Ranatra Research Articles

Water Scorpions, Water Stick-Insects Ranatra spp. (Insecta: Hemiptera: Nepidae)

Commonly mistaken for other objects due to its appearance, hence the common name water stick-insect, this slender reddish-brown insect is commonly found in fresh or brackish water (a mix of salt and fresh water) (Anufriyeva et al. 2016). They are ambush predators and will spend most of its time in the water waiting for prey. They are limited to the length of their raptorial forearms in terms of catching prey. In the southeastern United States, these insects are commonly referred to as water scorpions.
 Also published on the Featured Creatures website at http://entnemdept.ufl.edu/creatures/AQUATIC/Ranatra.html

A chromosomal analysis of Nepa cinerea Linnaeus, 1758 and Ranatra linearis (Linnaeus, 1758) (Heteroptera, Nepidae).

An account is given of the karyotypes and male meiosis of the Water Scorpion Nepa cinerea Linnaeus, 1758 and the Water Stick Insect Ranatra linearis (Linnaeus, 1758) (Heteroptera, Nepomorpha, Nepidae). A number of different approaches and techniques were tried: the employment of both male and female gonads and mid-guts as the sources of chromosomes, squash and air-drying methods for chromosome preparations, C-banding and fluorescence in situ hybridization (FISH) for chromosome study. We found that N. cinerea had a karyotype comprising 14 pairs of autosomes and a multiple sex chromosome system, which is X1X2X3X4Y (♂) / X1X1X2X2X3X3X4X4 (♀), whereas R. linearis had a karyotype comprising 19 pairs of autosomes and a multiple sex chromosome system X1X2X3X4Y (♂) / X1X1X2X2X3X3X4X4 (♀). In both N. cinerea and R. linearis, the autosomes formed chiasmate bivalents in spermatogenesis, and the sex chromosome univalents divided during the first meiotic division and segregated during the second one suggesting thus a post-reductional type of behaviour. These results confirm and amplify those of Steopoe (1925, 1927, 1931, 1932) but are inconsistent with those of other researchers. C-banding appeared helpful in pairing up the autosomes for karyotype assembly; however in R. linearis the chromosomes were much more uniform in size and general appearance than in N. cinerea. FISH for 18S ribosomal DNA (major rDNA) revealed hybridization signals on two of the five sex chromosomes in N. cinerea. In R. linearis, rDNA location was less obvious than in N. cinerea; however it is suggested to be similar. We have detected the presence of the canonical “insect” (TTAGG)n telomeric repeat in chromosomes of these species. This is the first application of C-banding and FISH in the family Nepidae.

Variations of behavioural patterns during development in the water stick insect

Variations 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.

The effect of water temperature on the functional response of the water stick insect Ranatra dispar (Heteroptera: Nepidae)

AbstractFunctional response curves were constructed for adult Ranatra dispar feeding on four different densities of notonectid prey at 15, 20, 25 and 30°C. Values for the attack‐rate and handling time were estimated from Roger's random predator equation. The most generally applicable response was the type II, with the mean number of prey eaten increasing with increase in temperature. The attack‐rate was linearly related to temperature while handling time decreased exponentially with increase in temperature, although values changed very little between 20 and 30°C. It is suggested that changes in metabolic activity and related ‘hunger’ effects on various components of predatory behaviour account for the observed number of prey eaten up to 25°C, however, an increase in the level of prey activity at 30°C may influence the observed number of prey caught (and eaten) at this higher temperature.

Choice of perch by the water stick insect

Several characteristics of an adequate perch site for the water stick insect, Ranatra linearis L. (Heteroptera: Nepidae) and variations of perch preference during post-embryonic development have been investigated. Under laboratory conditions adults preferred reeds ( Calamagrostis epigeros and Phragmites communis ) to the other plant species presented and avoided rushes ( Juncus sp.). These results confirmed Waitzbauer's (1976) observations that showed that Ranatra preferred Phragmites communis over Utricularia vulgaris in the field. During development, preference for one type of plant changed first from Lemna to Elodea , then after the 4th instar, from Elodea to reeds. Predator size in relation, to perch size did not appear to be the main factor influencing these changes of preference. Perch colour preference changed during development from green to brown. In addition, adults preferred vertical perches to horizontal ones, but approximately as many 1st and 2nd instar larvae were found on vertical perches as on horizontal ones. Renatra usually perched parallel to their support: in the majority of observations the longitudinal axis of the body formed an angle of between − 5° and + 15° with the vertical plane at all developmental stages.

