Ambient temperature affects free-flight performance in the fruit fly Drosophila melanogaster

To gain insight into how temperature affects locomotor performance in insects, the limits of flight performance have been estimated in freely flying fruit flies Drosophila melanogaster by determining the maximum load that a fly could carry following take-off. At a low ambient temperature of 15 °C, muscle mechanical power output matches the minimum power requirements for hovering flight. Aerodynamic force production rises with increasing temperature and eventually saturates at a flight force that is roughly equal to 2.1 times the body mass. Within the two-fold range of different body sizes, maximum flight force production during free flight does not decrease with decreasing body size as suggested by standard aerodynamic theories. Estimations of flight muscle mechanical power output yields a peak performance of 110 W kg⁻¹ muscle tissue for short-burst flight that was measured at an ambient temperature of 30 °C. With respect to the uncertainties in estimating muscle mechanical power during free flight, the estimated values are similar to those that were published for flight under tethered flight conditions. Accepted: 5 January 1999     

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.     

Tracking and chasing in houseflies (Musca)

The flight trajectories of free flying female and male houseflies have been analyzed in 3 dimensions. Both female and male flies track other flies. The turning velocity α (around the vertical axis) is linearly dependent upon the horizontal angle ψ_F (that is the angle between the trajectory of the tracking fly and the target) for small values of ψ_F in females and for the whole range of ψ_F in males. The 3-dimensional velocity υ _xyz of the chasing fly is linearly dependent upon the distance between leading and chasing fly in males but not in females. Male chasing thus appears to be more efficient than female tracking. It is shown that earlier assumptions on visual control of flight in female flies derived from experiments on fixed flying flies are justified.     

The constraints of body size on aerodynamics and energetics in flying fruit flies: an integrative view

Reynolds number and thus body size may potentially limit aerodynamic force production in flying insects due to relative changes of viscous forces on the beating wings. By comparing four different species of fruit flies similar in shape but with different body mass, we have investigated how small insects cope with changes in fluid mechanical constraints on power requirements for flight and the efficiency with which chemical energy is turned into aerodynamic flight forces. The animals were flown in a flight arena in which stroke kinematics, aerodynamic force production, and carbon dioxide release were measured within the entire working range of the flight motor. The data suggest that during hovering performance mean lift coefficient for flight is higher in smaller animals than in their larger relatives. This result runs counter to predictions based on conventional aerodynamic theory and suggests subtle differences in stroke kinematics between the animals. Estimates in profile power requirements based on high drag coefficient suggest that among all tested species of fruit flies elastic energy storage might not be required to minimize energetic expenditures during flight. Moreover, muscle efficiency significantly increases with increasing body size whereas aerodynamic efficiency tends to decrease with increasing size or Reynolds number. As a consequence of these two opposite trends, total flight efficiency tends to increase only slightly within the 6-fold range of body sizes. Surprisingly, total flight efficiency in fruit flies is broadly independent of different profile power estimates and typically yields mean values between 2–4%.     

Thermoregulation and flying habits of the Japanese sulfur butterfly Colias erate (Lepidoptera: Pieridae) in an open habitat

This study evaluated the impact of the thermal environment on the flying behavior of male Japanese sulfur butterflies Colias erate searching for females in an open habitat. Thoracic temperature was monitored before and after flight. Mean thoracic temperature of butterflies immediately after landing was consistently higher than, but independent of, ambient temperature. Although ground speed of flying butterflies was different between flight types, air speed against the butterfly was similar across flight types. The excess of thoracic over ambient temperature was lower in flying butterflies than in basking ones, as predicted by a model. This difference appeared to be due to air current, which enhanced heat loss. In a laboratory study, newly eclosed male butterflies were placed under an incandescent lamp to measure their thoracic temperature at different air current speeds. The excess of thoracic over ambient temperature decreased as the speed of air currents increased. When the air current was similar to the air speed against flying butterflies in the field, a substantial decrease occurred in the operative thoracic temperature.     

