that could be the problem or there could be just something in the wheat bread that isnt attractive to minnows. I have only used a minnow trap a few times in my life and i used to take a can of dog food and punch several holes in it and tie it inside the cage...... if u have two minnow traps or since u already know what wheat bread does... today or whenever you can try white bread and u can use the white as a control factor like in a science experiment and put wheat in the other trap if u have two and place them side by side because the affects might be different if one is in the shade and the other isnt so if u just have one trap just put it back with white bread in the same spot and wait about the same amount of time.... it could be pretty interesting what the outcome could be.