Structure and function of the elastic organ in the tibia of a tenebrionid beetle.

Many insects have a pair of claws on the tip of each foot (tarsus and pretarsus). The movement of the pretarsal claws is mediated by a long apodeme that originates from the claw retractor muscles in the femur. It is generally accepted that the pulling of the apodeme by the muscles flexes the claws to engage with a rough surface of a substrate, and the flexed claws return to their initial position by passive elastic forces within the tarso-pretarsal joint. We found that each tibia of the tenebrionid beetle Zophobas atratus had a chordal elastic organ that tied the apodeme to the distal end of the tibia and assisted the pulled apodeme to return smoothly. The elastic body of the elastic organ consists of a bundle of more than 1000 thin fibrils (0.3-1.5 µm in diameter) with a hairy yarn-shaped structure made by assemblies of intricately interwoven microfibers. Both ends of the fibrillar elastic body were supported by clusters of columnar cells. Ablation of the elastic organ often disturbed the rapid and smooth return of claws from a flexed position when the tarsal segments were forced to curve in order to increase the friction between the apodeme and surrounding tissues in the segments. The result suggests that rapid claw disengagement is an important step in each cycle of leg movements, and the elastic organ may have evolved to assist the reliable detachment of claws that engage tightly with the substrate when climbing or traversing inverted surfaces.

Olfactory Cues from Pathogenic Fungus Affect the Direction of Motion of Termites, Coptotermes formosanus.

Formosan subterranean termites, Coptotermes formosanus, tend to avoid pathogen odors when tested in Y-tube olfactometers, but approach and groom exposed nestmates to remove pathogens from their cuticle and maintain a healthy population. To better understand their differential reaction to pathogens and their odors, the relationship between odor cues and direction of motion was examined with the fungus Isaria fumosorosea K3 strain. The results indicate that nestmate odor was strongly attractive only in tests where fungal odors were present in both branches of the olfactometer. Termites generally avoid fungal odors when offered a choice without fungal odor. We also tested termite aversion to 3-octanone and 1-octen-3-ol, major surface chemical compounds of I. fumosorosea K3, and estimated the total mass of these compounds present on the conidial surface by direct extraction method. The total quantity of these chemicals on the surface of fungal conidia was estimated to be approximately 0.01 ng per 10(7) conidia. This study demonstrates a context dependent behavioral change in termites in response to the odors of pathogenic fungi.

Refuge size preference in the field cricket Gryllus bimaculatus.

Size preference for artificial refuges was examined in the adult field cricket Gryllus bimaculatus under laboratory conditions. Blinded crickets were placed individually in a container consisting of a circular arena and six different-sized artificial refuges (triangular tent-like shelters). The crickets were allowed to walk freely inside the container for a constant period. Size preference was evaluated by determining cumulative stay period in each shelter. When the depth of the shelters varied from 60 to 160 mm at 20-mm intervals, and the width was fixed at 30 mm, both males and females tended to remain in relatively longer shelters (≥ 140 mm). Females, in particular, exhibited a distinct preference for the longest shelter (160 mm). The width of the shelters was then varied from 20 to 40 mm at 4-mm intervals, and the depth was fixed at 100 mm. Although males did not show selectivity to specific shelters, females tended to select a shelter with a particular width (32 mm). These results suggest that adults of G. bimaculatus have size preferences for refuges under blinded conditions. However, the preferences may involve sexual differences as well.

A descending contralateral directionally selective movement detector in the praying mantis Tenodera aridifolia.

Extracellular recordings were made from a directionally selective neuron in the ventral nerve cord of mantises. The neuron's preferred direction of motion was forward and upward over the compound eye contralateral to its axon at the cervical connective. The neuron was sensitive to wide-field motion stimuli, resistant to habituation, and showed transient excitation in response to light ON and OFF stimuli. Its responses to drifting gratings depended on the temporal frequency and contrast of the stimulus. These results suggest that the neuron receives input from correlation-type motion detectors.

Responses of descending neurons to looming stimuli in the praying mantis Tenodera aridifolia.

