Mechanism of hemolymph circulation in the pupal leg of tenebrionid beetle Zophobas atratus

The long legs of insects require adequate hemolymph flow for maintaining their metabolism and functions. The visualization of hemolymph flow in a pupal leg of the tenebrionid beetle Zophobas atratus revealed that, in addition to a general circuit across all segments (podomeres) of the leg, there were two shortcut channels running within the femur, which is the largest podomere. A unidirectional hemolymph flow was forced by periodic pumping movements of the abdomen and regulated by a valve that exhibited a metamorphic change from a tongue-shaped to a flap-shaped structure. The results suggest that insects with a simple (open) circulatory system have evolved a sophisticated circulatory mechanism that distribute hemolymph adequately to the individual podomeres, which have diverse morphologies and functions.