S1-2.10 Jan. 4 Position Around a Tree: Consequences for Pheromone Detection LOUDON, C.*; MILLER, G. L.; FREED, S.; University of California, Irvine email@example.com
The usual flow pattern expected around a cylindrical object such as a tree in slow wind is predicted from fluid mechanics to have areas of faster flow (upwind) and slower recirculating flow with eddies (downwind). An organism located on the surface of a tree would therefore experience different flow depending on its circumferential position. If that organism was searching for a chemical signal, such as a pheromone plume, it might maximize its probability of chemodetection by placing itself in areas of greatest flow speed (the upwind surface of the cylinder, i.e. in front of the separation points). We tested whether wood roaches in the genus Parcoblatta exhibit such upwind positioning; they live in forests, and males actively fly from tree to tree while searching for females releasing sex pheromone. In contrast to an expectation of upwind preference, male cockroaches were evenly distributed around trees relative to upwind (measured with a novel feather boa flow visualization technique), even when the wind direction was relatively steady. We investigated whether sex pheromone could be detected at any location around a cylindrical surface in a laboratory flow chamber using Bombyx mori wing fanning as a bioassay. Although upwind moths arrayed on the surface detected pheromone more rapidly, pheromone detection occurred at least a third of the time at any position, which could explain the even distribution of Parcoblatta males around trees.