The photograph shows a colony that died out in January, with the queen in a tiny cluster surrounded by food. This had been a strong colony but had been troubled by high levels of varroa, despite treatment with formic acid in autumn. We discovered it had died when we went to treat with oxalic.
It is likely that the damage had been caused in late summer by the spread of virus before we treated.
This emphases the importance of monitoring varroa levels and treating early; it is especially important to treat at the end of July as soon as the honey crop is removed.