Responses to visual stimuli of some neurons that descend the nerve cord from the brain were recorded extracellularly in the mantis Tenodera aridifolia. Most of the recorded neurons showed their largest responses to looming stimuli that simulated a black circle approaching towards the mantis. The neurons showed a transient excitatory response to a gradually darkening or receding circle. The neurons showed sustained excitation to the linearly expanding stimuli, but the spike frequency decreased rapidly. The responses of the neurons were affected by both the diameter and the speed of looming stimuli. Faster or smaller looming stimuli elicited a higher peak frequency. These responses were observed in both recordings from the connective between suboesophageal and prothoracic ganglia and the connective between prothoracic and mesothoracic ganglia. There was a one-to-one correspondence of spike firing between these two recordings with a fixed delay. The neurons had the receptive field on ipsilateral side to its axon at the cervical connective. These results suggest that there is a looming-sensitive descending neuron, with an axon projecting over prothoracic ganglion, in the mantis nervous system.

Antennal motor activity induced by pilocarpine in the American cockroach.

The antennal motor system is activated by the muscarinic agonist pilocarpine in the American cockroach Periplaneta americana, and its output patterns were examined both in restrained intact animals and in isolated CNS preparations. The three-dimensional antennal movements induced by the hemocoelic drug injection were analyzed in in vivo preparations. Pilocarpine effectively induced prolonged rhythmic movements of both antennae. The antennae tended to describe a spatially patterned trajectory, forming loops or the symbol of infinity (infinity). Such spatial regularity is comparable to that during spontaneous tethered-walking. Rhythmic bursting activities of the antennal motor nerves in in vitro preparations were also elicited by bath application of pilocarpine. Cross-correlation analyses of the bursting spike activities revealed significant couplings among certain motor units, implying the spatial regularity of the antennal trajectory. The pilocarpine-induced rhythmic activity of antennal motor nerves was effectively suppressed by the muscarinic antagonist atropine. These results indicate that the activation of the antennal motor system is mediated by muscarinic receptors.

Morphological and optical properties of the corneal lens and retinal structure in the posterior large stemma of the tiger beetle larva.

The morphological and optical features of the corneal lens and retina have been examined in the posterior large stemma of the larva of the tiger beetle (Cicindela chinensis). A cup-shaped retina was positioned 55+/-6microm beneath the posterior margin of the corneal lens, which was 479+/-20microm in diameter and 391+/-18microm in thickness (n=41). A light path through an isolated corneal lens showed that the object at infinite distance was focused on the distal margin of the retina. Geometrical optics gave a value of 334+/-15microm (n=55) for the posterior focal length of the corneal lens. The refractive index of the corneal lens was estimated to be around 1.8, if the lens was considered to be homogenous in structure. The internal structure of the lens, including concentric lamellae, was presumed to contribute to such a high refractive index, because this was higher than that of insect cuticle. The retinal structure and how images were blurred at different focus levels were also examined. Data obtained for optics of the corneal lens and retinal structures are discussed with reference to the distinct visual behavior of the larva.

The dyf-3 gene encodes a novel protein required for sensory cilium formation in Caenorhabditis elegans.

Ciliated neurons in animals are important for the reception of environmental stimuli. To understand the mechanism of cilium morphogenesis in Caenorhabditis elegans, we analyzed dyf-3 mutants that are defective in uptake of a fluorescent dye and abnormal in sensory cilium structure. Expression of green fluorescent protein in sensory neurons of a dyf-3 mutant revealed that the mutant has stunted cilia and abnormal posterior projections in some sensory neurons. The dyf-3 gene encodes three proteins with different N-terminals. The largest DYF-3 protein has 404 amino acid residues that are 38% identical with those of a predicted human protein of unknown function. Expression of a functional dyf-3Colon, two colonsgfp fusion gene is detected in 26 chemosensory neurons, including six IL2 neurons, eight pairs of amphid neurons (ASE, ADF, ASG, ASH, ASI, ASJ, ASK and ADL) and two pairs of phasmid neurons (PHA and PHB). Expression of a dyf-3 cDNA in specific neurons of dyf-3 animals indicated that dyf-3 acts cell-autonomously for fluorescent dye uptake. Reduction of dyf-3Colon, two colonsgfp expression in a daf-19 mutant suggests that dyf-3 expression is regulated by DAF-19 transcription factor, and DYF-3 may be involved in the intraflagellar transport system.

Response properties of visual interneurons to motion stimuli in the praying mantis, Tenodera aridifolia.

