Tom
Most of the experience I had sectioning insects was looking at
dragonflies and dragonfly larvae almost 40 years ago but I did spend a
lot of time researching of methods to produce sections of the head
regions.
The most effective method I found was to concentrate on the processing
itself. I mixed melt equal parts of chloral hydrate and phenol together
by gentle warming and used as the chitin softening agent (I cannot claim
credit for this and chloral hydrate is probably difficult to get chloral
hydrate unless in business of shanghaiing sailors!)). This solution was
used after dehydration and specimens were left for up to a week in this
solution. Usually a day was adequate but did not hurt leaving much
longer. Then chloroform as an intermediary agent.
Most of the other methods that I tried such as softening with hydroxides
did not seem to be effective.
I think that effectiveness may depend largely on the insects and probably
will not work with thick shelled coleoptera.
Some of the older methods suggested snipping off a piece of the outer
chitin to allow penetration of agents through the rest of the body of the
insects.
An alternate is to use double embedding with celloidin-wax. Found this to
work but not as well as first method.
Yet another method was to use isopropyl alcohol dehydration in place of
ethanol dehydration to minimize hardening. Worked reasonably well for
larvae but was not as effective for  adult dragonflies.
If the insects have already been embedded I would recommend soaking the
block in water or using Mollifex.
If the chitin tends to separate you might try to use the technique of
wiping a block of 45 degree wax over the surface before cutting each
section. Failing this (and probably by this time after several
Guinesses)- try  painting a thin layer of celloidin on the surface, allow
to dry and then cut the sections. This is time consuming but sometimes
works.
Effects on DNA - no idea?
Barry

Tom Clarke wrote:

> Does anyone have any experience sectioning paraffin embedded insects?
> Are there any methods that can be used to soften the chitin without
> significantly damaging the other tissues (in particular, the DNA)?
>
>   -Tom Clarke-
>    Division of Biology
>    Kansas State University