Contents

1. Overview of Respiration
   1. Use of oxygen in metabolism of glucose ---> ATP for motion, growth, reproduction, feeding, digestion
   2. Oxygen to mitochondria - from ends of trachea by diffusion
   3. Rate varies with size, surface area, metabolic rate (elephant), activity, diapause
      1. Fastest and slowest respiration in insects
      2. Flight muscle = 30-50 X leg or heart = 180 mm³ / g / hr = 180 l / kg / hr
   4. Diffusion
      1. Depends on surface area, concentration differences
      2. Some Collembola respire through body wall
      3. Most pump oxygen through system - Use tubing system for transport
      4. Aquatic - modifications of terrestrial structures
          
2. Structures
   1. Spiracles
      1. Pleura of thorax and in abdomen
         1. Abdomen - seldom in pleura
            1. Overgrown by tergum or sternum
         2. None on head - except embryos of honey bees
            1. Ancestors may have had spiracles in head
         3. Maximum number
            1. 2 thorax - usually mesothorax
               1. occasionally in metathorax
            2. 8 abdominal
         4. May migrate during metamorphosis although origin in mesothorax

         Structure

      2. Peritreme - sclerite in which spiracles are located

1. Closure to regulate water loss
   1. Muscles on valves
   2. Persitigmatic gland keeps spiracle moist
2. Present in all but some apterygotes
3. Valves
   1. At exterior or behind atrium
   2. Cuticular plates, opened by muscles
   3. May rely on elasticity of cuticle
4. Atrium
   1. May be lined with hairs to trap dust
5. Sieve plate
   1. May cover opening
   2. Trap dust
   3. Keep water out
   4. Prevent entry of parasites
   5. Reduce flow rate & water loss
   6. Not in ventilatory spiracles
   7. Lacking in some hemiptera - simple opening without closing mechanism
6. Spiracles can eject toxic fluids
7. Gromphadorhina - hiss - alarm & courtship

2. Trachea

1. Invaginations of body wall
2. Lined with cuticle
3. Taenidia
   1. Spirals of cuticle
   2. Thickened - 3-4 loops - some overlap
   3. Several spirals together
   4. Diptera - single continuous spiral
4. Annuli - rings - structural support, some elasticity
5. Thickenings absent from air sacks
6. Differing structures
   1. Oval - ventilatory spiracles - can be compressed to move air
   2. Diffusion trachea - circular - no compression
7. Epidermis lacks basement membrane
8. Cuticle - epicuticle, exocuticle, endocuticle
9. Diameter constant or decreasing - silkworm - dragonfly
    

1. Air sacs
   1. Well developed in good fliers - Diptera, Hymenoptera
   2. Formed by fusion of trachea
      1. Thin walled
      2. Flexible
      3. Can act as exchange pump
      4. Thorax and or abdomen
   3. Functions
      1. Air reservoir - decreased distance for diffusion
         1. Locust
         2. Dragon fly
         3. Hemiptera
         4. Homoptera
      2. Decreased specific gravity of insect
         1. Increases surface area in relation to weight
         2. Important in flight
            1. Light weight
            2. Insulation between thorax, abdomen
         3. Aquatic - determines buoyancy
            1. Nematocerous larvae,
            2. Corethra
      3. Growth space for internal organs
         1. During instars of muscids
         2. Locust - 42% volume taken by trachea at beginning of nymphal instars - 3.8% at end - air sacs collapse as eggs grow
      4. Decrease volume of circulating blood
      5. Sound resonators
2. Tracheoles
   1. Small -
      1. Diameter - <1µm - 1/60 diameter at spiracle
   2. No taenidia
   3. Form blind tracheoles, reattach to trachea at molt
   4. Epicuticle only, lack wax, pores in cuticulin
   5. Enclosed in single cell (slide)
      1. Tracheoblast
      2. Nucleus near origin
      3. 2 plasma membranes
   6. May indent into cells in area of mitochondria
      1. Glands
      2. Fat body
      3. Muscle
   7. End between cells - epidermis
   8. Vary in abundance
      1. High - Fat body, muscle, testis, ovary, ganglia, imaginal discs
3. Molting
   1. Only trachea not tracheoles in most insects have cuticle to molt
      1. Tracheoles molt in some molts, some insects
   2. New epicuticle formed outside old
   3. Old epicuticle shed at molt - can see in cast skins
      1. Shed through spiracles
      2. Break at segmental lines
   4. Tracheoles may be new, reorganized
      1. Degree of reorganization depends on molt & organism
      2. If old tracheoles persist - join to tracheoles with rings of cement at junction
   5. Second spiracle may form - join to atrial chamber close to spiracle in former instar - may leave scar
       

