A certain type of insect trap uses a scented lure to attract rose beetles into a plastic bag from which it is difficult for them to escape  If several of these traps are installed in a backyard garden, the number of rose beetles in the garden will be greatly reduced
If only one trap is installed, however, the number of rose beetles in the garden will actually increase
When there is only one trap in the garden, the plastic bag quickly becomes filled to capacity, allowing some rose beetles to escape.