Three-dimensional characterization of the wind-borne pheromone tracking behavior of male hawkmoths, Manduca sexta

Abstract

We studied the relationship between vertical and lateral movements during free flight odor plume tracking by male moths, Manduca sexta, in a wind tunnel with the "horizon" set at different altitudes. Three-dimensional recordings revealed that the plume tracking males generated roughly equivalent movements vertically and laterally regardless of horizon height. We hypothesized that the moths' tracks would be narrower in the vertical plane when they were presented with visual patterns on the tunnel's side walls. Instead, we discovered that their tracks tended to be wider in the horizontal plane. Anecdotal observations of other moth species describe plume tracking flight in three dimensions as "spiraling", suggesting a specific predictable relationship between vertical and lateral movements. However, we found that the relative phase, frequency, and amplitude of the vertical versus lateral movements vary on a maneuver-by-maneuver basis with no predictable temporal or spatial relationship. Our analyses suggest that a moth's trajectory in 3D can best be described as progressing upwind toward the source while cutting through the plume from all directions with loops of different radii. This is a more precise description than the terms "zigzagging" and "counter-turning" which were derived from 2D analyses of this behavior.