3. Embryology

1. Form trachea from invagination of ectoderm
   1. Drosophila - 10 clusters of 80 cells each, no further division
   2. Cells migrate
2. Number reduced in development
   1. Begin with 12 pr - 1/ segment
   2. Reduce to 10 or less
3. May be altered in metamorphosis
4. Fusion
   1. Form lateral trunks
      1. Run anterior to posterior
      2. Form dorsal, ventral, visceral trunks
   2. Thorax may be partially isolated to serve flight muscles
   3. Form air sacs
   4. Genetically determined
      1. Characteristic of order, family, etc
      2. Breathless - Drosophila - stimulates branching(Review Science 274:2011) - influence cytoskeleton?? Interact with patterning proteins
      3. Can respond to environment - May be modified if O₂ levels low
5. Development begins in egg before air enters
   1. Fluid filled at various times
      1. Pneumatization - replace fluid with air as more oxygen demand
      2. Absorbed by surrounding tissues
      3. Differs with species
         1. Tenebrio - within egg
         2. Hemiptera - after hatch
         3. Mosquitoes - control mechanism-active transport?
         4. At hatch when spiracles exposed to air
         5. Without contact with air
            1. Aquatic - Dros, Lepidoptera
            2. Gas from tissue fluids
         6. Depends on activity
            1. Respiratory inhibitors
            2. CNS involved
            3. Wax coating on tracheoles - less hydrophilic
            4. Capillarity would need great deal of energy to empty tracheoles.

4. Organization of Tracheation

1. Primitive - branching from spiracle, no joining internally
2. More advanced
   1. Spriacular trachea lead to combined systems
      1. Dorsal trachea
          

1. Commisural- connect sides within system
1. Mesothoracic spur to head
2. Legs - 2 trachea
3. Wings - 2 trunks break into three spurs

5. Physiological demand for oxygen - related to structure

1. Related to
   1. Temperature
   2. Activity - flight, running, reproduction
2. Chemistry - double rate of reaction with every 10 degree increase in temp

1. Doesn't always hold for biological systems
   1. 40 degrees - inactivate enzymes
   2. Arctic insects - 50 x increase in rate with 10 degrees rather than two-fold
   3. Function of enzymes
      1. Desert insects - more heat tolerant
      2. Arctic species respond to small temp changes
      3. Some nonlinear responses to temp

6. Diffusion of gasses

1. Remember goal - delivery of oxygen to mitochondria, secondarily removal of carbon dioxide
2. Rate determined by number of factors
   1. Size of gas molecules
      1. Rate inversely proportional to square root of molecular weight
      2. O₂ = mw 32 = 1.2 X faster than CO₂ = mw 44
   2. Depends on difference in concentration of gas at two ends of system
      1. p = change in partial pressure
         x change in distance
      2. If no change in partial pressure over distance = no movement of gas
   3. Permeability of substrate
   1. P = permeability constant of gas in substrate
      1. oxygen in air = 11 ml min^-1 cm^-2 atm^-1 cm^-1 (atm^-1 = kPa^-1)
      2. oxygen in water = 3.4 X 10^-5 ml min^-1 cm^-2 atm^-1 cm^-1
      3. oxygen in frog muscle = 1.4 x 10^-5
      4. oxygen in chitin = 1.3 x 10^-6 ml min^-1 cm^-2 atm^-1 cm^-1
      5. oxygen in egg yolk = 3 x 10^-4
   2. Air 100,000 more permeable to oxygen than water or tissues
   3. Distance oxygen carried in trachea = 10,000 x distance in tissues
   4. Volume of gas transported by diffusion at NTP = J

