SANE, SP; DIEUDONNE, A; WILLIS, MA; DANIEL, TL; University of Washington; University of Washington; Case Western Reserve University; University of Washington: Mechanical forces on the antennae of a flying insects
Insect antennae are equipped with two sets of mechanosensory fields in their basal segments.One set, the Bohm’s bristles, are arranged as bristle fields on the scape and pedicel. The second set, the Johnston’s organs, are arranged circumferentially in the pedicel-flagellum joint. In flying insects, these neurons encode the low and high frequency stimuli due to external and self-generated antennal motion. Although past studies on antennal mechanosensors emphasize their role as airflow sensors, moths and butterflies rigidly hold and maintain their antennal position independent of the external air speed during flight. Moreover, the airflow around antennae is more complex than previously estimated and anemometric measurements of air speed near the antennae reveal a strong, self-generated component of airflow due to flapping. Because antennae vibrate at wing beat frequency, a large component of the net mechanical stimulus arises from antennal oscillation. To study the mechanosensory role of insect antennae, we measured their motion in a hovering hawkmoth, Manduca sexta , and calculated the resulting forces on its antennae. These calculations show that in addition to aerodynamic drag, the antennae of flying hawkmoths experience significant gyroscopic forces. Intracellular recordings from neurons in the Johnston’s organs reveal that they are capable of sensing the small amplitude vibrations and their frequency response falls in a range expected from Coriolis forces. When their flagella are amputated while keeping the basal mechanoreceptors intact, moths can initiate flapping but their ability for coordinated flight is severely compromised. This ability is however restored when the antennae are reattached and the mechanical loading restored. Together, these results suggest that antenna may be a crucial balancing organ during flight.
