Variations of behavioural patterns during development in the water stick insect

International audienceVariations of associations between different behavioural patterns were analysed during post-embryonic development in the water stick insect,Ranatra linearis L. (Heteroptera: Nepidae). Behavioural patterns recorded were: quiescence, swimming, crawling, leg waving, body swaying, respiratory ascents breathing, respiratory descents, grooming and feeding activities (predatory attempts, foreleg movements, ingestion). A factorial analysis of correspondance stressed the contrast between the organization of larval behaviour and that of adult behaviour. No behavioural patterns were dropped from the repertoire during post-embryonic development ofRanatra linearis and no new patterns developed in adults outside the reproductive period. Larval behaviour was characterized by more frequent respiratory activities and grooming and adult behaviour was characterized by more frequent locomotory activities. At all larval stages grooming was associated with respiratory activities and crawling, but not with feeding activities

Factors influencing the choice of predatory tactics in a water bug, Diplonychus indicus Venk. & Rao (Heteroptera: Belostomatidae)

International audienceThe tropical water bug Diplonychus indicus is a highly versatile predator that alternates quickly from active foraging to ambushing. The influence of hunger level, the presence of prey and environmental complexity on swimming, diving resting and foraging by adult males was investigated at the individual level, in a factorial experiment with three main treatments. There were simple relationships between these factors and the water bug's behaviour, and interactions between these three factors also affected foraging. The general distribution of foraging tactics between active search and ambushing was significantly influenced by the presence of perching sites (vegetation), but not by hunger levels although hungry bugs as well as bugs in the absence of perching sites were significantly more active than well-fed subjects or bugs in the presence of perching sites. In the presence of vegatation, predatory attempts included fewer dives and more attempts from ambush including preliminary orientations. Hunger level, however, did influence the distribution of ambush predatory tactics; the attempts by hungry subjects included more preliminary orientations. Capture efficiency was not affected by hunger level, but it was affected by the presence of perching sites. Under these experimental conditions the bugs appeared to be capable of modifying, to a certain extent, their predatory tactics in relation to the environment. Nevertheless, the choice of a predatory tactic did not appear to be taken on an all or none basis

Development of the compound eyes of the water stick insect, Ranatra linearis

International audienceRelationships between estimation of predator-prey distance prior to a capture attempt and some features of the compound eye are investigated at all stages of post-embryonic development. Interommatidial angles increase gradually from the anterior and the dorsal regions to the posterior and ventral regions. Facet diameters vary only slightly over the eye surface but increase with age. New ommatidia appear around the borders of eye after each moult. The older ommatidia are pushed away from the border. From one instar to another ommatidia change their direction of view from between 10d̀ to 30d̀ relative to the body axes. This change in direction far exceeds the calculated changes in direction that would be optimal if ommatidia were to continue viewing the same relative directions in space. This suggests a high degree of plasticity of the underlying neuronal networks

Predatory success in the water stick insect: The role of visual and mechanical stimulations after moulting

International audienceThe more foreleg femur and claw movements that a water stick insect, Ranatra linearis, performs during the 4-h period following a moult, the higher will be its subsequent strike efficiency. The amount of movement is influenced by external factors such as the presence of prey or light. The experiments reported here show that the absence of visual cues during the post-moult periods impairs subsequent performance, but not as much as the absence of both visual and mechanical cues. Perception of mechanical stimuli only during that period subsequently influences the accuracy of simple type strikes elicited when prey is near the forelegs; whereas perception of visual stimuli subsequently improves the accuracy of more complex predatory movements

General activity and foraging tactics in a water bug

International audienceDiplonychus indicus is a highly versatile predator that forages both actively and from ambush. However, no correlations between predatory mode changes and predatory performance have yet been evidenced. The hypotheses that time spent foraging actively was proportional to time spent locomotory active and that time spent ambushing was proportional to time spent quiescent were tested during animal development. Locomotory activity increases during development due to increases in both frequency and duration of swimming bouts. The frequency of position changes increases as well. Eggbearing males were less active than other adults. However, the proportion of active foraging did not vary significantly with developmental stage and no correlations between activity level and predatory mode were found. Changes in predatory tactics in Diplonychus indicus differ from those reported in other predators as they are not related to any of the usual biotic or abiotic factors

