Opomyza germinationis

The first task in keying Opomyza species is to establish whether the costal margin is darkened beyond vein R1 or not. In this specimen the costal vein itself is darkened, but it also has a row of black marginal setae. I'm not entirely sure whether it's the vein or the marginal setae that I'm supposed to be checking, but either way, darkened it is here.

female Opomyza germinationis showing wing, North Elmham (Norfolk, UK), 22nd June 2020

The darkened costal margin (whatever that exactly means) narrows it down to germinationis or petrei, and the following photos show characters of germinationis, namely the diffuse pale spots along the edge of the tergites and the absence of setulae on middle of the proepisternum.

same female Opomyza germinationis showing abdomen and proepisternum, North Elmham (Norfolk, UK), 22nd June 2020

The details of the ovipositor help too, with it being asymetrical in lateral view, so that the tip is nearer the top than the bottom (I think perhaps an easier way of describing this is that the bottom edge is more convex than the top). The figures in the key show a greater difference in the lengths of the pointy bits (sorry, not sure what they're called) above and below the ovipositor - the upper ones projecting much further towards the apex in germainationis compared to the lower one (more equal in petrei). The figure also shows this upper projection as being forked, which I have been unable to see on this.

same female Opomyza germinationis showing ovipositor ventrally and laterally in situ (2) and laterally removed from abdomen, North Elmham (Norfolk, UK), 22nd June 2020

female Opomyza germinationis showing lateral view of ovipositor, North Elmham Cathedral Meadows (Norfolk, UK), 12th October 2019

female Opomyza germinationis showing wing, proepisternum and lateral view of ovipositor, North Elmham Cathedral Meadows (Norfolk, UK), 8th November 2020