Control of high-speed jumps in muscle and spring actuated systems: a comparative study of take-off energetics in bush-crickets (Mecopoda elongata) and locusts (Schistocerca gregaria)

Abstract

The Orthoptera are a diverse insect order well known for their locomotive capabilities. To jump, the bush-cricket uses a muscle actuated (MA) system in which leg extension is actuated by contraction of the femoral muscles of the hind legs. In comparison, the locust uses a latch mediated spring actuated (LaMSA) system, in which leg extension is actuated by the recoil of spring-like structure in the femur. The aim of this study was to describe the jumping kinematics of Mecopoda elongata (Tettigoniidae) and compare this to existing data in Schistocerca gregaria (Acrididae), to determine differences in control of rotation during take-off between similarly sized MA and LaMSA jumpers. 269 jumps from 67 individuals of M. elongata with masses from 0.014 g to 3.01 g were recorded with a high-speed camera setup. In M. elongata, linear velocity increased with mass^0.18 and the angular velocity (pitch) decreased with mass^-0.13. In S. gregaria, linear velocity is constant and angular velocity decreases with mass^-0.24. Despite these differences in velocity scaling, the ratio of translational kinetic energy to rotational kinetic energy was similar for both species. On average, the energy distribution of M. elongata was distributed 98.8% to translational kinetic energy and 1.2% to rotational kinetic energy, whilst in S. gregaria it is 98.7% and 1.3%, respectively. This energy distribution was independent of size for both species. Despite having two different jump actuation mechanisms, the ratio of translational and rotational kinetic energy formed during take-off is fixed across these distantly related orthopterans.

Keywords: Biomechanics; LaMSA; MA; Orthoptera; Pitch.

Fig. 1

The bush-cricket used in the study (Mecopoda elongata) and jumping data methodology. a Picture of a first instar nymph. b Picture of an adult male. c First instar nymph example jump progression used in analysis. d Adult example jump progression used in analysis. COM = centre of mass

Fig. 2

Scaling in Mecopoda elongata. a Relationship between body mass and body length. b Relationship between body mass and leg length. Under isometry, both relationships should scale with mass^0.33

Fig. 3

Relationship between body mass and take-off velocity during jumps by bush-crickets (N = 67) and locusts (N = 44). a Linear velocity (m/s) at take-off. b angular velocity (rads/s) at take-off. Locust data from Goode and Sutton (2023)

Fig. 4

Translational kinetic energy (E_T) and rotational kinetic energy (E_R) of bush-cricket and locust jumps during take-off. Locust data from Goode and Sutton (2023)

Fig. 5

The percentage of total energy formed during take-off that goes into rotation for bush-crickets (n = 67) and locusts (n = 44). Locust data from Goode and Sutton (2023)