Miniature linear and split-belt treadmills reveal mechanisms of adaptive motor control in walking Drosophila

To navigate complex environments, walking animals must detect and overcome unexpected perturbations. One technical challenge when investigating adaptive locomotion is measuring behavioral responses to precise perturbations during naturalistic walking; another is that manipulating neural activity in sensorimotor circuits often reduces spontaneous locomotion. To overcome these obstacles, we introduce miniature treadmill systems for coercing locomotion and tracking 3D kinematics of walking Drosophila. By systematically comparing walking in three experimental setups, we show that flies compelled to walk on the linear treadmill have similar stepping kinematics to freely walking flies, while kinematics of tethered walking flies are subtly different. Genetically silencing mechanosensory neurons altered step kinematics of flies walking on the linear treadmill across all speeds. We also discovered that flies can maintain a forward heading on a split-belt treadmill by specifically adapting the step distance of their middle legs. These findings suggest that proprioceptive feedback contributes to leg motor control irrespective of walking speed and that the fly's middle legs play a specialized role in stabilizing locomotion.

Comparison of water and terrestrial jumping in natural and robotic insects

Jumping requires high actuation power for achieving high speed in a short time. Especially, organisms and robots at the insect scale jump in order to overcome size limits on the speed of locomotion. As small jumpers suffer from intrinsically small power output, efficient jumpers have devised various ingenuous schemes to amplify their power release. Furthermore, semi-aquatic jumpers have adopted specialized techniques to fully exploit the reaction from water. We review jumping mechanisms of natural and robotic insects that jump on the ground and the surface of water, and compare the performance depending on their scale. We find a general trend that jumping creatures maximize jumping speed by unique mechanisms that manage acceleration, force, and takeoff duration under the constraints mainly associated with their size, shape, and substrate.

A self-locking mechanism of the frog-legged beetle Sagra femorata

Insect legs play a crucial role in various modes of locomotion, including walking, jumping, swimming, and other forms of movement. The flexibility of their leg joints is critical in enabling various modes of locomotion. The frog-legged leaf beetle Sagra femorata possesses remarkably enlarged hind legs, which are considered to be a critical adaptation that enables the species to withstand external pressures. When confronted with external threats, S. femorata initiates a stress response by rapidly rotating its hind legs backward and upward to a specific angle, thereby potentially intimidating potential assailants. Based on video analysis, we identified 4 distinct phases of the hind leg rotation process in S. femorata, which were determined by the range of rotation angles (0°-168.77°). Utilizing micro-computed tomography (micro-CT) technology, we performed a 3-dimensional (3D) reconstruction and conducted relative positioning and volumetric analysis of the metacoxa and metatrochanter of S. femorata. Our analysis revealed that the metacoxa-trochanter joint is a "screw-nut" structure connected by 4 muscles, which regulate the rotation of the legs. Further testing using a 3D-printed model of the metacoxa-trochanter joint demonstrated its possession of a self-locking mechanism capable of securing the legs in specific positions to prevent excessive rotation and dislocation. It can be envisioned that this self-locking mechanism holds potential for application in bio-inspired robotics.

Jumping mechanism in the marsh beetles (Coleoptera: Scirtidae)

The jumping mechanism with supporting morphology and kinematics is described in the marsh beetle Scirtes hemisphaericus (Coleoptera: Scirtidae). In marsh beetles, the jump is performed by the hind legs by the rapid extension of the hind tibia. The kinematic parameters of the jump are: 139–1536 m s⁻² (acceleration), 0.4–1.9 m s⁻¹ (velocity), 2.7–8.4 ms (time to take-off), 0.2–5.4 × 10^–6 J (kinetic energy) and 14–156 (g-force). The power output of a jumping leg during the jumping movement is 3.5 × 10³ to 9.6 × 10³ W kg⁻¹. A resilin-bearing elastic extensor ligament is considered to be the structure that accumulates the elastic strain energy. The functional model of the jumping involving an active latching mechanism is proposed. The latching mechanism is represented by the conical projection of the tibial flexor sclerite inserted into the corresponding socket of the tibial base. Unlocking is triggered by the contraction of flexor muscle pulling the tibial flexor sclerite backwards which in turn comes out of the socket. According to the kinematic parameters, the time of full extension of the hind tibia, and the value of the jumping leg power output, this jumping mechanism is supposed to be latch-mediated spring actuation using the contribution of elastically stored strain energy.

Jumping Locomotion Strategies: From Animals to Bioinspired Robots

Jumping is a locomotion strategy widely evolved in both invertebrates and vertebrates. In addition to terrestrial animals, several aquatic animals are also able to jump in their specific environments. In this paper, the state of the art of jumping robots has been systematically analyzed, based on their biological model, including invertebrates (e.g., jumping spiders, locusts, fleas, crickets, cockroaches, froghoppers and leafhoppers), vertebrates (e.g., frogs, galagoes, kangaroos, humans, dogs), as well as aquatic animals (e.g., both invertebrates and vertebrates, such as crabs, water-striders, and dolphins). The strategies adopted by animals and robots to control the jump (e.g., take-off angle, take-off direction, take-off velocity and take-off stability), aerial righting, land buffering, and resetting are concluded and compared. Based on this, the developmental trends of bioinspired jumping robots are predicted.

