The document discusses digestion in insects. It covers digestion of chlorophyll, lipids, wax, proteins, keratin, hemoglobin, cellulose, and other compounds. Digestion involves enzymes in the saliva and midgut secretions that break down food into smaller molecules for absorption. Some insects rely on symbiotic microorganisms like bacteria and protozoa in their guts to digest plant materials like cellulose.

1. DIGESTION OF ARTIFICIAL AND
NATURAL DIETS
SUBMITTED BY
K.A.SINDHURA
MSc Agricultural Entomology
1st semester
Anand Agricultural University
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2.  A large part of the food ingested by insects is macromolecular in the form of
polysaccharides and proteins , while lipids are present as glycerides ,phospholipids and
glycolipids.
 Generally , only small molecules can pass into tissues and large molecules must be
broken down into smaller components before absorption occurs.
 Enzymes concerned with digestion are present in saliva and in the secretions of midgut,in
addition digestion may be facilitated by microorganisms in the gut.
 DEFINITION:-The process in the alimentary canal by which food is broken up physically,as
by the action of enzymes,converted into substances suitable for absorption into the body
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3. Digestive system in insectscont...
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4. DIGESTION OF CHLOROPHYLL:-
 Chlorophyll is green pigment found in cyanobacteria and the chloroplasts of algae
and plants.
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5.  The breakdown of chlorophyll by lepidopterous larvae appears to be fundamentally
different from that by ruminant in which phylloerythrin is formed by splitting off
magnesium and phytol.
 The silkworm and also the larva of the deathshead moth Acherontia break down
chlorophyll by splitting off phytol and ,magnesium,leaving a residue of phyllobombycin.
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6.  In the pentatomid Anasa , magnesium is stored in gut wall as a result of chlorophyll
breakdown, increases progressively from the proventriculus , where there is none, to the
posterior midgut .
Squash bug- Anasa tristiscont...
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7. DIGESTION OF LIPIDS:-
 Very little is known about the digestion of lipids in insects.
 Midgut cells produce several different esterases , which probably have specificity for
different substrates.
 In caterpillars,galactosyl diglycerides,phosphatidylglycerols and phosphatidylcholines are
hydrolised to di- and mono-acylglycerides and free fatty acids.
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8. DIGESTION OF WAX:-
 The diet of galleria larvae, which feed on honey-comb, consists largely of wax..
 It is believed to comprise all the alcohol components of the wax, a part of the fatty
acids and esters of high molecular weight.
 A large part of the digestion of the wax does appear, however, to be effected by the
secretion of the larvae itself.
 Lipase, lecithinase, and cholesterol esterase are present in extracts of the larvae,
and larvae extracts can hydrolyse beeswax.
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9.  Possibly the breakdown of some of the components is begun by the bacteria present in
the gut.
 A bacterium which utilizes the fatty acids and some of the esters in bees wax,but not the
hydrocarbons and higher alcohols, has been isolated from the gut contents of galleria
larvae.
 A large part of digestion occurs by lipase,lecthinase that are present in larva that can
hydrolyse beewax.
 A closely related species of waxworm , Plodia interpunctella, has been the subject of
research which isolated two strains of bacteria from the
gut, Enterobacter asburiae and Bacillus species which have been demonstrated as
capable of growing on and decomposing polyethylene plastic in a laboratory setting.
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10.  The caterpillar of G. mellonella has attracted interest for its ability to eat and
digest polyethylene plastic.
 In laboratory experiments with G. mellonella caterpillars, about 100 caterpillars
consumed 92 milligrams of a polyethylene-plastic shopping bag over the course of 12
hours.
 While it is clear that the caterpillars are consuming the plastic, more research needs to
be done to determine if this chemistry is the result of G. mellonella or its gut flora.
 The moth's larvae break down polyethylene to ethylene glycol and a mass loss of 13%
polyethylene over 14 hours has been documented in polyethylene films.
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11. DIGESTION OF PROTIENS:-
 The digestion of proteins involves endopeptidases, which attack peptide bonds
within the protein molecule, and exopeptidases, which remove the terminal amino
acids from the molecule.
 Within these general categories, the enzymes are classified according to the
nature of their active sites and the sites at which they cleave protein molecules.
 The principal endopeptidases in the majority of insects are the serine proteases,
trypsin and chymotrypsin, which have serine at the active site.
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12.  Trypsin cleaves peptide linkages involving the carboxyl groups of arginine and lysine
residues.
 Chymotrypsin is less specific, cleaving bonds involving the carboxyl groups of tyrosine,
phenylalanine and tryptophan preferentially, and bonds involving other amino acid
residues more slowly.
 Usually both types of enzyme are present in any insect with serine proteases.
