Metabolic Systems
Energy requirement 能量需求
•In order to maintain essential life processes
•To transform the chemical energy in the environment
into electrical, mechanical, osmotic, and other forms of
chemical energy.
•Digestion is a sequence of events that result in ever
finer degradation of the foodstuffs until it is broken
into monomers that are absorbed into the body and
reassembled as needed into host structures.
Metabolic Systems
Dietary Requirements 營養需求
•Insects require basically the same nutrients as most
other animals: a source of carbon , essential amino
acids , essential fatty acids , inorganic salts , vitamins
and a source of sterol. Water is also an essential
nutrient.
•Essential Nutrients are nutrients that require a diet
source since they cannot be synthesized from other
dietary nutrients or metabolic precursors.
•The process of hydrolytically breaking large
macromolecules into their component subunits
suitable for absorption into cells.
•The sources of transformed energy include the
ingested food that contains complex carbohydrates,
fats, and proteins.
•Foods broken down in the alimentary tract to the
simpler components and absorbed through the wall
of the midgut into the hemolymph.
•The circulatory system then transports these components
to all the cells of the body, which break them down even
further and capture the chemical energy they contain.
•Each cell may use the components immediately or they
may be used to synthesize reserves for later use.
•These processes of food breakdown, utilization, and
storage are strikingly similar in almost living things.
•Insects show diverse morphologies of their digestive
systems because of their diverse diets. Generally, the
higher the protein content, the shorter the intestine; the
lower the protein content, the longer the intestine.
•The metabolic systems of only a small number of insect
species have been examined, most often cockroaches,
blow flies, fruit flies, or caterpillars.
•The evidence for the existence of complete metabolic
pathways in insects has often been based on the
presence of certain key enzymes, reaction end products,
or intermediates.
•The determination of metabolic pathways in insects is
complicated by the presence of symbiotic
microorganisms that may provide some of the steps
missing in the insect.
•This symbiotic contribution makes it difficult to
establish whether the metabolic pathways are actually
present in the insect system.
Energy production from food
Chemical energy transformation
Ingestion
Digestion: Digestive enzymes
Symbiotic microorganism: vitamins etc
Absorption:: Utilization
Storage
Cockroach, blow fly, fruit fly, caterpillars
The Insect Alimentary Tract
Foregut(stomedeum)前腸– Ectodermal
Cuticle; intima; shed and renewed
。Food fragmentation; Food storage.
Midgut(mesenteron)中腸– Endodermal
。Food Digestion; Food absorption
Peritrophic membrane
Hindgut(protodeum)後腸–Ectodermal
。Collects and conducts waste products for excretion
。Nutrient reabsorption
。 Water and Salt balance and osmotic regulation
Diversity in insect feeding and the alimentary structures
(no typical digestive tract among insects )
Diversity in diets
Mouthpart structures
Specialization of digestive tract
Ecological niches
Discontinuous feeders
Predatory or carnivorous species
Food storage mechanism
Continuous feeders
Phytophagous insects
General Structure of Alimentary Canal
The digestive tract consists of a tube of epithelial cells
running from the mouth to the anus.
Three region of insect alimentary canal
Foregut: stomodeum; ectoderm; cuticle
Midgut: endoderm; peritrophic membrane
Hindgut: proctodeum; ectoderm; cuticle
Foregut, Midgut, Hindgut
•The stomodeum and
proctodeum both
arise as invaginations
of the embryonic
ectoderm and produce
the foregut and hindgut.
•The midgut forms from
endodermal tissues and
connects with the
foregut and hindgut
during embryogenesis.
Anterior structures and the foregut
Evolution of insects from a
primitive annelid ancestor
Anterior structures and the foregut
Mouthparts (mandibulate insects)口
Biting; Cutting; Grinding
Preoral cavity
Cibarium; Hypopharynx ; Salivarium
Stylet sheath: plant-feeding hemipterans
Preoral Cavity (cibarium)前口腔
Enclosed by the mouthparts and opens into the
oral cavity or mouth
Haustellate口吻(proboscis)
Cibarium 食料腔
Extrinsic visceral muscles
Intrinsic visceral muscles
Longitudinal muscles
Circular muscles
(labium)
Salivary gland 唾腺 for salivary secretions
Labial Glands下唇腺
Evolved from the epidermal cells of labium
Salivary duct
Saliva: solvent for food; lubricates the mouthparts
Digestive enzyme:
amylase, invertase, protease, chitinases
Predatory insects: inject saliva into their hosts
Toxin: act on nervous system due to host paralyze
Anticoagulants: blood feeding insects
Salivary gland 唾腺
Salivary enzymes may perform exodigestion:
Pectinase (aphids)
Hyaluronidase
Blood feeding insects (blood feeders)
Anticoagulins: agents to increase the rate of blood flow
Predatory insects: inject saliva into their hosts
Lipolytic and proteolytic enzymes in assassin bug.
