Ento Mini Test Excretion And Digestion

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Adaptions to liquid diets

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Rapid excretion of water from food beforeit comes into contact with digestiveenzymes:

1. Allows some sugars in food to be absorbedrapidly

2. Ensures enzymes are not excessively diluted

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Insects do it in many ways:

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1. Many adult Diptera -

1st part of midgut has specialised epithelium to absorbwater

2. Bloodsucking Hemiptera e.g. bedbugs1st part of midgut forms a large water-absorbing ‘crop’

In both 1 & 2 water bloodstreamMalpighian tubules hindgut

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Scale insects, cicadas and other Homoptera

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Digestive track has filter chamber, water from sap pass rapidly from midgut to hindgut. Crossing through plasma membranes through the trans-epithelial osmotic gradient.

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Larval adaptions:

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In many Hymenoptera & Neuroptera:

􀂄 End of midgut closed

􀂄 Midgut distended with faecal matter duringlarval development - reduces nest fouling

􀂄 Before pupation midgut & hindgut join - faecal pellet for entire larval life isevacuated

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Larval adaptions:

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Bumble bees incorporate empty pollengrains into a cocoon as reinforcement

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Absorption:

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-Products of digestion are absorbed byepithelium of gut- blood(haemolymph)

- Occurs most in midgut

- Carbohydrates (e.g. glucose) areabsorbed 1o in gastric caeca

- Haemolymph baths organs & transportsions & molecules for metabolism

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Storage:

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Fat body = 1o storage organ

-Stores energy reserves in form of fats,glycogen & protein

-Synthesises fatty acids & proteins

- Converts carbohydrates􀂄

e.g. glucose to trehalose

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Excretion:

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Excretory system performs a dual function:

1. Elimination of metabolic wastes

2. Maintenance & regulation of dissolvedsalts & water balance in body fluids

Both functions involve production ofexcretory fluid followed by differential (selective) resorption

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Excretory system:

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􀂄 Comprised of Malpighian tubules &rectum

􀂄 When present, Malpighian tubules varyin number from 2 to > 200.

􀂄 Tubules variable in length, are closed atthe distal end, & are formed from asingle layer of epithelial cells

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Composition of urine:

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􀂄 Depends on lifestyle & food

􀂄 Generally contains water, nitrogenouscompounds, pteridines, calcium carbonate,calcium oxalate & pigments

􀂄 Other nitrogenous compounds secreted in smallquantities

e.g. ammonia, urea, amino acids

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H:N ratios and water conservation:

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~ 80% of excreted nitrogen interrestrial insects is as uric acid

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Accessory excretory structures:

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1. Elimination of small molecules& water

- Accessory male glands incockroaches

-Excrete uric acid

-Labial glands in saturnid moths

Excrete large volume of potassiumbicarbonate (alkaline)

-Midgut in larval saturnid moths

Excretes K+

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Accessory excretory structures:

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2. Excretion of high molecular weigh substances --Pericardial cells

Along length of heart & aorta

-Nephrocytes

Specialised cells scattered round insect body

Both types of cells trap & destructively digestlarger molecules & return smaller molecules tohaemolymph

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Ingestion:

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1.Chewing insects

•Mandibles & maxillae cut off & shred food& push food into cibarium

•Hypopharynx pushes food into pharynx

•Food moved from pharynx by peristalsis

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Ingestion:

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2.Sucking insects

•Pharynx forms bulb like pharyngeal pumpthat pushes food through ‘beak’ to areaof peristaltic control

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Digestion=

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= breaking down & changing food so itcan be absorbed by gut epitheliumallowing entry into blood for distributionaround body

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Salivary (or 'labial) glands:

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Chewing insects

Saliva mixed in mouth

Sucking insects

Saliva may be injected into food & themixture sucked up

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Salivary glands can produce:

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1.Digestive enzymes

Labial glands are the 1 o source of amylasethat digests starch

In adult Lepidoptera & bees labial glandsproduce invertase that converts sucrose (adisaccharide) in nectar to glucose &fructose (which are monosaccharides)

This helps produce honey

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Salivary glands can produce:

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2.Anticoagulants

In blood-sucking insectsAnticoagulant causes pain or itching

3.Silk

In Lepidoptera & Hymenoptera

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Gut functioning: Foregut

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Allows storage of food in ‘crop’

Allows passage of food to midgut

Epithelial cells secrete cuticle that ispartially impermeable to enzymes

At posterior end is the proventriculus

Grinds food

In fleas, crushes blood corpuscles

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Gut functioning: Midgut

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1 o site for food absorption

No intima

Epithelial cells secrete enzymes:

Protease, lipase, amylase, invertase &maltase

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Gut functioning: Midgut

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Enzymes produced by either

1.Holocrine secretion

• Cells disintegrate

2.Merocrine secretion

•Enzymes released from vacuoles

Lined withperitrophic membrane= a chitin sheath. Also contains proteins andmucopolysaccharides

Protects epithelial cells from abrasion byforming a tube around food mass (c.f. mucusin vertebrate guts)

Permeable to enzymes

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Gut functioning: Hindgut

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1 o function to eliminate undigested food

Epithelial cells secrete cuticle that ispermeable to water

Hindgut absorbs water allowing waterconservation

Also absorbs salts, sugars & amino acids

Promotes symbiotic digestion

E.g. provides environment for cellulose digestingprotozoa in termites & wood roaches

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Extraintestinal digestion:

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Some insects, e.g. plant lice &predaceous bees, exude intestinalenzymes before food is consumed

Flesh eating maggots exude proteolyticenzymes from anus

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Nutrition:

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Diet may vary across life stages andsexes Nutrients may be stored during one lifestage for use in the next