Motor Pattern of the Stinging Response in the Honeybee APIS Mellifera

In the stinging response of the worker honeybee (Apis mellifera), rhythmic movements of the lancets on the stylet are produced by alternating contractions of a set of stinging muscles (a protractor, M198, and a retractor, M199) on each side during co-contraction of the frucula muscles (M197s) on both sides. In this study, stinging movements were elicited by tactile stimulation to the sternum in isolated abdomens, in intact animals and in preparations in which the connectives between the sixth and terminal abdominal ganglia were cut. There was a close relationship among the following three temporal variables of stinging motoneurone pattern: the interval between successive bursts of a stinging muscle, the duration of a burst and the time lag between the bursts of homologous stinging muscles on both sides. All of these variables increased linearly as the sting was inserted deeper into a soft object and the tension on the lancets increased. When sensory nerves from the proprioceptors (campaniform sensilla on the tapering sting shaft and hair plates at the basal cuticular plate) were cut on both sides, the relative timing of bursts of homologous stinging muscles on both sides and antagonistic stinging muscles on each side became more variable. When a proprioceptive input was removed from one side during penetration of the sting, the frequency of the bursts of stinging muscles was higher and the duration of bursts was shorter on the cut side than on the intact side; nevertheless, a sting muscle was still activated out of phase with its antagonistic muscle on the ipsilateral side and its homologous muscle on the contralateral side. These results suggest that the motor pattern driving the rhythmic movements of stinging muscles is produced by a central pattern generator consisting of a pair of oscillators located in the terminal abdominal ganglion and that the precise timing of the motor pattern in a hemiganglion is controlled mainly by proprioceptive inputs on its own side.