Mimicking a Superhydrophobic Insect Wing by Argon and Oxygen Ion Beam Treatment on Polytetrafluoroethylene Film

Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves and insect wings,whichenhance the hydrophobicity of the natural surfaces and play a role of self-cleaning.We presented the fabrication technology of asuperhydrophobic surface using high energy ion beam.Artificial insect wings that mimic the morphology and the superhydrophobocityof cicada’s wings were successfully fabricated using argon and oxygen ion beam treatment on a polytetrafluoroethylene(PTFE)film.The wing structures were supported by carbon/epoxy fibers as artificial flexible veins that were bondedthrough an autoclave process.The morphology of the fabricated surface bears a strong resemblance to the wing surface of acicada,with contact angles greater than 160°,which could be sustained for more than two months.     

Non-Jumping Take off Performance in Beetle Flight （Rhinoceros Beetle Trypoxylus dichotomus）

In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes offwithout jumping. In this study, we used 3-Dimensional （3D） high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be con- sidered as a main source of lift for heavy beetle.     

Variations in the arrangement of sensory bristles along butterfly wing margins

The surfaces of insect wings exhibit numerous sensilla, which have been suggested to have a behavioral function. Some evidence suggests that the sensory bristles along the wing margin of lepidopteran insects (butterflies and moths) are involved in the regulation of wing movement. We investigated the arrangement of sensory bristles along the wing margins of 62 species of papilionoid butterflies, using light-microscopic examination of mounts of whole wings after removing the scales surrounding the bristles. In the majority of the wings examined, bristles were located on the ventral wing surfaces and were continuously distributed along the wing margins, except in the vicinity of the wing bases. In some wings, bristles were also located on the dorsal wing surfaces, and were continuously or discontinuously distributed along the wing margins of different species. In a minority of the species studied, we observed bristle distribution in the vicinity of the wing base, discontinuous bristle distribution on both the dorsal and ventral wing surfaces, or an absence of bristles along the wing margins. This variation in the arrangement of bristles along the wing margins is discussed in relation to the reception and transmission of sensory information in the wings.     

Vortexlet models of flapping flexible wings show tuning for force production and control

Insect wings are compliant structures that experience deformations during flight. Such deformations have recently been shown to substantially affect induced flows, with appreciable consequences to flight forces. However, there are open questions related to the aerodynamic mechanisms underlying the performance benefits of wing deformation, as well as the extent to which such deformations are determined by the boundary conditions governing wing actuation together with mechanical properties of the wing itself. Here we explore aerodynamic performance parameters of compliant wings under periodic oscillations, subject to changes in phase between wing elevation and pitch, and magnitude and spatial pattern of wing flexural stiffness. We use a combination of computational structural mechanics models and a 2D computational fluid dynamics approach to ask how aerodynamic force production and control potential are affected by pitch/elevation phase and variations in wing flexural stiffness. Our results show that lift and thrust forces are highly sensitive to flexural stiffness distributions, with performance optima that lie in different phase regions. These results suggest a control strategy for both flying animals and engineering applications of micro-air vehicles.     

EVOLUTION AND CLASSIFICATION OF INSECT FLIGHT KINEMATICS

Classification of the main types of insect in-flight kinematics is proposed here, based on comparative data of wing movement during flapping flight. By comparing the described kinematic patterns with the results of studies of the vortex-wake structures of flying insects, these patterns can be explained as adaptations for overcoming the negative effects of mutual deceleration of fore- and hind wing starting vortex bubbles, which take place in insects with the most primitive type of wing kinematics. The aerodynamic efficiency of the flying system can be decreased if natural selection favors behavioral patterns that involve suboptimal wing kinematics.     

A century and a half of research on the evolution of insect flight

The gill and paranotal lobe theories of insect wing evolution were both proposed in the 1870s. For most of the 20th century, the paranotal lobe theory was more widely accepted, probably due to the fundamentally terrestrial tracheal respiratory system; in the 1970s, some researchers advocated for an elaborated gill (“pleural appendage”) theory. Lacking transition fossils, neither theory could be definitively rejected.Winged insects are abundant in the fossil record from the mid-Carboniferous, but insect fossils are vanishingly rare earlier, and all earlier fossils are from primitively wingless insects. The enigmatic, isolated mandibles of Rhyniognatha (early Devonian) hint that pterygotes may have been present much earlier, but the question remains open.In the late 20th century, researchers used models to study the interaction of body and protowing size on solar warming and gliding abilities, and stability and glide effectiveness of many tiny adjustable winglets versus a single, large pair of immobile winglets. Living stoneflies inspired the surface-skimming theory, which provides a mechanism to bridge between aquatic gills and flapping wings. The serendipitously discovered phenomenon of directed aerial descent suggests a likely route to the early origin of insect flight. It provides a biomechanically feasible sequence from guided falls to fully-powered flight.     