The Effect of Water Depth on the Predatory Behavior of the Water Stick Insect, Ranatra-Dispar (Heteroptera, Nepidae)

The effect of water depth and prey density on the capture success (as measured by the number of prey eaten) of the aquatic, sit-and-wait predator, Ranatra dispar, was examined in the laboratory. When water depth was held constant at 5, 10, 20 or 30 cm, prey densities of 10, 15, 30 or 40 prey per container had no effect at the two shallowest depths, where very few prey were caught or eaten at any density. At 20 and 30 cm, density had a significant effect with progressively more prey being consumed as density increased. When prey density was held constant at 1, 2, 4 or 8 prey per litre, water depth significantly affected the proportion of prey eaten. At each density, predators held in 5 cm of water and, to some extent, those in 10 cm consumed significantly fewer prey than those in 20 or 30 cm. It is suggested that fewer prey are caught in shallow water because: (1) the predator cannot put itself in the position which most favours an efficient strike; (2) the absence of a significant 'vertical' component in the environment reduces the effectiveness of the sensory organs in locating prey. The lower capture success in shallow water may cause adult R. dispar to avoid shallow water, thus providing a partial refuge in which small R. dispar can avoid competing with adults for prey of similar sizes.

The effect of predation risk on the predatory behaviour of a sit-and-wait predator,Ranatra dispar (Heteroptera: Nepidae), the water stick insect

Two primary defence behaviours, fore-leg extension to enhance crypsis and swimming to bottom and remaining motionless, of a predatory water bug,Ranatra dispar, are described along with their subsequent effect on foraging behaviour. It was hypothesised that hungry predators would respond less and for a shorter duration compared with recently fed individuals when exposed to a model threat stimulus, thereby tending to take a higher risk of predation during feeding than satiated animals. A greater proportion of animals responded overall with the leg extension response compared with the swimming response, although the mean duration of the former was significantly shorter than the latter response. A significantly higher proportion of nonfasted predators responded, and for a longer duration than fasted individuals. The type of model used significantly effected the proportion of animals that responded with leg extensions but not on its duration. In contrast, both number of animals and the duration of the swim/motionless behaviour were significantly effected by stimulus type. The subsequent effect of these 2 behavioural responses on feeding behaviour was examined and showed that although about the same number of predators removed prey from their mouthparts during both responses, significantly more prey were dropped, and therefore lost, during swimming. The results clearly indicate the significant effects that defensive behaviours have on time budgets in foraging behaviour.

The movement of water into submerged prey during feeding by the aquatic bug Ranatra dispar (Heteroptera: Nepidae), the water stick insect

By the use of a fluorescent dye it was shown that, during feeding by an aquatic bug, water from the external environment passes into the prey's body though puncture holes from previous feeding sites. Such a phenomenon, resulting in the diluting of the prey's body contents, may be used as a physiological stimulus to detect the quality of the prey, leading to movement to another part of the prey's body or discarding the prey.

The Feeding Behaviour of a Sit‐and‐Wait Predator, Ranatra dispar (Heteroptera: Nepidae): The Combined Effect of Food Deprivation and Prey Size on the Behavioural Components of Prey Capture

AbstractPrevious work has shown a significant effect of hunger on the predatory behaviour in a sit‐and‐wait predator Ranatra dispar, the water stick insect (Bailey 1986 a). The experiments reported here were designed to investigate the combined effect of prey size and hunger on the predatory behaviour in order to identify which behavioural components are effected. It was found that the hunger level determines whether R. dispar will initially be aroused or not but the distance at which the arousal takes place is influenced by the size of the prey. This is believed to reflect the capacity and interrelation between visual and mechanoreceptor, sensory organs. The decision to strike at a prey is, although again influenced by hunger, significantly affected by prey size. The distance of the prey when the strike takes place is affected by hunger not the size of the prey. The outcome of the strike is determined by the size of the prey, not the hunger level of the predator. This is believed to reflect the relationship between strike trajectory, leg morphology and prey size. Food deprivation affects all components of predatory behaviour of R. dispar leading up to prey capture, by increasing not only distance of response but also the number of strikes, hits, and captures per unit presentation of prey. It does not affect capture efficiency which remains at about 70 to 80 %. Food deprivation also increases the range of prey sizes that R. dispar responds to and attempts to capture. The effect of food deprivation is considered to reflect a motivational change in responsiveness to particular prey stimuli usually described as a sensitization of particular stimulus‐response relations rather than the food deprivation affecting the sensory mechanisms. The predatory success in relation to size of model prey suggested a hypothetical size that could be captured, irrespective of predator motivational level, which is based primarily on the relationship between the shape of the grasping leg and size of prey.

