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Thanks everyone, This is tremendously useful advice. I have stored some of my reference insects in plastic boxes for twenty years with, until now, no real problems. However, on the balance of the discussion here I think I will move everything into wooden store boxes. I will continue to use plastic only for short term storage of specimens awaiting ID and labelling. All will be kept in a well ventilated, warm room.

Now the issue is one of cost. As Susan says, plastic is way cheaper. A wooden storebox from Watkins & Doncaster is around ?30 - ?40! I was fortunate in getting four used boxes from W&D last time I bought some and these were only ?15 each. These are not available now, so I am posting a separate thread asking about suppliers of wooden store boxes. ;)