Though recovering the original colour of insect following to the alcoholic treatment is hard enough, but you must focus upon the removal of alcoholic substrate as alcohol is a dehydrator -- it removes the water particles that produces lustring effect over the chitin layer. Changes enacted by water are much faster than those by ethanol, in spite of ethanol’s more rapid spread across the elytral surface.

The beetle’s photonic structure is enclosed by a thin scale envelope preventing direct contact with the liquid. So far, the thin envelope has not attracted much attention because it is thought not to affect the coloration due to its subwavelength thickness of about 100 nm. However, scientists discovered reversible water-induced colour changes in the beetle elytra accidentally, after a dead specimen was placed in a wet glass vessel during a field collection, noting that the blue-violet coloration turned green upon contact with water. This hygrochromic behaviour was previously explained as resulting from the photonic structure being filled by water. 

These problems can be largely prevented in either of two ways. The best way is to “fix” the insect tissues and color by killing the specimens in boiling water. For smaller specimens, simply dip them in boiling water for about 30 seconds and then transferring them to 70 percent alcohol. Use more extended periods for large-bodied insects.

Because the body contents of a large specimen may dilute the preservative, it is best to replace or top off the original alcohol with fresh alcohol after a day or two.

After this special treatment, colors should not fade much. Over time, the alcohol may evaporate, so it may be necessary to add a bit more from time to time

Hope this much information could help your work.!!!!!!

Good Luck

Aarti

Thanks Aarti Rama,

I've know about theses matter... Alcohol is not good and I don't use it. But the beetle I've commented was collected by a friend and he didn't know about other killing ways...

Would have any way to "rehydrate" the specimens killed in alcohol?

As far I know there is no way to "restore"  the original colouration.

In my opinion and personal experience, alcohol is pure evil when it comes to beetles, and especially small ones (except when you want to extract some DNA of course). It makes them impossible to prepare and dissect without damage.

As Dmitry, I don't know any magic trick to give a dead Coleoptera its original colors back.

But most Cerambycidae and even Buprestidae preserved in alcohol do not change colour !! You can relax it in moist chamber and mount....yes alcohol is not good for beetles ..except when you want tissue for DNA....

hvg

Hi,

physical colours are produced by interference of the light traversing a series of transparent layers constituted by materials with different optical properties, in insects cuticle and air.  In your case, the conditions have been modified when air was replaced by alcohol.  If this is the case, letting the alcohol evaporating could probably restore the original situation.  If you have several individuals, you should try drying up one and see the result.

Good luck,

Claudio

This whole phenomenon is interesting...yes physical colors change...but in some beetles natural colours (golden shine) is seen in alcohol and lost in drying!!...Cassidinae for example !!

In some Jewel bugs or shield bugs as they are also called (Scutelleridae) the normal colour is well seen in alcohol (almost metallic green ground colour with black spots) but when dried all animasl becomes blue...no trace of green or black spots!!!!

physical (blue) coloration of butterfly wings is lost in alcohol and other organic solvents again....and drying restores it !! 

each case is different....so just dry your beetle 

hvg

that would be another dangerous thing....just dry that nothing happens....send photo....what is the size?? and where it was collected??

hvg

I used to show my students effects of dehydration on structural colors on the same specimen of Acanthosomatidae, preserved in alcohol through many years, just after evaporation of alcohol the structural colors returned. Maybe the humid environment is also useful.

Hermant Ghate, thanks. The size is about 3-4 centimeters. The specimen was collected in Brazil...

OK

would love to see photo when you do that....cerambs are always interesting

hvg

I think that the best way will be to rehydrate the specimen, by passing it through a graded alcohol-water series in small vials (the amount of liquid being only 1 cm over the specimen) like in the case of the histological technique. I think that three baths of 75%, 50 %, 25 % ethanol, followed by two baths of distilled water (the time to be passed in each bath by the specimen being comprised between 30 minutes to an hour) will be useful. But, you may think to progressively reduce the period of the water baths (e.g. 30 to 15 minutes), as the conjunctive tissue of the beetle  (mostly articular membranes) don't swell so much. And try to remove the beetle from the bath and move from time to time one articulation, in order to see if they are rehydrated enough. Hope that will help you.

I had a similar problem with Cerambycids injected with a 90% solution of ethanol. The elytra turns darker. The solution is to kill them in the frezeer and dry out at room temperature. I tried Ethyl acetate to remove the oily solution on the elytra but It did not work well. Also I tried boiling water and the oily solution was removed temporally but appear again few weeks later.