Design of Tendon-Driven Mechanism Using Geometrical Condition

A tendon-driven robot offers many advantages, such as easy designs for mass distribution that facilitate dexterous motion. A procedure to design such a robot using a single actuator to achieve the desired force direction and magnitude on an endpoint is presented herein. The force on the endpoint is generated by the single actuator and a wire that passes through pulleys attached on links. To set the pulley position for the desired force direction and magnitude, a geometrical condition is proposed. To evaluate the proposed method, a physical monopod robot was developed. We compared the calculated and physical forces on the endpoint of the physical robot for the desired directions. Finally, we confirmed that the proposed method provided the desired force on the endpoint without iterative trials.

Mosquitoes modulate leg dynamics at takeoff to accommodate surface roughness

Insects perform takeoffs from a nearly unquantifiable number of surface permutations and many use their legs to initiate upward movement prior to the onset of wingbeats, including the mosquito. In this study we examine the unprovoked pre-takeoff mechanics of Aedes aegypti mosquitoes from two surfaces of contrasting roughness, one with roughness similar to polished glass and the other comparable to the human forearm. Using high-speed videography, we find mosquitos exhibit two distinct leg actions prior to takeoff, the widely observed push and a previously undocumented leg-strike, where one of the rearmost legs is raised and strikes the ground. Across 106 takeoff sequences we observe a greater incidence of leg-strikes from the smoother surface, and rationalize this observation by comparing the characteristic size of surface features on the mosquito tarsi and each test surface. Measurements of pre-takeoff kinematics reveal both strategies remain under the mechanosensory detection threshold of mammalian hair and produce nearly identical vertical body velocities. Lastly, we develop a model that explicates the measured leg velocity of striking legs utilized by mosquitoes, 0.59 m s^-1.

Jumping mechanisms and performance in beetles. II. Weevils (Coleoptera: Curculionidae: Rhamphini)

We describe the kinematics and performance of the natural jump in the weevil Orchestes fagi (Fabricius, 1801) (Coleoptera: Curculionidae) and its jumping apparatus with underlying anatomy and functional morphology. In weevils, jumping is performed by the hind legs and involves the extension of the hind tibia. The principal structural elements of the jumping apparatus are (1) the femoro-tibial joint, (2) the metafemoral extensor tendon, (3) the extensor ligament, (4) the flexor ligament, (5) the tibial flexor sclerite and (6) the extensor and flexor muscles. The kinematic parameters of the jump (from minimum to maximum) are 530-1965 m s^-2 (acceleration), 0.7-2.0 m s^-1 (velocity), 1.5-3.0 ms (time to take-off), 0.3-4.4 μJ (kinetic energy) and 54-200 (g-force). The specific joint power as calculated for the femoro-tibial joint during the jumping movement is 0.97 W g^-1. The full extension of the hind tibia during the jump was reached within up to 1.8-2.5 ms. The kinematic parameters, the specific joint power and the time for the full extension of the hind tibia suggest that the jump is performed via a catapult mechanism with an input of elastic strain energy. A resilin-bearing elastic extensor ligament that connects the extensor tendon and the tibial base is considered to be the structure that accumulates the elastic strain energy for the jump. According to our functional model, the extensor ligament is loaded by the contraction of the extensor muscle, while the co-contraction of the antagonistic extensor and flexor muscles prevents the early extension of the tibia. This is attributable to the leverage factors of the femoro-tibial joint providing a mechanical advantage for the flexor muscles over the extensor muscles in the fully flexed position. The release of the accumulated energy is performed by the rapid relaxation of the flexor muscles resulting in the fast extension of the hind tibia propelling the body into air.

Jumping without slipping: leafhoppers (Hemiptera: Cicadellidae) possess special tarsal structures for jumping from smooth surfaces

Many hemipteran bugs can jump explosively from plant substrates, which can be very smooth. We therefore analysed the jumping performance of froghoppers (Philaenus spumarius, Aphrophoridae) and leafhoppers (Aphrodes bicinctus/makarovi, Cicadellidae) taking off from smooth (glass) and rough (sandpaper, 30 µm asperity size) surfaces. On glass, the propulsive hind legs of Philaenus froghoppers slipped, resulting in uncontrolled jumps with a fast forward spin, a steeper angle and only a quarter of the velocity compared with jumps from rough surfaces. By contrast, Aphrodes leafhoppers took off without their propulsive hind legs slipping, and reached low take-off angles and high velocities on both substrates. This difference in jumping ability from smooth surfaces can be explained not only by the lower acceleration of the long-legged leafhoppers, but also by the presence of 2–9 soft pad-like structures (platellae) on their hind tarsi, which are absent in froghoppers. High-speed videos of jumping showed that platellae contact the surface briefly (approx. 3 ms) during the acceleration phase. Friction force measurements on individual hind tarsi on glass revealed that at low sliding speeds, both pushing and pulling forces were small, and insufficient to explain the recorded jumps. Only when the tarsi were pushed with higher velocities did the contact area of the platellae increase markedly, and high friction forces were produced, consistent with the observed jumps. Our findings show that leafhoppers have special adhesive footpads for jumping from smooth surfaces, which achieve firm grip and rapid control of attachment/detachment by combining anisotropic friction with velocity dependence.