   J = -P p / x = change in partial pressure of O₂ / distance

   p / x Trachea to mito = 5kPa

   1 µm tracheole can serve tissue 20 µm in diameter using 1.5 - 3 ml / g^-1 min^-1

   Can be larger muscle if tracheoles indent muscle

3. Diffusion of oxygen and carbon dioxide
 

1. Carbon dioxide more soluble in water than oxygen
   1. Solubility of CO₂ in tissues 36 x that of oxygen
   2. Forms carbonic acid
      1. HCO₃^- <------> H₂CO₃ <------> H₂O + CO₂

Bicarbonate Carbonic acid ^--carbonic anhydrase

1. Mostly bicarbonate at physiological pH
1. Carbon dioxide is more permeable through cuticle
   1. 2-10% of CO₂ lost through cuticle for most insects
   2. 25% for stick insect
   3. More through intersegmental membrane
2. Oxygen debt
   1. Remember metabolism
      1. Glycolysis -----> 2 Pyruvates ------> lactate
      2. Or pyruvate into Krebs cycle & oxidative phosphorylation
      3. Insects live for days or hours without oxygen
         1. build up lactate
         2. Pupae of moths anaerobic at low temp
         3. Cecropia - anoxia ~ 2 days - 25 X normal lactate
         4. Development halted in anoxia
3. Surface area
   1. Krogh
      1. Comp. Physiol. of Respiratory Mechanisms 1940, 1970
      2. Calculated capacity of tracheal system
         1. Length
         2. Diameter (filled caterpillar tracheal with wax, dissected out)
         3. Oxygen consumption with time = metabolic rate
         4. Permeability constant of oxygen
      3. Concluded - surface area adequate for transport of oxygen by diffusion from trachea
      4. More recent - use argon
   2. Weis-Fogh - oxygen use during flight
      1. J. Exp. Biol. 41, 1964
      2. 40-80 µl / g Gromphadorhina
      3. 260 µl / g Locusta migratoria 5^th instar
      4. 500-900 ul / g Mature locust
      5. Adequacy of system depends on organization
         1. Modifications by increased number of tracheoles to rapidly metabolizing tissues - muscle, ovary, imaginal discs
         2. Theoretical maximum distance oxygen could diffuse from tracheoles to provide flight muscle with adequate oxygen = 6-8 µm
         3. Resting = 20 µm
         4. By dissection, maximum distance between tracheoles = 2-3 µm
         5. Invasive into muscle near mitochondria
   3. Chapman says convective movements (ventilation) of gas into / out of tracheal system also important
      
       