‘A prey in the hand’, multi-prey capute behaviour in a sit-and-wait predator,Ranatra dispar (Heteroptera: Nepidae), the Water Stick Insect

The Water Stick Insect,Ranatra dispar, is shown to be able to capute and hold a number of prey simultaneously. Capture of prey characteristically occurs in 3 distinct patterns (Type 1, 2 and 3), each characterized by a different number of prey caught. The time since las feeding by the predator has a significant effect on wether the predator will capture more than one prey. Once feeding starts, there is a critical period during which, if an encounter takes place the predator will attempt to capture either a second or third prey. The critical peroid is longer, the higher the motivation level of the predator. It is suggested that this prey-capture behaviour potentially increase the size of a meal as groups of prey move past the stationary prdator.

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

ABSTRACT. Relationships 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.

Density-Dependent Prey Selection in the Water Stick Insect, Ranatra linearis (Heteroptera)

(1) To test some aspects of foraging theory, all stages of the water stick insect Ranatra linearis L. were presented with a full range of size classes of water fleas (Daphnia) different relative and absolute densities, under controlled conditions in the laboratory. (2) Selection proved to be density-dependent. First instar nymphs showed a preference for small Daphnia; after the first moult the choice changed and as the predators grew, preference for big Daphnia increased. Ranatra were selective, first when relative densities for the preferred size class were low, then when absolute densities were high. The was generally made before striking, but selection was reinforced before rostral exploration. Size of prey, size of predator and prey density influenced the duration of a meal. (3) Adults increased their selectivity during a test in the presence of high prey densities. Adults performed more complex predatory movements towards large prey items towards small ones, and more towards both size classes in low densities than in high ones.

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

The 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.

Influence of the Duration of Deprivation on the Predatory Performance of the Water Stick Insect

Previous experiments showed that the absence of prey during the first 4 h after a moult impaired subsequent predatory performance in Ranatra linearis L. (Heteroptera, Nepidae). During that post-moult period, Ranatra perform more claw and femur foreleg movements in the presence of potential prey than in their absence, but they do not then catch or eat any prey. This study investigates whether deprivation during all or part of the post-moult period impairs subsequent performance to the same extent, in other words, when is the presence of potential prey necessary and sufficient to stimulate Ranatra. Zusammenfassung Nur wahrend 4 h nach jeder Hautung fuhren Stabwanzen (Ranatra linearis) viele ausergewohnliche femoral-tarsale Bewegungen mit den Vorderbeinen aus. Die Anwesenheit oder Abwesenheit potentieller Beute wahrend dieser Periode, besonders wahrend deren zweiter Halfte beeinflust direkt oder indirekt die Haufigkeit dieser Bewegungen und, erstaunlicherweise, auch spatere Fangbewegungen. Die Daten wurden auf verschiedenen Ebenen untersucht, um herauszufinden, welche Vorgange an dieser Art von Beuteerfahrung beteiligt sind. Im grosen und ganzen war der Fangerfolg der unerfahrenen Tiere niedriger: dies galt fur alle Arten von Fangbewegungen, die groste Schlagdistanz war kurzer, und die komplexen Fangbewegungen erschienen verhaltnismasig seltener. Demnach fuhrt Erfahrung in Anwesenheit von Beutetieren wahrend einer Nach-Hautungs-Phase zu einer Erweiterung des darauffolgenden Fangverhaltens, d. h. zu einem groseren Schlagareal und verhaltnismasig haufigeren komplexen Fangbewegungen. Die schlechtere Leistung nach Vorenthaltung jener Erfahrung beeinflust die Entwicklungszeit und das Uberleben.

Effect on predatory performance of the presence of prey after moulting in the water stick insect, Ranatra linearis

ABSTRACT. During the first 4h following moulting, Ranatra linearis L. (Heteroptera, Nepidae) perform numerous claw and femur foreleg movements, but do not then catch any prey (e.g. Daphnia). The frequency of these movements depends on the presence of potential prey, and is significantly higher in the presence of potential prey items than in their absence. The presence or absence of prey during these four post‐moult hours influenced subsequent performance. Ranatra moulting in the absence of prey showed later a lower catching success and a smaller proportion of complex predatory movements at all stages of development than did Ranatra moulting in the presence of prey, all other factors being similar. The importance of this deficit resulting from depriving Ranatra of the presence of prey during the post‐moult period is discussed.

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

AbstractThe 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.

Death‐feigning in Ranatra

Death‐feigning in Ranatra

Review of The Reactions of Ranatra to Light.

Review of The Reactions of Ranatra to Light.

The reactions of Ranatra to light

The reactions of Ranatra to light

NOTES ON THE STRIDULATION AND HABITS OF RANATRA FUSCA, PAL. B

Little is known regarding the sounds produced by the Rhynchota, and that little refers almost exclusively to the Cryptocerata, of which Corixa has had the most attention; and some few observations have been made on Nepa, Sigara and Notonecta. It seems to me, therefore, that it would be well to put on record the observations and notes made by me on the stridulation of Ranatra, together with a few other remarks on this insect.