Ultrasounds operate through emitting short wavelength, high frequency sound waves that are too high in pitch to be heard by the human ear.
Insects detect sound by special hairs located on the antennae or genitalia.
A University study confirmed that ultrasonic sounds have both a repellent effect as well as reduce mating and reproduction of insects.
Cockroaches respond to special ultrasounds by moving about a bit more than usual and appear eager to escape from the sound waves. Researchers were able to use the increased cockroach activity to good effect by increasing the rate at which they caught the roaches in sticky trap.