Movements of the hinged filter flap of the metathoracic spiracle (Sp2) are coordinated with wing beat cycle. During upstroke of the wings and the correlated down stroke of the halteres the flap opens. During down stroke of the wings and correlated upstroke of the halteres the flap closes. The opening facilitates the expiratory airflow through the Sp2. The closing of the flap restricts the inspiratory airflow to the mesothoracic spiracle (Sp1). Highspeed video, recording rate at 500 Hz, playback rate reduced to 7 fps. Female from field 85 mg.