.
• Adult fecundity and longevity of several grain
feeding insects depend upon adequate starch
consumption.
• Eg: long term survival of grain weevils ,
Sitophilus spp. is possible only if they consume
amylopectin rich starches which are readily
hydrolysed by their digestive amylase.

18. Digestion of carbohydrates
• Carbohydrates are generally absorbed in the form of
monosaccharides, and hence the poly and disaccharides
have to be broken down to their component
monosaccharides.
• Various enzymes are required for hydrolysis of sugars
which are secreted mainly by the salivary glands and the
epithelium of midgut.
• Two categories of carbohydrases are commonly
recognized: α and ßamylases, which hydrolyze the
glucosidic bonds of polysaccharides, and glycosidases,
which hydrolyze the glycosidic bonds of oligo and
disaccharides.

19. • α amylase : This acts on 1,4 α glucosidic
linkages in polysaccharides containing 3 or more
units of 1,4 α linked D-glucose units.
• Amylases are present in the salivary secretions
of a large number of hemipterans and
cockroaches.
• Amylase splits starch and glycogen to maltose.
• Salivary amylases of plant sucking insects help
in extra-intestinal hydrolysis of plant starch.

20. • The rate of hydrolysis of starch by α-amylase is
controlled by molecular weight and degree of
branching of the substrate.
• The branched-chain amylopectin molecule, which
makes up about 75% of starch, is usually hydrolyzed
at a higher rate than the straight-chain amylase,
which makes up the remaining 25% of most starches.
• The amylolytic activity of the salivary glands was
found to be much higher than that of the midgut,
suggesting that the ventricular amylase originates
from the salivary glands.

21. • Special digestive carbohydrases:
• Insects which are adapted to consume carbohydrate-
rich foods such as plant nectar and cellulose have
evolved specialized carbohydrate digestive
capabilities. Fore most among these insects are
honeybees and termites.

22. • The worker adult of honey bee Apis mellifera, is
dependent upon dietary nectar, containing mainly
glucose, fructose and sucrose, as a carbohydrate
source. Huber and Mathison (1976) have isolated
and characterized highlyactive sucrases from
A.mellifera that hydrolyze dietary sucrose to meet
the insect’s needs for tissue sugars and for honey
production.

23. • Cellulases: several insects have been adopted to
live and feed on dry wood. Among the wood
feeding insects some cannot digest cellulose and
so utilise the starch and sugars there by restricting
themselves to sap wood.
• Some can readily utilise cellulose either with the
help of protozoa or bacteria in their guts.
• Eg: Termites
• Some insects produce cellulases by themselves.
• Eg: cerambycids

24. • Cellulase aided by β-glucosidase, hydrolyzes
cellulose via cellodextrins, to cellotriose. and
glucose.
• In lower termites the gut contains specially modified
compartments for cellulase secreting protozoa, which
may comprise from 16 to 36% of the live weight of
termite.
• In higher termites the cellulase is produced by the
termite’s own ventricular cells.
• Digestive cellulases are also secreted by the salivary
glands and in the intestinal lumen of omnivorous and
specific wood consuming cockroaches.

25. • Hemicellulases: Hemicelluloses are mixtures of
pentosan or hexosan polysaccharides and are
usual components of wood.
• Some wood feeding beetles have enzymes in their
gut for hydrolysing hemicelluloses but are unable to
digest cellulose.
• Digestive glycosidases: Based on the nature of
glycosidic bond and the form of linkage of the
substate,5 digestive glycosidases are known to be
capable of hydrolysing all oligosaccharides and
glycosides containing the common
monosaccharides, (glucose, galactose and
fructose).

