[Syrphidae] attracting Brachyopa and others

[Frank Van de Meutter]

Hallo all,

i have a question regarding saproxylic hoverflies. Last year I have been 
experimenting with attracting saprun hoverflies by sawing the bleeding 
top off from a stump of oak felled the winter before. The stump produced 
a sap with the typical fermenting sap odour. I have laid this piece of 
trunk in a Malaisetrap in a garden. I have checked the trap almost daily 
the next days after work. Within the first week I caught several 
Brachyopa bicolor, B. pilosa, good numbers of ferdinandea cuprea, 
Caliprobola,... All species that I had never before caught with a 
malaisetrap in this place. Especially B. bicolor seems often to escape 
the traps is my experience as it flies somewhat higher up the trees (as 
B. insensilis) whilst B. pilosa en B. scutellaris may be found lower on 
trees as well (and may be caught somewhat more frequent).
Well, I conclude that this would work very efficiently if one wants to 
sample saproxylic sap-run species in a place, especially (as is often 
the case) when visible sapruns and flowering bushes are lacking and 
finding Brachyopa may be more difficult (I know that males can be found 
defending any stem in patches of sunligh, but still). I can also think 
of laying this piece of trunk with the sap in a suitable forest but 
where no sap runs can be found (or it would take hours to look for them) 
and attend this and stay on the lookout for Sphiximorpha, brachyopa, etc...

Now, has anyone had/done similar experiences/experiments before? And 
more importantly, can anyone think of a way to "develop" this method, 
such that we can come to a standardizes method to catch such syrphids? I 
don't see myself walking around each year with a chainsaw in the woods 
looking for bleedings trunks :-) I know that the sugar rich floeem of 
the trees ferments to alcohol, and that using alcohol in a malaisetrap 
may also atract some of the above fauna, but the difference with the 
"real" thing is still enormous, it seems (I have used alcohol before int 
he garden, but never with the same succes as with the "trunk"). Alcohol 
also doesn't come near to the typical fermenting smell of oak or other 
trees (every tree species has a little bit different smell is my 
opinion). But could we maybe tap some sap (can be easily done from 
birch, maybe also other trees?) and ent it with the right bacteria to 
produce the attracting odour?

Any experiences/ suggestions welcome!


Frank