Water Striders： The Biomechanics of Water Locomotion and Functional Morphology of the Hydrophobic Surface （Insecta： Hemiptera-Heteroptera）

Water striders are insects living on the water surface, over which they can move very quickly and rarely get wetted. We measured the force of free walking in water striders, using a hair attached to their backs and a 3D strain gauge. The error was calculated by comparing force and data derived from geometry and was estimated as 13%. Females on average were stronger （1.32 mN） than males （0.87 mN）, however, the ratio of force to weight was not significantly different. Compared with other lighter species, Aquarius paludum seems stronger, but the ratio of force to weight is actually lower. A. paludum applies about 0.3 mN.cm^-1 to 0.4 mN.cm 1 with its mid-legs, thus avoiding penetrating the surface tension layer while propelling itself rapidly over the water surface. We also investigated the external morphology with SEM. The body is covered by effectively two layers of macro-and micro-hairs, which renders them hydrophobic. The setae are long （40 μm-60μm） and stiff, being responsible for waterproofing, and the microtrichia are much smaller （〈10μm）, slender, and flexible, holding a bubble over the body when submerged.     

Skating and diving: Changes in functional morphology of the setal and microtrichial cover during ontogenesis in Aquarius paludum fabricius (Heteroptera, Gerridae)

We examined the morphology of setae and microtrichia in Aquarius paludum during larval development using a scanning electron microscope. We then conducted immersion experiments with larvae and adults in oxygenated and deoxygenated water. The adult water strider body is covered by a pilose double layer consisting of upper long setae (30-80 microm) and lower filiform microtrichia (5-9 microm). Only setae are present on the legs. Microtrichia on the larval body are very short: 0.5-0.6 microm in first and second instars, and 0.8-1.7 microm in third to fifth instars. Larval body setae are approximately as long as those of adults (25-50 microm), but are much less dense at 1,800-5,750 setae per mm(2) versus 15,000-20,000 setae per mm(2) in adults. The density of setae on the legs remains relatively constant throughout development (larvae: 15,000-20,000 setae per mm(2); adults: 20,000-26,000 setae per mm(2)). Immersion experiments demonstrated that young instars may use cuticular respiration. First- and second-instar larvae survived underwater for several hours without a visible air supply, although they did not survive in deoxygenated water. We posit that the short body microtrichia have a waterproofing function in larvae, whereas they create a compressible air bubble in adults. In adults, waterproofing is accomplished by the setae. The density and length of setae on the legs of larvae was nearly the same as that on the body and legs of adults and is presumably optimized for waterproofing. Thus, a change in morphometrical parameters can result in a large functional change in the same structure. We discuss this interpretation in both ecological and physiological contexts.     

Dry under water: Comparative morphology and functional aspects of air‐retaining insect surfaces

Superhydrophobic surfaces prevent certain body parts of semiaquatic and aquatic insects from getting wet while submerged in water. The air layer on these surfaces can serve the insects as a physical gill. Using scanning electron microscopy, we investigated the morphology of air‐retaining surfaces in five insect species with different levels of adaptation to aquatic habitats. We found surfaces with either large and sparse hairs (setae), small and dense hairs (microtrichia), or hierarchically structured surfaces with both types of hairs. The structural parameters and air‐film persistence of these surfaces were compared. Air‐film persistence varied between 2 days in the beetle Galerucella nymphaea possessing only sparse setae and more than 120 days in the bugs Notonecta glauca and Ilyocoris cimicoides possessing dense microtrichia (up to 6.6 × 10⁶ microtrichia per millimeter square). From our results, we conclude that the density of the surface structures is the most important factor that affects the persistence of air films. Combinations of setae and microtrichia are not decisive for the overall persistence of the air film but might provide a thick air store for a short time and a thin but mechanically more stable air film for a long time. Thus, we assume that a dense cover of microtrichia acts as a “backup system” preventing wetting of the body surface in case the air–water interface is pressed toward the surface. Our findings might be beneficial for the development of biomimetic surfaces for long‐term air retention and drag reduction under water. In addition, the biological functions of the different air retention capabilities are discussed. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

The contribution of setal blades to effective swimming in the aquatic mite Limnochares americana (Acari: Prostigmata: Limnocharidae)

Two rows (anterior and posterior) of long fine setae inserted on the 3rd, 4th and 5th segments of the last two pairs of legs of L. americana form functional swimming blades. Each swimming setal is mounted in a mobile basal socket, and the structure of the setal base and socket configuration ensure that the blades will be passively erected during the leg's power stroke to provide increased thrust and collapsed during the recovery stroke to reduce water resistance. The erect swimming blades increase the effective area for thrust by approximately 500%, making it possible for the mite to lift itself off the bottom. The IVth legs contribute the greater proportion of the thrust developed during paddling, and the 4th segment (genu) bears the largest swimming blades on both legs.     