Pest categorisation of Hishimonus phycitis

The Panel on Plant Health performed a pest categorisation of Hishimonus phycitis (Hemiptera: Cicadellidae) for the EU. H. phycitis is a well-defined species, occurring in tropical and subtropical Asian countries from Iran to Malaysia. H. phycitis is polyphagous. Hosts of particular relevance to the EU include Citrus spp. and Solanum melongena. While harmful in its own right as a leafhopper extracting host nutrients through feeding, it is regarded in the Middle East more significantly as a vector of Witches' broom disease of lime phytoplasma, which limits production of Citrus aurantifolia, and in India as a vector of brinjal little-leaf phytoplasma impacting S. melongena yields. H. phycitis is currently regulated by Council Directive 2000/29/EC, listed in Annex II/AI as Hishomonus phycitis (sic). Eggs planted on host plants for planting could provide a pathway for entry into the EU. The EU has eco-climatic conditions that are also found in countries where H. phycitis occurs although it is unknown whether H. phycitis occurs in those areas. There is therefore considerable uncertainty around EU establishment. Any establishment is likely to be limited to the warmest areas around the Mediterranean. As a free-living organism with adults capable of flight, spread within the EU would be possible but confined to the limited area where establishment could occur. Measures are available to inhibit entry via traded commodities (e.g. prohibition on the introduction of Citrus plants for planting; sourcing other hosts from pest free areas). H. phycitis does satisfy all of the criteria that are within the remit of EFSA to assess to be regarded as a Union quarantine pest. It is uncertain if eggs of H. phycitis would carry phytoplasmas into the EU as transovarial transmission from infected females to eggs has not been demonstrated.

Phenotypic disparity in Iberian short-horned grasshoppers (Acrididae): the role of ecology and phylogeny

BACKGROUND

The combination of model-based comparative techniques, disparity analyses and ecomorphological correlations constitutes a powerful method to gain insight into the evolutionary mechanisms that shape morphological variation and speciation processes. In this study, we used a time-calibrated phylogeny of 70 Iberian species of short-horned grasshoppers (Acrididae) to test for patterns of morphological disparity in relation to their ecology and phylogenetic history. Specifically, we examined the role of substrate type and level of ecological specialization in driving different aspects of morphological evolution (locomotory traits, chemosensitive organs and cranial morphology) in this recent radiation.

RESULTS

We found a bimodal distribution of locomotory attributes corresponding to the two main substrate type guilds (plant vs. ground); plant-perching species tend to exhibit larger wings and thicker femora than those that remain on the ground. This suggests that life form (i.e., substrate type) is an important driving force in the evolution of morphological traits in short-horned grasshoppers, irrespective of ancestry. Substrate type and ecological specialization had no significant influence on head shape, a trait that showed a strong phylogenetic conservatism. Finally, we also found a marginal significant association between the length of antennae and the level of ecological specialization, suggesting that the development of sensory organs may be favored in specialist species.

CONCLUSIONS

Our results provide evidence that even in taxonomic groups showing limited morphological and ecological disparity, natural selection seems to play a more important role than genetic drift in driving the speciation process. Overall, this study suggests that morphostatic radiations should not necessarily be considered as "non-adaptive" and that the speciation process can bind both adaptive divergence mechanisms and neutral speciation processes related with allopatric and/or reproductive isolation.

Jumping mechanisms and performance in beetles. I. Flea beetles (Coleoptera: Chrysomelidae: Alticini)

The present study analyses the anatomy, mechanics and functional morphology of the jumping apparatus, the performance and the kinematics of the natural jump of flea beetles (Coleoptera: Chrysomelidae: Galerucinae: Alticini). The kinematic parameters of the initial phase of the jump were calculated for five species from five genera (average values from minimum to maximum): acceleration 0.91–2.25 (×103) m s−2, velocity 1.48–2.80 m s−1, time to take-off 1.35–2.25 ms, kinetic energy 2.43–16.5 µJ, g-force 93–230. The jumping apparatus is localized in the hind legs and formed by the femur, tibia, femoro-tibial joint, modified metafemoral extensor tendon, extensor ligament, tibial flexor sclerite, and extensor and flexor muscles. The primary role of the metafemoral extensor tendon is seen in the formation of an increased attachment site for the extensor muscles. The rubber-like protein resilin was detected in the extensor ligament, i.e. a short, elastic element connecting the extensor tendon with the tibial base. The calculated specific joint power (max. 0.714 W g−1) of the femoro-tibial joint during the jumping movement and the fast full extension of the hind tibia (1–3 ms) suggest that jumping is performed via a catapult mechanism releasing energy that has beforehand been stored in the extensor ligament during its stretching by the extensor muscles. In addition, the morphology of the femoro-tibial joint suggests that the co-contraction of the flexor and the extensor muscles in the femur of the jumping leg is involved in this process.

