[Syrphidae] decline of hoverflies

[Pierre MILLE]

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 : André van Eck <eckvana at xs4all.nl>
À : Hoverfly discussion list <syrphidae at lists.nottingham.ac.uk>
Envoyé le : Mar 9 Février 2010, 11 h 13 min 31 s
Objet : Re: [Syrphidae] freeze tolerance in tree-hole species

Hi Frank,

I cannot imagine why these larvae should have any problems with a "little bit" of winter. 
Larvae can be found very deep in rotholes (see Rotheray's monography), and still have no problems getting to enough oxygen to survive. Also, there is almost no better insulation in nature, than wood. And because there is always enough air between the vessels of wood, there should be little problems for larvae to find oxygen there.
Many saprophagus Syrphidae live in countries and areas with much harsher winters than we experience here! 
Also one can imagine that, in times when it is very cold, just the larvae's activities will be lowered down. In those times they need less oxygen as well, I would say. 

It is very good that you want to go out looking for larvae (found Sphegina larvae myself only two days ago in the Netherlands). But focus on the living. And IF you would find dead ones (be sure they are dead when you find them), it's a "bonus" on the job. But dead larvae decay rather fast... 

Greetings, André





Frank Van de Meutter schreef: 
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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