Intracellular responses of motion-sensitive visual interneurons were recorded from the lobula complex of the mantis, Tenodera aridifolia. The interneurons were divided into four classes according to the response polarity, spatial tuning, and directional selectivity. Neurons of the first class had small, medium, or large receptive fields and showed a strong excitation in response to a small-field motion such as a small square moving in any direction (SF neurons). The second class neurons showed non-directionally selective responses: an excitation to a large-field motion of gratings in any direction (ND neurons). Most ND neurons had small or medium-size receptive fields. Neurons of the third class had large receptive fields and exhibited directionally selective responses: an excitation to a large-field motion of gratings in preferred direction and an inhibition to a motion in opposite, null direction (DS neurons). The last class neurons had small receptive fields and showed inhibitory responses to a moving square and gratings (I neurons). The functional roles of these neurons in prey recognition and optomotor response were discussed.

Mechanosensory control of antennal movement by the scapal hair plate in the American cockroach.

The voluntary movement of antennae of blinded cockroaches was examined in the tethered-walking condition. An object of metal plate was presented to a tip of a single antenna in order to induce tactile orientation behavior. Horizontal movements of the antenna before and during the object presentation were analyzed both before and after ablation of a mechanosensory organ, the scapal hair plate (S-HP), at the base of antenna. The resting antennal position shifted outwardly by about 20 degrees after the S-HP ablation. Spontaneous antennal movements in ablated animals became stiff and wider ranged. The tactile object was set at two different horizontal positions, 45 degrees and 90 degrees clockwise to the head, for the right side antenna. The number of contacts in a constant test period was significantly decreased in the tests at 45 degrees after ablation. Trajectories of antennal movements before and after contacts were categorized into four patterns. In the case that an antenna made contact with the object during its abduction (outward) movement, it then passed the object outwardly or withdrew inwardly. These were termed "outward-pass (O-P)" and "outward-withdrawal (O-W)" patterns, respectively. Similarly, contacts during the adduction (inward) movement were divided into "inward-pass (I-P)" or "inward-withdrawal (I-W)" pattern. Significant effects of the S-HP ablation appeared in the tests at 90 degrees : the I-P pattern mostly disappeared and was replaced by the I-W pattern. The results strongly suggest that the S-HP has crucial roles for controlling both spontaneous and stimulated movements of the cockroach antenna.

Foraging navigation of hornets studied in natural habitats and laboratory experiments.

Foraging flights have been studied in three species of hornets (Vespa mandarinia, V. simillima and V. analis) in the field and the laboratory. Hornets seem to use multiple navigational cues for visiting a familiar feeding place. They could orient towards the feeding place immediately after they rose in air from the nest without directly viewing the feeder. They could visit the feeding place after dark at a luminosity 8 lux. These data suggest that they can navigate for some distance with few external cues. Hornets also seem to rely on visual cues for their mid-range navigation. They used some structures on their way as navigational landmarks to negotiate. Individual hornets are supposed to have their own landmarks. Olfactory cues seem to be used to find a new feeding place or to recruit other member. In the approach flight hornets seemed to use multiple visual cues such as the visual characteristics of the feeder and the wider scenery around the feeder. Even if the feeder in training was removed during the test, they flew with a smooth course as if they were pin-pointing the missing feeder, but without sitting on the ground. Hornets learnt how to fly to reach the feeder without external cues after passing by the last visual landmark under conditions with extremely poor visual cues. The present work suggests that hornets retain multiple navigational cues during repeated foraging behavior, and which cues they use seems to depend upon environmental conditions.

Intracellular responses of antennal chordotonal sensilla of the American cockroach.

The responses of mechanoreceptor neurons in the antennal chordotonal organ have been examined in cockroaches by intracellular recording methods. The chordotonal organ was mechanically stimulated by sinusoidal movement of the flagellum. Stimulus frequencies were varied between 0.5 and 150 Hz. Receptor neurons responded with spike discharges to mechanical stimulation, and were classed into two groups from plots of their average spike frequencies against stimulus frequency. Neurons in one group responded to stimulation over a wide frequency range (from 0.5 to 150 Hz), whereas those in a second group were tuned to higher frequency stimuli. The peak stimulus frequency at which receptor neurons showed maximum responses differed from cell to cell. Some had a peak response at a stimulus frequency given in the present study (from 0.5 to 150 Hz), whereas others were assumed to have peak responses beyond the highest stimulus frequency examined. The timing for the initiation of spikes or of a burst of spikes plotted against each stimulus cycle revealed that spike generation was phase-locked in most cells. Some cells showed phase-independent discharges to stimulation at lower frequency, but increasing stimulus frequencies spike initiation began to assemble at a given phase of the stimulus cycle. The response patterns observed are discussed in relation to the primary process of mechanoreception of the chordotonal organ.