Thermal physiological ecology of Colias butterflies in flight

Summary As a comparison to the many studies of larger flying insects, we carried out an initial study of heat balance and thermal dependence of flight of a small butterfly (Colias) in a wind tunnel and in the wild.Unlike many larger, or facultatively endothermic insects, Colias do not regulate heat loss by altering hemolymph circulation between thorax and abdomen as a function of body temperature. During flight, thermal excess of the abdomen above ambient temperature is weakly but consistently coupled to that of the thorax. Total heat loss is best expressed as the sum of heat loss from the head and thorex combined plus heat loss from the abdomen because the whole body is not isothermal. Convective cooling is a simple linear function of the square root of air speed from 0.2 to 2.0 m/s in the wind tunnel. Solar heat flux is the main source of heat gain in flight, just as it is the exclusive source for warmup at rest. The balance of heat gain from sunlight versus heat loss from convection and radiation does not appear to change by more than a few percent between the wings-closed basking posture and the variable opening of wings in flight, although several aspects require further study. Heat generation by action of the flight muscles is small (on the order of 100 m W/g tissue) compared to values reported for other strongly flying insects. Colias appears to have only very limited capacity to modulate flight performance. Wing beat frequency varies from 12–19 Hz depending on body mass, air speed, and thoracic temperature. At suboptimal flight temperatures, wing beat frequency increases significantly with thoracic temperature and body mass but is independent of air speed. Within the reported thermal optimum of 35–39°C, wing beat frequency is negatively dependent on air speed at values above 1.5 m/s, but independent of mass and body temperature. Flight preference of butterflies in the wind tunnel is for air speeds of 0.5–1.5 m/s, and no flight occurs at or above 2.5 m/s. Voluntary flight initiation in the wild occurs only at air speeds 1.4 m/s.In the field, Colias fly just above the vegetation at body temperatures of 1–2°C greater than when basking at the top of the vegetation. These measurements are consistent with our findings on low heat gain from muscular activity during flight. Basking temperatures of butterflies sheltered from the wind within the vegetation were 1–2°C greater than flight temperatures at vegetation height.     

Weight Loading and Reproductive Status Affect the Flight Performance of Pieris napi Butterflies

Weight-induced mobility reductions can have dramatic fitness consequences and winged animals are especially sensitive to the trade-off between mass and locomotion. Data on how natural weight fluctuations influence a flying insect’s ability to take off are scarce. We therefore quantified take-off flight ability in Pieris napi butterflies in relation to reproductive status. Take-off flight ability (velocity and take-off angle) under suboptimal temperature conditions was recorded with a 3D-tracking camera system and was predicted to decrease with relatively larger weight loads. Our results show that relatively larger weight loads generally reduce flight speed in male butterflies and lower take-off angles in females. However, despite having a lower wing loading, mated male butterflies flew slower than unmated males. Our study suggests that retention of weight loads associated with reproduction impairs insect flight performance.     

光照、温度和湿度对桔小实蝇飞翔活动的影响

于2004年6月在云南元江芒果园内通过性诱剂诱捕,对桔小实蝇Bactrocera dorsalis(Hendel)的飞翔活动日节律进行了全天24h的监测,并就光照、温度和相对湿度3个环境因子的影响进行了测试和综合分析。研究表明,桔小实蝇雄成虫仅在白天有光照的情况下进行飞翔活动,夜晚停止飞翔。在1d内有2个飞翔活动高峰期,分别发生在上午8∶00~9∶00和下午18∶00~20∶00,且前者进行飞翔活动的虫量相对后者要大。在下午2∶00左右进入白天飞翔活动的低谷。光刺激是桔小实蝇飞翔活动的基本条件,其趋光性因芒果园内树荫下的光照强度变化而异,在100~200lux之间对桔小实蝇飞翔活动明显有利,而当光照强度低于100lux或高于200lux,飞翔活动也相应减小。气温总体上位于桔小实蝇飞翔活动的适宜范围,而下午低于60%的相对湿度对其飞翔活动有一定的抑制作用。气温、湿度和光照对桔小实蝇飞翔活动的作用机理各不相同并且各因子之间也相互作用,最终对桔小实蝇的飞翔活动产生综合效应。     

Neural correlates of flight activation and escape behavior in houseflies recovering from pyrethroid poisoning