7. Mechanics of gas exchange

1. Active ventilation
   1. Mechanical movement of air

1. Partial pressure of oxygen is higher in trachea giving greater gradient compared to tissues
2. Compression of large trachea and air sacs
   1. By increasing length of trachea - telescoping segments
      1. neck - prothorax
      2. thoracic - with wing movement
      3. abdomen
   2. Taenidia maintain diameter or collapse
   3. By muscle or hemolymph pressure - reversible ?heart vs hemocoel?
   4. Dorsal flattening
   5. Inspiratory muscles in each segment - Schistocerca
   6. Parastaltic movement
   7. Synchronization of opening / closing of spiracles - Periplaneta - directed flow
   8. Contraction before opening spiracles increases pressure
3. In general, other muscle movement has little effect - locomotion, heart, gut (Miller says ventilation with oscillating flow of hemolymph)
   1. may in small insects
   2. None - Gromphadorhina, Schistocerca
4. Generally found in large insects only
   1. Continuous - Schistocerca
   2. Periodic - Bryostria
   3. After activity - Periplaneta, dragonfly
      1. cycles 3 min at 10 min intervals
   4. Flight - bee, wasp, flies
      1. water made in lipid metabolism
         1. Locust 7g fat / kg / hr = 8.0 g H₂O / kg / hr
   5. Increase at molt - close spiracles while cuticle hardening
5. Efficiency
   1. 30-60% of tracheal volume emptied during ventilation
   2. Human - 30% max, resting 15%

1. Passive ventilation or flow diffusion respiration or Passive Suction Ventilation or discontinuous ventilation
   1. Observe oxygen uptake continuous
   2. CO₂ release in pulses
   3. Buck, Biol. Bull 1958

1. Fluttering - spiracles closed - partial opening - Prevent water loss in pupae. When in adults, most water lost through cuticle in adult stages so why use this???
   1. Keeps partial pressure of O₂ at about 3.5% while CO₂ increases to about 6%, then spiracles open
   2. As oxygen used, CO₂ stored in tissues(90%), hemolymph as bicarbonate
   3. Carbonic anhydrase in tissues, not hemolymph
   4. Partial vacuum in trachea - cannot collapse because of Taenidia
   5. Fluttering allows air to rush in
   6. Open spiracles
      1. CO₂ diffuses out of trachea and hemolymph
      2. 10% released from trachea
      3. Rest from carbonate, carbonic acid
   7. Cecropia pupae - open 15-30 min closed 7 hr
      1. water loss = 5% of body wt in 4 months
   8. Papilio pupae 3 x / hr in early pupal stage
      1. 1 x per day later
      2. increase near time of emergence
   9. Pattern of opening characteristic of species

 
8. Control of spiracular opening

1. Closed by muscle to valve or bar of cuticle attached to valve
2. Active agents
   1. CO₂ - housefly, Hyalophora
   2. Lactic acid - carbonic acid, other organic acids - fleas
3. Site of action
   1. Membrane
   2. Neuromuscular junction
   3. CO₂ receptors near spiracles - 1967 Burket & Schneiderman Science 156, Hoyle, JIP 4: Schistocerca
   4. CNS - Hyalophora pupae, dragonfly
   5. Direct on closing muscle - housefly - Case, Phys Zool, 1956
   6. Segmental nerve, ab ganglion, flea
   7. Neurosecretion - cockroach
   8. Can be modified by sensory input - brain, anterior thoracic ganglion, in response to external water or hydration
      1. Dragonfly closes immediately after flight if dehydrated, otherwise open 1-2 min
      2. Practical application - CO₂ anesthesia, drop in water, increase fumigant effects by adding CO₂ , keep spiracles open longer
4. Coordinated flow
   1. Synchronous opening and closing of spiracles to increase air flow
   2. Schistocerca - intake 1,2,3 out 10 abdominal
   3. Grasshopper, dragonfly - in thorax out abdomen
   4. Can modify pattern in flight - Schistocerca increases air flow 4-5 x, consumption increases 24 X
   5. Pumping systems for flight
5. Spiracles used may depend on behavior
   1. Aquatic - Hydrophilus - emerges head first - intake metathoracic
   2. Dytiscus - tail first - intake in terminal segments
       
6. Regulation of water loss (conflicts with Chapman p.457)
   1. If open in high CO₂ , can increase water loss 10x
      1. Locusta loses 3 mg / gm / hr, hyperventilation 6-8 mg / g / hr
      2. Anopheles - loses 2% of body wt in 30 min just after molting, if spiracles open, loses 23%
      3. Tsetse - leave spiracles open for evaporative cooling
   2. Adaptation to arid conditions
      1. Beetles - small, spiracles deeply sunken into trachea
      2. Open into subelytral space - humid
      3. Sieve plate  

