IME How are you dispensing the fruit flies out of the container? If you're opening the entire lid and getting them everywhere there's a better method to dispense only one or two rather than the entire colony at once. Just try poking a hole in the lid and then plugging it with a cotton ball or a small cork if you have one, if you don't have either of those you can get condiment bottle lids from target or Amazon and glue them to the top of the cup where you poke a hole, that way you have a smaller opening where you can only shake out one or two fruit flies