My question relates to the key in Kenneth Smith's handbook of 1969. I have a female specimen swept locally two days ago which keys out to L. nigrociliata. My first assumption (that I had the very common L. lutea) falls at the first fence where the decision is based upon a bristle on the middle tibia - which my specimen has and lutea does not. The key also points to females of nigrociliata having wing vein a1 ending 'very much beyond' the m fork, as mine does.
My query is: are Ken Smith's keys the best we have, and are they trustworthy.
The Handbook keys work well in most cases, but Lonchoptera, especially lutea, are very variable in colour, and sometimes in chaetotaxy as well. Your specimen has a left fore tibia with what appears to be a dorsal bristle about 1/3 from the base. The right fore tibia appears to have a dorsal bristle about 2/3 from the base. This would fit with lutea (having lost a couple of bristles). L. lutea very occasionally has a short av bristle on the mid tibia (as can nitidifrons). There are some pale post-occipital bristles on your specimen, more typical of lutea than nigrociliata.
I would ask what the habitat was. If you swept it near a stony stream or fast-flowing river (especially one with shingle), then nigrociliata is likely. If you were nowhere near such water, then I think your first assumption (lutea) is probable.
Thanks Tony for this useful info. The problem with the key in Ken Smith's handbook is that it starts by distinguishing two groups by the presence or absence of an anteroventral bristle on the distal half of the middle tibia. The attached picture clearly shows such a bristle - hence my query. If L. lutea occasionally has this second bristle I can't get much further. But there is also the point about the end of vien a1 relative to the m-fork.