Proprioceptors and fast antennal reflexes in the ant Odontomachus (Formicidae, Ponerinae)

In ants, antennal movements support the stimulus perception of olfactory and mechanosensory sensilla, most of which are located on the distal part of the antenna. In addition, sensory hair plates, campaniform sensilla, and Janet's organ provide the ant with proprioceptive information 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 ganglion. Particularly fast antennal movements occur during protective withdrawal of the antenna. Under natural conditions, antennal retraction in Odontomachus always precedes the rapid mandible strike. We have found no indication of monosynaptic coupling between the antennal proprioceptive afferents and the trigger motor neurons that release the mandible strike. Instead, complex neuronal interactions in the involved neuromeres 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 significance of fast antennal reflexes and of proprioceptive control is discussed.