Motor activity and trajectory control during escape jumping in the locust <Emphasis Type="Italic">Locusta migratoria</Emphasis>

We investigated the escape jumps that locusts produce in response to approaching objects. Hindleg muscular activity during an escape jump is similar to that during a defensive kick. Locusts can direct their escape jumps up to 50° either side of the direction of their long axis at the time of hindleg flexion, allowing them to consistently jump away from the side towards which an object is approaching. Variation in jump trajectory is achieved by rolling and yawing movements of the body that are controlled by the fore- and mesothoracic legs. During hindleg flexion, a locust flexes the foreleg ipsilateral to its eventual jump trajectory and then extends the contralateral foreleg. These foreleg movements continue throughout co-contraction of the hindleg tibial muscles, pivoting the locust’s long axis towards its eventual jump trajectory. However, there are no bilateral differences in the motor programs of the left and right hindlegs that correlate with jump trajectory. Foreleg movements enable a locust to control its jump trajectory independent of the hindleg motor program, allowing a decision on jump trajectory to be made after the hindlegs have been cocked in preparation for a jump.     

The Mechanics and Trajectory Control in Locust Jumping

Locusts (Locusta migratoria manilensis) are characterised by their flying ability and abiding jump ability. Research on the jumping mechanics and behavior of locusts plays an important role in elucidating the mechanism of hexapod locomotion. The jump gestures of locusts were observed using high-speed video camera at 250 fps. The reaction forces of the hindlegs were measured using two three-dimensional sensors, in case the two hindlegs attached on separated sensor plates. The jump gestures and reaction forces were used to illustrate the locust jumping mechanism. Results show that the trajectory control is achieved by rapid rolling and yawing movements of the locust body, caused by the forelegs, midlegs and hindlegs in different jumping phases. The final jump trajectory was not determined until hind tarsi left platform. The horizontal co-impulse between two hindlegs might play a key role in jump stability and accuracy. Besides, the angle between two hindlegs affects the control of jump trajectory but has a little effect on the elevation angle of a jump, which is controlled mechanically by the initial position of the hindlegs. This research lays the groundwork for the probable design and development of biomimetic robotics.     

The energetics of the jump of the locust Schistocerca gregaria.

The anatomy of the metathoracic leg is redescribed with particular reference to storage of energy in cuticular elements and the way in which the stored energy is used in jumping. The jump of adult male locusts requires an energy of 9 mJ and that of the female requires 11 mJ. The semilunar processes of each metafemur store 4 mJ at a stress of 15 N, and the extensor tibiae apodeme stores a further 3 mJ at the same stress. The total stored energy in both metathoracic legs is 14 mJ. The extensor tibiae muscle produces a maximum isometric force of over 15 N at 30 degrees C and, when loaded with the extensor apodeme and semilunar processes, attains this force in 0.3 sec with a strain of 0.8 mm. The peak power output is 36 mW or 0.45 W.g-1. The peak isometric force is attained when the tibia is fully flexed and the force falls as the tibia extends. The extensor tibiae muscle A band is 5.5 mum long and the peak force is over 0.75 N.m-2. The peak velocity of shortening is 7 mm.sec-1 or about 1.75 lengths/sec at 30 degrees C. The tensile strength of the extensor apodeme is 0.6 kN.mm-2 and Young's modulus is 19 kN.mm-2. The safety factor does not exceed 1.2 and the safety factor of the semilunar processes and tibial cuticle is little higher. The jump impulse lasts 25-30 msec. A velocity of 3.2 m.sec-1 is reached after a peak acceleration of 180 m.sec-2. The peak power output is 0.75 W at close to maximum velocity. Energy losses in rotating the femur and tibia are small and it is shown that the leg is able to extend at 7 times the normal rate with losses of about 20%. Most of the stored energy is converted to kinetic energy as the animal jumps. A model is based on the relaxation of a spring that has the properties of the elastic elements of the locust leg into a lever with the same kinematics as the locust leg produces a force-distance curve similar to that measured for locust jumps. The major part of the jump energy is stored before the jump.     

