Flight Boundary Layer Research Articles

How aphids fly: Take‐off, free flight and implications for short and long distance migration

Abstract An introduction to high‐speed photography and its entomological impact is provided, emphasizing the importance of high frame rates and high resolution. The take‐off and free flight of Drepanosiphum platanoidis and Myzus persicae were studied in still air using high‐speed photography in HD. The wing tip and body posture were tracked to show how they are displaced during each wingbeat cycle. The important structural elements of the wing are described. The wingbeat is driven by a reinforced leading edge, the pterostigma and costa. The remainder of the coupled fore‐ and hindwing acts as a single aerofoil that deforms during flight, due to sparse venation and a lack of cross veins. During flight, aphids use a ‘near clap and fling’ mechanism with a body pitch close to 90°. Rapid acceleration about the thoracic lateral axis into wing reversal generates enough lift for take‐off, typically within the first or second wingbeat. Unique footage shows that aphids demonstrate a high degree of flight control and manoeuvrability in the lab, occasionally using forward and inverted flight, two flight modes that are otherwise poorly known. While research into the impact of turbulent convection is needed, we posit that the strength of atmospheric forces presents a formidable challenge to aphid migrants. Above the flight boundary layer, migrating aphids may not easily oppose upwardly moving air, although if used, ‘frozen flight’ may cause them to descend on average. We evaluate five devices for insect flight research.

Autumn migration of the migrant hawker (Aeshna mixta) at the Baltic coast

BackgroundMigratory insects are important for the provision of ecosystem services both at the origin and destination sites but – apart from some iconic species – the migration routes of many insect species have not been assessed. Coastlines serve as a funnel where migrating animals including insects accumulate. Migratory behaviour and captures of dragonflies in bird traps suggest autumn migration of dragonflies along coastlines while the origin and regularity of this migration remain unclear.MethodsDragonfly species were caught at the bird observatory Kabli at the Baltic coast in Estonia in 2009, 2010 and 2015. For the 2015 data set, we used a stable hydrogen (H) approach to trace the potential natal origin of the migrant hawker (Aeshna mixta).Results1079 (2009), 701 (2010) and 88 (2015) A. mixta individuals were caught during the study periods (35, 37 and 11 days in 2009, 2010 and 2015, respectively). The migration period lasted from end of August to end of September. Based on the results from our stable isotope analysis, we identified two populations of A. mixta: One (range of isotope signatures of non-exchangeable H [δ2Hn wing]: −78‰ to −112‰) had a local likely origin while the other (δ2Hn wing: −113‰ to −147‰) migrated from northerly directions even in headwind from the South. The former showed an even sex ratio whereas the actively migrating population was dominated by males.ConclusionsOur results suggest a regular southbound autumn migration of A. mixta along the Baltic coast. However, nearly half of the sampled individuals originated from the surroundings suggesting either no, partial or “leap-frog” migration. Contrary to our expectation, A. mixta did not select favourable wind conditions but continued the southbound autumn migration in the flight boundary layer even in case of headwinds. The dominance of males might indicate migration as a result of competition for resources. Further repeated, large-scale studies along the Baltic coast are necessary to pinpoint the migratory pattern and the reason for migration of A. mixta. Such studies should also comprise locations north of the known species range of A. mixta because of the rapid climate-change induced range expansion.

Data acquisition system for PW-6U in flight boundary layer mapping

Purpose This paper aims to describe an idea for an integration process and tests of flight parameters measurement system, which supports infrared thermography (IRT) boundary layer mapping.

Sex‐specific dispersal by a parasitoid wasp in the field

AbstractAlthough parasitoid wasps are important regulators of herbivorous insect populations, very little is known regarding their movement under field conditions. Here, we examined the vertical and cardinal directionality of dispersal by Binodoxys communis (Gahan) (Hymenoptera: Braconidae: Aphidiinae), an exotic Asian parasitoid released as a biological control agent of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae: Aphidinae), in North American soybeans, Glycine max (L.) Merr. (Fabaceae). The patterns are consistent with time‐dependent, sex‐specific dispersal strategies; whereas males show flight that is devoid of vertical or cardinal directionality, females consistently move at or above soybean canopy height toward the east and north. Male capture rates also appear to be more correlated with local conditions than those of females. These results suggest that females actively cross the flight boundary layer (the space above which insect flight is largely wind‐driven as opposed to self‐directed) and follow air currents away from soybean fields, whereas males engage in more localized movement. The data also suggest differing response potentials of the sexes to changing local resource conditions (host availability, female availability, host plant cultivar). We discuss the implications for sex‐specific movement on the basic biology of introduced parasitoid species, and their applied role as potential agents in importation biological control programs.