Jumping mechanisms in flatid planthoppers (Hemiptera, Flatidae)

The jumping performance of three species of hemipterans from Australia and Europe belonging to the family Flatidae, were analysed from images captured at a rate of 5000 s-1. The shape of a flatid was dominated by large triangular or wedge-shaped front wings which, when folded, covered and extended above and behind the body to give a laterally compressed and possibly streamlined appearance. Body length of the three species of adults ranged from 7 to 9 mm and their mass from 8 to 19 mg. The propulsive hind legs were 30% longer than the front legs but only 36-54% of body length. Jumps with the fastest take-off velocities of 2.8-3.2 m s-1 had acceleration times of 1.4-1.8 ms. During such jumps adults experienced an acceleration of 174 - 200 g. These jumps required an energy expenditure of 76-225 μJ, a power output of 13-60 mW and exerted a force of 9-37 mN. The required power output per mass of jumping muscle in adults ranged from 24,000 to 27,000 W kg-1 muscle, 100 times greater than the maximum active contractile limit of normal muscle. The free-living nymphs were also proficient jumpers, reaching take-off velocities of 2.2 m s-1. To achieve such a jumping performance requires a power amplification mechanism. The energy store for such a mechanism was identified as the internal skeleton linking a hind coxa to the articulation of a hind wing. These pleural arches fluoresced bright blue when illuminated with ultraviolet light indicating the presence of the elastic protein resilin. The energy generated by the prolonged contractions of the trochanteral depressor muscles was stored in distortions of these structures and their rapid elastic recoil powered the synchronous propulsive movements of the hind legs.

The green leafhopper, Cicadella viridis (Hemiptera, Auchenorrhyncha, Cicadellidae), jumps with near-constant acceleration

Jumping insects develop accelerations that can greatly exceed gravitational acceleration. Although several species have been analysed using different tools, ranging from a purely physical to a morpho-physiological approach, instantaneous dynamic and kinematic data concerning the jumping motion are lacking. This is mainly due to the difficulty in observing in detail events that occur in a few milliseconds. In this study, the behaviour of the green leafhopper, Cicadella viridis, was investigated during the take-off phase of the jump, through high-speed video recordings (8000 frames s(-1)). We demonstrate that C. viridis is able to maintain fairly constant acceleration during overall leg elongation. The force exerted at the foot-ground interface is nearly constant and differs from the force expected from other typical motion models. A biomechanical model was used to highlight that this ability relies on the morphology of C. viridis hind legs, which act as a motion converter with a variable transmission ratio and use the time-dependent musculo-elastic force to generate a nearly constant thrust at the body-ground interface. This modulation mechanism minimizes the risk of breaking the substrate thanks to the absence of force peaks. The results of this study are of broad relevance in different research fields ranging from biomechanics to robotics.

Jumping mechanisms in dictyopharid planthoppers (Hemiptera, Dicytyopharidae)

The jumping performance of four species of hemipteran bugs belonging to the family Dictyopharidae, from Europe, South Africa and Australia were analysed from high speed images. The body shape in all was characterised by an elongated and tapering head that gave a streamlined appearance. The body size ranged from 6-9 mm in length and 6-23 mg in mass. The hind legs were 80-90 % of body length and 30-50% longer than the front legs, except in one species in which the front legs were particularly large so that all the legs were of similar lengths. Jumping was propelled by rapid and simultaneous depression of the trochantera of both hind legs, powered by large muscles in the thorax and was accompanied by extension of the tibiae. In the best jumps, defined as those with the fastest take-off velocity, Engela accelerated in 1.2 ms to a take-off velocity of 5.8 m s-1 which is the fastest achieved by any insect so far described. During such a jump, Engela experienced an acceleration of 4830 m s-2 or 490 g while other species in the same family experienced 225 - 375 g. The best jumps in all species required an energy expenditure of 76 - 225 μJ, a power output of 12 - 80 mW and exerted a force of 12 - 29 mN. The required power output per mass of jumping muscle ranged from 28000 - 140200 W kg-1 muscle and thus greatly exceeded the maximum active contractile limit of normal muscle. To achieve such a jumping performance, these insects must be using a power amplification mechanism in a catapult-like action. It is suggested that their streamlined body shape improves jumping performance by reducing drag, which for a small insect, can substantially affect forward momentum.