Wettability and Contaminability of Insect Wings as a Function of Their Surface Sculptures

Abstract The wing surfaces of 97 insect species from virtually all relevant major groups were examined by high resolution scanning-electron-microscopy, in order to identify the relationships between the wing microstructures, their wettability with water and their behaviour under the influence of contamination. Isolated wings with contact angles between 31.6° and 155.5° were artificially contaminated with silicate dusts and subsequently fogged until drops of water (“dew”) formed and rolled off. The remaining particles were counted via a digital image analysis system. Remaining particle values between 0.41% and 103% were determined in comparison with unfogged controls. Some insects with very unwettable wings show a highly significant “self-cleaning” effect under the influence of rain or dew. Detailed analysis revealed that there is a correlation between the wettability and the “SM Index” (quotient of wing surface/(body mass)^0.67) with values ranging from 2.42 to 57.0. Furthermore, there is a correlation between the “self-cleaning” effect and the SM Index, meaning that taxa with a high SM Index, e.g. “large-winged” Ephemeroptera, Odonata, Planipennia, and many Lepidoptera, have very unwettable wings and show high particle removal due to dripping water drops. The “small-winged” insects, such as Diptera and Hymenoptera, and insects with elytra, such as Blattariae, Saltatoria, Heteroptera and Coleoptera, show completely opposite effects. This is clearly a result of the fact that species with a high SM Index are, in principle, more restricted in flight by contamination than species with a low SM Index which can also actively clean their own wings. The wings primarily serve a protection function in insects with elytra, so that the effects of contamination are probably of minor importance in these insects. Copyright © 1996 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.     

Veins improve fracture toughness of insect wings

During the lifetime of a flying insect, its wings are subjected to mechanical forces and deformations for millions of cycles. Defects in the micrometre thin membranes or veins may reduce the insect’s flight performance. How do insects prevent crack related material failure in their wings and what role does the characteristic vein pattern play? Fracture toughness is a parameter, which characterises a material’s resistance to crack propagation. Our results show that, compared to other body parts, the hind wing membrane of the migratory locust S. gregaria itself is not exceptionally tough (1.04±0.25 MPa√m). However, the cross veins increase the wing’s toughness by 50% by acting as barriers to crack propagation. Using fracture mechanics, we show that the morphological spacing of most wing veins matches the critical crack length of the material (1132 µm). This finding directly demonstrates how the biomechanical properties and the morphology of locust wings are functionally correlated in locusts, providing a mechanically ‘optimal’ solution with high toughness and low weight. The vein pattern found in insect wings thus might inspire the design of more durable and lightweight artificial ‘venous’ wings for micro-air-vehicles. Using the vein spacing as indicator, our approach might also provide a basis to estimate the wing properties of endangered or extinct insect species.     

Effects of Methanol on Wettability of the Non-Smooth Surface on Butterfly Wing

The contact angles of distilled water and methanol solution on the wings of butterflies were determined by a visual contact angle measuring system. The scale structures of the wings were observed using scanning electron microscopy, The influence of the scale micro- and ultra-structure on the wettability was investigated. Results show that the contact angle of distilled water on the wing surfaces varies from 134.0° to 159.2°. High hydrophobicity is found in six species with contact angles greater than 150°. The wing surfaces of some species are not only hydrophobic but also resist the wetting by methanol solution with 55% concentration. Only two species in Parnassius can not resist the wetting because the micro-structure （spindle-like shape） and ultra-structure （pinnule-like shape） of the wing scales are remarkably different from that of other species. The concentration of methanol solution for the occurrence of spreading/wetting on the wing surfaces of different species varies from 70% to 95%. After wetting by methanol solution for 10 min, the distilled water contact angle on the wing surface increases by 0.8°-2.1°, showing the promotion of capacity against wetting by distilled water.     

