•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.

Energy requirement 能量需求

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.  

Metabolic Systems

•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.

Chemical energy transformation

IngestionDigestion: Digestive enzymes Symbiotic microorganism: vitamins etcAbsorption:: Utilization Storage

Cockroach, blow fly, fruit fly, caterpillars

Energy production from food

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 diets Mouthpart structures Specialization of digestive tract Ecological niches Discontinuous feeders Predatory or carnivorous species Food storage mechanism

Continuous feeders Phytophagous insects

Diversity in insect feeding and the alimentary structures

(no typical digestive tract among insects )

General Structure of Alimentary Canal

The digestive tract consists of a tube of epithelial cells running from the mouth to the anus.

Foregut: stomodeum; ectoderm; cuticleMidgut: endoderm; peritrophic membraneHindgut: proctodeum; ectoderm; cuticle

Three region of insect alimentary canal

•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.

Foregut, Midgut, Hindgut

Anterior structures and the foregut

Evolution of insects from a primitive annelid ancestor

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

Anterior structures and the foregut

Extrinsic visceral muscles Intrinsic visceral muscles

(labium)

Longitudinal musclesCircular muscles

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

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.

Digestion and absorption

Cell types of midgut

Columnar cells: principle cells; Regenerative cells: group in nidiGoblet cells: single cell distributionEndocrine cells: single cell distributionGastric 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: 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.

Peritrophic Membrane 圍食膜

Functions of Peritrophic membran

Protection Selective permeability

Digestion area: enzymes binding

Detoxification

Barrier of microorganism

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.

Protection

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

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, m

ono- and disaccharides and amino acids. High M.W. sugars (starch) and proteins (casein, albumin, gelatin) are retained.

Diptera: 4-5 nm

Grashopper: 25-35nm

Ultrafilter

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 bondsExopeptideses: remove terminal amino acids from peptide chainDipeptidase - splits free dipeptides amino acids. Special ProteasesKeratinase - digests wool. Tineola, dermestids, Mallophaga Tineola: Cysteine desulfhydraseCollagenase - 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 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 

Digestion of carbohydrates

4

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

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.

Digestion of carbohydrates

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 termitesFungus-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 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 carbohydrates

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

Digestion of lipids

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 acidsEsterases: 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 compoundsPhosphatases: digest the phospholips remove the fatty acid portion from phosphatides Galleria, wax moth, may utilise about 50% of beeswaxLecithinnaseCholinesterase

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.

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.

Hindgut 後腸

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)

Guanosine triphosphate (GTP)

Uridine triphosphate (UTP)

adenine

ribose

triphosphate

diphosphate

High energy bond

Redox : oxidation process & reduction process

Two carbon molecules

Large molecules break down

Chemical energy transfer

Nicrtinamide adenine dinucleotide

Flavin adenine dinucleotide

Nitrogenous wasteselimination

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 insectsConverted by fat body cellsConcentration : 0.5 to 5.0 g/100ml

May keep high concentration in hemolymphReduced osmotic effectsHigh conc. may facilitates diffusion into all cellsFacilitate 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

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 幾丁質

Chitin synthesis

Source: glucose or trehalose in hemolymph ---> glucosePhosphorylation: ---> glucose-6-phosphate ---> fructose-6-phosphate Aminaiton: ---> glucosamine-6-phosphate Acetylation: ---> N-acetylglucosamine-6-phosphate ---> N-acetylglucosamine-1-phosphateActivation: ---> 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 components11 nonessential amino acids

L-form isomersD-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

GlutamateAspartate Alanine

Amino acid degradation acetyl CoA, pyruvate, citric acid cycle intermediates

ammonia

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 waterHigh 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 requirementsMost 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 structureDietary 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 andpupal 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, a

nd is synthesized by the insects, although some species grow faster with vitamin C in the diet. ＞ Drosophila, Tribolium and cockroaches do not require di

etary 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 retinenephotosensitive pigment in insect vision and Aedes reared for ageneration 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 regulationEnzyme 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 bothCommensals 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 andmay actually have inhibitory effects.

 

Orientation vision, odor, shape, color, size. BitingHungerOdorPhysical characteristics - edge, smoothness 

Food Selection

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.

NADPH2

NADP

Fp

Fp– Fe3+

Fe2+

S

SOH

O2

Cyt P450

Fe2+

Cyt b52+

Fe3+

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.