Material response characterization of a low-density carbon composite ablator in high-enthalpy plasma flows

Future space exploration missions beyond Earth’s orbit, such as sample returns from Mars, will use ablative materials for the thermal protection system in order to shield the spacecraft from the severe heating during reentry. In this paper, we present the results of an elaborate test campaign on a lightweight carbon composite ablator with the aim of defining a procedure for material response characterization in a 1.2-MW inductively heated Plasmatron facility, suitable to reproduce the hypersonic flight boundary layer environment. Three different test gases were used, air, nitrogen, and argon, at surface temperatures exceeding 3300 K. A comprehensive experimental setup was developed including a nonintrusive technique to measure surface recession by means of a high-speed camera. Surface degradation was strongly test gas dependent, while mass loss was mainly driven by in-depth decomposition of phenolic resin. Emission spectroscopy helped us identify C2 as a product of dissociating hydrocarbons, as well as cyanogen, suggesting surface nitridation. Melt flow at the surface and silicon emission indicated degradation of the glass microspheres used as additional filler. In air plasma, oxidation was inferred to be the main mechanism for ablation.

Predicting Insect Migration Density and Speed in the Daytime Convective Boundary Layer

Insect migration needs to be quantified if spatial and temporal patterns in populations are to be resolved. Yet so little ecology is understood above the flight boundary layer (i.e. >10 m) where in north-west Europe an estimated 3 billion insects km−1 month−1 comprising pests, beneficial insects and other species that contribute to biodiversity use the atmosphere to migrate. Consequently, we elucidate meteorological mechanisms principally related to wind speed and temperature that drive variation in daytime aerial density and insect displacements speeds with increasing altitude (150–1200 m above ground level). We derived average aerial densities and displacement speeds of 1.7 million insects in the daytime convective atmospheric boundary layer using vertical-looking entomological radars. We first studied patterns of insect aerial densities and displacements speeds over a decade and linked these with average temperatures and wind velocities from a numerical weather prediction model. Generalized linear mixed models showed that average insect densities decline with increasing wind speed and increase with increasing temperatures and that the relationship between displacement speed and density was negative. We then sought to derive how general these patterns were over space using a paired site approach in which the relationship between sites was examined using simple linear regression. Both average speeds and densities were predicted remotely from a site over 100 km away, although insect densities were much noisier due to local ‘spiking’. By late morning and afternoon when insects are migrating in a well-developed convective atmosphere at high altitude, they become much more difficult to predict remotely than during the early morning and at lower altitudes. Overall, our findings suggest that predicting migrating insects at altitude at distances of ≈100 km is promising, but additional radars are needed to parameterise spatial covariance.

Animal Orientation Strategies for Movement in Flows

For organisms that fly or swim, movement results from the combined effects of the moving medium - air or water - and the organism's own locomotion. For larger organisms, propulsion contributes significantly to progress but the flow usually still provides significant opposition or assistance, or produces lateral displacement ('drift'). Animals show a range of responses to flows, depending on the direction of the flow relative to their preferred direction, the speed of the flow relative to their own self-propelled speed, the incidence of flows in different directions and the proportion of the journey remaining. We here present a classification of responses based on the direction of the resulting movement relative to flow and preferred direction, which is applicable to a range of taxa and environments. The responses adopted in particular circumstances are related to the organisms' locomotory and sensory capacities and the environmental cues available. Advances in biologging technologies and particle tracking models are now providing a wealth of data, which often demonstrate a striking level of convergence in the strategies that very different animals living in very different environments employ when moving in a flow.