Sticky predators: a comparative study of sticky glands in harpactorine assassin bugs (Insecta: Hemiptera: Reduviidae)

Zhang, G. and Weirauch, C. 2011. Sticky predators: a comparative study of sticky glands in harpactorine assassin bugs (Insecta: Hemiptera: Reduviidae). —Acta Zoologica (Stockholm) 00 : 1–10. For more than 50 years, specialized dermal glands that secrete sticky substances and specialized setae have been known from the legs of New World assassin bugs in the genus Zelus Fabricius (Reduviidae: Harpactorinae). The gland secretions and specialized ‘sundew setae’ are involved in enhancing predation success. We here refer to this predation strategy as ‘sticky trap predation’ and the specialized dermal glands as ‘sticky glands’. To determine how widespread sticky trap predation is among Reduviidae, we investigated taxonomic distribution of sticky glands and sundew setae using compound light microscopical and scanning electron microscopical techniques and sampling 67 species of Reduviidae that represent 50 genera of Harpactorini. We found sticky glands in 12 genera of Harpactorini and thus show that sticky trap predation is much more widespread than previously suspected. The sticky glands vary in shape, size and density, but are always located in a dorsolateral position on the fore tibia. Sundew setae are present in all taxa with sticky glands with the exception of Heza that instead possesses unique lamellate setae. The sticky trap predation taxa are restricted to the New World, suggesting a New World origin of this unique predation strategy.     

Morphology and evolution of the wing bullae in South American Leptophlebiidae (Ephemeroptera)

Insects were the first animals to take to the skies, and have been flying for over 320 million years. The order Ephemeroptera is, or at least is part of, the most early-diverging lineage of extant winged insects. The extant species present a very short adult life span, mainly dedicated to reproduction and dispersal of eggs. Mating and egg-laying behavior depend on flight. Wings are structures to fly and as such face a number of physical and physiological challenges. The convex curvature along the anterior–posterior axis of the wing generates a camber that must be carefully regulated. One of the most interesting ways of wing bending is provided by the bullae, which have been defined as short sections of flexible chitin, where the flexion lines cross veins. Although the bullae have been frequently used as taxonomic characters, there is no study focused on their morphology, although their prevalence on the wings of mayflies strongly suggests a role in flight. In order to identify evolutionary trends of these structures within Ephemeroptera, we constructed a matrix with comparative anatomy data of the bullae from whole mounts of the wings of 300 specimens belonging to 70 species of several mayfly families, as well as scanning microscopy samples of selected specimens. We also surveyed the number of bullae and their distribution in the wings of the different species within the South American Leptophlebiidae clade. We optimized the characters onto the latest published phylogeny for Leptophlebiidae.     

Genital morphology and taxonomy of the water strider Aquarius remigis (Say) (Insecta, Hemiptera-Heteroptera: Gerridae)

The shape of the dorsal vesical plate was used to determine the extent of morphological differentiation among populations of the water strider Aquarius remigis (Say) (Hemiptera-Heteroptera: Gerridae), and between species assigned to the A. remigis species group. Populations were sampled throughout North America and Mesoamerica, and included paratypes of A. remigoides Gallant & Fairbairn, and material collected from the type localities of A. amplus (Drake & Harris) and A. nyctalis (Drake & Hottes). If taxonomy is to be inferred from the shape of the dorsal vesical plate, as suggested by previous authors, several taxonomic issues need to be reconsidered. First, there was one species distributed widely across North America and deep into Mexico that is very likely to represent A. remigis , meaning that populations from the western USA previously assigned to ' A. nyctalis ' should be synonymized with this species. Second, A. remigoides as currently defined also includes some populations of A. remigis , and is probably much less widely distributed in the south-eastern USA than previously thought. A hybridization zone in Pennsylvania between A. remigis and A. remigoides , as inferred from measurements of body size and allozyme electrophoresis, is not congruent with data from the male genitalia, which indicated a transition zone between the two forms in Virginia much further to the south. Finally, A. amplus was widespread in Mexico, reaching into Guatemala to the south and into Arizona to the north.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 381–398.     

