ONTOGENIC SCALING OF JUMP PERFORMANCE IN THE AFRICAN DESERT LOCUST (SCHISTOCERCA-GREGARIA)

Ontogenetic growth was used as a model for the effect of body size on jumping performance of the African desert locust (Schistocerca gregari a). Using models that generated relationships between morphology and b ody size proposed by McMahon and the relationships between morphology and performance described by Hill, we generated testable predictions o f how jumping performance measures may change as a function of body ma ss. Data were collected over an ontogenetic sequence that ranged from 1-day-old first instars to 45-day-old adults. Performance was quantifi ed using a high-sensitivity, three-dimensional force plate. Performanc e parameters quantified included the force, acceleration, take-off vel ocity, kinetic energy and power output. With the exception of power ou tput, each measure of performance scaled to body mass in a manner cons istent with the predictions of the elastic similarity model. Power out put scaled to body mass in a manner consistent with the predictions of the constant stress similarity model. As we noted previously for the scaling of flexural stiffness of the metathoracic tibiae, the elastic similarity model is approximated by the performance of the locust in s pite of the morphological design that deviates from that model's predi ctions. These results indicate that the jump has separate functions in the flightless juvenile instars and in the flying adult stage of the life history. Juvenile locusts produce take-off velocities of between 0.9 and 1.2 m s-1 that are relatively scale-independent. The take-off velocity in juveniles produces a distance of ballistic travel that ave rages between 20 and 30 cm. In adults, the take-off velocity is also r elatively scale-independent at a level approximately twice as high as in juveniles (i.e. 2.5 m s-1). This velocity is coincident with the mi nimum flight speed reported by Weis-Fogh and a minimum flight speed th at we have estimated using actuator disc theory. We suggest that, in j uveniles, the jump is designed to achieve a characteristic distance tr avelled and in adults the jump is designed to achieve a minimum veloci ty necessary to fly.