Sinapis is widespread and common in southern France and often quite easy to tell in flight as it has a slow, floppy flight. I'm not quite sure how it stays airborne sometimes. Illustrations in books generally show the unh as being dusted with grey scales in a characteristic sinapis pattern, to a greater or lesser extent according to sex (females more heavily dusted) and brood (first brood more heavily dusted). However, in Var I find the second brood unh to be almost unmarked with grey scales and to have a distinct pale yellow tinge.

These are supposed to be indicators of the Eastern Wood White (L. duponcheli), although these individuals are clearly sinapis. The antennal club is brown in duponcheli and has distinct white spot in sinapis, although this may only apply to the males - see 10387 belowclearly a brown antenna all round, but equally clearly a female sinapis. Another reliable indicator is that for duponcheli the unf costa has dark scaling in the basal region which does not extend into the cell, whereas in sinapis it does.

There is another differentiator only visible on the uppersidethe upf vein 1 has a hump below the cell - see 7219 below - but this will only be visible from the upperside as vein 1 will not be visible from an underside view. Differentiating the first brood is not at all difficult as the duponcheli unh is almost completely dusted with green or grey scales in a very characteristic pattern which I have not seen.

Some sinapis may actually be the recently-discovered Réal's Wood White (L. reali), a species so similar to sinapis that only an examination of the genitalia can tell them apart for certain. Reali flies in Ireland but not in mainland Britain, and in certain discrete regions in Europe including much of the far east of France.

There are some alleged external differences, notably that the unh post-discal band of grey scales is quite pronouncedly curved. Of the photos on this page, not many have any significant degree of grey scaling, and of those that do, none seem particularly curved, and I cannot see any reason to assume that they are anything other than sinapis, although 12548 just might be, and 18007 perhaps.

observations

a second brood male. The unh grey markings of the Var specimens are very light, and the general colouring underside very much yellower than as shown in T&L, and on this basis it looks very much like the illustration of the much rarer  duponcheli, although I am fairly certain it is sinapis because the white tips of the antennae are clearly visible. This just serves to demonstrate how difficult it is to identify some species from (very good) illustrations in books; it often needs two or more indicators to be certain.

a first brood male, I suspect, based on its apparent taking salts and rather lighter dusting of unh grey scales.

a second brood male, based on the lighter dusting of grey unh scales. The post-discal line of grey scaling is at an angle and probably too straight to suggest reali.

another second brood male with a virtually unmarked unh, in an upright pose often adopted when taking salts from wet soil.

a first brood female, I think, based on the very heavy dusting of grey unh scales.

a heavily dusted first brood female.

I had my doubts as to whether this could be duponcheli given the extensive degree of green scaling on the unh, significantly different from any sinapis I had seen in Var, and it was from a region where duponcheli was known to occur. The brown antennal tip served for a while to add evidence of duponcheli, but an examination of the antennae of all of my Leptidea photos indicated that the antenna clue only relates to males. The pattern is not a sufficient match for duponcheli and the unf scaling along the cost extends quite clearly into the cell, so this is conclusive evidence of sinapis, albeit a rather non-standard one. Having visited the UK Natural History Museum archives and viewed the extensive specimens of duponcheli, none of which deviated from the "classic" duponcheli pattern, this removed any possibility that duponcheli might vary sufficiently to permit some level of doubt for 20135.

I was trying to get a lucky snap of the upperside of this slow-flying Leptidea upperside caught in flight. On closer inspection I began to wonder if it might be duponcheli for several reasonsthe upperside is very white and the black upf apical marks are very small, both clues to duponcheli; the underside of the antennal tip shows no sign of white (which would indicate sinapis if 7219 is a male) although maybe the detail level is not good enough to be conclusive of this; most significantly, the upf vein 1 in the basal area shows a very clear "hump" (arrowed in the illustration below, but much clearer in the enlarged version) and this is considered to be definitive (if rarely seen in the wild) evidence of duponcheli; the sinapis vein is much flatter, and on this basis, I would tend to say 7219 is duponcheli, but further evidence (the unh of the first brood which flies in May-June has a characteristic pattern as noted above - this should/would be obvious in flight) is needed to be 100% certain.