Influence of Saharan dust outbreaks and atmospheric stability upon vertical profiles of size-segregated aerosols and water vapor

Vertical profiles of aerosols and meteorological parameters were obtained using a hot air balloon and motorized paraglider. They were studied under anticyclonic conditions in four different contexts. Three flights occurred near sunrise, and one took place in the central hours of the day. The effects of North African dust intrusions were analyzed, whose entrance to the study area took place above the Stable Boundary Layer (SBL) in flight 1 and below it in flight 2. These flights have been compared with a non-intrusion situation (flight 3). A fourth flight characterized the profiles in the central hours of the day with a well-formed Convective Boundary Layer (CBL). With respect to the particle number distribution, the results show that not all sizes increase within the presence of an intrusion; during the first flight the smallest particles were not affected. The particle sizes affected in the second flight fell within the 0.35–2.5 μm interval. Under situations of convective dynamics, the reduction percentage of the particle number concentration reduces with increasing altitude, independently of their size, with respect to stability conditions. The negative vertical gradient for aerosols and water vapor, characteristic of a highly stable SBL (flight 3) becomes a constant profile within a CBL (flight 4). There are two situations that seem to alter the negative vertical gradient of the water vapor mixing ratio within the SBL: the presence of an intrusion and the possible stratification of the SBL based on different degrees of stability.

Optimal strategies for insects migrating in the flight boundary layer: mechanisms and consequences

Directed aerial displacement requires that a volant organism's airspeed exceeds ambient wind speed. For biologically relevant altitudes, wind speed increases exponentially with increased height above the ground. Thus, dispersal of most insects is influenced by atmospheric conditions. However, insects that fly close to the Earth's surface displace within the flight boundary layer where insect airspeeds are relatively high. Over the past 17 years, we have studied boundary-layer insects by following individuals as they migrate across the Caribbean Sea and the Panama Canal. Although most migrants evade either drought or cold, nymphalid and pierid butterflies migrate across Panama near the onset of the rainy season. Dragonflies of the genus Pantala migrate in October concurrently with frontal weather systems. Migrating the furthest and thereby being the most difficult to study, the diurnal moth Urania fulgens migrates between Central and South America. Migratory butterflies and dragonflies are capable of directed movement towards a preferred compass direction in variable winds, whereas the moths drift with winds over water. Butterflies orient using both global and local cues. Consistent with optimal migration theory, butterflies and dragonflies adjust their flight speeds in ways that maximize migratory distance traveled per unit fuel, whereas the moths do not. Moreover, only butterflies adjust their flight speed in relation to endogenous fat reserves. It is likely that these insects use optic flow to gauge their speed and drift, and thus must migrate where sufficient detail in the Earth's surface is visible to them. The abilities of butterflies and dragonflies to adjust their airspeed over water indicate sophisticated control and guidance systems pertaining to migration.

Migration of the painted lady butterfly,Vanessa cardui, to north‐eastern Spain is aided by African wind currents

1. Thousands of records of migratory butterfly species such as Vanessa cardui flying just above ground-level on fixed compass bearings have led to the common belief that these insects migrate within the so-called 'flight-boundary layer', where movements are relatively independent of the wind. 2. Given the selective advantages of windborne migration and the existence of a number of observations of flights of V. cardui from the upper levels of the atmosphere, we tested the hypothesis that migration from North Africa to southern Europe in this species is influenced by synoptic-scale wind currents. 3. Even with modern technology, it is extremely difficult to observe high-altitude flights directly, so we rely on an indirect approach that examines whether or not arrival peaks in north-eastern Spain are associated with winds blowing from Africa. 4. Arrivals of V. cardui were determined for the spring period (1 March-27 June, 1997-2006) at 79 sites in the Catalan Butterfly Monitoring Scheme. Wind patterns were described on the basis of synoptic-scale maps, transport models and back-trajectories calculated for each day of the spring period. 5. We found a strong association between migration and winds from North Africa, both for the whole data set (1997-2006; chi(2) = 4.7, P = 0.03) and for a restricted data set that excludes years in which the species was very scarce (chi(2) = 7.26, P = 0.007). 6. Episodes of massive northward migration within the species' flight-boundary layer also coincided with spells of winds from North Africa, suggesting a connection between low-altitude (observational) and high-altitude flights (inferred from wind patterns). 7. Finally, on the assumption that migration in V. cardui is windborne, a source-receptor transport model applied to spring abundance data in north-eastern Spain enables us to identify the most probable population source areas in North Africa.

