Failure of stationary but not of flying honeybees (Apis mellifera) to respond to magnetic field stimuli

Michael M. Walker, Diane L. Baird, M. E. Bitterman
1989 Journal of Comparative Psychology  
Trained individual honeybees (Apis melliferd) to feed to repletion from a well of sucrose solution so constructed that shock could be delivered when the proboscis was in contact with the solution. If shock was signaled by vibration of the substrate or by an airstream, the animals learned readily to avoid it by breaking contact briefly, but there was no response to change (either constant or time-varying) in the ambient magnetic field. When, however, a magnetic field anomaly in the region of the
more » ... n the region of the food well signaled to flying animals that contact would be punished with shock, hesitation to settle was greater in presence than absence of the anomaly. Parallel results were obtained with light, to which flying Ss clearly responded but to which stationary Ss hardly responded at all. We conclude that stationary bees detect magnetic field stimuli but do not process them successfully in the training situation. In previous experiments (Walker & Bitterman, 1985) , it has been shown that flying honeybees {Apis melliferd) can be trained to discriminate earth-strength magnetic fields; this evidence has set the stage for a detailed psychophysical analysis of magnetoreception. Out of an interest in achieving better control of stimulation than is possible in work with flying subjects (which must be depended on to expose themselves to the magnetic fields), we turned in the present experiments to a method of conditioning stationary bees that was developed recently in this laboratory (Abramson, 1986) . The work is done with individual foragers that have been pretrained to fly back and forth between the hive and the sill of an open laboratory window, where they feed to repletion on a target containing a well of sucrose solution. During the feeding a conditioned stimulus (CS) is turned on and followed 5 s later by a brief shock (the unconditioned stimulus or US) that the animal can learn to avoid by breaking contact with the sucrose solution. (Typically, it flies up from the target for a short time.) With vibration of the substrate or a stream of air directed at the animal as the CS, conditioning is dependably rapid (Abramson, 1986; Abramson & Bitterman, 1986a , 1986b , and we hoped at the outset of this work that it would be rapid also with magnetic stimuli. In fact, however, the animals hardly responded at all, despite the fact that the magnetic stimuli (produced by passing direct currents through coils below the target) were exactly the same as those discriminated by flying bees in earlier work. Although these results were disappointing, they were not entirely surprising, because the question of whether movement is required for conditioning to magnetic field stimuli had already been suggested by the results of work with pigeons One purpose of this first experiment was to provide a formal demonstration of the failure of stationary bees to avoid shock signaled by a magnetic anomaly known to be detectable by flying bees. Accordingly, we trained a group of animals just as in the exploratory work, turning on the current that produced the anomaly 5 s before and turning it off immediately after the scheduled shock. A second purpose was to try to understand the anticipated failure. The hypothesis considered was that honeybees were sensitive only to change in the magnetic field which is continuous for bees flying through the field generated by the coil but only momentary for stationary bees (occurring when the current through the coil is turned on) and discontiguous with shock. If it is change that is detected, the procedure used in our exploratory work is in effect a trace conditioning procedure, which may be judged from work with vertebrates to be much less powerful than the more common delay procedure. To test this hypothesis we trained other animals with magnetic fields that were varied systematically during the CS-US interval. Method, Subjects. The subjects were experimentally naive honeybees from our laboratory hives. They were selected at random from groups of foragers at a feeding station providing 10%-12% sucrose solution. A single animal was picked up in a matchbox, carried to the sill of an open laboratory window, and set down on a target containing a well of 50% sucrose solution. While the animal was feeding, it was marked with a spot of colored lacquer, and after feeding to repletion, it was allowed to fly back to the hive. The bee usually returned to the target within a few minutes, but if it did not it was recaptured at the feeding station and placed again on the target. Training began when the bee returned to the target of its own accord. 62
doi:10.1037/0735-7036.103.1.62 fatcat:sayrc4totff4ne2rxs2mybp34m