The antennal sensilla of the praying mantis Tenodera aridifolia: a new flagellar partition based on the antennal macro-, micro- and ultrastructures.

In insects, the antenna consists of a scapus, a pedicellus, and a flagellum comprising many segments (flagellomeres). These segments possess many morphological types of sensory organs (sensilla) to process multimodal sensory information. We observed the sensilla on flagellomeres in praying mantis (Tenodera aridifolia) with both scanning and transmission electron microscopes. We classified the sensilla into six types: chaetic, campaniform, coelocapitular, basiconic, trichoid and grooved peg sensilla, and inferred their presumptive functions on the basis of their external and internal structures. In addition, based on their distribution, we newly divided the flagellum into 6 distinct parts. This new division leads to a better understanding about the sexual dimorphism and the antennal development in the mantises. The sexual difference in distribution of the grooved peg sensilla suggests that this type of sensilla may play a role in sex-pheromone detection in mantis, which is a rare case of double-walled sensilla mediating this function.

Coordinated movements of the head and body during orienting behaviour in the praying mantis Tenodera aridifolia.

The visual orienting behaviour towards prey in the free-moving mantis was investigated with a high-speed camera. The orienting behaviour consisted of head, prothorax, and abdomen rotations. Coordinated movements of these body parts in the horizontal plane were analysed frame-by-frame. Rotations of these body parts were initiated with no or slight (≤40 ms) differences in timing. The initiation timing of prothorax-abdomen rotation was affected by its initial angle before the onset of orienting. There were positive correlations in amplitude among head-prothorax, prothorax-abdomen, and abdomen rotations. The ratio of these rotations to total gaze rotation was affected by the initial prothorax-abdomen angle before the onset of orienting. Our data suggest that coordinated movements of the head, prothorax, and abdomen during orienting are ballistic events and are pre-determined according to visual and proprioceptive information before the onset of orienting.

Antennal and locomotor responses to attractive and aversive odors in the searching cockroach.

The behavioral responses to attractive and aversive odors were examined in blinded adult male cockroaches under tethered-walking conditions. A sex pheromone-like stimulant derived from adult virgin females and artificially synthesized limonene were used as attractive and aversive odor sources, respectively. When a searching animal was stimulated with the attractive female-derived odor, the horizontal deflections of both the antennae were increased, and in most cases the vertical antennal positions were shifted downward. The stimulation also significantly decreased the walking speed of the animal. These behavioral changes imply a careful search in the immediate surroundings. The aftereffect of the sex pheromone was more pronounced on locomotion than on antennal movement. On the other hand, stimulation with the aversive odor (limonene) tended to suppress active antennal movement, and also increased the walking speed. Immediately after the withdrawal of the aversive odor, the active movement of the antennae was resumed, and the walking speed rapidly decreased to a level approximately the same as that of the control period. These results indicate that the responses to the qualitatively opposite types of odor are reciprocal to each other with regard to both antennal movement and locomotion.

An arthropod cuticular chitin-binding protein endows injured sites with transglutaminase-dependent mesh.

In mammals, the cornified cell envelope forms beneath the plasma membrane in epithelia and provides a vital physical barrier consisting of insoluble proteins cross-linked by transglutaminase (TGase). In the horseshoe crab Tachypleus tridentatus, TGase is stored in hemocytes and secreted in response to the simulation of bacterial lipopolysaccharides. Here we characterized a TGase substrate designated as caraxin that was identified in horseshoe crab cuticle. One of the homologs, caraxin-1, possessed a unique domain structure consisting of N-and C-terminal heptad repeats and a central domain with a tandem-repeated structure of a pentapeptide. Western blotting showed the specific localization of caraxin-1 in sub-cuticular epidermis. Moreover, we identified the pentapeptide motif to be a chitin-binding unit. Analytical ultracentrifugation revealed that caraxin-1 exists as an oligomer with 310-350 kDa, which is approximately 20-mer based on the molecular mass of the monomer. The oligomers were cross-linked by TGase to form an elaborate mesh with honeycomb structures, which was electron-microscopically found to be different from the clotting mesh triggered by lipopolysaccharide-induced hemocyte exocytosis. We determined several cross-linking sites in the N-and C-terminal domains of caraxin-1. The replacements of Leu to Pro at positions 36 and 118 in caraxin-1 reduced the alpha-helix content, which destroyed the TGase-dependent mesh, thus indicating the importance of the N-and C-terminal domains for the proper mesh formation. In arthropods, TGase-dependent protein cross-linking may be involved in the initial stage of host defense at the sub-cuticular epidermis, as in the case of mammalian skin.

