I use the following technique.
1) With a wire mesh strainer I scoop up a strainer full of flour media, insects and all. I then sift the flour media out back into the original container.
2) I then place that strainer over a bowl and wait about 5 min.
You will get adult beetles (which the frogs do not care for), as well as pupa (also not fans of) and larva (which they DO CARE for).
*notice that some flour made it's way into the bowl, you want to avoid having flour covered larva being eaten*
3) Dump the remaining strainer contents back into the original culture.
The contents of the bowl need to be strained again. Repeat the process again. This will reduce the flour, adults and pupa that make it into the bowl.
4) Serve the larva into feeder cups or bowls. The larve live in a dry water free environment. They get their water from the air. In a humid dart frog enclosure they will literally drown from the moisture in the air of a terrarium. A feeder bowl is a good way to remove any uneaten/drowned larva.
I hope this helps some readers. It's how I do it anyways.