Responses of locusts in a paradigm which tests postural load compensatory reactions

The abilities of locusts to generate postural load compensatory reactions were tested by placing them in a chamber that was mounted on a swivel joint and repetitively swayed (an adaptation of the paradigm of Nashner). Tests were performed when animals stood upon a screen on the wall of the cage and sinusoidal displacements were imposed that repeatedly forced the animal away from and toward the side of the chamber upon which it was standing. Myographic activities of muscles of the middle legs and the angle of the chamber relative to the horizontal plane were recorded during these tests. Locusts were readily able to maintain postures during these tests. Myographic recordings of activities of muscles of the mesothoracic legs showed repetitive bursting in the trochanteral levator, tibial flexor and tarsal levator muscles that was coupled to the cycles of movement of the chamber. Similar bursts were not regularly recorded in antagonist muscles. Comparison of the phase of onset of bursting among different muscles demonstrated that the levator and flexor muscles are activated nearly synchronously during the phase of movement when the surface upon which the animal was standing was being moved away from it. Measurements of the forces developed by all the legs during similar reactions in semi-restrained preparations showed that these bursts can regularly generate force levels in excess of 3 times the animal's weight. We conclude that the patterns of muscle activity seen during tests in which animals were swayed could effectively function in postural load compensation. These patterns of activity are compared with similar responses of vertebrates.