Submitted to: Physiological Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/15/2014
Publication Date: 7/29/2014
Citation: Kuenen, L.P., Gilbert, C. 2014. Visual ground pattern modulates flight speed of male Oriental fruit moths. Physiological Entomology. DOI: 10.1111/phen.12072. Interpretive Summary: It has been known for at least 30 years that male moths flying upwind to a pheromone source need to see a ground pattern or other stationary visual cues in order to steer and regulate their upwind progress. Twenty years ago, we verified a 1950's hypothesis that these males fly upwind faster when they fly higher; however, the angular size of the transverse floor stripes was an uncontrolled variable. Here we demonstrated that decreasing the angular size of visual cues/stripes (and thereby increasing the number of visual cues) also elicited faster upwind progress. Thus, height alone was not the only factor affecting the moths' responses. Interestingly, the moths' flights over circles/dots was only little affected by flight height compared to the changes observed over striped patterns. The visually richer environment outdoors presents insects with a greater task of visual guidance upwind; a task they perform masterfully.
Technical Abstract: Male Grapholita molesta (Busck) were allowed to fly upwind along horizontal sex pheromone plumes in laboratory flight tunnels. Flying males experienced tunnel floor patterns (tunnel-width stripes perpendicular to the wind line) that were varied in width both longitudinally an laterally. Males' uptunnel velocity increased as stripe width was decreased both longitudinally and laterally. Increased flight height above these striped patterns also led to increased uptunnel velocity as reported earlier and its effect on flight speed was greater than the changes in floor pattern. Measurement of OFM flight at 3 heights over floor patterns with randomly distributed dots/circles resulted in no significant changes in net uptunnel speed; however, there was small and significant increase (P < 0.05) in the moths' ground speed along their flight tracks. It remains for us to decipher the insects' ability to use object size, shape and orientation during their upwind flight.