Ontogeny of flight initiation in the fly <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>: implications for the giant fibre system

There are two modes of flight initiation in Drosophila melanogaster—escape and voluntary. Although the circuitry underlying escape is accounted for by the Giant fibre (GF) system, the system underlying voluntary flight initiation is unknown. The GF system is functionally complete before the adult fly ecloses, but immature adults initially fail to react to a stimulus known to reliably evoke escape in mature adults. This suggests that escape in early adulthood, ∼2-h post-eclosion, is not automatically triggered by the hard-wired GF system. Indeed, we reveal that escape behaviour displays a staged emergence during the first hour post-eclosion, suggesting that the GF system is subject to declining levels of suppression. Voluntary flight initiations are not observed at all during the period when the GF system is released from its suppression, nor indeed for some time after. We addressed the question whether voluntary flight initiation requires the GF system by observing take-off in Shak-B ² mutant flies, in which the GF system is defunct. While the escape response is severely impaired in these mutants, they displayed normal voluntary flight initiation. Thus, the escape mechanism is subject to developmental modulation following eclosion and the GF system does not underlie voluntary flight. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Flight initiations in Drosophila melanogaster are mediated by several distinct motor patterns

We have monitored the patterns of activation of five muscles during flight initiation of Drosophila melanogaster: the tergotrochanteral muscle (a mesothoracic leg extensor), dorsal longitudinal muscles #3, #4 and #6 (wing depressors), and dorsal ventral muscle #Ic (a wing elevator). Stimulation of a pair of large descending interneurons, the giant fibers, activates these muscles in a stereotypic pattern and is thought to evoke escape flight initiation. To investigate the role of the giant fibers in coordinating flight initiation, we have compared the patterns of muscle activation evoked by giant fiber stimulation with those during flight initiations executed voluntarily and evoked by visual and olfactory stimuli. Visually elicited flight initiations exhibit patterns of muscle activation indistinguishable from those evoked by giant fiber stimulation. Olfactory-induced flight initiations exhibit patterns of muscle activation similar to those during voluntary flight initiations. Yet only some benzaldehyde-induced and voluntary flight initiations exhibit patterns of muscle activation similar to those evoked by giant fiber stimulation. These results indicate that visually elicited flight initiations are coordinated by the giant fiber circuit. By contrast, the giant fiber circuit alone cannot account for the patterns of muscle activation observed during the majority of olfactory-induced and voluntary flight initiations.Abbreviations DLM/DLMn dorsal longitudinal muscle/motor neuron - DVM/DVMn dorsal ventral muscle/motor neuron - GF(s) giant fiber interneuron (s) - PSI peripherally synapsing interneuron - TTM/TTMn tergotrochanteral muscle/motor neuron     

The adaptive significance of alpine melanism in the butterfly Parnassius phoebus F. (Lepidoptera: Papilionidae)

Summary The adaptive significance of alpine melanism, the tendancy for insects to become darker with increased elevation and latitude, was investigated using the butterfly Parnassius phoebus. The effects on temperature dependent activity of five components of overall wing melanism, as well as size, were examined. The components of wing melanism examined were the transparency of the basal hindwing and distal fore-wing areas, the width of the black patch in the basal hind-wing area and the proportion of black to white scales in that area, and the proportion of the distal fore-wing covered by predominantly black scaling.The body temperature of dead specimens was correlated with air temperature, solar radiation, the width of the black patch at the base of the wings, and the proportion of black to white scales at the base of the wings. The minimum air temperatures and solar radiation levels required for initiation of flight did not vary with wing melanism of P. phoebus, in contrast to the results found for Colias butterflies by Roland (1982). However, under environmental conditions suitable for flight initiation, males with a higher proportion of black to white scales in the basal area of the hind-wing, and wider basal black patches, spent a greater proportion of time in flight at low air temperatures and low insolation. Increased basal wing melanism was also associated with increased movement of males within a population. In contrast, melanism in the distal area of the wings has no effect on activities which are dependant on body temperature. The amount of time spent feeding did not vary with differences in wing melanism. I suggest that in dorsal basking, slow-flying butterflies (Parnassius) basal wing color affects body temperature primarily during flight (rather than while basking), such that butterflies with darker wing bases cool down less rapidly because they absorb more solar radiation during flight.     