26. They are:
• α glucosidase- hydrolyses maltose, sucrose,
trehalose, raffinose, stchyose.
• α galactosidases: hydrolyse melibiose,
raffinose, stachyose.
• β glucosidase- hydrolyse cellobiose,
gentiobiose.
• β galactosidase- hydrolyses lactose
• β fructofuranosidase- hydrolyses sucrose,
raffinose

27. Absorption
• In general carbohydrates are absorbed in the midgut
in the form of monosaccharides.
• But some insects show absorption of disaccharides
and trisaccharides also.
• Eg: In braconid wasp, Microplitis crocipes, red
pumpkin beetle and the boll weevil disaccharides are
absorbed.
• There are two important limiting factors which control
the rate of sugar absorption.
1.The rate of release of fluid from the crop into midgut.
2. The rate of conversion of absorbed glucose into
trehalose.

28. • The synthesis and accumulation of hemolymph
trehalose appear to play a central role in
carbohydrate adsorption by maintaining a steep
concentration gradient of glucose between the
intestinal lumen and the haemolymph, there by
facilitating glucose uptake by the physical process of
diffusion

29. • Glucose absorbed by the epithelial cells is
transferred to the haemolymph and then transported
to the fat body for synthesis of trehalose and its
release into haemolymph.
• This results in the maintenance of a high trehalose
and low glucose concentration in the haemolymph
that in turn facilitates glucose absorbption by
maintaining a steep concentration gradient between
intestinal lumen and haeolymph.
• Absorption of mannose, fructose and galactose is
slower, since their conversion into trehalose and
glycogen is comparitively slower.

30. Excretion and detoxication
Regulation of carbohydrate excretion:
 Malphigian tubules produce an ultrafiltrate of the haemolymph
solutes that passes into the hindgut where selective resorption
of glucose,trehalose and amino acids takes place
 It is possible that an enzymatically controlled selective
permeability of the malpighian tubules is involved in the
conservation of hemolymph sugars.
e.g. the isolated malpighian tubules from adult blowfly
Calliphora vomitoria, have been shown to restrict their output
of trehalose and glucose. Trehalose may be hydrolyzed in the
tubule wall, and glucose may be reabsorbed by the tubule
itself.

31. • The excretion of a carbohydrate rich honeydew by
homopterous insects illustrates a special adaption to
accommodate a high carbohydrate and low nitrogen
diet.
• Aphids and coccids have an intestinal filter chamber
which concentrates ingested nitrogen compounds at
the expense of sugars, many of which pass through
the alimentary canal without being absorbed.
• Some insect species have evolved special
mechanisms for using unabsorbed or excreted
carbohydrates and eliminated digestive
carbohydrases in ways which have provided them
with adaptive value.

32. • Some homoptera are able to use eliminated carbohydrates to
produce spittle or protective chambers.
• Eg.The malpighian tubules of cercopid larvae secrete a
glycosaminoglycan which has been found to improve the
spreading properties of spittle.
• Insect feces may contain enzymes which have adaptive value
for the insects.
• Leaf cutting ant, Atta colombica tonsipes produce faecal
enzymes α-amylase, chitinase, and proteinase, liberate
soluble sugars and aminoacids from the debris permitting
rapid growth of mycelia of the cultivated fungus.
• The ants feed on the fluid contained within the mycelia of the
cultivated fungus.

33. Detoxication
• This reactions transform foreign organic
compounds into less toxic metabolites often
involve the formation of glycosides.
• A glycoside is formed when the toxicant or its
metabolite combines with a monosaccharide
residue through an acetal linkage at first carbon
atom.
• This reaction usually takes in the fat body.
Glycosides are important in detoxication
mechanisms because they are more polar and less
toxic than the unconjugated aglycone and are
therefore more rapidly excreted.

34. • Detoxication involving the formation of β-
glucoside takes place as follows :
• UTP +D-glucose 1-phosphate= pyrophosphate +
UDPglucose. (glucose-1- phosphate uridyltransferase)
• UDP glucose + phenol= UDP + aryl β-D-glucoside.
(UDPglucosyl transferase)
• Eg: this reactions have been found to occur
in fat body of many insects like cockroach,
locusts, housefly.