Jumping mechanisms in gum treehopper insects (Hemiptera, Eurymelinae)

Jumping in a species of Australian gum treehopper was analysed from high speed images. Adults and nymphs of Pauroeurymela amplicincta lived together in groups that were tended by ants, but only adults jumped. The winged adults with a body mass of 23 mg and a body length of 7 mm had some morphological characteristics intermediate between those of their close relatives the leafhoppers (Cicadellidae) and the treehoppers (Membracidae). They, like leafhoppers, lacked the prominent prothoracic helmets of membracid treehoppers, but their large hind coxae were linked by press studs (poppers), that are present in leafhoppers but not treehoppers. The hind legs were only 30-40% longer than the other legs and 67% of body length. They are thus of similar proportions to the hind legs of treehoppers but much shorter than those of most leafhoppers. Jumping was propelled by the hind legs, that moved in the same plane as each other beneath and almost parallel to the longitudinal axis of the body. A jump was preceded by full levation of the coxo-trochanteral joints of the hind legs. In its best jumps, the rapid depression of these joints then accelerated the insect in 1.4 ms to a take-off velocity of 3.8 m s-1 so that it experienced a force of almost 280 g. In 22% of jumps, the wings opened before take-off but did not flap until airborne when the body rotated little in any plane. The energy expended was 170 µJ, the power output was 122 mW, and the force exerted was 64 mN. Such jumps are predicted to propel the insect forwards 1450 mm (200 times body length) and to a height of 430 mm if there is no effect of wind resistance. The power output per mass of jumping muscle far exceeded the maximum active contractile limit of muscle and indicates that a catapult-like action must be used. This eurymelid therefore outperforms both leafhoppers and treehoppers in its faster acceleration and in its higher take-off velocity.

Jumping mechanisms of treehopper insects (Hemiptera, Auchenorrhyncha, Membracidae)

The kinematics and jumping performance of treehoppers (Hemiptera, Auchenorrhyncha, Membracidae) were analysed from high speed images. The 8 species analysed had an 11 fold range of body mass (3.8 mg to 41 mg) and a 2 fold range of body lengths (4.1 to 8.4 mm). Body shape was dominated by a prothoracic helmet that projected dorsally and posteriorly over the body, and in some species forwards to form a protruding horn. Jumping was propelled by rapid depression of the trochantera of the hind legs. The hind legs were only 30 – 60 % longer than the front and middle legs, and 47 – 94% the length of the body in different species. They were slung beneath the body and moved together in the same plane. In preparation for a jump, the hind legs were initially levated and rotated forwards so that the femora were pressed into indentations of the coxae. The tibiae were flexed about the femora and the tarsi were placed on the ground directly beneath the lateral edges of the abdomen. Movements of the front and middle legs adjusted the angle of the body relative to the ground, but for most treehoppers this angle was small so that the body was almost parallel to the ground. The rapid depression of the hind legs accelerated the body to take-off in 1.2 ms in the lighter treehoppers and 3.7 ms in the heavier ones. Take-off velocities of 2.1 – 2.7 m s-1 were achieved and were not correlated with body mass. In the best jumps, these performances involved accelerations of 560 – 2450 m s-2 (g forces of 47- 250), an energy expenditure of 13.5 – 101 µJ, a power output of 12 – 32 mW and exerted a force or 9.5 – 29 mN. The power output per mass of muscle far exceeds the maximum active contractile limit of normal muscle. Such requirements indicate that treehoppers must be using a power amplification mechanism in a catapult-like action. Some jumps were preceded by flapping movements of the wings, but the propulsive movements of the hind legs were critical in achieving take-off.

Jumping mechanisms and performance of snow fleas (Mecoptera, Boreidae)

Flightless snow fleas (snow scorpion flies, Mecoptera, Boreidae) live as adults during northern hemisphere winters, often jumping and walking on the surface of snow. Their jumping mechanisms and performance were analysed with high speed imaging. Jumps were propelled by simultaneous movements of both the middle and hind pairs of legs, as judged by the 0.2 ms resolution afforded by image rates of 5000 frames s(-1). The middle legs of males represent 140% and the hindlegs 187% of the body length (3.4 mm), and the ratio of leg lengths is 1:1.3:1.7 (front:middle:hind). In preparation for a jump the middle legs and hindlegs were rotated forwards at their coxal joints with the fused mesothorax and metathorax. The first propulsive movement of a jump was the rotation of the trochantera about the coxae, powered by large depressor muscles within the thorax. The acceleration time was 6.6 ms. The fastest jump by a male had a take-off velocity of 1 m s(-1), which required 1.1 μJ of energy and a power output of 0.18 mW, and exerted a force about 16 times its body weight. Jump distances of about 100 mm were unaffected by temperature. This, and the power per mass of muscle requirement of 740 W kg(-1), suggests that a catapult mechanism is used. The elastic protein resilin was revealed in four pads at the articulation of the wing hinge with the dorsal head of the pleural ridge of each middle leg and hindleg. By contrast, fleas, which use just their hindlegs for jumping, have only two pads of resilin. This, therefore, provides a functional reference point for considerations about the phylogenetic relationships between snow fleas and true fleas.