Silk-producing lepidopterans:
labial gland as silk gland
salivary gland evolved from mandibular gland
Pharynx 咽- the first region of foregut
characterized by dilator muscles from the
ventral tentorium and the dorsal fronts
muscular
sucking insects: vacuum lumen (pump)
Esophagus食道– Simple tubular
undifferentiated part, serves to pass food from
the pharynx to the crop.
Diverticula分枝盲囊:
Adult Diptera and Lepidoptera :
Pharyngeal receptors can determine and separate the ingested food
Crop嗉囊 - Enlarged area for food storage.
Food storage
May be folded, or modified into a lateral diverticulum (分枝
盲囊)in fluid feeders.
The secretion and absorption do not occur in the crop.
Because the intima limitation, but crop of Periplaneta to be
permeable to free fatty acid.
Digestion
Digestion can occur because salivary enzymes pass back with
the food and midgut enzymes are regurgitated forward.
The proventricular valve prevents the movement of solid food,
but not the regurgitation of fluids.
Proventriculus前胃
Generally a grinding function (muscular structure); various
Modified control the passage of food; retaining food (valve).
Muscular spincter:
beetles
Gizzard lined with teeth:
cockroach
Backwardly pointing spines:
fleas
The proventriculus projects into
the crop and armed with spines:
bees
Cockroaches and crickets have sclerotized plates
or teeth (denticles) for breaking up food
Denticles absent in fluid feeders
Fleas have spines for rupturing RBC
Bees have denticles (mobile lips) arranged as
sieve-like spines to strain pollen from the nectar.
The pollen is collected as a bolus and passed to the
midgut for digestion while the nectar is retained in
the crop for regurgitation to be formed into honey,
back at the hive (honey = bee barf!).
Midgut 中腸
Digestion and absorption
Most distinctive midgut cells are tall and columnar
with regular microvilli forming a brush-border on
the lumen side.
The microvilli supported by abundant of actin
filaments, great increase the area of the cell
membrane for nutrients absorption.
Schistocerca americana: 9000 microvilli/cell
about 500cm2 total midgut lumen area.
Cell types of midgut
Columnar cells: principle cells;
Regenerative cells: group in nidi
Goblet cells: single cell distribution
Endocrine cells: single cell distribution
Gastric caecae:
Columnar cells
柱狀細胞
Principle cells
Endodermal origin,
microvilli and folds
(abundant)
Digestive enzymes
synthesis and secretion
Nutrients absorption
These columnar cells contain abundant
mitochondria, ER, Golgi bodies and serve to both
secrete digestive enzymes and absorb the
products of digestion. The digestive enzyme
secreted by exocytosis or apocrine secretion.
The columnar cells have tight junctions and
septate desmosome and are covered by a
basement membrane on the hemolymph side
Regenerative cells再生細胞
Columnar cell regenerate
Midgut cells regenerate at the rate of 40-120 hours
group in nidi
The midgut is surrounded by poorly developed layers of muscles
over the epidermal cells. In the converse of the foregut, the
circular muscles cover the columnar cells with the longitudinal
muscles on the hemolymph side. The muscle layers are bounded
by a thin connective tissue sheath.
Goblet cells杯狀細胞
single cell distribution
Regulate the ion transport:
potassium ion
Processing of K+ transport:
[V-ATPase → H+ pump]
[K+/H+ antiporter]
[ it’s high energy consumption
(10% of total ATP)]
Goblet cells occur in the midgut of Lepidoptera and
Trichoptera. They secrete K+ from the hemolymph
into the lumen of the intestine.
They are especially important in Lepidoptera larvae
where the midgut is alkaline. This is important
because both the toxin of Bacillus thuringiensis and
baculovirus are active in lepidopteran larvae because
of the alkalinity (pH 10) of the midgut.
Goblet cells may also assist in excreting excess K+
from the hemolymph. They may also participate in
storage excretion of metals.
Deposit excretion and discharge during moult.
