[Syrphidae] decline of hoverflies

Sat Feb 20 16:02:56 GMT 2010

Hello everyone,

I wonder if each of you have noticed in their respective countries to lower numbers of hoverflies or a decline comparable to that of wild bees. 
I began the study of hoverflies and I am also interested in wild bees. 
It was noticed a significant decline in bumblebees and I wonder if because of agirculture intensive use of pesticides and the heatwaves of 2003 and 2006 had an impact on hoverflies. Is this you would have noticed that some types have disappeared ?

Best wishes 
Pierre

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Pierre MILLE 
3 avenue des buttes blanches
95220 Herblay

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De : "Bartsch, Hans D" <hans.bartsch at telia.com>
À : Hoverfly discussion list <syrphidae at lists.nottingham.ac.uk>
Envoyé le : Ven 12 Février 2010, 14 h 26 min 08 s
Objet : Re: [Syrphidae] freeze tolerance in tree-hole species

Dear all, 
I can only confirm from the Stockholm area what most allready have written. I was breeding Myatropa florea larvae in a small bucket (with wooden chips in water) the other year and everything froze to one block of ice. Nevertheless the larvae pupated and hatched next spring without problems. So do not touch and don´t get worried! The only thing to remember is that there should be drier material for the larvae to pupate in when that time cames. 
Best wishes 
Hans
----- Original Message ----- 
>From: Frank Van de Meutter 
>To: Hoverfly discussion list 
>Sent: Tuesday, February 09, 2010 2:27 PM
>Subject: Re: [Syrphidae] freeze tolerance in tree-hole species
>
>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
>>>_______________________________________________
>>>Syrphidae mailing list
>>>Syrphidae at lists.nottingham.ac.uk
>>>http://lists.nottingham.ac.uk/mailman/listinfo/syrphidae
>>>
>>>    
>>_______________________________________________
>>Syrphidae mailing list
>>Syrphidae at lists.nottingham.ac.uk
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>>  
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