Post-Moult Behaviour in the Water-Stick Insect Ranatra Linearis

International audienceThe four hour period in Ranatra nymphs between moulting and cuticle darkening is characterized by particular foreleg movements: (i) slow opening and closing of claws (OCT); (ii) moving foreleg femur tips towards the head (B2F). Post-moult behaviour has been divided into three phases: phase 1, lasting about 25 min, claws usually closed, few OCT movements and few B2F movements occur; phase 2 with claws open and forelegs stretched out in front, lasts on average 25 min; during longer phase 3 (205 min on average) many OCT and B2F movements occur. Age does not influence the duration of phases. The number of OCT and B2F movements during phase 3 increases significantly with age. An environmental factor such as presence of potential prey can influence this behaviour. Phases 1 and 3 last longer in absence of prey items than in their presence. The rates of B2F and OCT movements during phase 3 are significantly higher in the presence of prey, for all instars

A Study of the Postural Variations in the Foreleg of Ranatra Linearis (Insecta Heteroptera)

International audienceA correlation between the foreleg postures of Ranatra linearis, specific states of its alimentary canal linked with intestinal transport (checked by direct observation and dissection), and its responsiveness to an alimentary stimulus is described. The emptier the midgut, the more the forelegs are bent backwards towards the head and the further apart these two forelegs are one from the other. A study of the extinction of prey capture behaviour shows that the more the forelegs are bent backwards towards the head, (the smaller the coxa-femur angle) and the further apart the two forelegs one from the other, the more numerous the responses to repeated presentations of an alimentary stimulus will be. For a specific initial posture the responses to repeated presentations of an alimentary stimulus are less numerous if the model is presented in the part of the perceptual space above the forelegs (stimulating the visual receptors only) than if it is moved through the entire perceptual field (stimulating femoral mechanoreceptors as well as visual receptors). For a specific initial foreleg posture these responses will be more numerous if the behavioural sequence is interrupted nearer the beginning. The first responses in a series of presentations of an alimentary stimulus are always more complete than later responses. The duration of the intervals between two successive responses in a given series varies according to the initial posture of the forelegs, and so does the quantity of food eaten

Variations of foraging tactics in a water bug, Diplonychus indicus

International audienceThe predatory behaviour ofDiplonychus indicus Venk. & Rao (Heteroptera: Belostomatidae), a tropical water bug, appeared to be highly versatile. Male adultD. indicus alternated from active foraging to ambushing during the same observation. The predatory movements described here were divided into 7 different categories. Five include ambushing and no active search: simple capture, strike, lunge and strikes following a preliminary vertical or horizontal orientation. Two include active search: dive and swimming bout.Success rates of capture varied with predatory movement category and with predatorprey distance. Attempts including lunges had the highest success rate. Attempts including short lunges, small vertical or horizontal turns or short dives were less likely to be successful than attempts including relatively longer lunges, larger vertical or horizontal turns or longer dives

Mechanismes intervenant dans l'estimation des distances predateur-proie chez Ranatra

International audienceData from previous experiments on predator-prey distance estimation during ontogeny are compared to theoretical interpretations. In Ranatra the relationships between performance (maximum reactive distances), effectors (length of forelegs) and receptors (eyes) do not remain constant during nymphal development, contrary to Mantids (Maldonado et al., 1973). The hypothesis of an automatic morphological adaptation occurring after each moult cannot be retained.Burkhardt et al.'s (1973) theoretical analysis of binocular vision in insects was applied to Ranatra : for the first four nymphal instars, the calculated limits of binocular vision coincide with maximum reactive distances. This could explain why these animals do not react to prey items presented at distances equal to the length of their forelegs before the 5th instar. The theoretical limits of binocular vision are further away than the maximum capture distances and the length of their forelegs for 5th instar nymphs and adults ; the length of their forelegs would then limit capture possibilities.Des résultats expérimentaux antérieurs sur l'ontogenèse de l'estimation des distances prédateur-proie sont confrontés à des interprétations théoriques. Chez la ranatre les relations entre performances (distances maximales de réaction), effecteurs (longueur des pattes ravisseuses) et récepteurs (yeux composés) ne restent pas constantes pendant le développement larvaire, contrairement à ce qui a été observé chez la mante religieuse. L'hypothèse d'une adaptation automatique et morphologique après chaque mue doit être éliminée.L'analyse théorique de la vision binoculaire des insectes de Burkhardt et al. (1973) a été appliquée à la ranatre : pour les quatre premiers stades larvaires les limites calculées de la vision binoculaire coincident avec les limites maximales de réaction. Cela expliquerait pourquoi ces animaux ne réagissent pas à des proies présentées à des distances égales à la longueur des pattes ravisseuses avant le 5è stade larvaire. Au 5è stade larvaire et chez l'adulte ces limites de vision sont supérieures aux distances maximales de capture et aussi à la longueur des pattes ravisseuses. Ce serait alors cette dernière valeur qui limiterait les possibilités de capture