Preparing for escape: an examination of the role of the DCMD neuron in locust escape jumps

Many animals begin to escape by moving away from a threat the instant it is detected. However, the escape jumps of locusts take several hundred milliseconds to produce and the locust must therefore be prepared for escape before the jumping movement can be triggered. In this study we investigate a locust’s preparations to escape a looming stimulus and concurrent spiking activity in its pair of uniquely identifiable looming-detector neurons (the descending contralateral movement detectors; DCMDs). We find that hindleg flexion in preparation for a jump occurs at the same time as high frequency DCMD spikes. However, spikes in a DCMD are not necessary for triggering hindleg flexion, since this hindleg flexion still occurs when the connective containing a DCMD axon is severed or in response to stimuli that cause no high frequency DCMD spikes. Such severing of the connective containing a DCMD axon does, however, increase the variability in flexion timing. We therefore propose that the DCMD contributes to hindleg flexion in preparation for an escape jump, but that its activity affects only flexion timing and is not necessary for the occurrence of hindleg flexion.     

Neural circuits for jumping in the locust

The locust jump consists of three distinct phases: Cocking: a rapid flexion of both hindleg tibia and locking of both tibia in full flexion. Co-contraction: simultaneous contractions in hindleg flexor and extensor muscles lasting about 0.5 s resulting in the storage of energy for the jump in elastic elements of the legs and muscles. Triggering: a sudden inhibition of flexor activity to allow the shortening of the contracted extensors and the release of the energy stored during the co-contraction phase. The neural circuitry controlling these three phases is now reasonably well understood. Some of its major features are: (1) pairs of large identifiable interneurons in the thoracic ganglia for evoking the cocking response (C-neurons) and for triggering the jump (M-neurons), (2) a central excitatory pathway from extensor to flexor tibiae motoneurons to ensure simultaneous activation of extensor and flexor motoneurons during the initial part of the co-contraction phase, (3) a positive feedback pathway from cuticular receptors to extensor motoneurons for maintaining extensor activity during the co-contraction phase, (4) proprioceptive feedback to the trigger interneurons for increasing their excitability during the co-contraction phase and thereby allowing a variety of external stimuli to activate the trigger neurons and evoke a jump, (5) presynaptic inhibition of visual pathways to the trigger neurons to ensure that the trigger neurons are not activated by the simultaneous occurrence of visual and auditory stimuli in the absence of proprioceptive input, and (6) a pair of multifunctional visual movement detecting neurons which can initiate cocking or trigger the jump depending on the animal's state.     

1H NMR investigation of thermally triggered insulin release from poly(N-isopropylacrylamide) microgels

We describe investigations of insulin release from thermoresponsive microgels using variable temperature (1)H NMR. Microgel particles composed of poly(N-isopropylacrylamide) were loaded with the peptide via a swelling technique, and this method was compared to simple equilibrium partitioning. Variable temperature (1)H NMR studies suggest that the swelling loading method results in enhanced entrapment of the peptide versus equilibrium partitioning. A centrifugation-loading assay supports this finding. Pseudo-temperature jump (1)H NMR measurements suggest that the insulin release rate is partially decoupled from microgel collapse. These types of direct release investigations could prove to be useful methods in the future design of controlled macromolecule drug delivery devices.     

刺槐对降雨的截持作用

基于林冠截持和干流现象的物理机制,通过进行一些假设简化,建立了刺槐单株林木的林冠截持量和干流量的模型,并对它们的应用简单地提出了建议。     

To be or not to be a locust? A comparative analysis of behavioral phase change in nymphs of Schistocerca americana and S. gregaria

Phenotypic plasticity in behavior induced by high rearing density is often part of a migratory syndrome in insects called phase polyphenism. Among locust species, swarming and the expression of phase polyphenism are highly correlated. The american grasshopper, Schistocerca americana, rarely swarms even though it is closely related to the swarming Old World desert locust, S. gregaria, as well as two swarming New World locusts. Anecdotal field observations of locust-like behavior in S. americana indicate that it may express behavioral phase polyphenism, but empirical investigations are lacking. In this study, I tested the hypothesis that S. americana expresses locust-like density-dependent changes in behavior during both the first and final nymphal instars. I then compared the expression of behavioral phase change between S. americana and S. gregaria. First instar S. americana exhibited significant geographic variation in behavior with grasshoppers from a North Carolina population expressing more pronounced density-dependent changes relative to grasshoppers from a Texas population. The behavior of final instar S. americana was only slightly affected by rearing density and there was no evidence for a difference between populations. Comparison with S. gregaria revealed that the magnitude of density-dependent behavioral change, particularly among final instar nymphs, was much reduced in S. americana.     