Locomotor Behavior of Flightless Harmonia axyridis Pallas (Col., Coccinellidae)

To improve the efficiency of the lady beetle H. axyridis as a biological control agent against aphids, a flightless population was obtained by feeding adults with a mutagen and selecting their progeny for nonflying but otherwise morphologically normal individuals. These flightless adults attempted to fly but immediately fell. They softened their fall by opening their elytrae and wings. The inability to fly could result from change in their flying behavior compared to control adults. The flight duration was very much shorter, and the wing beat frequency and, more particularly, the amplitude of the wing beats were clearly lower. More time was spent in the other components of the flight behavior such as wing rotation, wing immobility, and wing folding. The sequence of these patterns differed slightly, due mainly to change in their frequency. The locomotor behavior was not modified by the mutation, which affected only the wing muscles. Searching behavior of mutant adults differed from that of control adults only in that they took longer to encounter and ingest aphids. Nevertheless, the larval growth and reproductive rate remained unchanged. The behavioral and biological features of these flightless adults indicate that it should be possible to use them in biological control programs.     

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.     

Biomechanics and biomimetics in insect-inspired flight systems

Insect- and bird-size drones—micro air vehicles (MAV) that can perform autonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 10⁴–10⁵ or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agile manoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control system to modulate power output from the muscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and active mechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.     

Effect of sex,age and morphological traits on tethered flight of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) at different temperatures

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a pest of fruit and vegetable production that has become established in 42 countries in Africa after its first detection in 2003 in Kenya. It is likely that this rapid expansion is partly due to the reported strong capacity for flight by the pest. This study investigated the tethered flight performance of B. dorsalis over a range of constant temperatures in relation to sex and age. Tethered flight of unmated B. dorsalis aged 3, 10 and 21 days was recorded for 1 h using a computerized flight mill at temperatures of 12, 16, 20, 24, 28, 32 and 36 °C. Variations in fly morphology were observed as they aged. Body mass and wing loading increased with age, whereas wing length and wing area reduced as flies aged. Females had slightly larger wings than males but were not significantly heavier. The longest total distance flown by B. dorsalis in 1 h was 1559.58 m. Frequent short, fast flights were recorded at 12 and 36 °C, but long-distance flight was optimal between 20 and 24 °C. Young flies tended to have shorter flight bouts than older flies, which was associated with them flying shorter distances. Heavier flies with greater wing loading flew further than lighter flies. Flight distances recorded on flight mills approximated those recorded in the field, and tethered flight patterns suggest a need to factor temperature into the interpretation of trap captures.     

The effects of latitude,body size,and sexual selection on wing shape in a damselfly

Under natural selection, wing shape is expected to evolve to optimize flight performance. However, other selective factors besides flight performance may influence wing shape. One such factor could be sexual selection in wing sexual ornaments, which may lead to alternative variations in wing shape that are not necessarily related to flight performance. In the present study, we investigated wing shape variations in a calopterygid damselfly along a latitudinal gradient using geometric morphometrics. Both sexes show wing pigmentation, which is a known signal trait at intra‐ and interspecific levels. Wing shape differed between sexes and, within the same sex, the shape of the hind wing differed from the front wing. Latitude and body size explained a high percentage of the variation in wing shape for female front and hind wings, and male front wings. In male hind wings, wing pigmentation explained a high amount of the variation in wing shape. On the other hand, the variation in shape explained by pigmentation was very low in females. We suggest that the conservative morphology of front wings is maintained by natural selection operating on flight performance, whereas the sex‐specific differences in hind wings most likely could be explained by sexual selection. The observed sexual dimorphism in wing shape is likely a result of different sex‐specific behaviours. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 263–274.     

昆虫翅型分化的调控及翅多型性的进化

翅多型现象普遍存在于各昆虫类群,一些学者就昆虫翅多型进行了大量的研究工作。根据昆虫翅型的分化,可划分为长翅型和短翅型,长翅型具飞行能力,而短翅型不能飞行。一些昆虫种类,如蚜虫,出现无翅个体,被称为无翅型。除飞行能力外,长翅型和短翅型在行为、生理等方面也存在差异。文章主要就环境因素对翅型分化的影响、翅多型的内分泌控制机理、翅多型的遗传机制及其进化等作一概述。     

The wing morphology of limnephilid caddisflies in relation to their habitat preferences

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Development of wing morphology in the Indian pygmy batPipistrellus mimus

The growth and development of the wing parameters of the Indian pygmy batPipistrellus mimus was studied under natural conditions. Newborn young were marked with nontoxic coloured paint and were later marked with split rings. The wingspan and wing area showed linear growth until the age of five weeks, after which the rate of growth decreased. The observations on flight showed that at the age of 19 days the young were able to flutter their wings, at the age of 22 days they flew for a short distance and at the age of 29 days they exhibited sustained flight. The development of wing loading and aspect ratio are also presented. The decrease in wing loading as the bat grows is discussed as an advantage to sustain flight. The aspect ratio showed a high degree of scatter at early stages of life which decreased at the later period of growth. In general the development of wing morphology ofP. mimus is similar to that of other vespertilionid bats.     

