I found this associated with spring flowers such as Ramsoms
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I have found two spelling variations on the Genus in Peer reviewed Journals
Portevina Journal of Natural History 25(4):945 - 969 (1991)
Portevinia more widely found
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One of my favourite hoverflies. It seems that you can find it pretty much wherever Ramsons grows, at least round me. Any small wood with Ramsons seems to hold the species. The males are easy to find, but the females fly low amongst the plant and are more tricky to see. Worth looking for in a couple of months time.
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Thats an interesting observation which would make a nice little study ie Flight Height flower proximity and gender I have seen as you say two general different flight patterns around the flowers but attributed that to wind conditions etc I wonder if females are predissposed to fly closer to the flower as a mating strategy. (The second link added above is specific to Ramsoms)
Lat/Lng: 53.9, -2.1
OS grid ref: SD9952