Rhodinus: hemoglobin→hematin
Endocrine cells內泌細胞
single cell distribution
Involved in the regulation of enzyme production
Insulin family: glucagons, somatostatin, β-endorphins
Tachykinin family: myotropins: as cardioaccelerators
stimulate muscle contraction
FMRF Famide-immunoreactive peptides
function in digestion
Allatostatin-like peptides: regulate CA activity
Gastric caecae胃盲囊:
Increase the surface area for secretion and absorption
Create a countercurrent flow within the gut for efficient
of digestion and absorption
Food detoxification: secondary compounds
Peritrophic Membrane圍食膜
Peritrophic membrane: peritrophic matrix (PM)
Consists of chitin microfibrils, proteins, carbohydrates
PM consist of chitin and proteins, is secreted by the midgut
cells, function as a wall to separate the food from midgut
epithelium, and they does not invaginate into the cecae.
Composition - chitin and protein: 3.7-12.9% chitin; 21–47 %
protein. Insects secrete no mucous and the PM is chitin which
is composed of acetylglucosamine -a mucopolysaccharide.
Biochemically mucopolysaccha-rides and mucoprotein and
chito-protein are closely related.
Functions of Peritrophic membran
Protection
Selective permeability
Digestion area: enzymes binding
Detoxification
Barrier of microorganism
Protection
PM is present in most insects whether they feed
on solid food or only fluids. For prevent the food
particle contact withthe epithelial cells of midgut,
avoiding damage. The PM is absent in Homoptera
and Heteroptera that feed only on plant juices.
Harmful chemical, like tannic acid, may be keep
at the small pockets which formed by PM, and then
eliminate with feces. These phytophagous insects
must have certain physicochemical properties of
the matrix in the pockets.
Barrier
The PM likely acts as a barrier to micro-organisms
thus reducing infection by protecting the gut
epithelium from abrasions by the food and as a
barrier to bacteria.
Separation
Efficient for enzyme activity.
Digestive enzyme binding
Aminopeptidase
Ultrafilter
PM pores are up to 0.2μm across and act as an
ultrafilter to screen out large molecules. No
hindrance to digestion products or digestive
enzymes.
P.M. permeable both ways to H2O, salts, acids,
mono- and disaccharides and amino acids. High
M.W. sugars (starch) and proteins (casein, albumin,
gelatin) are retained.
Diptera: 4-5 nm
Grashopper: 25-35nm
Types of PM formation
Type I: PM secret from whole cells of midgut
Orthoptera, Odonata, Coleoptera, Hymenoptera
Ephemeroptera, Lepidoptera larvae
This type is a delamination from the whole surface of
the midgut.
Consists of concentric lamellae - separate thin sheets
elaborated from the cell surface - a chitin containing
material. Wasp and bee: 1/2 doz. membrane/day several
layers, one inside the other.
In Periplaneta, the PM consists of three layers of fibrils
deposited at 60º to 90º to each other. The fibrils are formed
into a network around the microvilli of the epithelium.
Type II: anterior region cells of the midgut
Diptera, Dermaptera
Diptera and some other orders, the PM is secreted as
a viscous fluid at the anterior end of the midgut. This
fluid is forced through a mold press from by the
stomodeal invagination and the wall of the midgut so
that its forms a tube which becomes the membrane.
This membrane is formed continuously at a rate of 6
mm/h in Eristalis (Diptera). Usually larmina form is
present.
Countercurrent flow creation
Endoperitrophic space
Ectoperitrophic space
Gastric caecae
Digestion of cockroach
Preliminary digestion: crop
Further digestion: midgut:
slight acidic to neutral in pH
Fermentation chamber locate at anterior hindgut:
alkaline in pH; Bacteria symbionts
Water reabsorption occur at rectum
Dry fecal pellet form at rectum and then deposit
The digestive process about 20 hour for solid
food
Digestion of plant feeder
Specialization of alimentary tract
Digestion of the larvae of Lepidoptera insects
No digestion occur in foregut
Digestion taking place in endoperitrophic and
ectoperitrophic space
Countercurrent flow mechanism; High pH value
in midgut
Digestion of liquid plant feeding:
Homoptera, Hemiptera
Dilute nutrients; elongation of alimentary tract
Filter chamber specilization
Digestion of proteins
Protein digestion:
proteolytic enzyme: proteases; peptidases
Endopeptidases: cleave internal peptide bonds
Exopeptideses:
remove terminal amino acids from peptide chain
Dipeptidase - splits free dipeptides amino acids.
Special Proteases
Keratinase - digests wool. Tineola, dermestids, Mallophaga
Tineola: Cysteine desulfhydrase
Collagenase - splits connective tissue component of animals,
Lypoderma and Lucilia綠蠅
Endopeptidases:
cleave internal peptide bonds
Serine proteases: serine
Trypsin: cleave protein chains on the carboxyl
side of basic a.a.
