Effects of altering flow and odor information on plume tracking behavior in walking cockroaches, Periplaneta americana (L.).

Animals using odor plumes to locate resources are activated to track these plumes by the presence of an attractive odor, and typically steer toward the source using directional cues from the flowing air or water bearing the odor. We challenged freely walking virgin male cockroaches, Periplaneta americana, to track plumes of airborne female pheromone and then video-recorded and analyzed their responses as the odor plume and wind were independently manipulated. Plume tracking males that experienced the total loss of directional air flow halfway to the odor source showed little change in their performance, and 100% were able to quickly locate the pheromone source. By contrast, males experiencing a sudden loss of odor while tracking a plume rapidly changed their behavior; often turning downwind and retracing their steps to the release point, or walking in loops, but rarely moving upwind to the previous location of the source. In a subsequent experiment, in order to determine whether a memory of the previously experienced wind direction could provide the directional information necessary to locate an odor source, we challenged males to track plumes in zero wind after pre-exposing them to: (1) wind and pheromone, (2) wind only, and (3) neither wind nor pheromone. These were compared to males tracking a wind-borne pheromone plume, in which case, all males were able to locate the pheromone source. Our results show that males require the detection of wind and pheromone simultaneously during plume tracking in order to quickly and efficiently locate the odor source. These results are consistent with those reported from flying moths tracking wind-borne pheromone plumes, and suggest that the control system underlying this behavior requires ongoing simultaneous experience with wind and odor information during the performance of the behavior to operate efficiently.