AERODYNAMICS,THERMOREGULATION, AND THE EVOLUTION OF INSECT WINGS: DIFFERENTIAL SCALING AND EVOLUTIONARY CHANGE

We examine several aerodynamic and thermoregulatory hypotheses about possible adaptive factors in the evolution of wings from small winglets in insects. Using physical models of Paleozoic insects in a wind tunnel, we explore the potential effects of wings for increasing gliding distance, increasing dispersal distance during parachuting, improving attitude control or stability, and elevating body temperatures during thermoregulation. The effects of body size and shape, wing length, number, and venation, and meteorological conditions are considered. Hypotheses consistent with both fixed and moveable wing articulations are examined. Short wings have no significant effects on any of the aerodynamic characteristics, relative to wingless models, while large wings do have significant effects. In contrast, short wings have large thermoregulatory effects relative to wingless models, but further increases in wing length do not significantly affect thermoregulatory performance. At any body size, there is a wing length below which there are significant thermoregulatory effects of increasing wing length, and above which there are significant aerodynamic effects of increasing wing length. The relative wing length at which this transition occurs decreases with increasing body size. These results suggest that there could be no effective selection for increasing wing length in wingless or short-winged insects in relation to increased aerodynamic capacity. Our results are consistent with the hypothesis that insect wings initially served a thermoregulatory function and were used for aerodynamic functions only at larger wing lengths and/or body sizes. Thus, we propose that thermoregulation was the primary adaptive factor in the early evolution of wings that preadapted them for the subsequent evolution of flight. Our results illustrate an evolutionary mechanism in which a purely isometric change in body size may produce a qualitative change in the function of a given structure. We propose a hypothesis in which the transition from thermoregulatory to aerodynamic function for wings involved only isometric changes in body size and argue that changes in body form were not a prerequisite for this major evolutionary change in function.     

Comparative and functional morphology of wing coupling structures in Trichoptera: Annulipalpia

Several orders of morphologically four‐winged insects have evolved mechanisms that enforce a union between the mesothoracic and metathoracic wings (forewings and hindwings) during the wing beat cycle. Such mechanisms result in a morphologically tetrapterous insect flying as if it were functionally dipterous, and these mechanisms have been described for several insect orders. The caddisfly suborders Annulipalpia and Integripalpia (Trichoptera) each have evolved a wing coupling apparatus, with at least three systems having evolved within the suborder Annulipalpia. The comparative and inferred functional morphology of the putative wing coupling mechanisms is described for the annulipalpian families Hydropsychidae (subfamilies Macronematinae and Hydropsychinae), Polycentropodidae and Ecnomidae, and a novel form‐functional complex putatively involved with at‐rest forewing‐forewing coupling is described for Hydropsychidae: Smicrideinae. It is proposed that the morphology of the wing coupling apparatuses of Hydropsychinae and Macronematinae are apomorphies for those clades. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Surface-skimming stoneflies and mayflies: the taxonomic and mechanical diversity of two-dimensional aerodynamic locomotion

The best supported hypothesis for the evolutionary origin of insect wings is that they evolved from articulated, leg-derived respiratory structures of aquatic ancestors. However, there are no fossils of the immediate ancestors of winged insects, and it is difficult to imagine how a functional transition from gills to wings could have occurred. Recent studies of surface-skimming locomotion in stoneflies and mayflies offer a plausible solution by showing how rudimentary wings and muscle power can be used to accomplish two-dimensional aerodynamic locomotion on the surface of water. Here we extend that line of research by examining the phylogenetic distribution and mechanistic diversity of surface skimming in stoneflies, along with a limited examination of mayflies. These investigations reveal both a broad taxonomic occurrence and a fine gradation of mechanically distinct forms. Distinct forms of wing-flapping surface skimming include (1) stoneflies that flap their wings weakly while maintaining their body in contact with the water and undulating their abdomen laterally in a swimming-like motion, (2) stoneflies that skim while elevating their body above the water and maintaining all six legs on the surface, (3) stoneflies and mayflies that skim with only four legs on the water surface, (4) stoneflies that skim with only their two hind legs on the surface, and (5) stoneflies that, beginning with a series of leg motions nearly identical to hind-leg skimmers, use their hind legs to jump from the water into the air to initiate flapping flight. Comparisons across these forms of skimming show that wing-beat amplitude, horizontal velocity, and the verticality of aerodynamic force production increase as the body orientation becomes more upright and contact with the water is minimized. These behaviors illustrate a mechanical pathway by which flying insects could have evolved from swimming ancestors via a series of finely graded intermediate stages. The phylogenetic distribution of skimming and flight in stoneflies does not indicate any clear directionality toward either greater or lesser aerodynamic abilities; however, the broad and apparently basal phylogenetic distribution of skimming taxa supports the hypothesis that the common ancestor of stoneflies was a surface skimmer. This may also be true for the common ancestor of stoneflies and mayflies, that is, the first winged insects. We combine these data with fossil evidence to form a synthetic model for the evolution of flying insects from surface skimmers.     