Recovery from pyrethroid poisoning was studied in groups of adult female houseflies treated with LD50 doses of trans-permethrin or deltamethrin. The first overt sign of recovery was the appearance of normal posture, which was followed by jumping behavior and finally, coordinated flight when the flies had fully recovered. Prior to full recovery, treated houseflies were able to maintain normal posture and usually jump, but they could not fly. When tethered, these flightless houseflies responded to loss of tarsal contact by initiating normal patterned activity in the dorsolongitudinal flight muscles, yet the wings did not move. In flightless flies displaying jumping behavior, electrical stimulation of the brain evoked responses in the pleurosternal muscle, which controls thoracic tension during flight. Thus, many of the motor systems responsible for flight behavior seemed to be functional in flightless flies. Carbofuran, a carbamate anticholinesterase known to initiate spontaneous flight behavior from within the central nervous system, failed to elicit this response in flightless flies. These results suggested that the flightless condition was due to a disruption in central nervous pathways, and not to peripheral neuromuscular block. The pattern of recovery of different behaviors analyzed in this study was found to be consistent with the Jacksonian Hierarchy Principle, and the utility of this principle in guiding the design of new behavior-modifying compounds is discussed.     

Postural Changes Accompany Perch Location Changes in Male Butterflies (Asterocampa leilia) Engaged in Visual Mate Searching

Males of the nymphalid butterfly Asterocampa leilia perch and wait during the morning at places where females are likely to appear. Males leave their perches to court passing females and chase away intruding males. As air and ground temperatures rise during the morning, males switch from perching on the ground to perching off the ground (average height = 0.87 m) for thermoregulatory reasons. To evaluate how this switch in perch location might affect mate detection, I have investigated how the three-dimensional posture of the male's body and head varies with perch location and how conspecifics fly through male perching areas. The body posture of males varies with perch location, as measured by pitch and roll relative to gravity, and yaw relative to the sun. Moreover, the pitch and roll of the head relative to the body is adjusted in a way that compensates for variation in body pitch and roll. These results, along with information on conspecific flight altitudes, suggest that when a male is perched on the ground his visual system is positioned in such a way that he is less likely to detect conspecifics flying nearby than when he is perched off the ground. Hence, it appears that early in the morning visual detection of mates and intruding males may be compromised by thermoregulatory concerns.     

Body temperature regulation,energy metabolism,and foraging in light-seeking and shade-seeking robber flies

Summary Robber flies (Diptera: Asilidae) were studied in Panama from May through August. Of the 16 species examined, 5 perched and foraged in the sun and 11 perched and foraged in the shade. Thoracic body temperatures of light-seeking flies ranged from 35.2–40.6°C during foraging. Light-seeking flies regulated body temperature behaviorally by microhabitat selection and postural adjustments, and physiologically by transferring warmed haemolymph from the thorax to the cooler abdomen. Thoracic temperatures of shade-seeking flies passively followed ambient temperature in the shade and these flies did not thermoregulate. None of these robber flies warmed endothermically in the absence of flight. Resting oxygen consumption ( ) of both groups scaled with body mass to the 0.77 power. The factorial increment in resulting from hovering flight ranged from 12 to 56. The increased markedly with body temperature in light-seeking flies and probably explains the greater foraging effort observed in these species. Wing loading of all 16 species of robber flies scaled with body mass to the 0.39 power. Large light-seeking flies had heavier wing loading than large shade-seeking flies. The differences in body temperature and wing loading between light-seeking and shade-seeking robber flies may be related to differences in flight speed and maneuverability during foraging.     

Fine structural alterations with age in the fat body of the adult male housefly,Musca domestica

Summary The fat body of the adult housefly is composed of two types of cells, the lipid-and glycogen-rich fat body cells and the oenocytes. A comparison of the fine structure of the abdominal fat body in 4-day old and 31–35 day old male houseflies indicated an increase in lipid and a decrease in glycogen content in the fat body cells of old flies. Oenocytes of old flies exhibit deteriorative alterations with an accumulation of secondary lysosomes. Both fat body cells and oenocytes in senile flies are ingested by hemocytes.Supported by a grant from the National Science Foundation.     

Moving in a moving medium: new perspectives on flight

One of the defining features of the aerial environment is its variability; air is almost never still. This has profound consequences for flying animals, affecting their flight stability, speed selection, energy expenditure and choice of flight path. All these factors have important implications for the ecology of flying animals, and the ecosystems they interact with, as well as providing bio-inspiration for the development of unmanned aerial vehicles. In this introduction, we touch on the factors that drive the variability in airflows, the scales of variability and the degree to which given airflows may be predictable. We then summarize how papers in this volume advance our understanding of the sensory, biomechanical, physiological and behavioural responses of animals to air flows. Overall, this provides insight into how flying animals can be so successful in this most fickle of environments.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.     

