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Hi,

I've been asked to explore the syrphid fauna of rot holes in a German park. The rot holes there are usually several metres up in the trees. Further, it is not allowed to destroy the habitat, i.e. cut the trees or remove material from the rot holes (there is a population of Osmoderma eremita...). Does anyone have experience with a trap designed for colleting flies from rot holes which is good esp. for syrphids?

Dieter

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I have not had experience, but I would suggest fixing fine netting around the rotholes, to this fix an upturned plastic funnel, and to the uppermost (thin tubular) end of the funnel fix a collecting container - something like a small plastic bottle shoud do. The flies should crawl up towards the light (as in the malaise trap principle). You could use ducting tape to join these things together, but be careful not to leave any sticky areas exposed on the inside of the apparatus, that flies could get stuck on.

I hope to try this method myself sometime.

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Many thanks, Nigel. Will try it. The few results from various traps installed at tree trunks I found do not report many syrphids. I believe that this is a methodical problem as, for example, window traps are also very bad for hoverflies. Would be nice to find somebody who has experience with a trap that works well...

Best regards,
Dieter

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Dieter,
I think one of the problems with trapping Syrphids emerging from rot holes is that the larvae frequently leave the hole and pupate elsewhere. However, some will find somewhere dry at the top of the rot hole and so will remain as a pupa within the rothole. However many do leave as larvae, which means that you will not find them by covering the rothole with an emergence trap for adults. I have bred Myathropa florea in plastic bottles at home and most of the larvae crawled up the sides of bottle into netting placed over the bottle. These needed to be removed and kept in a new container, with sterile but not completely dry substrate in which they can pupate.
The best technique is certainly to remove some of the rothole material and breed out at home/in the laboratory. However I have only ever managed to breed Myathropa florea in this way, nothing else yet.:(

Good luck with your survey.