The wing vestiture of the non-ditrysian Lepidoptera (Insecta). Comparative morphology and phylogenetic implications

The ultrastructure of the dorsal forewing vestiture in exemplars of all family group taxa of non‐ditrysian Lepidoptera is examined, and the evolutionary implications at family level and above are discussed. Wing‐scale terminology is reviewed. Three different types of bilayer wing‐scale covering are recognized; only a few groups have a single‐layer wing‐scale covering. The general scale arrangement is random, but a few taxa have clustered scale arrangements and scattered heteroneurans have scales arranged in transverse rows. Cross ribs are present in all taxa, but only as vestiges in eriocraniid cover scales. Ridge dimorphism is widespread in Neolepidoptera. Surprisingly, ridges and cross ribs on the adwing scale surface are of general occurrence in Neopseustidae and Hepialidae, and are even found on parts of the ground scales of many other Neolepidoptera. Morphological evidence strongly indicates that the fused wing‐scale types found in non‐Coelolepidan Lepidoptera and Neolepidoptera are independently evolved, as evidenced from the presence of vestigial perforations. Absence of perforations is not infallible evidence that a scale is solid. Microtrichia are independently reduced in a number of taxa and probably re‐evolved in at least higher nepticulids. Wing vestiture and scale characters indicate that Tischerioidea may be the sister group of Ditrysia.     

Functional morphology of the feeding apparatus of the nymph of Farrodes sp. (Ephemeroptera: Leptophlebiidae)

Farrodes nymphs are specialized periphyton/biofilm scrapers. Their maxillae are the most specialized mouthparts, but other elements, with their systems of variously modified setae, are designed to obtain and transport food particles to the pharynx with a minimum of loss. The morphology and adaptations of these mouthparts and related head areas, as well as associated musculature, are described.     

Setal morphology of the grooming appendages of Macrobrachium rosenbergii (Crustacea: Decapoda: Caridea: Palaemonidae) and review of decapod setal classification

Setae are vital in grooming activities and aiding in the removal of epibionts and sedimentary fouling from the body surfaces of decapod crustaceans. Thus, the setal structures and their arrangement on the grooming appendages and sensory structures of the commercially important shrimp, Macrobrachium rosenbergii, were examined using scanning electron microscopy. Macrobrachium rosenbergii is extensively grown in aquaculture and exhibits unique male morphological forms, termed morphotypes. The three male morphotypes are termed blue‐clawed males, orange‐clawed males, and small‐clawed or undifferentiated males and all three differ in their dominance, behavior, body morphology, and reproductive success. Seven setal types, two of which have never been described in the literature, are identified on the grooming appendages (third maxillipeds, first, second, and fifth pereopods) and antennae: simple, serrate, serrulate, spiniform, pappose, crinoid, and spinulate. The latter two setae are newly identified. Certain setal types, such as serrate and serrulate setae were located and associated with specific grooming appendages such as the first pereopods. The types of setae on the grooming appendages varied among females and male morphotypes and the novel setal types (crinoid and spinulate) were found only on two of the male morphotypes. A literature review of terminology related to the structure of setae and setal types in decapod crustaceans is offered as the usage of various terms is ambiguous and conflicting in the literature. The intention of this review is to provide future authors with a comprehensive collection of terms and images that can be used to describe various aspects of setal morphology in decapods. J. Morphol. 275:634–649, 2014. © 2014 Wiley Periodicals, Inc.     

Morphology and neurophysiology of tarsal vibration receptors in the water strider Aquarius paludum (Heteroptera: Gerridae)

Substrate vibratory information receptors are extensively studied in insects and spiders, however for water surface dwelling species little data is available. We studied the vibration receptive organs in tarsi of the water strider Aquarius paludum, using light, transmission and scanning electron microscopes, and recorded the neural activity of the organs in response to vibrational stimuli, which were afterwards analysed with a custom made spike sorting program.We found that the tarsal chordotonal organ has one set of three scoloparia: one in the tarsomere I and two in the tarsomere II, all of which consisted of a few scolopidia. The chordotonal organ clearly responded to vibratory stimulation. Furthermore, we found that a pair of large subapical emergent dorsal setae, which had been deemed mechanosensory by previous authors, are not so. In turn, four ventral subapical trichobothria that are in direct contact with the water surface during locomotion, proved to be mechanosensory. The anatomical and ultrastructural observations support these electro-physiological results.     

Leaf morphology of hosts and nonhosts of the thrips Heliothrips haemorrhoidalis (Bouché)

This study highlights the morphological differences between two groups of plants; those that are recorded as hosts of the thrips Heliothrips haemorrhoidalis (Bouché) and those that remain free from infestation. Scanning electron microscope techniques were used to describe the morphology of the leaf surface of 19 species in order to help identify which morphological features could play a role in the selection of plant species by thrips from among a diverse botanical collection. H. haemorrhoidalis had a preference for species with leaves that were coriaceous, with one or both surfaces being smooth. Plants evading these thrips commonly possessed glandular trichomes. Thus morphology may have a role in deterring thrips from the leaf surface, as well as influencing the behaviour of predators that control thrips. Further detailed studies into the chemistry of leaves of hosts and nonhost species may help to further our understanding of selection mechanisms.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 109–130.     

