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The shiny exoskeleton of Blow flies: What is it composed of?


Bio-Hazard
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http://forums.hypography.net/forums/showthread.php?t=15713

 

In that website you'll see the discussion I was having with others in trying to find out the physiological structure of different types of fly. What i'm trying to discover here is how their biochemical reactions create their exoskeleton to be shiny and metallic. Seemingly google doesn't have enough information because I can't use any terms. I wouldn't know the physiological terms that make up a fly or even its biomolecular structure.

 

If I read correctly, I think i tripped across something that discussed it was actually a decaying skin matter left over after their body defeats bacteria from things such as feces.

I'm not sure on that, though.

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What i'm trying to discover here is how their biochemical reactions create their exoskeleton to be shiny and metallic.
To the best of my knowledge, a fly's outer skin is covered with tiny scales composed of keratin, and in the same way a butterfly's scaled wings causes a coulorful effect, the fly looks kinda metallic.
I think Boerseun’s on the right track.

 

One of the apparent mysteries of molecular biology is the presence on some birds of blue feathers. All birds are fairly genetically close, and none have genes that can express proteins that absorb and emit light in such a way to appear blue. So how do they have blue feathers?

 

The resolution of the mystery is that, while the chemical pigments available in feathers is limited, they can produce very fine, regular structures, including ones that act as optical refraction gratings. The proof of this is to take a blue feather (jay feathers can be found outside, peacock feathers at craft stores) and grind it into a fine powder. The powder is not blue, but brown!

 

I suspect the same is true of the bright blue chitin of bottle fly bodies and wings. Googling “beetle color refraction” turns up something about this in beetle shells, though “fly color refraction” doesn’t turn up anything in the first few dozen hits.

 

I wonder, if bottle fly shells were ground into a powder, if they would lose their blue color?

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To the best of my knowledge, a fly's outer skin is covered with tiny scales composed of keratin, and in the same way a butterfly's scaled wings causes a coulorful effect, the fly looks kinda metallic.

 

I don't think my post helped at all, and I will therefore stop typing.

 

It is not composed of keratin, but of a mix of the polysaccarid chitin and various proteins:

 

The exoskeleton can roughly be divided in 5 parts, the basement membrane, the epidermis, the endocuticle, the exocuticle and the epicuticle.

 

The epidermis is a secretory tissue (1 cell thick), which is responsible for forming the basement membrane, as well as the other layers of the exoskeleton.

 

From bottom to top:

 

The basement membrane separates the exoskeleton from the hemocoel (the insect body cavity, where organs are located).

Epidermal layer (1 cell thick)

Cuticle layers:

- endocuticle (microfibrils of chitin embedded in a protein matrix)

- exocuticle (same as endocuticle, but usually pigmented)

- epicuticle (a multilayered waterproof structure)

- cuticulin (lipoproteins)

- wax layer (lipids)

 

A cross section:

http://www.cals.ncsu.edu:8050/course/ent425/tutorial/Exo2a.gif

 

 

As you all probably know, some parts of insect skeleton are very hard and inflexible, while other parts, such as joints are rather flexible. This is due to differences in the resilin/sclerotin ratio in the various parts of the skeleton. Sclerotin is a protein that makes the exoskeleton hard, while resilin makes it flexible.

 

You can read more about the insect exoskeleton here:

http://www.cals.ncsu.edu:8050/course/ent425/tutorial/integ.html

 

So, what creates the metallic color in insects?

 

The multilayered epicuticula of insects may have tiny ridges, fold and bumps that makes light rays reflect differently, a phenomenon also known as interference.

 

Here are some articles about structural colors:

 

Beetles:

http://www.scipress.org/journals/forma/pdf/1702/17020123.pdf

http://www.fcla.edu/FlaEnt/fe80p132.pdf

 

Butterflies:

http://iparla.labri.fr/publications/2004/GP04/GONZATO_Butterfly_WSCG2004.pdf

 

Animals in general:

http://jeb.biologists.org/cgi/reprint/201/16/2343.pdf

 

Nature in general:

http://www.osa-opn.org/view_file.cfm?doc=%24(%5C%2F%26K%20%20%20%0A&id=%24(LO*J0%20%20%0A

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I think Boerseun’s on the right track.

 

One of the apparent mysteries of molecular biology is the presence on some birds of blue feathers. All birds are fairly genetically close, and none have genes that can express proteins that absorb and emit light in such a way to appear blue. So how do they have blue feathers?

 

The resolution of the mystery is that, while the chemical pigments available in feathers is limited, they can produce very fine, regular structures, including ones that act as optical refraction gratings. The proof of this is to take a blue feather (jay feathers can be found outside, peacock feathers at craft stores) and grind it into a fine powder. The powder is not blue, but brown!

 

___Just to clarify, the source of pigmentation in all birds is not equal or even known. The source of the red in a male Western Tanager is thought to come from something he eats, but just what that is remains a mystery. I can't look at the Jays at my feeders now without thinking of my mortor & pestle. :)

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