The forewing tegulae:: their significance in steering manoeuvres and free flight in Locusta migratoria

The flight system of Locusta migratoria is widely used to investigate the principles of sensory-motor control. The four tegulae are proprioceptors of the flight system that are active during the downstroke and provide afferent input to flight-system neurons. While the role of the hindwing tegulae in the flight motor pattern has been well characterized, the role of the forewing tegulae is unclear. We tested whether the forewing tegulae may be more important for the generation of intentional steering manoeuvres than for generation of the basic flight motor pattern. Following ablation of the forewing tegulae, tethered flying locusts continued to generate characteristic intentional steering manoeuvres in open-loop conditions. In contrast, we found that locusts were less likely to sustain unrestrained free flight following ablation of the forewing tegulae. We also found that the number of spikes in a forewing depressor muscle increased, as did the hindwing to forewing delay in elevator-muscle activation after ablation of the forewing tegulae. We conclude that the forewing tegulae promote free flight in locusts and we discuss the role they may play in locust flight.