Complex dynamics of desert locust plagues

Abstract. 1. Spectral analysis of 66 years of locust swarm abundance data failed to reveal any significant cycles although the dominant cycle detected in a de-trended series, adjusted to take account of a significant partial autocorrelation for a lag of 1 year, had a periodicity of 16 years.
2. Although some estimates of the intrinsic rate of increase (r) of desert locusts are indicative of chaos, reconstructions of locust dynamics using response surface methodology (RSM) suggested exponential stability. This was also true for data for the West African Region alone and inclusion of rainfall data from the Sahel improved the significance of an RSM model for West Africa.
3. The observed positive relationship between locust abundance and rainfall in West Africa confirmed the importance of rain; but the variance of the locust abundance also increased with rainfall, making rainfall alone a poor predictor. However, this heteroscedastic pattern was reproducible by a simple logistic model with a chaotic r and a variable K. This was not the case when a stable value for r was used.
4. The available data and current methodologies are insufficient to provide unequivocal conclusions on locust dynamics, which are complicated by phase changes and associated switches in r values.     

Nitric oxide: an unconventional messenger in the nervous system of an orthopteroid insect

Nitric oxide (NO) is a membrane-permeant messenger molecule generated from the amino acid L-arginine. NO can activate soluble guanylyl cyclase leading to the formation of cyclic GMP (cGMP) in target cells. In the nervous system, NO/cGMP signalling is thought to play essential roles in synaptic plasticity during development and also in the mature animal. This paper examines biochemical, cell biological, and physiological investigations of NO/cGMP signalling in the nervous system of the locust, a commonly used neurobiological preparation. Biochemical investigations suggest that an identical enzyme is responsible for both NO synthase (NOS) and NADPH-diaphorase activity after tissue fixation. Immunocytochemical staining of an olfactory center in the locust brain shows that NOS-immunoreactivity colocalizes with NADPH-diaphorase at the cellular level. The cytochemical staining of NO donor and target cells in adult animals suggests functions in olfaction, vision, and sensorimotor integration. During development, NO is implicated in axonal outgrowth and synaptogenesis. The cellular distribution of NO-responsive cells in neural circuits reflects potential functions of NO as a retrograde synaptic messenger, as an intracellular messenger, and as a lateral diffusible messenger independent of conventional synaptic connectivity.     

A simple device for measuring a vertical jump: description and results

A simple and cheap device has been designed which makes it possible to quantify a vertical jump. The parameters which can be measured or calculated with this device include: height of the jump, duration of thrust, maximal velocity and thus the corresponding maximal power output. The device was tested on 22 young soccer players for whom the height of the jump (0.47 m, SEM 0.015) and maximal power output (34.9 W. kg-1, SEM 1.04) were considered. The device is proposed for assessing training methods and sports aptitude.     

Locust flight initiation: a comparison of normal and artificial release

Flight initiation was analysed in the migratory locust, Locusta migratoria L. using conventional and high‐speed video systems. Flight was initiated by three methods: normal jump, free fall and controlled catapult. Parameters evaluated were time from release to wing‐opening, body angle, speed, height gain, wing‐opening, initial wing‐beat frequency. Fastest wing‐opening occurred following a normal jump. A catapult device allowed manipulation of the launching parameters: speed and angles at launching. It appeared that in an artificially catapulted start there was a minimum speed (v > 0.75 m/s) required to initiate flight. However, under free‐fall conditions a mean speed of v = 0.6 m/s at wing‐opening was observed. When the different parameters of the controlled catapult start were equal to those for normal jump then the time to wing‐opening was found to be extended for the catapult launch. However, other parameters were not affected, occasionally even a ‘kick in air’ was observed. The catapult launches indicated that within about three wing‐beat cycles the animals showed active flight, with positive lift and constant or increasing speed, compared to a ballistic trajectory. Our results indicate that a controlled catapult device will prove useful to the study of sensory and central processes underlying free flight initiation.     

The mechanics of elevation control in locust jumping

How do animals control the trajectory of ballistic motions like jumping? Targeted jumps by a locust, which are powered by a rapid extension of the tibiae of both hind legs, require control of the take-off angle and speed. To determine how the locust controls these parameters, we used high speed images of jumps and mechanical analysis to reach three conclusions: (1) the extensor tibiae muscle applies equal and opposite torques to the femur and tibia, which ensures that tibial extension accelerates the centre of mass of the body along a straight line; (2) this line is parallel to a line drawn from the distal end of the tibia through the proximal end of the femur; (3) the slope of this line (the angle of elevation) is not affected if the two hind legs extend asynchronously. The mechanics thus uncouple the control of elevation and speed, allowing simplified and independent control mechanisms. Jump elevation is controlled mechanically by the initial positions of the hind legs and jump speed is determined by the energy stored within their elastic processes, which allows us to then propose which proprioceptors are involved in controlling these quantities.     