Trypsin breaks the peptide bond at lysine or arginine
(dibasic amino acids). Break down protein to peptones
and polypeptides (absorb form).
Chymotrypsin: cleaves protein chains on the
carboxyl side of aromatic a.a.
tyrosine, phenylalanine, tryptophan
Exopeptideses:
remove terminal amino acids from peptide chain
Carboxypeptidases: carboxyl end of peptide chain
Aminopeptidases: N-terminal of the peptide chain,
Metal ion
as co-enzyme
Proteins digestion of mosquitoes
Secretagogus:
Early trypsin, 2 hr after blood meal
Late form of trypsin, 12 hr after blood meal,
Response for most of proteolytic activity, its
transcription were activated by early trypsin and
blood meal
Absorption: diffuse or active transport
Digestion of carbohydrates
Digestion of polysaccharides and disaccharides in food
Disaccharides
-glucosidase - most common glucosidase in insects
1-4, -glucosidic linkage
β-fructosidase; -galactosidase; β- galactosidase….et al.
β-glucosidase: phyotphagous
Invertase ; Trehalase
4
Polysaccharides
Amylases digest starch or glycogen.
Starch is degraded to maltose and glycogen to glucose.
Exoamylase: splits off maltose residues
Endoamylase: attack bonds well within the starch molecule
Digestion of carbohydrates
Cellulose digestion - requires two enzymes a celllulase to
degrade cellulose to cellobiose (-1,4-glucoglucoside) and
a hemi-cellulase (cellobiase) to degrade cellobiose to
glucose.
Most insects are able to use only the cell contents of plants,
not the cell walls, some spp. can degrade breakdown
products of plant cell walls such as: lignans, hemicellulose
and cellobiose. Anobiidae, Cerambycidae and
Ctenolepisma (silverfish) possess a cellulase and digest
plant parts completely.
Phytophagous insects
Endo-β-1,4-glucanases:
β-1,4-glucosidic bonds in the cellulose chain
Exo-β-1,4-glucanases: cleave cellobioise residues
from end of the chain
β-glucosidase: break down cellobioise into glucose
Produced by endosymbiotic microorganism: termites,
wood roaches
In termites a close symbiotic relationship: a flagellate resides
in an expansion of the hindgut and forms up to 30% of live
wt. of the insect. They digest cellulose to glucose which the
flagellates convert to acetic acid and the acetic acid is used by
the termite instead of glucose.
In termites, the protozoa are lost when the intima of the
hindgut is molted but proctodeal feeding (feeding on wood
bits and flagellates in the feces) re-infects the termite.
In Cryptocercus glucose is released from the protozoa and used directly
by the host after passing forward to the midgut. Protozoa here move into
the space between the hindgut epithelial cells and the cuticle after
apolysis. The flagellates are left in the new hindgut lumen after ecdysis.
Bacterial symbionts: for cellulose digestion
cockroaches
beetles
Fungus-growing termites
Fungus-growing ants
ingest the fungus enzymes for cellulose digestion
Produced by insect its self:
silverfish, cerambycid beetle larvae, firebrats, higher
termites, and Autralian wood-eating cockroach,
Panesthia cribrata
Monosaccharides absorption:
Passive transport usually
Active glucose transporter
Taken up by the fat body cells
Digestion of carbohydrates
Digestion of polysaccharides and disaccharides in food
Glycosidases: midgut secretion
Hydrolyze the glycosidic bonds between sugar residues
α-glucosidase: α-glucosides of sucrose,
maltose, trehalose, melezitose
β-glucosidase: β-glucosides of cellobiose, gentiobiose
α-galacosidase: α-galacosides melibiose and raffinose
β-fructosidase: β-fructosides sucrose,
gentianose, raffinose
Amylases: α-glucosidic linkage in starch and glycogen
Trehalase: hydrolyzes trehalose into 2 glucose molecules
Digestion of lipids
Lipid absorption: fatty acids and diacylglycerols
Absorbed on the anterior midgut, gastric caecae or
crop of Periplaneta
Major types of lipid in plants
Monogalactosyl diglycerides: chloroplasts
Digalactosyl diglycerides
Triacylglycerols: storage tissues such seeds
Major types of lipid in animals
Triacylglycerols
Phospholipids
Cholesterol
Major types of lipid in plants
Monogalactosyl diglycerides: chloroplasts
Digalactosyl diglycerides
Triacylglycerols: storage tissues such seeds
Major types of lipid in animals
Triacylglycerols
Phospholipids
Cholesterol
Lipid is usually ingested as triacylglycerides.