Jumping mechanisms and performance of pygmy mole crickets (Orthoptera, Tridactylidae)

Pygmy mole crickets live in burrows at the edge of water and jump powerfully to avoid predators such as the larvae and adults of tiger beetles that inhabit the same microhabitat. Adults are 5–6 mm long and weigh 8 mg. The hind legs are dominated by enormous femora containing the jumping muscles and are 131% longer than the body. The ratio of leg lengths is: 1:2.1:4.5 (front:middle:hind, respectively). The hind tarsi are reduced and their role is supplanted by two pairs of tibial spurs that can rotate through 180 deg. During horizontal walking the hind legs are normally held off the ground. Jumps are propelled by extension of the hind tibiae about the femora at angular velocities of 68,000 deg s−1 in 2.2 ms, as revealed by images captured at rates of 5000 s−1. The two hind legs usually move together but can move asynchronously, and many jumps are propelled by just one hind leg. The take-off angle is steep and once airborne the body rotates backwards about its transverse axis (pitch) at rates of 100 Hz or higher. The take-off velocity, used to define the best jumps, can reach 5.4 m s−1, propelling the insect to heights of 700 mm and distances of 1420 mm with an acceleration of 306 g. The head and pronotum are jerked rapidly as the body is accelerated. Jumping on average uses 116 μJ of energy, requires a power output of 50 mW and exerts a force of 20 mN. In jumps powered by one hind leg the figures are about 40% less.

The mechanics of azimuth control in jumping by froghopper insects

Many animals move so fast that there is no time for sensory feedback to correct possible errors. The biomechanics of the limbs participating in such movements appear to be configured to simplify neural control. To test this general principle, we analysed how froghopper insects control the azimuth direction of their rapid jumps, using high speed video of the natural movements and modelling to understand the mechanics of the hind legs. We show that froghoppers control azimuth by altering the initial orientation of the hind tibiae; their mean angle relative to the midline closely predicts the take-off azimuth. This applies to jumps powered by both hind legs, or by one hind leg. Modelling suggests that moving the two hind legs at different times relative to each other could also control azimuth, but measurements of natural jumping showed that the movements of the hind legs were synchronised to within 32 mus of each other. The maximum timing difference observed (67 micros) would only allow control of azimuth over 0.4 deg. to either side of the midline. Increasing the timing differences between the hind legs is also energetically inefficient because it decreases the energy available and causes losses of energy to body spin; froghoppers with just one hind leg spin six times faster than intact ones. Take-off velocities also fall. The mechanism of azimuth control results from the mechanics of the hind legs and the resulting force vectors of their tibiae. This enables froghoppers to have a simple transform between initial body position and motion trajectory, therefore potentially simplifying neural control.

Jumping kinematics in the wandering spider Cupiennius salei

Spiders use hemolymph pressure to extend their legs. This mechanism should be challenged when required to rapidly generate forces during jumping, particularly in large spiders. However, effective use of leg muscles could facilitate rapid jumping. To quantify the contributions of different legs and leg joints, we investigated jumping kinematics by high-speed video recording. We observed two different types of jumps following a disturbance: prepared and unprepared jumps. In unprepared jumps, the animals could jump in any direction away from the disturbance. The remarkable directional flexibility was achieved by flexing the legs on the leading side and extending them on the trailing side. This behaviour is only possible for approximately radial-symmetric leg postures, where each leg can fulfil similar functions. In prepared jumps, the spiders showed characteristic leg positioning and the jumps were directed anteriorly. Immediately after a preliminary countermovement in which the centre of mass was moved backwards and downwards, the jump was executed by extending first the fourth and then the second leg pair. This sequence provided effective acceleration to the centre of mass. At least in the fourth legs, the hydraulic and the muscular mechanism seem to interact to generate ground reaction forces.

Energy storage and synchronisation of hind leg movements during jumping in planthopper insects (Hemiptera, Issidae)

The hind legs of Issus (Hemiptera, Issidae) move in the same plane underneath the body, an arrangement that means they must also move synchronously to power jumping. Moreover, they move so quickly that energy must be stored before a jump and then released suddenly. High speed imaging and analysis of the mechanics of the proximal joints of the hind legs show that mechanical mechanisms ensure both synchrony of movements and energy storage. The hind trochantera move first in jumping and are synchronised to within 30 micros. Synchrony is achieved by mechanical interactions between small protrusions from each trochantera which fluoresce bright blue under specific wavelengths of ultra-violet light and which touch at the midline when the legs are cocked before a jump. In dead Issus, a depression force applied to a cocked hind leg, or to the tendon of its trochanteral depressor muscle causes a simultaneous depression of both hind legs. The protrusion of the hind leg that moves first nudges the other hind leg so that both move synchronously. Contractions of the trochanteral depressor muscles that precede a jump bend the metathoracic pleural arches of the internal skeleton. Large areas of these bow-shaped structures fluoresce bright blue in ultraviolet light, and the intensity of this fluorescence depends on the pH of the bathing saline. These are key signatures of the rubber-like protein resilin. The remainder of a pleural arch consists of stiff cuticle. Bending these composite structures stores energy and their recoil powers jumping.

