[Syrphidae] freeze tolerance in tree-hole species

[Frank Van de Meutter]

Thanks to all for the swift responses (including several private ones).

I am well aware that many species may easily cope with frost just by the 
simple observation that they do occur in colder climates than is here 
the case. No doubt frost-tolerance will be species- and possibly 
population-specific. Therefore I still deem it possible that (high) 
mortality may occur in some Belgian species, especially in less optimal 
habitats (small holes that easily freeze, holes that are too open, ...). 
Ore maybe some southern species/populations that had shifted over the 
past 15 warm winters to Belgium will now be affected? Also note that 
species distributions in other groups may be directly linked to survival 
of larvae in relation to temperature, why not in treehole syrphids? (we 
do have nothern and southern treehole syrphid species in Europe, don't we?
As such frost may be responsible for -why not- strong population 
fluctuations in time or range shifts.
Anyways, I already observed a Myathropa larva caught in ice - within a 
couple of weeks I will  see whether such animals may survive (I now 
rather have the impression I could break it in two if I broke the ice :)).

cheers,

Frank




Wouter van Steenis schreef:
> Dear Frank and others,
>
> Don't worry about them larvae and a little frost. In Nebraska (USA) I 
> received 6 Mallota bautias larvae from Patrick Monk. He collected them on 
> October 4 2003. I kept them in a small plastic container with less than half 
> a liter of the substrate collected together with the larvae.
> I had the container in a small shed next to our house with temperatures 
> equal to outside temperature.
> Then winter came. It froze 20 degrees Celsius at daytime for some weeks. I 
> don't know the minimum temperature, it must have been quite a bit colder. 
> Both the larvae and the substrate were completely frozen. Shaking the 
> container sounded like rattling a box with small wood pellets or something.
> In spring the larvae came on temperature and went on living as if nothing 
> happened. They pupated April 11 and 12 2004. The adults emerged April 27-29 
> 2004.
> I know there is quite some literature on how insects manage to freeze and 
> stay alive. It has something to do with changing all water content for carbo 
> hydroxides so no harm will be done to the cells while freezing.
> Off course these frozen insects won't have any cell activity, so they 
> probably do not need any oxygen either.
>
> Good luck with your winter search party!
>
> Wouter
>
> ----- Original Message ----- 
> From: "Frank Van de Meutter" <Frank.VandeMeutter at Bio.kuleuven.be>
> To: <syrphidae at lists.nottingham.ac.uk>
> Sent: Tuesday, February 09, 2010 10:55 AM
> Subject: [Syrphidae] freeze tolerance in tree-hole species
>
>
>   
>> Hi all,
>>
>> I planned this winter to start a search for some rare water filled 
>> treehole/treecavities inhabiting syrphids in Belgium. Winter is however 
>> particularly harsh here (and over much of Europe), and all these small 
>> water bodies that I visited are frozen for more than six weeks now. It 
>> appears to me that the whole of the water content in the tree rotholes and 
>> cavities is now frozen. This makes me question whether syrphid larvae will 
>> be able to survive these conditions? Even if not all is frozen, they 
>> should experience oxygen shortage? Comparably, in ponds and pools, it is 
>> known that severe frost may also wipe out a considerable fraction of the 
>> aquatic community (though I know nothing on syrphids living there). When 
>> the water starts to melt I will see whether many dead larvae can be found. 
>> Right now, I would like to ask whether anyone has some previous 
>> experience/knowledge on this?
>>
>>
>> beste wishes,
>>
>> Frank
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>>     
>
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