Studies On the Function of the Abdominal Rotation Response in Pupae of Tenebrio Molitor

The present series of experiments was undertaken to develop an understanding of the function of the abdominal rotation response (ARR) in Tenebrio molitor pupae. This response, which composes virtually the entire observable behavioral repertoire of the pupae, can be described as a relatively vigorous circular rotation of the abdominal segments elicited by tactile or electrical stimulation. The experimental strategy employed involved collecting evidence that appeared relevant either directly or indirectly to several "possible" functions derived from an a priori consideration of what little was known of the behavior. Improved functional hypotheses, rather than conclusive proof, was the overall aim. Experiments 1 and 2 focused on the possible utility of the ARR as an escape response. A rapid series of ARRs resulting in locomotion were elicited by administering a potentially lethal heat/light stimulus. There was a tendency for the pupae to move away from (as opposed to toward) the direction of the source of stimulation. Experiment 3 investigated the effect of shock stimulus intensity on habituation of the ARR. Increased intensity resulted in a greater probability of eliciting ARRs, more vigorous ARRs, and less rapid habituation. Experiment 4 examined the speed of recovery from habituation to a repeated tactile stimulus. Results showed that recovery followed a negatively accelerated increasing function with approximately 50 percent recovery occurring within 15 min, and almost complete recovery by 2 hr following the termination of stimulation. Experiment 5 compared tactile stimulus habituation for 10 independent groups of pupae differing in developmental age. Young pupae (days 1 & 2) and old pupae (days 9 & 10) showed little habituation. Mid-phase animals (days 5 & 6) habituated most readily. Experiment 6 employed six newly pupated subjects (day 1) mounted in such a way that "spontaneous" ARRs could be continuously recorded (via a photocell system) throughout the entire pupal stage. All animals made spontaneous ARRs. The data were bimodal with most of the responses observed early (days 1 & 2) and late (days 8, 9 & 10) in the stage. In Experiment 7 new pupae (day 1) were positioned on a point drawn on a paper surface. Animals were checked on each day of development and the distance moved across the surface was recorded. Results indicated that animals were quite active (minimum of 40 percent showing movement on any day), and that the fluctuation in this activity, a