The proventriculus of the carpenter bee, Xylocopa virginica virginica (L.), with special reference to bacteria-containing luminal tunnels

Four tunnels off the lumen of the proventriculus of the carpenter bee, Xylo copa virginica virginica, have been discovered. Light and electron microgra phs revealed the presence in the tunnels of gram-positive, rod-shaped bacte ria, some of which showed division stages. The occurrence of the bacteria e xclusively in the tunnels-not in the lumen of the proventriculus-makes spec ulation as to their function difficult. The function of the tunnels is also obscure, as no glands were seen emptying into them. The bacteria may be sy mbionts that release enzymes into the tunnels, which are subsequently trans ported to the midgut to aid digestion. They could also be parasites. This i s the first report of such bacterial-containing tunnels in insects.