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Odor-guided flight in moths

The scenario we study in Manduca sexta, the tobacco hornworm moth, is typical of many, if not most, species of moths. Males and females both become active at sunset and take flight. If a female is ready to mate she then lands and begins to produce and release her sex-attractant pheromone from a specialized gland near the tip of her abdomen. smoke plume Sex pheromones are typically made up of a few, to many, different chemical compounds and specifically attract males of only one species. Females usually release their pheromones during a specific time of night, and during this time the males of her species are most attracted to her pheromones. Often, when closely related species have similar pheromones, cross-attraction is avoided when each of these species switches their mating periods to different times of the night. The female's pheromone evaporates from the surface of her pheromone gland and is carried away by the gentle evening breezes making an invisible plume of pheromone molecules. We use chemical smoke to visualize what a pheromone plume would look like if we could see it.


Male Moth Behavior in Pheremone Plume

When a male moth encounters a plume of pheromone his behavior changes in a few very characteristic ways:

Moth flight path
  1. He turns into the wind and begins flying slowly upwind (the wind direction is critical information for any animal tracking an odor plume since moving into the wind while smelling the odor should usually take you in the direction of the odor source).
  2. He begins to execute a continuous series of turns back-and-forth across the wind. The timing of these turns is usually so regular that it has long been suggested that upon encountering pheromone a timing circuit in the central nervous system of the moth is activated, and this timing circuit serves to initiate the turns.
  3. As the male flies slowly upwind tracking the plume, he also maintains his altitude near that of the pheromone plume. The result of the influence of the female's pheromone on the male's flight control systems is the zigzagging upwind flight track that characterizes this behavior.

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