Optomotor reaction and fixation of walking colorado beetles (Coleoptera: Chrysomelidae): Course control aspects

The paths of Colorado beetles (Leptinotarsa decemlineata Say)in a featureless environment are circular. This behavior is explained by an internal asymmetry. To stabilize the path, the fixation reaction or the optomotor response must work against this asymmetry. The turning behavior was examined in stationary patterns of vertical stripes different at spatial wavelengths (). The internal asymmetry was tested in a horizontally striped pattern. A stable fixation reaction was found only for 120 °. The results suggest that larger intrinsic turning tendencies shifts the stable point of the fixation reaction. The same vertically striped patterns were rotated to examine the following reaction of the beetle. It is concluded that the fixation component of the response of these insects, in particular, does not differ in the two situations.     

Behavioural assessments of neurotoxic effects and neurodegeneration in zebrafish

Altered neurological function will generally be behaviourally apparent. Many of the behavioural models pioneered in mammalian models are portable to zebrafish. Tests are available to capture alterations in basic motor function, changes associated with exteroceptive and interoceptive sensory cues, and alterations in learning and memory performance. Excepting some endpoints involving learning, behavioural tests can be carried out at 4 days post fertilization. Given larvae can be reared quickly and in large numbers, and that software solutions are readily available from multiple vendors to automatically test behavioural responses in 96 larvae simultaneously, zebrafish are a potent and rapid model for screening neurological impairments. Coupling current and emerging behavioural endpoints with molecular techniques will permit and accelerate the determination of the mechanisms behind neurotoxicity and degeneration, as well as provide numerous means to test remedial drugs and other therapies. The emphasis of this review is to highlight unexplored/underutilized behavioural assays for future studies. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.     

Studying the Neural Basis of Adaptive Locomotor Behavior in Insects

Studying the neural basis of walking behavior, one often faces the problem that it is hard to separate the neuronally produced stepping output from those leg movements that result from passive forces and interactions with other legs through the common contact with the substrate. If we want to understand, which part of a given movement is produced by nervous system motor output, kinematic analysis of stepping movements, therefore, needs to be complemented with electrophysiological recordings of motor activity. The recording of neuronal or muscular activity in a behaving animal is often limited by the electrophysiological equipment which can constrain the animal in its ability to move with as many degrees of freedom as possible. This can either be avoided by using implantable electrodes and then having the animal move on a long tether (i.e. Clarac et al., 1987; Duch & Pflüger, 1995; Böhm et al., 1997; Gruhn & Rathmayer, 2002) or by transmitting the data using telemetric devices (Kutsch et al, 1993; Fischer et al., 1996; Tsuchida et al. 2004; Hama et al., 2007; Wang et al., 2008). Both of these elegant methods, which are successfully used in larger arthropods, often prove difficult to apply in smaller walking insects which either easily get entangled in the long tether or are hindered by the weight of the telemetric device and its batteries. In addition, in all these cases, it is still impossible to distinguish between the purely neuronal basis of locomotion and the effects exerted by mechanical coupling between the walking legs through the substrate. One solution for this problem is to conduct the experiments in a tethered animal that is free to walk in place and that is locally suspended, for example over a slippery surface, which effectively removes most ground contact mechanics. This has been used to study escape responses (Camhi and Nolen, 1981; Camhi and Levy, 1988), turning (Tryba and Ritzman, 2000a,b; Gruhn et al., 2009a), backward walking (Graham and Epstein, 1985) or changes in velocity (Gruhn et al., 2009b) and it allows the experimenter easily to combine intra- and extracellular physiology with kinematic analyses (Gruhn et al., 2006).We use a slippery surface setup to investigate the timing of leg muscles in the behaving stick insect with respect to touch-down and lift-off under different behavioral paradigms such as straight forward and curved walking in intact and reduced preparations.     

Orientation in high-flying migrant insects in relation to flows: mechanisms and strategies

High-flying insect migrants have been shown to display sophisticated flight orientations that can, for example, maximize distance travelled by exploiting tailwinds, and reduce drift from seasonally optimal directions. Here, we provide a comprehensive overview of the theoretical and empirical evidence for the mechanisms underlying the selection and maintenance of the observed flight headings, and the detection of wind direction and speed, for insects flying hundreds of metres above the ground. Different mechanisms may be used—visual perception of the apparent ground movement or mechanosensory cues maintained by intrinsic features of the wind—depending on circumstances (e.g. day or night migrations). In addition to putative turbulence-induced velocity, acceleration and temperature cues, we present a new mathematical analysis which shows that ‘jerks’ (the time-derivative of accelerations) can provide indicators of wind direction at altitude. The adaptive benefits of the different orientation strategies are briefly discussed, and we place these new findings for insects within a wider context by comparisons with the latest research on other flying and swimming organisms.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.     

