Some differences between Linnaemya picta and Linnaemya tessellans

This year I have collected many specimens of Linnaemya picta but, so far, only one Linnaemya tessellans.

Here are some photos that illustrate two of the differences between these two species.

L. picta (also L. rossica):  "Gena with larger black hairs/small bristles - some of which are at least half the thickness of the bristles below the vibrissa":

L. tessellans:  "Gena with only fine hairs (at least some of the lower ones also fair) - distinct from the single line of bristles extending down from the vibrissa":

L. picta (also L. rossica):  "Costal cell with a uniform covering of microscopic hairs":

L. tessellans:  "Costal cell of the wing with only approximately half its area covered in the microscopic hairs found over most of the wing":

Update on Thu 2014-12-25 by Tristram Brelstaff

See also this post by Chris Raper at the Tachinid Recording Scheme.