Aerial distribution, flight behaviour and eggload: their inter‐relationship during dispersal by the sweetpotato whitefly

1. The aerial distribution ofBemisia tabaciGennadius (the sweetpotato whitefly) was studied during the early ascent phase of flight, to test the degree to which dispersal patterns reflect the flight behaviour of individuals.2.Marked whiteflies were trapped at four heights between 0 and 7·2 m above fallow ground, and at six distances between 0 and 100 m from the insect source. Insects were trapped during a 2–3 h period after the initiation of flight activity during the summers of 1995 and 1996.3.Analysis of trap catch data revealed a clear negative exponential relationship between height and aerial distribution, and a slightly weaker negative power relationship between distance and aerial distribution. Marked insects were caught in the uppermost traps adjacent to the source, indicating that a portion of the population had a strong capacity for ascent out of the flight boundary layer.4.Eggload decreased with the height, but not the distance, at which whiteflies were trapped. Mean eggload close to the ground was significantly greater than that for those trapped at 4·8 and 7·2 m, supporting the hypothesis that there is a trade‐off between flight and oogenesis in weak‐flying insects.5.Air temperatures during the trapping periods were positively correlated with the proportion of male and femaleB. tabacicaught in the highest traps, but not in the most distant traps.6.The significance of these results for accurate prediction of whitefly dispersal is discussed, and the importance of individual's behaviour in determining dispersal patterns of small insects is emphasized.

Insect migration: Variability and success in a capricious environment

AbstractStochastic effects of climate and weather have a pervasive influence on the induction, performance and evolution of migration. In wing‐dimorphic species, their influence on habitat quality, and on rates of development of the migrant itself, maintains variation in responses to environmental cues determining wing‐form and migratory behaviour. Migrants flying above their flight boundary layer rely on winds to disperse them across landscapes in which their habitats are distributed. Patterns of distribution of habitat patches, and the influence of changing windspeeds and direction on the displacements of migrants, result in selection for variation in migratory potential at each migration. In subsequent migrations, this variation and stochastic effects of the winds on groundtracks of individual migrants ensure that their destinations ‘sample’ the landscapes they travel over. The extent and resolution of this sampling, by which migrants reach favourable habitats, depend on the components of migratory potential, their mode of inheritance, and genetic correlations between them, as well as on the characteristics of the winds on which they travel.

高速飛行における境界層内気体噴き出しによる熱防御

高速飛行における境界層内気体噴き出しによる熱防御

A Possible Role of the Boundary Layer in Insect Flight

IT has been recently proposed by Greenewalt1 that the observed wing-beat frequency of insects and birds is equivalent to the characteristic frequency of the flight system as a mechanical oscillator. Evidence for this has come primarily from work on those higher orders of insects in which direct neural control of frequency is absent (‘asynchronous’ type of Roeder2). From this point of view the inverse variation of wing-beat frequency with air density reported in some species by Chadwick and Williams3 and Sotavalta4 appears anomalous. Evidence is given here which shows that such an anomaly may be due to a factor hitherto not considered in investigations of the flight of small insects: a variation of effective wing inertia with air density due to a functionally significant additional mass corresponding to a volume of air ‘attached’ to the wings.

Boundary Layer and Wake Survey Measurements in Flight and in the Wind Tunnel

Boundary Layer and Wake Survey Measurements in Flight and in the Wind Tunnel

The Boundary Layer in Flight

THE authorities of the Institute of the Aeronautical Sciences have decided, so I am instructed, that the Wright Brothers' Lecture should deal with subjects upon which the lecturer is engaged at the time, rather than with a general survey of some wide branch of aeronautical knowledge. This decision has the advantage that the lecturer is actively interested in the subject about which he talks, but it leaves to chance the question whether he is in a position to end his lecture with simple and clear cut conclusions. I mention this because the problem upon which we are working at Cambridge, and about which I shall speak, is not yet solved and my lecture must, perforce, be confined to a discussion of aims and methods and of results so far obtained; it does not contain that simple statement of conclusions which is the ultimate aim of all good research. After this explanation you will not, I hope, be disappointed when the lecture ends on a note of interrogation.