Morphological variation associated with dispersal capacity in a tree‐killing bark beetle Dendroctonus ponderosae Hopkins

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Aerodynamic aspects of formation flight in birds

In formation flight each wing flies in an upwash field generated by all other wings of the formation. This leads to a reduction in flight power demand for each wing as well as for the whole formation.Methods of theoretical aerodynamics are used to calculate the flight power reduction for arbitrarily shaped flight formations with any number of birds. These methods are applied to homogeneous and inhomogeneous flight formations in which birds of the same kind or birds of different span, aspect ratio and weight may be present.The total flight power reduction of the whole formation strongly depends on the lateral distance of the wings. A longitudinal displacement of the wings in flight direction has no influence on the total flight power reduction but only on their distribution on the involved individuals. The local flight power reduction is highest in the inner parts of the formation and decreases towards the apex and towards the side edges of the formation. Small and light individuals are automatically favoured by larger and heavier birds. It is shown that some minor portion of twist is necessary to fly in a formation without a rolling moment. In addition it turns out that the optimum flight speed of a formation is slightly lower than the optimum flight speed of single individuals.     

The aerodynamic costs of warning signals in palatable mimetic butterflies and their distasteful models

Bates hypothesized that some butterfly species that are palatable gain protection from predation by appearing similar to distasteful butterflies. When undisturbed, distasteful butterflies fly slowly and in a straight line, and palatable Batesian mimics also adopt this nonchalant behaviour. When seized by predators, distasteful butterflies are defended by toxic or nauseous chemicals. Lacking chemical defences, Batesian mimics depend on flight to escape attacks. Here, I demonstrate that flight in warning-coloured mimetic butterflies and their distasteful models is more costly than in closely related non-mimetic butterflies. The increased cost is the result of differences in both wing shape and kinematics. Batesian mimics and their models slow the angular velocity of their wings to enhance the colour signal but at an aerodynamic cost. Moreover, the design for flight in Batesian mimics has an additional energetic cost over that of its models. The added cost may cause Batesian mimics to be rare, explaining a general pattern that Bates first observed.     

Bird predation selects for wing shape and coloration in a damselfly

Wing shape is related to flight performance, which is expected to be under selection for improving flight behaviours such as predator avoidance. Moreover, wing conspicuousness, usually involved in sexual selection processes, is also relevant in terms of predation risk. In this study, we examined how predation by a passerine bird, the white wagtail Motacilla alba, selects wing shape and wing colour patch size in males of the banded demoiselle Calopteryx splendens. The wing colour patch is intra‐ and intersexually selected in the study species. In a field study, we compared wings of live damselflies to wings of predated damselflies which are always discarded after predation. Based on aerodynamic theory and a previous study on wing shape of territorial tactics in damselflies, we predicted an overall short and broad wing, with a concave front margin shape to be selected by predation. This shape would be expected to improve escaping ability. Moreover, we predicted that wing patch size should be negatively selected by predation. We found that selection operated differently on fore‐ and hindwings. In contrast to our predictions, predation favoured a slender general forewing shape. However, the predicted wing shape was favoured in hindwings. We also found selection favouring a narrower wing colour patch. Our results suggest different roles of fore‐ and hindwings in flight, as previously suggested for Calopteryx damselflies and shown for butterflies and moths. Forewings would be more involved in sustained flight and hindwings in flight manoeuvrability. Our results differ somehow from a recently published work in the same study system, but using another population, suggesting that selection can fluctuate across space, despite the simplicity of this predator–prey system.     

Comparing wing loading,flight muscle and lipid content in ant‐attended and non‐attended Tuberculatus aphid species

Although all Tuberculatus aphids possess wings, some species associated with ants exhibit extremely low levels of dispersal compared with those not associated with ants. Furthermore, phylogenetic interspecific comparisons find significantly higher wing loading (i.e. higher ratio of body volume to wing area) in ant‐attended species. This observation indicates that ant‐attended species may allocate more of their body resources to reproductive traits (i.e. embryos) rather than flight apparatus (i.e. wings, flight muscle and lipid). The present study focuses on two sympatric aphid species and aims to investigate the hypothesized trade‐off in resource investment between fecundity and the flight apparatus; specifically, the ant‐attended Tuberculatus quercicola (Matsumura) and non‐attended Tuberculatus paiki Hille Ris Lambers. Species differences are compared in: (i) morphology, (ii) embryo production, (iii) triacylglycerol levels and (iv) wing loading and flight muscle. The results show that T. quercicola has a larger body volume, higher fecundity and higher wing loading compared with T. paiki, which has a smaller, slender‐shaped body, lower fecundity and lower wing loading. No significant difference is found between the species with respect to the percentage of triacylglycerol content in dry body weight. The flight muscle development is significantly lower in T. quercicola than in T. paiki. These results indicate that the additive effect of higher wing loading and the lower amount of flight muscle development in T. quercicola may increase the physical difficulty of flight, and hence be responsible for its lower dispersal ability. The trade‐off between fecundity and dispersal documented in wing‐dimorphic insects may therefore be applicable to T. quercicola, which has fully developed wings.     