Effects of varying sex pheromone component ratios on the zigzagging flight movements of the oriental fruit moth,Grapholita molesta

As the ratio of (E)-8-dodecenyl acetate (E8–12Ac) to (Z)-8-dodecenyl acetate (Z8–12Ac) increased past optimal low levels in the pheromone blend, fewer males were able to fly 2.5 m upwind to the source. The tracks of males that flew in plumes of such high-(E)off-blends were slower and narrower than those of males flying to lower-(E)blends. The tracks were narrower, first of all, because as the proportion of E8–12Ac increased, the males steered more into the wind. More of their thrust was directed upwind and therefore their groundspeed to either side of the windline was reduced. In addition, males also reduced their airspeeds to high-(E)blends, which contributed to the decreased groundspeeds and narrower tracks. No significant changes in the frequency of counterturning were found in response to increasing proportions of E8–12Ac. The inability to continue upwind flight in a plume of an off ratio was indicated by in-flight arrestment in the plume. Arrestment resulted from changes in the course angles steered by the males and the airspeeds flown.     

Visual Responses of Crayfish Ocular Motoneurons: An Information Theoretical Analysis

Motoneuron responses were elicited by global visual motion and stepwise displacements of an illuminated stripe. Stimulus protocols were identical to those used in previous behavioral studies of compensatory eyestalk reflexes. The firing rates and directional selectivity of the motoneuron responses were measured with respect to four stimulus dimensions (spatial frequency, contrast, angular displacement and velocity). The directional selectivity of the motoneuron response was correlated to the previously measured gain of the reflex for each stimulus dimension. The information theoretical analysis is based upon Kullback-Leibler (K-L) distances which measure the dissimilarity of responses to different stimuli. K-L distances for single neurons are strongly influenced by the mean rate difference of the responses to any pair of stimuli. Because of redundancy, the joint K-L distances of pairs of neurons were less than the sum of the K-L distances of the individual neurons. Furthermore, the joint K-L distances were only weakly influenced by correlations among coactivated neurons. For most of the stimulus dimensions, the K-L distances of single motoneurons were not sufficient to account for the stimulus discriminations exhibited by the eyestalk reflex which typically required the summed output of 2 to 5 motoneurons. Thus the behaviorally relevant information is encoded in the motoneuron ensemble. The minimum time required to discriminate the direction of motion (the encoding window) for a single motoneuron is about 380 to 480 ms (including a 175 ms response latency) for stepwise displacements and up to 1.0 s for global motion. During this period a motoneuron fires 2 to 3 impulses.     

Influence of pheromone concentration and ambient temperature on flight of the gypsy moth, Lymantria dispar (L), in a sustained-flight wind tunnel

Abstract. The effects of pheromone concentration and ambient temperature on male gypsy moth, Lymantria dispar (L.) (Lepidoptera), flight responses to pheromone were investigated in a wind tunnel. As the pheromone dose increased from 10 ng to 1000 ng, males flew at progressively slower airspeeds and ground speeds, and reduced their wingbeat frequencies. Furthermore, the moths steered significantly smaller course angles as the pheromone concentration increased, indicating that they were adopting a more upwind heading. The overall width of the flight tracks also decreased when males flew in more concentrated pheromone plumes. Estimation of plume dimensions using a male wing-fanning assay showed that as pheromone dosage increased, the resultant active spaces became wider, indicating that an inverse relationship existed between the dimensions of the time-averaged plume and the width of track reversals and that most turns were initiated within the plume. When males were flown at cool (20°C) and warm (26°C) ambient temperatures but to equivalent pheromone emission rates, they exhibited higher airspeeds and ground speeds at the higher temperature but steered larger course angles. Track widths, and length of track legs were, however, similar at the two temperatures. The mean turning frequency was nearly the same (c. 4 turns/s) across all the concentrations and temperatures tested even though the moths' thoracic temperature differed by 5°C when the ambient temperature was varied.