Two hives - one very strong, the other very weak. It doesn't sound to me as if bad weather is the culprit - I could be wrong, of course.
Not 'looking over your shoulder', as it were, it's difficult to say for sure, but providing you've discounted disease within the weak colony, my money would be on the possibility of 'forager drift' - where one colony has become strong at the expense of the other.
Are your hives positioned in such a way that returning foragers are more likely to encounter one hive before the other ? That would do it. If so, then swapping the hive positions over for a while should initially sort out the problem, after which they'd need to be positioned more equally so that drifting doesn't occur in future.
If it's not that, could you describe just how weak the weaker colony is ? If it's down to a cupful of bees, for example, it might be better to just let them go and split the more powerful colony to replace it. There is a size limitation, below which it's almost impossible to recover a colony. Giving them a frame of bees may result in the weak colony being killed-off, whereas giving them a frame of capped brood without bees may not work either, as there won't be enough bees to cover that brood with, until it's emerged. So much depends on what you mean by 'weak'.
'best, LJ
Topic: Using a strong hive to help a weak one? (Read 1688 times)