Larger insects such as cockroaches are often used for the analysis of insect walking because their large size makes them easier to observe. Some insects that might be interesting and useful to study are too small for capture by standard video techniques. Drosophila has been an important model organism for genetic studies for almost a century. Much is known about its genes and numerous mutants are available for study. Some of the mutants affect locomotion and could contribute new understanding if methods are available to track and analyze the movements of Drosophila flies.That technology is now available. Mendes and colleagues describe the application of frustrated Total Internal Reflection (fTIR) to detect Drosophila leg movements and a means to analyze those movements by computer. What is fTIR? If you hold a glass of water in your hand and look through the glass, the ridges of your fingertips become visible. This phenomena is due to fTIR. The pads on the end of the fly legs create an fTIR effect that can be used to determine the position of the legs during movements.
Using the fTIR technique, Mendes and colleagues found that Drosophila use a variety of gaits, including some that are not well defined. The most common gait is the tripod gait (alternating triangle) in which three legs swing forward and the other three push backward against the ground. The tripod gait is used during all walking speeds by the fly. During slower movements, a tetrapod gait in which 4 legs are planted while the other two swing forward is common.
Mendes and colleagues monitored Drosophila lacking receptors on their legs that are responsible for sensory feedback. These flies had the same leg movements as the non-mutant flies at faster walking speeds. This suggests that the leg movements of Drosophila are controlled by central pattern generators in the nervous system that are independent of sensory feedback. Such studies are important to understand how insects control locomotion. Such understanding can lead to new insights into control of locomotion in human designed robots.
* Quantification of gait parameters in freely walking wild type and sensory deprived Drosophila melanogaster. César S Mendes, Imre Bartos, Turgay Akay, Szabolcs Márka, Richard S Mann. eLife 2013;2:e00231