飞蝗抱对行为的进化意义及两型间相异的交配策略

飞蝗Locusta migratoriaL.不仅交配时间长,而且进行频繁的、长时间的交配前抱对。一般认为,交配前抱对行为是雄虫为了等待时机获取适时的交配。最近的研究表明,飞蝗的交配时间与P2值(最后交配雄虫子代的比例)、交配前抱对时间与交配时间存在显著的正相关关系,即飞蝗长时间的交配前抱对行为能延长其后续的交配时间,从而提高P2值。飞蝗具变型现象,散居型和群居型在形态特征、生理机能、行为及体色等方面存在明显差异。最近的研究结果显示,散居型较群居型具更高的P2值,较短的交配前抱对和较长的交配时间。冲绳和筑波种群散居型成虫的交配前抱对时间与交配时间存在显著的正相关关系,而群居型无此相关性。这些结果证实飞蝗散居型和群居型之间存在着繁殖策略的差异。     

A robust numerical algorithm for studying biomolecular transport processes

We present a numerical algorithm that is well suited for the study of biomolecular transport processes. In the algorithm a continuous Markov process is discretized as a jump process and the jump rates are derived from local solutions of the continuous system. Consequently, the algorithm has two advantages over standard numerical methods: (1) it preserves detailed balance for equilibrium processes, (2) it is able to handle discontinuous potentials. The formulation of the algorithm also allows us to calculate the effective diffusion coefficient or, equivalently, the randomness parameter. We provide several simple examples of how to implement the algorithm. All the MATLAB functions files needed to reproduce the results presented in the article are available from www.amath.unc.edu/Faculty/telston/matlab_functions.     

A simple strategy for jumping straight up

Jumping from a stationary standing position into the air is a transition from a constrained motion in contact with the ground to an unconstrained system not in contact with the ground. A simple case of the jump, as it applies to humans, robots and humanoids, is studied in this paper. The dynamics of the constrained rigid body are expanded to define a larger system that accommodates the jump. The formulation is applied to a four-link, three-dimensional system in order to articulate the ballistic motion involved. The activity of the muscular system and the role of the major sagittal muscle groups are demonstrated. The control strategy, involving state feedback and central feed forward signals, is formulated and computer simulations are presented to assess the feasibility of the formulations, the strategy and the jump.     

昆虫的生物光电效应与虫害治理应用

农业虫害的治理需要依据为害昆虫的特性提出与环境适宜、生态兼容的技术体系和关键技术。为害昆虫表现了对敏感光源具有个体差异性和群体一贯性的趋光性行为特征,并通过视觉神经信号响应和生理光子能量需求的方式呈现出生物光电效应的作用本质。利用昆虫的这种趋性行为诱导增益特性,一些光电诱导杀虫灯技术以及害虫诱导捕集技术广泛地应用于农业虫害的防治,具有良好的应用前景。     

Role of Olfactory and Visual Cues in the Attraction/Repulsion Responses to Conspecifics by Gregarious and Solitarious Desert Locusts

Desert locusts [Schistocerca gregaria Forskål (Orthoptera, Acrididae)] change phase in response to population density: solitarious insects avoid one another, but when crowded they change to the gregarious phase and aggregate. The attraction/repulsion responses of gregarious and solitarious locusts maintain phase differences in locust populations. Despite considerable research, the cues for aggregation are poorly understood; moreover, the repulsion response of solitarious locusts has not previously been investigated. This study analyzes the role of visual and olfactory stimuli in triggering these different responses to conspecifics. Isolation-reared insects were repelled by both olfactory and visual stimuli from other locusts. Crowd-reared insects were attracted by the combination of olfactory and visual cues. In addition, olfactory stimuli affected other behaviors in both phases, and behavioral differences between isolation- and crowd-reared locusts were clear even in the absence of conspecifics. The sensory and neurological mechanisms underlying these responses are not well understood and will form the basis for neurobiological investigations of locust phase.