35. Carbohydrates in structural components and
pigments:
• Chitin:
• The principal structure of the insect body is chitin,
consisting mainly unbranched chains of ß-(1,4)-2-
deoxy-D-glucose (N-acetyl –D-glucosamine).
• Chitin forms an integral structural component of the
insect’s endo and exo cuticle, tracheae, intestine
(including the peritrophic membrane) and
reproductive tract, making this aminopolysaccharide
the major carbohydrate present in insect tissues.

36. • Integumental chitin is synthesized in the epidermal
cells from UDP-2-acetamido-2-deoxy-D-glucose.p
• recursor for this is synthesized in the epidermis or in
the fat body.

38. Carbohydrates in metamorphosis
• Metamorphic changes in both endopterygote and
exopterygote insects involve substantial depletions of
their carbohydrate reserves.
• During this period glycogen and trehalose supply
glucose which serves an energy source and a
substrate for the synthesis of pupal and adult tissues,
especially the cuticle.
• In preparation for metamorphosis insects usually
attain their maximum carbohydrate content as
mature non-feeding larvae.
• At this time their carbohydrate reserves are present
mainly as glycogen in the fat body and trehalose in
the hemolymph.

39. • Fully grown larvae of Galleria mellonella contains
only about 1% carbohydrate on a fresh weight
basis.
• It relies mainly upon lipids as energy source during
metamorphosis.
• These limited carbohydrate reserves are mainly
present in the fatbody as glycogen, and
haemolymph as trehalose.
• During metamorphosis these reserves are used as
immediate energy source and for the synthesis of
chitin of larval and pupal cuticle during the pupal
and adult moults.

40. • Studies with lepidopteran, H.cercopia, suggest that
the amino sugar derived from cuticular chitin
contributes to the general carbohydrate pool during
metamorphosis.
• In this species, Bade and Wyatt determined that there
was a decrease in the glycogen and trehalose content
during the spinning period of the last instar , followed
by an apparent increase at the time of the pupal
ecdysis.
• The increase appeared to occur because soluble
carbohydrates were synthesized from the amino sugar
derived from chitin.
• At the onset of metamorphosis, dipterous larvae
usually contain larger carbohydrate reserves than
lepidopterous larvae.

42. Carbohydrates in flight muscles
• The initiation and maintenance of insect fight
require a highly efficient oxidative metabolism
which is provided by carbohydrates and lipids .
• Eg: Many species of Hymenoptera , Diptera ,
and orthoptera utilize carbohydrate as a flight
fuel , whereas many species of Hemiptera , and
other orthoptera use a more balanced
combination of carbohydrate and lipid.

43.  Insects may use different energy sources
according to the stage of flight.
 Eg: Although the oxidation of fatty acids provides
the energy for sustained flight in locusts ,
carbohydrate is used as a readily mobilized
substrate to initiate flight.
 Jutsum and Goldsworthy have shown that adult
males of Locusta migratoria. rely upon energy
derived from the oxidation of carbohydrates
during the first 30min of flight.
 Most adult diptera rely upon carbohydrate
reserves to provide energy for the maintenance of
flight .

44. Carbohydrates in reproduction and embryonic
development
• Carbohydrates are necessary for the normal
functioning of the male and female reproductive
systems , as well as for the development of the
embryo.
• In males , sugars form an important constituent
of the testes and the seminal plasm.
• In females , the accumulation of carbohydrate
yolk in the oocyte is an essential preparatory
step for the successful development of the
embryo.

45. Male reproductive system
• In the male reproductive system of the honeybee
Apis mellifera, most of the carbohydrates of the
reproductive system were present in the testes.
• Glucose and fructose were most abundant and
made up 83% of the testicular carbohydrates.
• With in the semen most of the carbohydrates,
which include fructose, glucose, and trehalose,
were present in the plasm rather than
spermatozoa.
• Glucose and trehalose, together with amino acids,
probably serve as an energy source for sperm
maintenance in both the seminal vesicle and
spermatheca.