Jumping performance of planthoppers (Hemiptera, Issidae)

The structure of the hind limbs and the kinematics of their movements that propel jumping in planthopper insects (Hemiptera, Auchenorrhyncha, Fulgoroidea, Issidae) were analysed. The propulsion for a jump was delivered by rapid movements of the hind legs that both move in the same plane beneath the body and parallel to its longitudinal axis, as revealed in high-speed sequences of images captured at rates up to 7500 images s(-1). The first and key movement was the depression of both trochantera about their coxae, powered by large depressor muscles in the thorax, accompanied by rapid extension of the tibiae about their femora. The initial movements of the two trochantera of the hind legs were synchronised to within 0.03 ms. The hind legs are only 20% longer than the front and middle legs, represent 65% of the body length, and have a ratio of 1.8 relative to the cube root of the body mass. The two hind coxae have a different structure to those in frog- and leafhoppers. They are fused at the mid-line, covered ventrally by transparent cuticle, and each is fixed laterally to a part of the internal skeleton called the pleural arch that extends to the articulation of a hind wing. A small and pointed, ventral coxal protrusion covered in microtrichia engages with a raised, smooth, white patch on a dorsal femur when a hind leg is levated (cocked) in preparation for a jump. In the best jumps by a male Issus, the body was accelerated in 0.8 ms to a take-off velocity of 5.5 m s(-1), was subjected to a force of 719 g and was displaced a horizontal distance of 1.1 m. This performance required an energy output of 303 microJ, a power output of 388 mW and exerted a force of 141 mN, or more than 700 times its body mass. This performance implies that a catapult mechanism must be used, and that Issus ranks alongside the froghopper Philaenus as one of the best insect jumpers.

Jumping strategies and performance in shore bugs (Hemiptera, Heteroptera,Saldidae)

The jumping movements of the hemipteran shore bug (Saldula saltatoria, sub-order Heteroptera, family Saldidae) were analysed from sequences of images captured at 5000 frames s–1. Adult Saldula weigh ∼2.1 mg and are ∼3.5 mm long. The hind legs that propel jumping are 180% longer than the front legs and 90% of body length, but non-jumping species in the same family have longer hind legs relative to the lengths of their bodies. Jumps were powered by large trochanteral depressor muscles in the thorax in two different strategies. In the first (used in 24% of jumps analysed), a jump was propelled by simultaneous extension of the two hind legs powered by rapid depression movements about the coxo-trochanteral joints, while both pairs of wings remained closed. In the second strategy (74% of jumps), the wings were opened before the hind legs began to move. At take-off, the position of the wings was variable and could be 8–21 ms into either elevation or depression. When the hind legs alone propelled a jump, the body was accelerated in 3.97±0.111 ms at a take-off angle of 52±6.5° to a take-off velocity of 1.27±0.119 m s–1; when the wings also moved, the body was accelerated in 3.86±0.055 ms at a take-off angle of 58±1.7° to a take-off velocity of 1.29±0.032 m s–1. These values are not different in the two jumping strategies. In its best jumps the take-off velocity reached 1.8 m s–1 so that Saldula experienced an average acceleration of 529 m s–2, equivalent to almost 54g, expended 3.4 μJ of energy, while exerting a force of 1.1 m N. The power requirements for jumping indicate that a catapult mechanism must be used in which the trochanteral depressor muscles contract and store energy in advance of a jump. These jumps should propel it to a height of 105 mm or 30 times its body length and distances of 320 mm. The two jumping strategies achieve the same jumping performance.

The effect of leg length on jumping performance of short- and long-legged leafhopper insects

To assess the effect of leg length on jumping ability in small insects, the jumping movements and performance of a sub-family of leafhopper insects(Hemiptera, Auchenorrhyncha, Cicadellidae, Ulopinae) with short hind legs were analysed and compared with other long-legged cicadellids (Hemiptera,Auchenorrhyncha, Cicadellidae). Two species with the same jumping characteristics but distinctively different body shapes were analysed: Ulopa, which had an average body length of 3 mm and was squat, and Cephalelus, which had an average body length of 13 mm with an elongated body and head. In both, the hind legs were only 1.4 times longer than the front legs compared with 1.9–2.3 times in other cicadellid leafhoppers. When the length of the hind legs was normalised relative to the cube root of their body mass, their hind legs had a value of 1–1.1 compared with 1.6–2.3 in other cicadellids. The hind legs of Cephalelus were only 20% of the body length. The propulsion for a jump was delivered by rapid and synchronous rotation of the hind legs about their coxo-trochanteral joints in a three-phase movement, as revealed by high-speed sequences of images captured at rates of 5000 s–1. The hind tarsi were initially placed outside the lateral margins of the body and not apposed to each other beneath the body as in long-legged leafhoppers. The hind legs were accelerated in 1.5 ms (Ulopa) and 2 ms(Cephalelus) and thus more quickly than in the long-legged cicadellids. In their best jumps these movements propelled Ulopa to a take-off velocity of 2.3 m s–1 and Cephalelus to 2 m s–1, which matches that of the long-legged cicadellids. Both short-legged species had the same mean take-off angle of 56° but Cephalelus adopted a lower angle of the body relative to the ground(mean 15°) than Ulopa (mean 56°). Once airborne, Cephalelus pitched slowly and rolled quickly about its long axis and Ulopa rotated quickly about both axes. To achieve their best performances Ulopa expended 7 μJ of energy, generated a power output of 7 mW, and exerted a force of 6 mN; Cephalelus expended 23μJ of energy, generated a power output of 12 mW and exerted a force of 11 mN. There was no correlation between leg length and take-off velocity in the long- and short-legged species, but longer legged leafhoppers had longer take-off times and generated lower ground reaction forces than short-legged leafhoppers, possibly allowing the longer legged leafhoppers to jump from less stiff substrates.

