[Syrphidae] freeze tolerance in tree-hole species

Pierre MILLE mille_pierre at yahoo.fr
Tue Feb 9 14:03:52 GMT 2010

Hello everyone,
Let me introduce myself my name is Peter and I live near Paris in France. I am a beginner in the study of hoverflies and recently subscribed to this forum. 
I am not confronted with such temperature differences, but I was wondering if there is a threshold when tempérarure is very low for the survival of hoverflies. Do you also have noticed a decline in the number of hoverflies due to different heat waves.
Best Wishes

Pierre MILLE 
3 avenue des buttes blanches
95220 Herblay


--- En date de : Mar 9.2.10, Frank Van de Meutter <Frank.VandeMeutter at Bio.kuleuven.be> a écrit :

De: Frank Van de Meutter <Frank.VandeMeutter at Bio.kuleuven.be>
Objet: Re: [Syrphidae] freeze tolerance in tree-hole species
À: "Hoverfly discussion list" <syrphidae at lists.nottingham.ac.uk>
Date: Mardi 9 Février 2010, 14h27

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 :)). 



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 
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!


----- 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,

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