The TGL is degraded DGL(diglycerides),
MGL(monoglycerides)
FFA (free fatty acids)
Glycerol.
The absorbed lipid were transformed into
diacylglycerols by midgut cells
Lipophrins: help the lipid, cholesterol and
phospholipids transport in hemolymph
Lipolytic digestive enzymes
Lipases: lipolytic enzyme of triacylglycerols
Cleave insoluble glycerides of long-chain fatty acids
Esterases: act on glycerides of short-chain acids
Hydrolyzing carboxyl esters into alcohol and
carboxylate
May break down the cholesterol,
Important in the resistance to insecticides and
plant 2nd compounds
Phosphatases: digest the phospholips
remove the fatty acid portion from phosphatides
Galleria, wax moth, may utilise about 50% of beeswax
Lecithinnase
Cholinesterase
Insoluble in water of lipid:
Dietary lipids may be incorporated into polar
fraction for solubilization
There are no equivalent of vertebrate bile salts to
assist in solubilizing lipids, but the alkaline pH of
the midgut and the presence of lipid and FFA
liberated by digestion may assist in keeping the
lipid emulsified for better digestion.
Hindgut後腸
The hindgut is ectodermal in origin and lined by
cuticle that is thinner and more permeable than the
foregut.
Except around the rectum, the musculature is not
well-developed.
The rectal pads are tall columnar cells. Where
present the longitudinal muscles are external to the
circular. Longitudinal muscles are often collected
into strands opposite the gaps between adjacent
rectal pads.
Ileum迴腸: undifferentiated tube running back to the rectum
Ileum迴腸
Undifferentiated tube running back to the rectum.
Termites forms a pouch in which the flagellates live.
Scarabaeoidea larvae form the fermentation chamber
Heteroptera: removal of water from hemolymph.
Blowfly larvae certain cells are concerned in the
excretion of ammonia.
Ostrinia: cells of the ileum secrete the hormone
Proctodone
Endosymbiosis內共生現象
Symbionts: protozoa; bacterial; fungi
Termites: paunch
Scarabaeidae (larva): fermentation chamber
Cockroaches
Crickets
Rectum直腸
Enlarged sac; certain regions have the rectal pads,
there are usually 6 rectal pads;
Important in the reabsorption of water, salts and amino
acids from the urine
Some aquatic insects, such as larval Anisoptera
and Hlodidae, there are tracheal gills in the rectum,
and the water is pumped in and out of the rectum
so that the water round the gills is constantly
renewed. And the forcible ejection of water may
propel itself forwards rapidly.
Principal cells
Chloride cells:
Fresh water living insects for inorganic ions uptake
Cuticle permeability of hindgut
Metabolic processes in insects
Metabolism : differentiated into two processes
Catabolism : enzymatic degradation
Anabolism : enzymatic synthesis
Energy requirement
Energy transfers
Adenosine triphosphate (ATP)
Guanosine triphosphate (GTP)
Uridine triphosphate (UTP)
Nicrtinamide adenine dinucleotide (NAD+)
Flavin adenine dinucleotide (FAP)
Adenosine triphosphate (ATP)
adenine
triphosphate
ribose
diphosphate
Guanosine triphosphate (GTP)
High energy bond
Uridine triphosphate (UTP)
Redox : oxidation process & reduction process
Large molecules break down
Two carbon molecules
Chemical energy transfer
Flavin adenine dinucleotide
Nicrtinamide adenine dinucleotide
Nitrogenous wastes
elimination
Ammonia
Urea
Uric acid
Metabolism of Carbohydrates
The important carbohydrates in insects
Glycogen 肝醣 : storage carbohydrate
able to be store within cells
flight muscle : energy source of wings flight
fat body : may immediately converted to trehalose
around the digestive tract:
Trehalose 海藻醣 花粉醣: hemolymph sugar
disaccharide ; α-1.1 glycosidic linkage
α-D-glucopyranosyl-α-D-glucopyranoside
Both are able to provide an immediate source of energy
Carbohyrates metabolism in insects
Glycogen mobilization
Hemolyph sugar decline; such as stavation
Hyperglycemic hormone (HGH) release
Hypertrehalosemic hormone HTH
produced & release by corpus cardiacum
HGH activates the inactive phosphorylase kinase
results in glycogen-1-phosphate produced
and then ultimate formation of trehalose
Adipokinetidc hormone AKH
plays a similar role in mobilizing glycogen reserves
Trehalose
Major hemolymph sugar in insects
Converted by fat body cells
Concentration : 0.5 to 5.0 g/100ml