Active tactile sensing for localization of objects by the cockroach antenna.

Antennal movement during tactile orientation behavior was examined three-dimensionally in American cockroaches during tethered walking. When a wooden rod was presented to the tip of one antenna in an upright orientation at one of the three different horizontal positions (30 degrees , 60 degrees , or 90 degrees from the center of the head), the animal touched it repeatedly with the antenna, and tried to approach it (positive thigmotaxis). Positional shifts were also observed for the contralateral unstimulated antenna. The ipsilateral antenna tended to touch the object during inward movement (adduction) at all three test angles. The cumulative turn angle made during a continuous test period of 24 s clearly depended on the object's position; however, the contact frequencies were almost the same regardless of the position. The relationships between contact frequency and some locomotion parameters were also investigated on a shorter time scale of 3 s. The contact frequency positively correlated with the turn angle, with the accuracy of orientation at all three test angles, and with the translation velocity at test angles of 30 degrees and 60 degrees . It is concluded that the performance during tactile orientation can be represented effectively by the frequency with which the antennae touch the attractive objects.

The fine structure of the lateral ocellus of the dobsonfly larva.

The lateral ocelli of the dobsonfly (Protohermes grandis, Neuroptera) larva have been examined with light and electron microscopy. The larva has six ocelli on both sides of the head, each containing a single corneal lens. A conical crystalline body, of some 10-20 cells is situated immediately posterior to the lens. From 100 to 300 elongated retinular cells are arranged perpendicular to the crystalline body except at the innermost surface of the lens, where they are absent. The distal process of each retinular cell is enclosed by a tube-like rhabdom formed by the close association of microvilli from the same and adjacent distal processes. The distal process contains many mitochondria, multivesicular bodies, microtubles and pigment granules. In the dark-adapted ocellus the pigment granules are concentrated near the nucleus which lies under the rhabdomic layer. The granules diffuse toward the rhabdomic microvilli during light adaptation. Each retinular cell has a single axon, which extends from the ocellus as an ocellar nerve fiber into the optic lobe, where it frequently synapses upon second order neurons. In addition to these afferent synapses, there are two other synaptic combinations: (1) a feedback synapse from a second order neuron to a retinular axon, and (2) a synapse between second order neurons. These results suggest that photic signals reach the more proximal part of the brain via second order neurons after some degree of integration in the optic lobe.

Spatio-temporal patterns of antennal movements in the searching cockroach.

To characterize the spatio-temporal patterns of antennal behavior in insects, the voluntary movement of both right and left antennae was examined in the cockroach Periplaneta americana. The position of the tip of the antenna (flagellum) is controlled by two mobile joints at its base (the scape and the pedicel) and by the neck. Horizontal and vertical components of movement at the antennal basal joints exhibited rhythmic activities during locomotory (walking) and non-locomotory (pausing) states in the searching animal. In both states, the horizontal component was slower than vertical one. Joint-manipulation experiments suggested that the faster vertical component is due mainly to movements of the scape-pedicel joint, while the slower horizontal component may originate from the head-scape joint. Large horizontal deflections of the antenna corresponded consistently with the yaw component of head movement. The trajectories of the antennae showed little patterned regularity in most animals. In a few cases, however, loop-like patterns appeared. The area scanned by an antenna was narrower in the walking state than in the pausing state, mainly because of a decrease in the horizontal angular range. Cross-correlation analyses revealed that the coupling between right and left horizontal antennal motor systems and that for the vertical systems were both significantly stronger in the walking state than during pausing. These results indicate that the spatio-temporal pattern of antennal movements changes dynamically depending on the animal's behavioral state.