 However, in many Coleoptera and in blood-sucking Hemiptera, the main
endopeptidases have cysteine or aspartic acid at their active centers (Murdock et al.,
1987). They are called cathepsins.
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13. Proteases are of two types
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14. DIGESTION OF KERATIN:-
 Keratin is a protein occurring in wool, hair and feathers.
 Hard keratins contain 8–16% cystine and disulfide linkages between cystine residues
render the protein very stable.
 Eventhough , a number of insects normally feed on keratinous materials.
 These include larvae of the clothes moth (Tineola), carpet beetles (Dermestidae) and
numerous biting lice.
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15. Tineola larva has a complex mixture of proteolytic enzymes . In addition
to those normally present in caterpillars, it possesses a highly active cysteine
desulfhydrase which produces hydrogen sulfide from cysteine.
 This contributes to the strong reducing conditions in the gut which promote the
breaking of disulfide bonds in the keratin.
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16. DIGESTION OF HAEMOGLOBIN:-
 The digestion of the haemoglobin has been investigated in number of insects.
 In Rhodnius it may remain undigested for several weeks,but it later changed to
oxyhaemoglobin and methaemoglobin.
 The final product is said to be biliverdin , some of which is excreted in the faeces.
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17. cont...
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18.  Acid hematin is formed in the hindgut,and the contents of rectum appear to be
largely free haematin.
 Thus most of the globin is assimilated and the iron porphyrin is excreted unchanged.
 The intermediate product in haemoglobin breakdown is thought to be
verdohemochromogen,but it has not been possible to demonstrate this in the gut wall.
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19.  Digestion of hemoglobin in Anopheles an Aedes is very complete and only a
small amount of protohematin can be found in the feces.
 It has been suggested that hemolysis of erythrocytes in the diverticulum of
mosquitoes is brought about by bacteria which inhabit this region.
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20. DIGESTION OF CELLULOSE :
Cellulose is polymer of glucose in which the glucose molecules are joined by 1–4 linkages.
 The chains of cellulose are unbranched and may be several thousand units long: Hydrogen
bonds occur within and between cellulose molecules , resulting in a crystalline state which
contributes to the resistance of cellulose to digestioncont...
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21. CRICKETS AND COCKROACHES:-
 Bacteria are responsible for cellulose digestion in larval scarabid beetles and in
some crickets and cockroaches.
 The former commonly feed in decaying wood and they acquire the bacteria with the
food.
 Conditions in the fermentation chamber are highly reducing
 Detritus-feeding cockroaches, such as Periplaneta, and crickets have bacteria in
the hindgut. They may be attached to projections from the intima of the hindgut and
they enhance the insects’ ability to digest plant polysaccharides, such as xylans,
pectins and gums, and oligosaccharides, such as raffinose.
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22.  Leaf-cutting ants are dependent on specific fungi for larval food. Worker ants cut leaves,
and other parts, from living plants and carry them to the nest. Here, the ants chew the
plant fragments, removing the waxy cuticle and possibly also removing existing micro-
organisms on the plant surface
 Using feces, they build the chewed fragments into a garden which they inoculate with
hyphae from an existing garden. The fungi are Basidiomycetes that only occur in the
nests of these ants
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23. AMBROSIA BEETLES:-
 Ambrosia beetles (some Scolytinae and nearly all Platypodidae) are
associated with fungi that enable them to use the xylem of woody plants.
The fungi are the principle food of both larvae and adults, and their key role
is probably in concentrating nitrogen, present in very low concentrations in
the wood
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24.  Termitidae have huge numbers of flagellate protozoans in the ileum enlarging as a paunch .
 These organisms may constitute more than 25% of the wet weight of the insect.
 The protozoans engulf fragments of plant material and ferment the cellulose, producing
acetate and other organic acids, carbon dioxide and hydrogen.
 Fermentation is an anaerobic process and conditions in the paunch are highly reducing . The
organic acids are absorbed in the hindgut and provide a large proportion of the respiratory
substrate used by the insect.
 Other termites use fungi to digest cellulose.
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25. cont...
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26.  Species of the subfamily Macrotermitinae cultivate fungi of the genus Termitomyces in
fungus gardens.
 These gardens are formed from feces containing chewed, but only partially digested plant
fragments.
 The fungus grows on this comb, producing cellulolytic enzymes, and the termites then feed
on the fungus and the comb.
 In doing so they ingest the cellulases produced by the fungus. These may contribute to
cellulose digestion in the termite gut.
Fungal gardens of Macrotermitinae
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27. REFERENCES
 The Insects
Structure and function
Fourth edition
R.F.Chapman
 The principles of insect physiology
V.B.Wrigglesworth F.R.S
 Insect Physiology
Kenneth.D.Roedee
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