May keep high concentration in hemolymph
Reduced osmotic effects
High conc. may facilitates diffusion into all cells
Facilitate for glucose absorption from gut
Energy transfer pathway
Glycerol 3-phosphate shuttle
NADH impermeability of the
mitochondrion membrane
Glycerol 3-phosphate shuttle
NADH impermeability of the
mitochondrion membrane
Chitin幾丁質
Major component of procuticle and peritrophic membrane
Also produced by protozoans and fungi
20-40% (may be up to 50%)of total dry weight of cuticle
Polymer of N-acetyl-D-glucosamine; by 1-4 β-linkages
Chitin synthesis
Source: glucose or trehalose in hemolymph
---> glucose
Phosphorylation:
---> glucose-6-phosphate
---> fructose-6-phosphate
Aminaiton:
---> glucosamine-6-phosphate
Acetylation:
---> N-acetylglucosamine-6-phosphate
---> N-acetylglucosamine-1-phosphate
Activation:
---> uridine diphospho N-acetylglucosamine
Polymerization:
---> chitin
Phosphorylation
Aminaiton
Acetylation
Activation
Polymerization
Chitin microfibrils: 2.8 nm in thickness, 1500 residues
estimated by 18 chitin chains;
Cross-linked by hydrogen bonds between chitin chains
α,β,γcrystallographic orientations
Parallel orientation within a layer
Layers is rotated by a constant angle
Chitin microfibrils are covalently linked to the
surrounding proteins
Chitin is chemical stable:
Insoluble in water, dilute acids, alcohol, organic
solvents, and concentrated alkali
Chitin in concentrated alkali at high temperature
the acetyl groups are detached to form the chitosan
Chitin degradation
Chitinase
chitobiose
N-acetylglucosamine
Metabolism of proteins
20 essential amino acids
9 essential amino acids
must be ingested as
dietary components
11 nonessential amino acids
L-form isomers
D-form isomers
Amino acids Interconversion
Functions of amino acids
Osmotic contribution: may be 30% of total osmotic activity
Prominently in many biochemical pathways
proline: as a metabolic substrate for flight energy
tyrosine: necessary for cuticular sclerotization
glutamate: neurotransmitter of motor & muscle
Structure protein source: cuticular sclerotization
Consists of the vitellogenins
Source of storage protein
Storage protein
Essential for metamorphosis
reproduction
general body maintenance
Storage hexamerins M.W. 500,000
consists of 6 similar subunits; M.W 70,000 to 90,000
provide the a.a. source for protein synthesis in the
developmental phases that do not feed
as hemocyanins in crustaceans & celicerate arthropods
synthesized by fat body
release into hemolymph during the later larval stage
may recaptured by fat body after metamorphosis
Lipophorins
Lipoproteins serve as a lipid transporter in hydrophilic
environment
Juvenile hormones also be transported by lipophorins
Transamination
Amino acid metabolism
The keto acids ususlly
as ending product
and than conversion
into ammonia
Glutamate
Aspartate
Alanine ammonia
Amino acid degradation
acetyl CoA, pyruvate, citric acid cycle intermediates
Proline and glutamate: high concentraiton in hemolymph
serve as substrates for the citric acid cycle
Flight : blow fly
first few second: proline conc. decline; alanine increase
pyruvate accumulation for energy transfer
proline converted to glutamate by proline dehydrogenase
Proline
as the predominant substrate for flight metabolism
tsetse fly, Colorado potato beetle
Metabolism of lipids
Metabolism of lipids
Insolubility in water
High solubility in nonpolar organic solvents
Energy source : fat
fatty acid : long hydrocarbon chain
terminal carboxylate group
physical characteristics
chain length
unsaturation degree (double bond)
i.e. shorter chain and more unsaturation : more fluid
Metabolism of lipids
Carbohydrates醣類
Primarily for energy
There are no specific carbohydrate requirements
Most hexoses, oligosaccharides and sugar alcohols are
suitable, e.g. sucrose, fructose, glucose, maltose, trehalose,
lactose, and sorbitol.
Most pentose sugars are unsatisfactory.
Adult Diptera, Hymenoptera and Lepidoptera live well on
carbohydrates alone. They survive and are active on
carbohydrate
diets, but usually require protein to stimulate reproduction.
Fatty Acids脂肪酸
Used for energy and cell structure
Dietary lipid is not required since high amounts of fat are
formed from carbohydrates.
Most insects do not require dietary PUFAs.