9. Neuronal control of ventilation

1. Abdominal expiratory muscles - vary in # muscles, segments
2. Nerve cell bodies at base of 1^st and 2^nd lateral nerves from ab ganglia
3. May lack dorsal inspiratory muscles
   1. Some orthopterans have paired longitudinal inspiratory muscles
   2. Innervated by second lateral nerve
4. Spiracular muscles
   1. Median nerve, ventromedial cell bodies
   2. Lateral nerve in cockroach
5. Firing
   1. Alternating rhythm to get flow
   2. Internal receptors
   3. Segmental delay - anterior to posterior or reverse
   4. Regulated by oscillatory interneurons
   5. Oxygen and carbon dioxide can influence
   6. Pacemaker
      1. Localized in Schistocerca - metathoracic ganglion fused with ab ganglia 1-3
      2. Periplaneta = 2 & 3 abdominal ganglion
      3. Nauphoeta = both
   7. Stimulated by CO₂ receptors ?
      1. Brain, thorax
      2. May cause hyperpolarization or depolarization
      3. Snyder et al. 1980. JIP 26:699
         1. Nauphoeta cinerea
         2. opens spiracles immediately when given CO₂
         3. pH --> ventilation
      4. Miller & Weis-Fogh 1967
         1. Normal pH = 7.084
         2. 6.91 to 6.0 ---> increase in ventilation
         3. Naturally goes to about 8.8 in tethered flight
             
   8. Pacemaker - several cells
      1. May be coupled with other functions
         1. muscle contraction
         2. chirp
         3. auditory interneurons in courtship  

10. Aquatic respiration

1. General
   1. No problem with water loss
   2. Some diffusion through cuticle -cutaneous
      1. Metabolic rate must be proportional to surface area
   3. Some mosquitoes can develop in well aerated water even with trachea filled with oil - amt of oxygen important
   4. Many can survive temporarily with only surface breathing
2. Specialized structures
   1. Air tubes - siphons
      1. Break surface tension - hairs to keep water out
      2. At end of spiracles
      3. Modified antennae
   2. Hydrophobic lipids in tracheoles
      1. special epidermal glands in dipteran larvae
   3. Hydrofuge hairs around spiracle
   4. Trachea open under elytra
   5. Pump water in and out of rectum - dragonfly larvae
   6. Carry water bubble
      1. bubbles
         1. From surface
            1. may move to surface at night when oxygen levels in water drop
         2. Associate with aquatic plants
            1. bite into intracellular spaces filled with oxygen
            2. special air siphon into plant - beetle larvae
      2.  
3. Mechanism that allows use of more oxygen than initially stored in bubble
   1. Air stored in bubble is passed into the body through spiracle(s) in contact with bubble
   2. oxygen passes from bubble to trachea leaving high nitrogen concentration
      1. Atmosphere - 21% oxygen, 79% nitrogen
      2. Well aerated water - 33% oxygen, 64% nitrogen, 3% carbon dioxide
   3. Nitrogen has low solubility in water so oxygen passes from water into bubble 3 x as fast as nitrogen goes into water
      1. oxygen diffuses from water into bubble
      2. 13 X as much oxygen as in initial bubble
   4. Rahn & Paganelli, Respiration. 1968. Phys 5: Math for gills

1. Decrease in bubble size

pN₂ > pN₂ of water

pO₂ << pO₂ of water

1. Duration of bubble depends on
   1. diffusion coefficient
   2. solubility coefficient
   3. temperature - months in cold water