The Growth Form of Croton pullei (Euphorbiaceae) - Functional Morphology and Biomechanics of a Neotropical Liana

Abstract: Croton pullei (Euphorbiaceae) is a woody climber of the lowland rainforest in French Guyana and Surinam. During ontogeny, a shift from a juvenile free-standing growth phase to an older supported growth phase is observed. The following biomechanical parameters were studied: structural Young's modulus, structural torsional modulus, flexural stiffness and bend to twist ratios. Changes in anatomical development were also analysed for different stages of development of C. pullei which differ significantly in their mechanical properties. Free-standing plants show a nearly constant structural Young's modulus and structural torsional modulus during ontogeny, with flexural stiffness increasing proportionally with the axial second moment of area. These patterns are typical for “semi-self-supporting plants". In contrast, supported plants show a significant decrease in structural Young's modulus in older stem parts, as well as a decrease in structural torsional modulus. Due to the decrease in structural Young's modulus, flexural stiffness does not increase proportionally with the axial second moment of area. These patterns are typical for non-self-supporting lianas. In all supported plants, a sudden transition occurs from early dense wood to a wood type with a much higher proportion of large diameter vessels. In contrast, only the dense wood type is present in all tested free-standing plants. The data are compared with results from other climbing species of the same study area and discussed with reference to observed features characterizing the growth form and life history of C. pullei.     

Comparative Morphology of Arthropod Exterior Surfaces with the Capability of Binding a Film of Air Underwater

The air-binding surfaces of aquatic and semi-aquatic insects and spiders were examined under a scanning electron microscope. The bristles that are instrumental in binding the film of air show distinctive characteristics within each phylogenetic group. Very small species can often maintain themselves in a bubble of air underwater although they lack the dense bristle coat characteristic of larger plastron breathers. Relatively large insects generally require a morphologically adapted chamber in which to carry their air supplies. The ecological advantages of an underwater respiration employing portable air are discussed.     

Apioceridae (Insecta: Diptera): cladistic reappraisal and biogeography

Twenty members of the fly families Apioceridae and Mydidae are compared in terms of 77 adult characters. Cladistic analysis of 91 synapomorphies provides a well corroborated reconstruction of lineage relationships, and reveals that the Apioceridae is paraphyletic with respect to the Mydidae. In order to render the Apioceridae monophyletic, the genus Rhaphiomidas and the subfamily Megascelinae of the Apioceridae are transferred to the Mydidae. The subfamily Rhaphiomidinae is reinstated to accommodate Rhaphiomidas , comprising the most plesiomorphic mydids. The relationships of the remaining subfamilies of Mydidae are discussed in the context of these findings. The genus Apiocera is divided into four subgenera, the type subgenus Apiocera Westwood in Australia, Pyrocera subgen. nov. in North America, and the subgenera Ripidosyrma Hermann and Anypenus Philippi are applied to the South African and South American species, respectively. A key to the four subgenera of Apiocera is provided. The biogeographic relationships of the subgenera and genera of the Apioceridae and the Megascelinae are discussed. Although considered an example of a transantarctic or Gondwanan group, we argue that the distribution of the Apioceridae predates the Mesozoic supercontinent Gondwanaland and extends onto sections of Pangaea, and should be termed 'Pangaean'. The cladistic relationships between the genera of Apioceridae and Megascelinae are consistent with the geological vicariance of the fragments of Pangaea on which they now occur.     

Transmission and Ecology of Trypanosomatid Flagellates of Water Striders (Hemiptera: Gerridae)

An investigation of transmission and ecology of the monogenetic trypanosomatids, Blastocrithidia gerridis and Crithidia flexonema , in Gerris is described. Motile free-living flagellates of both species were found in the faeces of Gerris and in the water on which the bugs inhabited. Transmission of both trypanosomatid species occurred from naturally infected wild-caught bugs to flagellate-free laboratory-bred bugs via water. Crithidia flexonema was also transmitted to laboratory-bred bugs after being isolated in culture. Observations of experimentally infected bugs indicate that C. flexonema flagellates are imbibed and pass through the fore- and midgut to the hindgut where they become attached and multiply. There was no evidence to suggest transovarial transmission. In a 3-yr investigation into the prevalence of trypanosomatids in a natural population of adult Gerris odontogaster , it was found that the infection rate varied between 19% and 100%. There was no significant difference in infection rates between females and males. The infection rate peaked for each year in late spring or early summer. The significance of these results is discussed in relation to the ecology and behaviour of Gerris . The results indicate that the infections are maintained in hibernating bugs over winter.