Odor-modulated orientation in walking male cockroaches Periplaneta americana, and the effects of odor plumes of different structure.

The location of distant resources using odor information usually also requires information on the flow of air (or water) through the environment together with the expression of internally programmed steering responses. The orientation responses of virgin male Periplaneta americana L. to wind and the female sex-pheromone component (-)-periplanone-B were video-recorded in a laboratory wind tunnel and quantified. P. americana males showed no preferred walking orientation when released in zero wind in the absence of pheromone. When introduced into 25 cm s(-1) wind in the absence of pheromone, 79% of males walked downwind. Upon introduction to a plume of (-)-periplanone-B in wind, 100% of males walked upwind in the pheromone plume to the source. Males were then challenged with wind-borne plumes of (-)-periplanone-B of four different temporal/spatial structures. In nearly all cases, the only statistically significant changes in behavioral parameters measured from their walking tracks were observed from males tracking the treatment consisting of the most turbulent plume. The plume-tracking performances of males challenged with the other three less turbulent plumes were visually and quantitatively similar, regardless of the width. Males tracking all four plumes showed evidence of turns resulting from multiple mechanisms. Some of the observed maneuvers were temporally regular counterturns, suggesting steering according to an ongoing internal program, while others could have been triggered by encountering the change in odor concentration between pheromone and clean air at the lateral boundary of the plume or chemotactically upon the detection of changes in odor concentration.