Dart Den

I live in the North of England, where temperatures get quite cold in winter, even inside the house.
The owner at a local pet store of mine has told me that the cold can kill flies and slow them in their metamorphosis through life (from the worm like larvae to the fly). On cue of his warning, I've witnessed a few cultures having drastic population drops. Has anyone else noticed this, and if so, how does one keep their cultures alive? It won't be mites as i keep my cultures on mite paper. Is it the cold or some other reason for the drops. If it matters, i use melanogaster cultures.
Thanks in advance.
Scar

Correct. Cold temperatures will severely inhibit growth and breeding of fruit flies.

Ideal temps are 77-78°F or 25-26°C.

You can make an insulted box or perhaps, a cabinet...heated by a small incandescent bulb or possible a heat mat ect, to store your cultures in.

Incidentally....what is your average house Temperatures - Day and Night ?

Hmm, average house temperature depends on whether the heating is on or not. If it is, it is probably around the mid to higher 70's. If its off, then its around the mid to lower 60's. Sorry i cant be more precise.
I've place the fruit flies in a box, lined with foil to reflect heat inside in my hot water tank room (a small room, where the hot water is stored). Its quite warm in there so i hope that should work well.
Thanks for the help!