Kinematic compensation for wing loss in flying damselflies

Flying insects can tolerate substantial wing wear before their ability to fly is entirely compromised. In order to keep flying with damaged wings, the entire flight apparatus needs to adjust its action to compensate for the reduced aerodynamic force and to balance the asymmetries in area and shape of the damaged wings. While several studies have shown that damaged wings change their flapping kinematics in response to partial loss of wing area, it is unclear how, in insects with four separate wings, the remaining three wings compensate for the loss of a fourth wing. We used high-speed video of flying blue-tailed damselflies (Ischnura elegans) to identify the wingbeat kinematics of the two wing pairs and compared it to the flapping kinematics after one of the hindwings was artificially removed. The insects remained capable of flying and precise maneuvering using only three wings. To compensate for the reduction in lift, they increased flapping frequency by 18 ± 15.4% on average. To achieve steady straight flight, the remaining intact hindwing reduced its flapping amplitude while the forewings changed their stroke plane angle so that the forewing of the manipulated side flapped at a shallower stroke plane angle. In addition, the angular position of the stroke reversal points became asymmetrical. When the wingbeat amplitude and frequency of the three wings were used as input in a simple aerodynamic model, the estimation of total aerodynamic force was not significantly different (paired t-test, p = 0.73) from the force produced by the four wings during normal flight. Thus, the removal of one wing resulted in adjustments of the motions of the remaining three wings, exemplifying the precision and plasticity of coordination between the operational wings. Such coordination is vital for precise maneuvering during normal flight but it also provides the means to maintain flight when some of the wings are severely damaged.     

Relationship between body size and flying-related structures in Neotropical social wasps (Polistinae,Vespidae, Hymenoptera)

Body size influences wing shape and associated muscles in flying animals which is a conspicuous phenomenon in insects, given their wide range in body size. Despite the significance of this, to date, no detailed study has been conducted across a group of species with similar biology allowing a look at specific relationship between body size and flying structures. Neotropical social vespids are a model group to study this problem as they are strong predators that rely heavily on flight while exhibiting a wide range in body size. In this paper we describe the variation in both wing shape, as wing planform, and mesosoma muscle size along the body size gradient of the Neotropical social wasps and discuss the potential factors affecting these changes. Analyses of 56 species were conducted using geometric morphometrics for the wings and lineal morphometrics for the body; independent contrast method regressions were used to correct for the phylogenetic effect. Smaller vespid species exhibit rounded wings, veins that are more concentrated in the proximal region, larger stigmata and the mesosoma is proportionally larger than in larger species. Meanwhile, larger species have more elongated wings, more distally extended venation, smaller stigmata and a proportionally smaller mesosoma. The differences in wing shape and other traits could be related to differences in flight demands caused by smaller and larger body sizes. Species around the extremes of body size distribution may invest more in flight muscle mass than species of intermediate sizes.     

Beyond aerodynamics: The critical roles of the circulatory and tracheal systems in maintaining insect wing functionality

Insect wings consist almost entirely of lifeless cuticle; yet their veins host a complex multimodal sensory apparatus and other tissues that require a continuous supply of water, nutrients and oxygen. This review provides a survey of the various living components in insect wings, as well as the specific contribution of the circulatory and tracheal systems to provide all essential substances. In most insects, hemolymph circulates through the veinal network in a loop flow caused by the contraction of accessory pulsatile organs in the thorax. In other insects, hemolymph oscillates into and out of the wings due to the complex interaction of several factors, such as heartbeat reversal, intermittent pumping of the accessory pulsatile organs in the thorax, and the elasticity of the wall of a special type of tracheae. A practically unexplored subject is the need for continuous hydration of the wing cuticle to retain its flexibility and toughness, including the associated problem of water loss due to evaporation. Also, widely neglected is the influence of the hemolymph mass and the circulating flow in the veins on the aerodynamic properties of insect wings during flight. Ventilation of the extraordinarily long wing tracheae is probably accomplished by intricate interactions with the circulatory system, and by the exchange of oxygen via cutaneous respiration.     