46. Female reproductive system
• In the female system, carbohydrates are necessary
for vitellogenesis and for the formation of the
glycosaminoglycans present in the vitelline
membrane and the chorion.
• Vitellogenesis involves the accumulation of
carohydrate, lipid, and protein yolk with in the
oocyte to meet the structural and metabolic needs
of the developing embryo.
• A substantial portion of the yolk is derived from
nutrient reserves of the fat body and haemolymph.

47. • Glycogen serves as the principle carbohydrate
yolk, and is usually synthesized in the ovary from
glucose and trehalose derived from the fat body
and hemolymph.
• In those insects where vitellogenesis occurs during
the pharate adult stage, the carbohydrate yolk is
laid down prior to eclosion at the expense of fat
body glycogen and hemolymph trehalose.
• Eg. Glycogen stored in the fat body of Bombyx
mori is released into the haemolymph as trehalose
and taken up by the developing oocytes in the
pharate adult.

48. • Glycogen is synthesized in insect ovaries during
the terminal phase of vitellogenesis.
• Insect oocytes may also store carbohydrates as
prosthetic groups of vitellogenic proteins.
• Ex. vitellogenin found in the haemolymph and
oocytes of the adult females of the cricket ,
Acheta domesticus is a glycoprotein and the
purified vitellogenin of Blatella germanica has
been shown to contain 8% carbohydrate and
7.6% lipid.

49. Embryonic development
• During embryonic development, carbohydrate and
lipid yolk provide the main substrate for energy
production.
• Measurements of the respiratory quotient of whole
eggs have shown a general tendency for the
quotient to decrease from about 1.0 to 0.7 during
embryonic development, suggesting that
carbohydrate yolk is utilized before lipid yolk.
• In the developing egg, glycogen is mobilized as
glucose and trehalose which are present together
with small amounts of others sugars.

50. • Trehalose makes up about 90%of the total free sugars
present in the early embryo of the grasshopper,
Aulocara ellioti.
• Carbohydrate metabolism has also been examined in the
embryos of the ovoviviparous Madeira cockroach,
Lucophaea maderae. The embryos appear to synthesize
glycogen during the early and mid sages of their
development and mobilize it just before parturition.
• Besides serving as an important energy source, glycogen
yolk also provides glucose for the synthesis of the chitin
which is laid down in the cuticle of the first stage larva.
• Glycogen yolk also provides precursors for the synthesis of
polyols, especially glycerol and sorbitol, in those species
which undergo an embryonic diapause.

51. Carbohydrates in diapause maintenance
• Diapause is state of developmental arrest
which enables an insect to survive under
adverse environmental conditions and
synchronizes the active stages of its life
cycle with available food sources.
• Diapause is a genetically controlled life
phase in which preparatory biochemical
adjustments occur such as the accumulation
of lipid and carbohydrate reserves.

52. • Most diapausing insects rely upon reserves of
triglycerides, glycogen, and trehalose, and to a
lesser extent upon proteins and amino acids to
support their metabolism.
• In diapausing larvae, pupae, adults these reserves
are accumulated mainly in the fat body and
hemolymphduring the active feeding period which
precedes the onset of diapause.
• Glycogen and trehalose reserves appear to be
most valuable during the early stages of dipause.

53. • They supply glucose to meet the limited energy
demands and serve as precursors for the
synthesis of polyhydric alcohols.
• These polyols accumilate in the tissues and
contribute to increased cold hardiness of the
insects.
• Polyols protect the insects by enhancing
supercooling in those species where freezing
would prove fatal and by minimising damage in
the freezing tolerant insects.
• Nature and quantity of carbohydrate and lipid
reserves present during diapause have been
examined in several species.

54. • Newly diapaused larvae of Diatraea grandiosella
contain about 52% lipid and 5% glycogen on a
dryweight basis.
• Diapausing pupae of Pieris brassicae accumulate
substantial amounts of trehalose which functions as
nutrient reserve and cryoprotectant.
• Maximum concentration of 12% trehalose and 4%
glycogen on a dry weight basis is present in
diapausing pupae compared with respective values
of 6% and 10% in diapausing pupae.

55. Troll-Haired' Insect