Lepidoptera spp. may need linoleic acid ( 亞 油 酸 ) and
linolenic
acids(亞麻酸) for proper wing formation, or as slow larval
growth and
pupal failure.
Either cholesterol (zoophagous) or sitosterol (phytophagous)
must be supplied. Sitosterol, a plant sterol, is converted to
cholesterol.
Amino Acids胺基酸
Used for building proteins in the body
The amino acids are derived from the proteins consumed
by the insect. Suitability of a protein is based on its amino
acid composition.
The ten essential amino acids are required by insects:
(T.T. Hallim, VP) tryptophan, threonine, histidine,
arginine, lysine, leucine, isoleucine, methionine, valine,
and phenylalanine
An insect spp. may be adapted to its protein source.
＞Pink bollworm grows best on an artificial diet with an
amino acid composition comparable to cotton, as contrasted
with an artificial diet made with casein (milk sugar).
＞Culex pipiens is a bird feeder that also feeds on humans. C.
pipiens lays twice as many eggs when fed on bird blood as
human blood.
Some adult insects obtain their protein from the larva.
＞Saturniid silkmoths have no mouthparts and obtain all the
protein needed for eggs from larval feeding.
＞Autogenous mosquitoes make eggs without taking a
blood meal by using protein stored in the fat body from the
larva.
Diptera and some other insects require protein feeding to
initiate reproduction. This is and action on the endocrine
system to stimulate JH production or EDNH.
Excess protein can be toxic to due accumulation of excess
nitrogenous wastes.
Vitamins維他命
Most of these serve as cofactors for enzymes in general
metabolic processes found in all animals. Needs similar to
those of vertebrates.
◎The water soluble vitamins
－ ( 維 生 素B群 ): thiamine( 硫胺素 ), riboflavin( 核黃素),
nicotinic acid(菸鹼酸), pantothenic acid(泛酸), biotin(生物素
), and choline( 膽 素 ) are required. Folic acid( 葉 酸 ),
pyridoxine, inositol( 肌 醇 ), and carnitine( 肉 鹼 ) may be
required.
－Vitamin C is present in quantity in the tissues of insects,
and is synthesized by the insects, although some species grow
faster with vitamin C in the diet.
＞Drosophila, Tribolium and cockroaches do not require
dietary vitamin C.
＞Periplaneta fat body homogenates can synthesize vitamin
C from glucose or fructose.
◎Oil-soluble vitamins:
－A, D and E are not needed, although A is used for the retinene
photosensitive pigment in insect vision and Aedes reared for a
generation in the absence of vit. A or b-carotene have impaired vision.
Minerals礦物質
Na, K, Ca, Mg, Cl, P, Fe, Cu, I, Mn, Co, Zn, Ni,
Minerals are used for:
Osmotic regulation
Enzyme cofactors
Vertebrate salt mixtures are often used as a source of
minerals for insect diets, but they are often imbalanced for
insects.
For phytophagous insects, K levels are often too low in
vertebrate saltmixtures and elevation of the K provides
better survival.
Plants are high in K, and K is often higher in the blood of
phytophagous insects than it is in vertebrate blood or in
zoophagous insect spp.
Dietary Factors of Unknown Importance
Symbiotes - casual to obligate
Symbiotes共生: two organisms of different species that live
in intimate association with each other.
Mutualists互利共生- advantage of both
Commensals片利共生- one species (usually the smaller)
benefits but the other, the host, does not.
Parasites寄生 - a species that receives nourishment from its
host.
Phoresis傳運- the host transports the symbiont.
Nutrient reserves - nutrients are passed from one growth
stage to the next: larva to larva, larva to adult via pupa
Phagostimulants - nutritionally adequate diet but
unpalatable.
Nutritional state of the organism:
Sex - female reproductive stage
Development -
Larva have uniform needs for growth
Adults have wide amino acid requirements for
reproduction
or for maintenance
Nutrition of the parent - transovarial passage of nutrients
Nutrient balance - vitamin requirements dictated by protein
consumption. Balance of essential nutrients may be of
importance since an organism may eliminate excessive
amounts of nutrients until the proper balance is restored.
Excess nutrients may expend energy for growth or other
processes and
may actually have inhibitory effects.
Food Selection
Orientation - vision, odor, shape, color, size.
Biting
Hunger
Odor
Physical characteristics - edge, smoothness
Feeding
Presence of secondary plant compounds that serve as
phagostimulants many without nutrient value.
Absence of physical barriers Passiflora have hooked
trichomes that puncture Heliconius larvae prolegs and
cause death by bleeding.