Surface Laser Scanning of Fossil Insect Wings

Primary homologization of wing venation is of crucial importance in taxonomic studies of fossil and recent insects, with implications for large-scale phylogenies. Homologization is usually based on relative relief of veins (with an insect ground plan of alternating concave and convex vein sectors). However, this method has led to divergent interpretations, notably because vein relief can be attenuated in fossil material or because wings were originally flat. In order to interpret better vein relief in fossil insect wings, we tested the application of non-contact laser scanning. This method enables high resolution three-dimensional (3-D) data visualization of a surface, and produces high quality images of fossil insect wings. These images facilitate and improve interpretation of the homologization of wing venation. In addition, because the surface information is digitised in three axes (X, Y, Z), the data may be processed for a wide range of surface characteristics, and may be easily and widely distributed electronically. Finally, this method permits users to reconstruct accurately the fossils and opens the field of biomechanical interpretation using numerical modelling methods.     

Aerodynamic performance of a hovering hawkmoth with flexible wings: a computational approach

Insect wings are deformable structures that change shape passively and dynamically owing to inertial and aerodynamic forces during flight. It is still unclear how the three-dimensional and passive change of wing kinematics owing to inherent wing flexibility contributes to unsteady aerodynamics and energetics in insect flapping flight. Here, we perform a systematic fluid-structure interaction based analysis on the aerodynamic performance of a hovering hawkmoth, Manduca, with an integrated computational model of a hovering insect with rigid and flexible wings. Aerodynamic performance of flapping wings with passive deformation or prescribed deformation is evaluated in terms of aerodynamic force, power and efficiency. Our results reveal that wing flexibility can increase downwash in wake and hence aerodynamic force: first, a dynamic wing bending is observed, which delays the breakdown of leading edge vortex near the wing tip, responsible for augmenting the aerodynamic force-production; second, a combination of the dynamic change of wing bending and twist favourably modifies the wing kinematics in the distal area, which leads to the aerodynamic force enhancement immediately before stroke reversal. Moreover, an increase in hovering efficiency of the flexible wing is achieved as a result of the wing twist. An extensive study of wing stiffness effect on aerodynamic performance is further conducted through a tuning of Young's modulus and thickness, indicating that insect wing structures may be optimized not only in terms of aerodynamic performance but also dependent on many factors, such as the wing strength, the circulation capability of wing veins and the control of wing movements.     

Preliminary study of wing interference patterns (WIPs) in some species of soft scale (Hemiptera,Sternorrhyncha, Coccoidea,Coccidae)

The fore wings of scale insect males possess reduced venation compared with other insects and the homologies of remaining veins are controversial. The hind wings are reduced to hamulohalterae. When adult males are prepared using the standard methods adopted to females and nymphs, i.e. using KOH to clear the specimens, the wings become damaged or deformed, an so these structures are not usually described or illustrated in publications. The present study used dry males belonging to seven species of the family Coccidae to check the presence of stable, structural colour patterns of the wings. The visibility of the wing interference patterns (WIP), discovered in Hymenoptera and Diptera species, is affected by the way the insects display their wings against various backgrounds with different light properties. This frequently occurring taxonomically specific pattern is caused by uneven membrane thickness and hair placement, and also is stabilized and reinforced by microstructures of the wing, such as membrane corrugations and the shape of cells. The semitransparent scale insect’s fore wings possess WIPs and they are taxonomically specific. It is very possible that WIPs will be an additional and helpful trait for the identification of species, which in case of males specimens is quite difficult, because recent coccidology is based almost entirely on the morphology of adult females.     

Patterns on the insect wing

The evolution of wings and the adaptive advantage they provide have allowed insects to become one of the most evolutionarily successful groups on earth. The incredible diversity of their shape, size, and color patterns is a direct reflection of the important role wings have played in the radiation of insects. In this review, we highlight recent studies on both butterflies and Drosophila that have begun to uncover the types of genetic variations and developmental mechanisms that control diversity in wing color patterns. In butterflies, these analyses are now possible because of the recent development of a suite of genomic and functional tools, such as detailed linkage maps and transgenesis. In one such study, extensive linkage mapping in Heliconius butterflies has shown that surprisingly few, and potentially homologous, loci are responsible for several major pattern variations on the wings of these butterflies. Parallel work on a clade of Drosophila has uncovered how cis-regulatory changes of the same gene correlate with the repeated gain and loss of pigmented wing spots. Collectively, our understanding of formation and evolution of color pattern in insect wings is rapidly advancing because of these recent breakthroughs in several different fields.