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Great, thanks a lot for your thoughts about it! And for the key - you're right, it's a bit vague without any illustrations. I'd also see small fleshy projections laterally, but if you can exclude V. pellucens, V. bombylans should be correct.
It would be interesting how the V. zonaria larvae look like, but anyhow I've never ever seen that species and V. bombylans is quite common here.