If you use a short time of exposure of moisture for softening, it will likely not harm much the DNA acquisition, even nuclear which is more sensitive. It seems that the temperature (or combination of temperature and general humidity) where the specimen is preseved will affect more to microbial activity and degaradation of DNA rather than short-spanned relaxation of a specimen. I have no references of real measures to offer, but this is indirectly mentioned by, eg.: Mutanen, M., Wahlberg., N. & Kaila, L.. (2010) Comprehensive gene and taxon coverage elucidates radiation patterns in moths and butterflies Proc. R. Soc. B 2010 277, 2839-2848.

Thank you very much Lauri ! The final decision between soften the specimen (with the risk of DNA degradation) or cutting the wing out of the specimen is always difficult to make...

Here is a sentence from the reference you mentionned (Mutanen et al., 2010):

" In several cases, air-dried specimens up to 10 years old yielded DNA of good quality, indicating that also nuclear DNA of unrelaxed material kept in dry and cool conditions can successfully be amplified using standard extraction and sequencing protocols even after a relatively long time of preservation (Wahlberg & Wheat 2008). Notably, material of the ANIC and some private collections were found to be very useful, emphasizing the importance of proper preservation conditions in museum collections, and at the same time warning against water relaxation of specimens, as such an operation almost certainly fragments the nuclear DNA."

Thanks Jon, I agree with you that it should be better to only soften the wing. Unfortunately, it is more difficult with very old and dry specimens. When you put the wing between slides, you have a serious risk to break e.g. a leg, an antenna, or the head, ... So when I have to analyse very old specimen, I would rather prefer to soften the complete specimen. Some specimens are rare and precious for entomological collection, so I cannot take that risk ;o(

But when possible, you are right, soften the wing would be the best: no DNA degradation + no mutilation of the specimen.

In my experience with butterflies and moths, relaxing specimens is very risky to the preservation of DNA. It does not take long for mold to infect the specimens.

Rather than removing wings, many people are removing a few legs from one side of the specimen before relaxing, which does not detract from its aesthetic or morphological integrity, but ensures that the DNA is as good as it was when originally preserved in the field.

A method of extracting DNA without conferring visible, external morphological damage to such specimens.

Gilbert MTP, Moore W, Melchior L, Worobey M (2007) DNA Extraction from Dry Museum Beetles without Conferring External Morphological Damage. PLoS ONE 2(3): e272. doi:10.1371/journal.pone.0000272

I am told here at the NHM London that relaxed material is almost useless for DNA, but i have not reference only word from other lepidopterists.

Don't have a question just want to thank you for all your questions and answers now i have an idea how to go about using museum specimen for my research.

I donot think so it will effect DNA.

In my experience, relaxing relatively large insects - e,g, grasshoppers - effectively destroys their DNA. Be aware that many museum specimens are based on specimens that have been dried after capture, then later relaxed and pinned. These are likely to be useless for molecular systematics.