Insects Circulatory System

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Respiratory System

Caterpillars have lungs

Inside view of the “lung” (Mill 1998 after Carroll 1866) (Locke 1998)

Locke’s caterpillar of choice

Brazilian skipper or Canna leafroller, Calpodes ethlius (Stoll) (Lepidoptera; Hesperiidae) Larval Photo by Drees. Adult Photo by Paul Opler

In Calpodes and larvae from 13 other families of Lepidoptera •Most have spiracle 8 large than spiracle 7 •All have tufts associated with 8th spiracle •All has a distinct pattern of tracheation in the telson

Gaseous exchange occurs through tracheoles that penetrate between cells. Not all tissues are permanently tracheated (i.e. hemocytes) Not all trachea supply cellular tissues (i.e. tufts at spiracle 8)

The tracheal system in the last three segments of a live caterpillar.

How do tufts differ from trachea in other segments?
•Terminal tracheoles turn back on themselves and end in knots in hemolymph •Cuticle between the taenidia is very thin •Attachment to muscle and connective tissue strings suspending the heart keep tufts in constant motion •Aerating trachea (Locke 1998)

The branched tufts of trachea and tracheoles that provide blood cells with oxygen a) The number of hemocytes (red) in a tuft increases when a caterpillar is subjected to oxygen starvation. b) Oxygen-starved granulocytes (blue) entering a tuft resume the characteristics of those in a well-oxygenated environment (red). c) In the tokus – a ‘lung’-like compartment — the hemocytes become closely apposed to the thin-walled tracheae and tracheoles.

(Mill 1998)

Common misconception:
Insect tracheal system is inefficient at transport of gases

Oxygen is delivered 200,000 times faster and carbon dioxide 10,000 faster than in blood. The largest insects know to exist would get adequate oxygen supply and carbon dioxide removal through simple diffusion (e.g Meganeura...