Despite a century of manned flight, when it comes to aerobatics, we're still a long way behind insects. And even though their agility can be extremely frustrating when evicting an unwanted guest, insects can teach us a great deal about the complex forces that keep them aloft and the mechanisms that control them. Michael Dickinson is fascinated by all aspects of insect flight: from the aerodynamic forces they generate to the complex neural systems that control each intricate wing beat. But it hadn't been possible to correlate variations in insect wing beats and the muscles that control them,with the effects they have on a flight path until recent technical developments allowed Claire Balint, a student in the Dickinson lab, to simultaneously monitor flight muscle activity and wing movements to see how flies steer their erratic path(p. 3813).
But flies are notoriously mobile; the only way for Balint to collect the high speed flight recordings she needed to analyse the insect's wing movements was to tether the insect in a flight arena while focusing three ultra-high speed cameras on the flapping insect to capture its intricate manoeuvres. And by skilfully inserting microscopic electrodes into five of the insect's flight muscles, she could record flight muscle activity simultaneously as they flew into a mild headwind. But Balint also needed to measure the aerodynamic forces generated by each wing beat before she could begin correlating the insect's muscle activity with the forces generated. Digitising the positions of both right and left wings over a total of almost 870 wingbeats, Balint was able to calculate the forces generated by the wings as they moved through the air, as well as measuring them on a scaled-up mechanical model, before beginning the painstaking task of correlating the forces that keep the insect aloft with individual muscle activity.
Balint explains that `although a reasonably robust theory exists for predicting the forces resulting from an arbitrary change in wing motion, the link between aerodynamically relevant changes in wing kinematics and the activity of specific steering muscles was less clear'. She and Dickinson also knew that certain muscle groups were responsible for three individual aspects of the insect's wing beat movements; the downstroke deviation, the dorsal amplitude and a shift in the ventral amplitude known as `mode'. Undaunted by the enormous amount of data generated by the flapping insects, Balint began analysing the aerodynamic forces generated by the insects according to each of these wing beat features, to see how they affected the insect's aerodynamic performance. Thanks to this novel approach, the team soon realised that specific sets of muscles were responsible for different aspects of the insect's aerobatic armoury. `The basalare muscles primarily control lift and roll by varying the downstroke force, the muscles of pteralae III and I control thrust and yaw by controlling the upstroke force and an unknown muscle group controls lift and roll by varying the upstroke force inclination',explains Balint.
Having found that it's the flies' ability to control several force generating mechanisms in concert that allows them to dodge and weave so effectively, Dickinson is keen to know more about the elusive insect's flight and pursuit strategies.