[MikeHardman]

Just to point out that, although a lot of the damage done by the citrus leaf miner is to the leaves, it is quite happy eating inside the fruit. Here's one from my garden today!
(There were external signs, so it was not a complete surprise.)
The larva is right in the middle of the photo; the little dark bit is its head.

[Alisdair]

I wonder if that really is a citrus leaf miner. This would be an odd time of year to find them around (the adults don't seem to get active in southern Greece until around late April or May, too cold earlier), and on the very rare occasions that they attack fruit they don't seem to go much below the surface of the softest rind. That black mark could perhaps be the mouth hooks of an ordinary Mediterranean fruit fly larva, which can be quite a serious pest of citrus fruits in the Med - though again you'd be very unlucky to have it attacking your fruit in winter, as they tend not to be active until later.

[MikeHardman]

Alisdair - you're right - thanks for the correction.
I confirm the larvae (there were two) are just like those in this web page -
http://www.organicgardeninfo.com/mediterranean-fruit-fly.html.
I can't be sure of the species, but it looks very similar.

[I suggest you change the subject of this topic, for the benefit of those searching/browsing the forum in future.]

[Alisdair]

Changed subject (was Citrus leaf miner larva in clementine) as suggested.