Circulatory and Ventilatory Movements of the Abdomen in Mosquitoes

The lateral walls of the abdomen in freshly emerged male and female mosquitoes undergo intermittent bursts of peristaltic contractions. These movements, which may be quite violent, are lost at about 24 h in females at 30 degrees C but persist in males for a further 24-30 h; they are regained, however, in both sexes after a meal, even in adults 2 weeks old. The movements are associated with the muscles of the ventral diaphragm and are interpreted as being mainly circulatory in function. Rhythmic lateral contractions of a gentler nature occur throughout the life of adult mosquitoes; they are associated with the alary muscles and are interpreted as being mainly ventilatory in function. In mature unfed adults the abdominal tergites overlap the pleurae in which lie the spiracles; the lateral contractions cause this longitudinal fold to undergo a rhythmic flapping motion of variable amplitude but constant frequency. It is suggested that this flapping fold protecting the spiracles also has a ventilatory function and could perhaps be interpreted as the primordial insect wing in its early non-alary form and function. An independent peristaltic wave sometimes occurs along this fold in young adults.