Effects of wind on the behaviour and distribution of mosquitoes and blackflies

Flight activity of haematophagous insects can be greatly reduced by wind, but species inhabiting woods and other sheltered sites will be less affected than those living in more exposed areas. If flight is suppressed this may lead to reductions in blood-feeding and oviposition and thus a reduction in their reproductive capacity. Although wind usually inhibits flight it appears that newly emerged adults of some mosquito species are specially adapted to take-off and flight in windy weather, thus promoting dispersal and colonization of new areas. Dispersal of simuliids and mosquitoes can be very important in control programmes as they can create problems of recolonization. Because air turbulence and convection are usually greatest during the day, simuliids and day-flying mosquitoes are more likely to be swept into the upper air and carried long distances than mosquito species that are active at night.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel     

Mating behavior and thermoregulation of the reindeer warble fly,Hypoderma tarandi L. (Diptera: Oestridae)

Hypoderma (=Oedemagena) tarandi L. (Diptera: Oestridae) is characterized by a mating strategy in which both sexes meet and mate at two types of distinct topographical landmarks. In the expansive, treeless vidda (= tundra-like) biome, mating places are unique, rocky areas located along rivers and streams or in rocky areas of drying river and stream beds. In wooded valleys below the vidda, flies mated at certain topographical areas along dirt road tracks/paths. Thermoregulatory activities of males occupying perches at mating places included selection of substratum at perch site, orientation of body to sun's rays, crouching, stilting, and flights into upper cooler air. On warm sunny days males perched for just 1–2 min before flying up into cooler air to promote cooling. Laboratory and field studies revealed that flies could not metabolically cool down when held at 25–38°C. Time spent at mating places depended on temperature, duration of sunshine, and wind velocity. Males were very aggressive in pursuing allHypoderma-sized objects that passed by them or that landed near them, but they did not defend specific perch sites. Males either pursued and caught females in flight, or they hopped onto females that landed near them. During 5 years, 74 males and 14 females were seen at mating places. Dissection of six females caught at mating places revealed them to be recently eclosed flies full of fat body and with all eggs intact; two not paired with males were non-inseminated. Three experimentally paired females remainedin copulo for 10, 13, and 19.5 min.     

Flight costs of long,sexually selected tails in hummingbirds

The elongated tails adorning many male birds have traditionally been thought to degrade flight performance by increasing body drag. However, aerodynamic interactions between the body and tail can be substantial in some contexts, and a short tail may actually reduce rather than increase overall drag. To test how tail length affects flight performance, we manipulated the tails of Anna''s hummingbirds (Calypte anna) by increasing their length with the greatly elongated tail streamers of the red-billed streamertail (Trochilus polytmus) and reducing their length by removing first the rectrices and then the entire tail (i.e. all rectrices and tail covert feathers). Flight performance was measured in a wind tunnel by measuring (i) the maximum forward speed at which the birds could fly and (ii) the metabolic cost of flight while flying at airspeeds from 0 to 14 m s⁻¹. We found a significant interaction effect between tail treatment and airspeed: an elongated tail increased the metabolic cost of flight by up to 11 per cent, and this effect was strongest at higher flight speeds. Maximum flight speed was concomitantly reduced by 3.4 per cent. Also, removing the entire tail decreased maximum flight speed by 2 per cent, suggesting beneficial aerodynamic effects for tails of normal length. The effects of elongation are thus subtle and airspeed-specific, suggesting that diversity in avian tail morphology is associated with only modest flight costs.     

On the mechanism of speed and altitude control in Drosophila melanogaster

ABSTRACT The total power output of tethered flying Drosophila melanogaster in still air depends on translational velocity components of image flow on the eye, whereas the orientation of the average flight force in the midsagittal plane of the fly is widely independent of visual input (Götz, 1968). The fly does not seem to control the vertical and the horizontal force component independently. Freely flying flies nevertheless generate different ratios between lift and thrust, simply by changing the inclination of their body. By the combined adjustment of the body angle and the total power output a fly appears to be able to stabilize height and speed (David, 1985). Here a possible mechanism is proposed by which the appropriate torque about the transverse body axis could be generated. Translational pattern motion influences the posture of the abdomen and the plane of wing oscillation. Thus the position of the centre of gravity relative to the flight force vector is changed. When abdomen and stroke plane deviate from an equilibrium state, a lever is generated by which the force vector will rotate the fly about its transverse axis.     

Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs

The flight ability of animals is restricted by the scaling effects imposed by physical and physiological factors. In comparisons of the power available from muscle and the mechanical power required to fly, it is predicted that the margin between the powers should decrease with body size and that flying animals have a maximum body size. However, predicting the absolute value of this upper limit has proven difficult because wing morphology and flight styles varies among species. Albatrosses and petrels have long, narrow, aerodynamically efficient wings and are considered soaring birds. Here, using animal-borne accelerometers, we show that soaring seabirds have two modes of flapping frequencies under natural conditions: vigorous flapping during takeoff and sporadic flapping during cruising flight. In these species, high and low flapping frequencies were found to scale with body mass (mass ^−0.30 and mass ^−0.18) in a manner similar to the predictions from biomechanical flight models (mass ^−1/3 and mass ^−1/6). These scaling relationships predicted that the maximum limits on the body size of soaring animals are a body mass of 41 kg and a wingspan of 5.1 m. Albatross-like animals larger than the limit will not be able to flap fast enough to stay aloft under unfavourable wind conditions. Our result therefore casts doubt on the flying ability of large, extinct pterosaurs. The largest extant soarer, the wandering albatross, weighs about 12 kg, which might be a pragmatic limit to maintain a safety margin for sustainable flight and to survive in a variable environment.     

Into turbulent air: size-dependent effects of von Kármán vortex streets on hummingbird flight kinematics and energetics

Animal fliers frequently move through a variety of perturbed flows during their daily aerial routines. However, the extent to which these perturbations influence flight control and energetic expenditure is essentially unknown. Here, we evaluate the kinematic and metabolic consequences of flight within variably sized vortex shedding flows using five Anna''s hummingbirds feeding from an artificial flower in steady control flow and within vortex wakes produced behind vertical cylinders. Tests were conducted at three horizontal airspeeds (3, 6 and 9 m s⁻¹) and using three different wake-generating cylinders (with diameters equal to 38, 77 and 173% of birds'' wing length). Only minimal effects on wing and body kinematics were demonstrated for flight behind the smallest cylinder, whereas flight behind the medium-sized cylinder resulted in significant increases in the variances of wingbeat frequency, and variances of body orientation, especially at higher airspeeds. Metabolic rate was, however, unchanged relative to that of unperturbed flight. Hummingbirds flying within the vortex street behind the largest cylinder exhibited highest increases in variances of wingbeat frequency, and of body roll, pitch and yaw amplitudes at all measured airspeeds. Impressively, metabolic rate under this last condition increased by up to 25% compared with control flights. Cylinder wakes sufficiently large to interact with both wings can thus strongly affect stability in flight, eliciting compensatory kinematic changes with a consequent increase in flight metabolic costs. Our findings suggest that vortical flows frequently encountered by aerial taxa in diverse environments may impose substantial energetic costs.     

Temporary flightlessness as a potential cost of reproduction in pre-laying Common Eiders Somateria mollissima

The rapid growth and reabsorption of the avian ovary is thought to be adaptive, as it reduces predation risk and the metabolic cost of flight. In this paper, we use an extreme case of parental investment to show how the survival of gravid birds may be impaired by reduced take-off ability. In still air, temporary flightlessness is regularly observed in female Common Eiders Somateria mollissima preparing for breeding. From a sample of pre-laying females collected in the Baltic Sea, we quantified the relationships among body reserves, organ mass and take-off ability using a general model of take-off performance. Average body mass at the beginning and end of follicular growth was, respectively, 32% and 43% higher than winter body mass. Wing-loading increased significantly during ovary development whereas the relative mass of flight muscles decreased. In contrast, organ mass and somatic body mass were constant from early follicular growth until laying, indicating that the observed increase in body mass was caused by ovary growth. The average specific lift production of individuals collected at the beginning of follicular growth was 9.7 N/kg, which is similar to the lift required to become airborne (9.8 N/kg). As ovary mass increased, lift production decreased to 9.2 N/kg at the onset of laying. These results indicate that temporary flightlessness results from the accumulation of large body reserves and subsequent ovarian growth. Predators of Common Eiders are diverse and may come from air, water and land. We suggest that temporary flightlessness may decrease adult survival through predation, and may represent an important cost of reproduction.