what is the lowest temperature at which maggots will respire. and why do they not respire below this temperature
I cannot say exactly what the lowest temperature would be, probably somewhere around zero. It isn't easy to say - at freezing temperatures there is a likelihood that ice crystals would form in their cells and kill them - so they wouldn't respire (or do anything else!) then. Respiration stops if it is too cold for the enzymes that control it to work.