[Nhcoll-l] Issues with low temperature treatment?

[Paolo Viscardi]

Hi Tonya,

Freezing is very effective. We've frozen all sorts of specimens over the
years at -30°C, including small dioramas with glass fronts and glass lidded
insect drawers. We bag and double seal specimens prior to freezing, partly
to manage humidity through the process and partly to prevent meltwater
causing damage. We've had very few issues, apart from two problems that
occurred when freezing insect drawers.

One was that the drawers were individually bagged during the summer, and
when frozen the decrease in pressure inside the sealed bag led poorly
attached plastazote drawer liners to lift, causing damage to specimens when
the pins were pushed against the glass lid (this was totally unexpected!).
We addressed this by changing the wrapping protocol, so we wrapped a large
computer crate filled with insect drawers rather than individual
drawers, which created a much lower pressure differential.

The other issue was with carded insect specimens attached with very old
animal glue. When freezing at -30°C we found that in a few instances where
the adhesive had been applied a little heavy-handedly, the blob of glue
failed during freezing. We suspected that the rapid drop to a very low
temperature caused internal stresses to develop that overcame the stability
of the adhesive causing it to unlace, so we switched the freezing protocol
to a longer freeze at -20°C and we did not encounter any further issues.

If it's of use we published this in the NatSCA Journal:
https://natsca.org/sites/default/files/publications/JoNSC-Vol6-HerreroChandlerViscardi2018.pdf
with some images and more details.

Cheers,

Paolo



On Thu, 29 Feb 2024 at 07:03, Joachim Händel <
Joachim.Haendel at zns.uni-halle.de> wrote:

> Hi Tonya,
> we have been using this method for over 10 years with very good results.
> A physicist told me that lower temperatures (-30 °C) are better than -20
> °C, as smaller ice crystals form here.
> Above all, it is more effective against collection pests.
> We freeze the objects at -32 °C for at least a week.
> The problem is not actually the freezing, but the thawing.
> However, condensation forms during thawing, which could damage the
> objects. It is therefore best to wrap the specimens as tightly as possible
> in foil, trapping as little air as possible. This should minimize the
> amount of moisture in the air that condenses during thawing.
> Condensation can attack the wires inside or soften the objects a little or
> damage the ink on old labels.
>
> It is not necessary to wrap insect-drawers separately in foil (in my
> opinion!). I have carried out tests and found that the wooden boxes buffer
> the fluctuations in humidity very well.
>
> However, it is important to remove the objects carefully from the freezer
> (especially delicate insects) and leave them to thaw in peace, as the
> frozen structures are fragile and can be damaged by vibrations.
>
> Good luck
> Joachim
>
> --
> Joachim Haendel
>
> Center of Natural History Collections
> of the Martin Luther University (ZNS)
> - Entomological Collection -
>
> Domplatz 4
> D-06099 Halle (Saale)
> Germany
>
> Phone:  +49 345 - 55 26 447
> Email: joachim.haendel at zns.uni-halle.de
>
> >>> "Haff, Tonya (NCMI, Crace)" <Tonya.Haff at csiro.au> 29.02.2024, 06:53
> >>>
>
> Hello all,
>
>
>
> I am wondering if any of you can give me feedback how your specimens have
> responded to low temperature treatment for pests. Specifically, I’m
> interested in what types of specimens you’ve used low temperature on
> (freezing), at what temperatures, and if you’ve observed any negative
> effects on your specimens as a result of colder temperatures? I’m
> especially interested if any of you all use temperatures between -30 and
> -40C, and whether or not you’ve noticed any effect on your specimens,
> relative to say -20C. We are trying to optimise our pest treatment while
> mitigating risk to our dry specimens, which include pinned insects, study
> skins, and bones. We will be using refrigerated shipping containers to do
> this work, which will be on large numbers of specimens at a time.  I think
> we understand the parameters, but I would be very interested to hear
> especially about direct experience, caveats, things to watch out for, etc.
>
>
>
> Thanks so much!
>
>
>
> Tonya
>
>
>
> -------------------------------------------------
>
> Dr. Tonya M. Haff
>
> Collection Manager
>
> Australian National Wildlife Collection
>
> CSIRO
>
> +61(0)419569109
>
> https://www.csiro.au/en/about/facilities-collections/collections/anwc
>
>
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