THE EVOLUTION OF INSECT WINGS AND THEIR SENSORY APPARATUS

The development of wings has undoubtedly played a major role in the en ormous diversification of insects. New insights into the evolutionary history of insect wings are available from paleontological, physiologi cal and biomechanical studies. A recent hypothesis, derived primarily from paleontological evidence, is that wings arose from leg exites, sm all flaps associated with proximal leg segments We present data from s tudies on physical models that are consistent with this hypothesis. Th e exites would have been moveable, and measurements on scaled models s how that they would have generated aerodynamic lift by unsteady mechan isms associated with vortex shedding. An examination of the sensory st ructures found on insect wings is also consistent with the interpretat ion of proto-wings as leg exites. In addition to mechanosensory bristl es, such as are found all over the body, the wings of modem insects ca rry campaniform sensilla sensitive to cuticular deformation and contac t chemoreceptors whose stimulation elicits a feeding response. Both cl asses of receptors are also found on the legs of modern insects but no t on the thorax, favoring the leg exite theory.