Learning and orientation to odor in the bug Rhodnius prolixus Stal 1859 under laboratory conditions

Two experiments are described investigating learning and orientation in the triatomine Rhodnius prolixus. In experiment 1, Pavlovian conditioning was investigated. The experiment differed from our previous work in that the intensity of the conditioned and unconditioned stimuli were reduced and the number of training trials increased. Once again, no evidence for Pavlovian conditioning was found. In experiment 2, an "orientation arena" was developed in which the orientation of R. prolixus to a human forearm was investigated when an area of the forearm was impregnated with the odor of ruda or almizcle compared to a forearm with no odor. The various paths of the animal from the bottom of the arena until ascending and piercing the forearm, located at the top of the arena, was scored using a grid system and videotaped. The results indicated that under the no odor condition R. prolixus predominately travels in a straight line from the bottom of the arena to the top where the forearm is located. In contrast, the most variable number of paths occurred with exposure to ruda. Exposure to almizcle elicited straight line paths but other paths were evident, although not as variable as that observed with ruda.