They begin to associate the bowl with food. Works very well.
I came up with this method all on my own, right Trayton?

Another trick Trayton devised (perhaps others do this too), is to take the lid off the 5L cricket tubs and turn the lid offcentre (half a turn) if that makes sense. So you now have 4 corners open. You then tilt it so one corner is at the bottom just above the bowl, and you blow gently into the top hole. The crickets cant stand it and come screaming out the bottom hole and pour into the bowl.