Maggots on blueberries
I suspect you may have two different problems. I would give the plant an application of Fruits Boost, a new plant strengthener available from Harrod Horticultural. This will help the roots in the container find any available nutrients and water and help them resist any attack from soil borne pathogens, which may be causing problems. Fruits Boost also contains some biostimulants to give the plant a boost and help cropping. As for the small maggot I think this will be a caterpillar, I suggest you spray the pyrethrum based; Insect Killer Spray on it and any others you find. This kills on contact and is safe to use on edible plants. You can eat the fruit 24 hours after application. I hope this helps.