Wednesday, 12 June 2013

Portevinia maculata and Ramsons

At this time of the year a number of woodlands contain carpets of ramsons Allium ursinum, which scent the air with garlic. At the beginning of June I visited two such woods at Fawsley as part of the Wildlife Trust's Bioblitz. I was particularly keen to find the hoverfly that is associated with ramsons, Portevinia maculata. It is not a particularly striking species, with its grey dusted spots but it is not frequently recorded in Northants. According to "The Flora of Northamptonshire and the Soke of Peterborough", recently compiled by Gill Gent and Rob Wilson, ramsons occur in about 75 tetrads in Northants. However I only have records of P. maculata from three.  It is almost certainly present in most sites where there is an extensive and well established population of ramsons so must be well under-recorded in the county. The fly's association with ramsons is strong. It's larvae are miners of the bulbs of ramsons and adults can be easily found when the ramsons is in flower and the weather is warm enough for the hoverflies to seek nectar. I have attached a couple of photos in the hope that more records will be made. It is easily recognised from the grey spots on the abdomen, so long as you make sure it is a hoverfly you are looking at. Similar-looking higher flies will have bristly bodies, whereas this hoverfly does not have prominent bristles and shows the "false margin" on the wings created by the two outer cross-veins running parallel to the outer hind edge.

Portevinia maculata on ramsons flowers.

Portevinia maculata showing grey dusted abdominal spots and the "false margin" on the outer edge of the wing, seen more easily in the lower wing.

Ramsons in a wood in Northants in early June.

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