PROPRIOCEPTORS AND FAST ANTENNAL REFLEXES IN THE ANT ODONTOMACHUS (FORMICIDAE, PONERINAE)

In ants, antennal movements support the stimulus perception of olfacto ry and mechanosensory sensilla, most of which are located on the dista l part of the antenna. In addition, sensory hair plates, campaniform s ensilla, and Janet's organ provide the ant with proprioceptive informa tion about the position, velocity, and acceleration of their antennae. We describe the morphology of these proprioceptors and their afferent neurons with special reference to the trap-jaw ant genus Odontomachus . All these sensory neurons terminate in the dorsal lobe, the part of the brain that also contains antennal motor neurons and that controls antennal movements. Neurons originating from campaniform. sensilla and Janet's organ send additional collaterals into the subesophageal gang lion. Particularly fast antennal movements occur during protective wit hdrawal of the antenna. Under natural conditions, antennal retraction in Odontomachus always precedes the rapid mandible strike. We have fou nd no indication of monosynaptic coupling between the antennal proprio ceptive afferents and the trigger motor neurons that release the mandi ble strike. Instead, complex neuronal interactions in the involved neu romeres are more likely to control the timing of the two reflexes. The normal behavioral sequence of antennal retraction can be reversed by artificially releasing the mandible strike earlier than normal. The si gnificance of fast antennal reflexes and of proprioceptive control is discussed.