Counter Measure: An Ithomiid butterfly larva is gregarious
and spins a silk scaffold over the trichomes of its Solanum
host).
Absence of phytotoxins and secondary plant chemicals:
Potato and tomato leaves form a protease inhibitor when
injured. The material forms rapidly in damaged and
adjacent leaves within a few hr. This inhibitor does not
affect plant proteases and may be aimed specifically at
animal digestive enzymes.
Allylglucosinolate (ALGL) is a crucifer chemical toxic to
noncruciferous-feeding insects but not to crucifer feeders.
ALGL is acutely toxic to Papilio polyxenes larvae which
do not normally feed on crucifers. However, Pieris rapae
a crucifer pest is not affected by high concentration of
ALGL. Spodoptera eridania a general feeder is inhibited
by high ALGL but not by low concentration.
ALGL is an example of a feeding barrier to herbivorous
insects.
Resistance to phytotoxins
Insects have adapted to host plants and may have digestive
enzymes called mixed function oxidases (MFOs) and consist
of a group of enzymes called cytochrome P450s.
MFOs degrade foreign chemicals in the body and protect
the body against toxic compounds.
This allows an insect to degrade host secondary plant
chemicals that act as phytotoxins to protect the plant from
insect predation.
The MFOs are rapidly inducible (e.g. 2 min to several hr to
days). Spp. with inducible MFOs can detoxify a wide array
of secondary plant chemicals.
This permits a wider array of plants as potential host for the
insect.
Insects spp. with highly inducible MFOs are polyphagous
whereas those with poorly inducible MFOs are largely
monophagous.
Polyphagous spp. are more insecticide resistant than
monophagous insects, probably because they have the
ability to induce the MFOs which can degrade and detoxify
insecticides.
Micro-Organisms and Nutrition
－Rhodnius contain actinomycetes(放線菌)
－Yeasts occur in Anobiids and Cerambycids
－Fungi in Scolytid bark beetles
－ Termites and the cockroach, Cryptocercus contain
protozoa.
－Cockroaches contain intracellular bacteria
－Micro-organisms are significant sources of nutrients in
insects.
＞ Mycetocytes or mycetomes ( 懷 菌 細 胞 )are specialized
cells and tissues that contain symbiotic microorganisms
that supply essential nutrients to their host.
－Spp. with restricted diets especially require
microorganisms.
For example, spp. that consume sterile blood throughout
their lives, such as bedbugs and sucking lice, contain
mycetomes with abundant microorganisms.
Spp. that feed on blood during part of their life, such as
mosquitoes, tabanid flies and fleas, lack mycetomes.
－Rhodnius and Triatoma have no intracellular symbiotes,
but contain Actinomyces in the gut that produce B-vitamins.
These Reduviids will not produce eggs or grow if reared on
sterile blood.
－If the louse Pediculus is deprived of mycetome and
symbiotes, growth and reproduction are suppressed unless
the insects are provided a single dose of B vitamins.
＞Larvae of bark beetles persisted for 6 years without
pupation in vials of sterile oak bark but pupated in 5days
once unsterile bark was provided.Probably this was the
result of B vitamins from bacteria.
－ Cockroach fat body contains bacteriocytes containing
obligate symbiotic bacteria which may be the source of
essential amino acids and vitamins such as vitamin C.
＞The bacteria may fix N for amino acids and produce
methionine and cystine from sulfate.
＞The urocytes of the fat body surround the bacteriocytes
and the uric acid that is storage-excreted in the urocytes
may be recycled into amino acids during periods of
starvation.
◎Symbiotes are transferred by specific processes from
parent to
progeny to insure effective reinfection.
－Bacterial layer over the egg surface invades the oocyte
－In roach, bacteriocytes infiltrate the ovary and pass
bacteroids to the egg by fusion with the oocyte.
－In the bostrychid Rhizopertha, microorganisms invade
the testes and mix with sperm and are passed to the
female during mating and subsequently invade the egg..
－ In Trypetid fruit flies, microorganisms invade the
ovipositor and enter the egg through the micropyle at
oviposition.
－Anobiid yeast collects on the shell and the larva eats the
shell.
－In Glossina (tsetse fly) larva are nourished by milk glands
in utero and the symbiotes are transferred in the milk.
－In termites, proctodeal feeding occurs.
＞A liquid is excreted that consists of wood fragments and
protozoa that other individuals eat to replenish the gut
flagellates that they lost at the molt of the hindgut intima.
－In Cryptocercus, the hindgut flagellates move into the
space between the intima and the hindgut epithelium after
apolysis.