Soaring and manoeuvring flight of a steppe eagle Aquila nipalensis

We used an onboard inertial measurement unit, together with onboard and ground‐based video cameras, to record the movements of the body, wings and tail of a steppe eagle Aquila nipalensis during wide‐ranging flight. The eagle's flight consisted of a more or less continuous sequence of banked turns, interrupted by occasional wing tucks and roll‐over manoeuvres, and ultimately terminated by a wing‐over manoeuvre leading in to a diving landing approach. The flight configuration of the bird, and its pattern of movement during angular perturbations, together suggest that the eagle is inherently stable in pitch and yaw, and perhaps also in roll. The control inputs used to generate roll moments during banked turns were too subtle to be detected. Control of yaw and pitch during banked turns involved a consistent pattern of tail movement, wherein the tail was spread and depressed immediately before the turn, and then overbanked with respect to the bird during the latter part of the turn. Differential adjustment of wing posture is probably also involved in the control of banked turns, but it was only consistently apparent during more extreme roll manoeuvres. For example, roll‐over and wing‐over manoeuvres were both accomplished by differential changes in the angle of incidence and spread of the wings. In general, however, the bird appeared to maintain positive loading on its wings at all times, except during extreme flight manoeuvres.     

Design and Demonstration of Insect Mimicking Foldable Artificial Wing Using Four-Bar Linkage Systems

In this work, we develop an artificial foldable wing that mimics the hind wing of a beetle （Allomyrina dichotoma）. In real flight, the beetle unfolds forewings and hind wings, and maintains the unfolded configuration unless it is exhausted. The artificial wing has to be able to maintain a fully unfolded configuration while flapping at a desirable flapping frequency. The artificial foldable hind wing developed in this work is based on two four-bar linkages which adapt the behaviors of the beetle＇s hind wing. The four-bar-linkages are designed to mimic rotational motion of the wing base and the vein folding/unfolding motion of the beetle＇s hind wing. The behavior of the artificial wings, which are installed in a flapping-wing system, is observed using a high-speed camera. The observation shows that the wing could maintain a fully unfolded configuration during flapping motion. A series of thrust measurements are also conducted to estimate the force generated by the flapping-wing system with foldable artificial wings. Although the artificial foldable wings give added burden to the flapping-wing system because of its weight, the thrust measurement results show that the flapping-wing system could still generate reasonable thrust.     

Skipping flights in Ypthima butterflies (Lepidoptera: Nymphalidae)

The skipping flight patterns of three species of Ypthima (Lepidoptera: Nymphalidae) were analyzed using high‐speed video recordings to clarify how wings move and how driving forces are produced. All three species showed a flight pattern that includes a pause that accounts for about 50% of a flap cycle when their wings completely close after each upstroke. The observed pause causes the “skipping” flight trajectory based on the clap–fling mechanism. Pause duration was correlated with upstroke wing motion, suggesting the contribution of the latter to a long pause duration. This is also supported by the temporal relationship between the wing and body motions. The aerodynamic power necessary for the pause flight was calculated for the three species.     

Initiation of flight muscle apoptosis and wing casting in the red imported fire ant Solenopsis invicta

Abstract Newly‐mated Solenopsis invicta flight queens cast (shed) their wings within 24 h. An examination of their flight muscle cells reveals numerous apoptotic (terminal deoxynucleotidyl transferase mediated dUTP nick end labelling positive) nuclei. By contrast, flight muscle cells of mature alate virgin (MAV) females removed 24 h earlier from a managed laboratory colony exhibit neither wing casting nor the presence of apoptotic nuclei. Using MAV‐females, the initiation of flight muscle apoptosis and wing casting is compared with artificial mating using seminal fluid with sperm, seminal fluid with no sperm, saline as a negative control, the mating flight as simulated in the laboratory, elevated CO₂ exposure, application of methoprene (a juvenile hormone analogue), or injection of 20‐hydroxyecdysone. Numerous apoptotic nuclei are revealed in the flight muscle cells of mated dealate females 24 h after a natural mating flight but not in MAV‐females controls. Only artificial mating of MAV‐females reveals a similar pattern of apoptotic nuclei flight muscle 24 h after insemination. None of the other factors tested induces flight muscle cell apoptosis in MAV‐females. Methoprene dissolved in methyl ethyl ketone, at a concentration of 0.44 ng per μL per ant, stimulates 90% of MAV‐females to shed their wings within 24 h, as opposed to 10% or less wing shedding for the methyl ethyl ketone control and all other treatments.