Meeting Abstract
Halteres are the dumbbell-shaped, reduced hindwings found in Diptera (true flies) and are a defining feature of the order. During flight, the halteres beat in antiphase with the wings and function as gyroscopic sensors of Coriolis force produced during whole body manoeuvres. This rapid sensory mechanism is one of the reasons why flies are amongst the most agile and manoeuvrable of all flying insects. However, in order to detect the tiny Coriolis forces, halteres must be exquisitely tuned so that the signal is not masked by the much larger inertial forces due their own acceleration. This is believed to be achieved by beating in a perfect plane, which allows the orthogonal component of the Coriolis forces to be detected in isolation from the primary forces. However, this has not been confirmed experimentally. Here, we use time-resolved microtomography to visualise the halteres in tethered blowflies, Calliphora vicina, during induced roll manoeuvres. We used the measured 3D haltere kinematics to calculate the corresponding dynamics. Surprisingly, we found large primary forces acting in the same plane as the Coriolis forces. These were caused by significant out-of-plane motions at the haltere base, and may be an artefact of tethering. Furthermore, this base motion produces a force that matches the Coriolis forces that would be produced by a constant pitching motion. Flies will therefore be sensing a fictitious force during tethered flight that could result in changes to their behaviour and requires careful consideration when designing such experiments.