Jumping in a wingless stick insect,Timema chumash(Phasmatodea,Timematodea, Timematidae)

The stick insect Timema chumash belongs to a sub-order of the phasmids that is thought to have diverged early from other stick insects, and which is restricted to the southwest of North America. It jumps by rapidly extending the tibiae of both its hind legs simultaneously from an initially fully flexed position, unlike any other stick insect that has been described. The hind legs are 1.5 times longer than the front and middle legs, but still represent only half the length of its body, and the femoro-tibial joints show few specialisations for jumping. In its best jumps, the wingless body is accelerated in 12 ms to a take-off velocity of 0.9 m s–1 and experiences an acceleration of 75 m s–2, the equivalent of 8 g. This performance requires an energy expenditure of 19 μJ,generates a power output of 1.6 mW and exerts a force of 3.6 mN. The jump propels the body forward a distance of 80 mm from a mean take-off angle of 39°. Heights of 20 mm were also achieved. Elevation of the jump was controlled by the initial position of the hind legs; when the hind tibiae and femora projected above the dorsal outline of the body the jump was forwards,when parallel with the long axis of the body the jump was backwards and could result in somersaulting. The jumping movements would appear to displace Timema in different directions away from a potential predator.

Kinematics of jumping in leafhopper insects (Hemiptera, Auchenorrhyncha,Cicadellidae)

The jumping movements and performance of leafhopper insects (Hemiptera,Auchenorrhyncha, Cicadellidae) were analysed from high-speed sequences of images captured at rates up to 5000 frames s–1. The propulsion for a jump was delivered by rapid and synchronous movements of the hind legs that are twice the length of the other legs, almost as long as the body, and represent 3.8% of the body mass. The wings were not moved before take-off, but the jump frequently launched a flight. The front and middle legs set the attitude of the body in preparation for a jump but were usually raised from the ground before take-off. The movements of the hind legs occurred in three distinct phases. First, a levation phase of 15–30 ms, in which both hind legs were moved forward and medially so that they were positioned directly beneath the body with their tibio-tarsal joints pressed against each other. Second, a holding phase lasting 10–200 ms, in which the hind legs remained stationary in the fully levated position. Third, a rapid jump phase,in which both hind legs were simultaneously depressed about their coxo-trochanteral joints and extended at their femoro-tibial joints. This phase lasted 5–6 ms on average, with the fastest movements accomplished in 2.75 ms and involving rotations of the coxo-trochanteral joints of 44 000 deg. s–1. In the best jumps by Aphrodes, a peak take-off velocity of 2.9 m s–1 was achieved by an acceleration of 1055 m s–2, equivalent to 108 times gravity. This jumping performance required an energy output of 77 μJ, a power output of 28 mW and exerted a force of 19 mN, or 100 times its body mass.

Jumping behaviour in a Gondwanan relict insect (Hemiptera: Coleorrhyncha:Peloridiidae)

Jumping by a relict insect, Hackeriella veitchi (Hacker 1932),belonging to the ancient Coleorrhynchan line that diverged from other Hemiptera in the late Permian, was analysed from high-speed images captured at rates of 2000 s–1 and from its anatomy. This 3 mm long,flightless insect weighs up to 1.4 mg and can jump by rapid movements of the hind legs that accelerate the body in 1.5 ms to a take-off velocity of 1.5 m s–1. This performance requires an energy expenditure of 1.1μJ and a power output 0.74 mW, and exerts a force of 1.24 mN. It achieves this with a body design that shows few specialisations for jumping compared with those of other groups of Hemipterans such as the froghoppers or leafhoppers. The hind legs are only 10% longer than the front and middle legs by virtue of longer tibiae and tarsi, and are only 65% the length of the body. The main thrust for a jump is provided by the rapid rotation of the fused trochanter and femur about the coxa of a hind leg, in a movement that forces the hind tarsus against the ground and raises the body to take off. In some jumps the two hind legs move together, but in others the movements may not be closely synchronised, thereby imparting a rotation on the body that is maintained once airborne. When the time difference is larger, the rapid movement of just one hind leg results in the insect falling from its perch in an adaptive escape response.