4. Cutaneous diffusion

1. Some exchange through cuticle
   1. Much of exchange for larvae through cuticle
   2. Closed tracheal system exchanges gasses with water - Physical gills
   3. Usually have hairs of some sort, modified elytra, antennae, legs
   4. Highly tracheated
2. Tracheal gills - may fly spiracle grows out into cuticular extensions
   1. Tracheal gills of caddis fly - controversial - can cut off and still survive
3. Rectal gills - dragonfly - to surface if oxygen too low
   1. Draw water into rectum
   2. Ephemeroptera, Trichoptera (caddis), Plecoptera (stone), Odonata
4. Plastron (gas gill)
   1. bubble held in hydrofuge hairs
   2. up to 25 X 10⁶ / mm²
   3. Water cannot break in
   4. cannot be replaced by water = permanent gill if water well aerated
   5. may cover most of body - usually millions of hairs per mm², bent at tip - hemiptera
   6. can work in reverse (taking oxygen from insect) if water too low in oxygen content - usually find plastrons in insects in well aerated water
   7. silk web - large surface resistant to wetting, do not collapse until 4-5 atmospheres of pressure (1 atm 33 ft)
   8. More oxygen available by moving water
   9. Important in insects / arachnids prone to flooding (Hebets & Chapman, 2000) - survive submersion 24 hrs - Florida Keys hurricanes - Whip spiders - book lungs
5. Spiracular gills - flap of cuticle with trachea, aeropyles
   1. Flies, beetles
       

11. Respiratory function of hemolymph

1. Pigments as transport molecules
   1. Thought at ends of tracheoles in some species
   2. Not much evidence
2. No oxygen carrying capacity in most insects
   1. No more than water with proteins & sugars
3. Special mechanisms
   1. Blood sinus - evidence not good
   2. Hemoglobin
      1. Chironomid larvae - in mud where p O₂ is low
      2. Up to 10 types in one species
      3. Different forms at different times in development
      4. ½ mw of mammalian
      5. Dimer (mam = tetramer)
      6. High affinity or low depending on species
      7. More affected by CO (monoxide) - irreversible
      8. May be free in hemolymph
      9. From fat body
      10. Low carrying capacity - 12 min -
          1. although effective in low oxygen environment
          2. more rapid recovery from short-term decrease in oxygen - diving, etc.
      11. 20 - 30% concentration of human
      12. May depend on iron intake
4. Endoparasites
   1. Gasterophilus - dipteran
      1. Stomach of horses
      2. Modified fat body cells
      3. Along trachea are filled with hemoglobin
   2. Notinectid - Ansiops (Hemip) Hb prolongs diving time
      1. (Mills, too detailed on gills)
5. Other Endoparasites
   1. Much like aquatic forms
   2. Exchange gasses through cuticle
   3. Oxygen from blood of host
   4. Rich tracheal system near cuticle
   5. Trachea open through skin or tracheal system of host - Tachinids
   6. Evaginate gut
      1. Hymenoptera, Diptera
      2. Evidence for gas exchange weak
6. Eggs
   1. Aquatic eggs - usually no respiratory structures
   2. Terrestrial eggs have oxygen exchange area - preserve water
   3. Aeropyles
      1. Small holes or tubes on surface
      2. Porous air-filled regions - lamellar, channels
         1. may act as plastron if encounter water short term
         2. may serve as water traps - some eggs take up water during development
      3. Submerged eggs or those subject to long-term dessication often have snorkels or horns
         1. Diptera, Hemiptera, Hymenoptera
      4. Tracheal system moves air to deep tissues later in development
7. "Lungs" in caterpillars, hemocytes for oxygen transport M. Locke 1998
   1. Calpodes
   2. 8^th abdominal segment (huge spiracles) and tokus
   3. Trachea do not end up in tissues
   4. Enter tokus, separate hemolymph compartment at tip of abdomen
   5. Trachael tuft moves because attached to heart, alary muscles, 13 families of leps, lung rather than "hemopoietic" organ
   6. More circulating hemocytes in anoxia by occluding 8^th segment spiracles (in pupae hemocytes don't circulate much)

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