SPRAYBERRY, J.D.H.; HOWELL, S.; Univ. of Washington: Hawk moths, flower tracking and frequencies: implications for functional performance

Hawk moths hover rather than perch when feeding from flowers. However, flowers in nature are not static targets; natural currents or airflow generated by moth wing beats induce flower motion during feeding events. The interaction between feeding and flower motion has significant functional and ecological consequences: a hawk moth�s ability to track a moving flower depends on that motion’s amplitude and frequency. The volume of nectar available may also affect feeding efficacy and the importance of precise tracking in this pollinator-plant relationship. Nectar volumes of flowers pollinated by the hawk moth Manduca sexta range from 3 to 80 uL. To explore how tracking and nectar uptake rate are related, we used an artificial flower equipped with a nectary that could hold up to 1100 uL nectar. The flower was mounted on a computer controlled robot arm that could move in vertical, horizontal and looming directions. Films of moths feeding from the robotic flower were digitized to obtain tracking performance and the quantity of nectar consumed was recorded for each feeding bout. For both vertical and looming directions with a nectar volume of 20 uL feeding rate drops over 50% with any flower motion. For the looming direction with a nectar volume of 1100 uL feeding rates were relatively insensitive to flower motion (remaining within 20% of control values). Past records of tracking performance used the moths� ability to follow the flower as a metric. Macroglossum stellatarum shows distinct tuning in tracking performance, peaking at 2 Hz. Preliminary studies on Manduca sexta show a peak at 1 Hz. Our results show that any flower motion with a naturally occurring nectar volume results in decreased feeding rate. This suggests feeding rate is not tightly correlated with past records of tracking performance.