垂直监测昆虫雷达研究进展

昆虫雷达可以远距离、 大范围、 快速地探测迁飞昆虫, 这极大促进了人类对昆虫迁飞行为的认识。垂直监测昆虫雷达技术是从20世纪70年代发展起来的一种监测高空迁飞昆虫种群的新工具。与传统的扫描雷达相比, 垂直监测昆虫雷达可以获得目标的位移速度、 位移方向、 定向、 体型大小和形状等参数, 因此, 对目标的识别能力更为精确。此外, 垂直监测昆虫雷达实现了在微机控制下的自动运行, 这使得应用昆虫雷达开展迁飞昆虫的日常监测成为可能。本文综述了垂直监测昆虫雷达的发展和应用, 介绍了设计原理和回波参数的解算方法, 讨论了其存在的不足及改进方案, 最后并对其在未来昆虫雷达网络建设中的应用进行了展望。     

Orientation Cues for High-Flying Nocturnal Insect Migrants: Do Turbulence-Induced Temperature and Velocity Fluctuations Indicate the Mean Wind Flow?

Migratory insects flying at high altitude at night often show a degree of common alignment, sometimes with quite small angular dispersions around the mean. The observed orientation directions are often close to the downwind direction and this would seemingly be adaptive in that large insects could add their self-propelled speed to the wind speed, thus maximising their displacement in a given time. There are increasing indications that high-altitude orientation may be maintained by some intrinsic property of the wind rather than by visual perception of relative ground movement. Therefore, we first examined whether migrating insects could deduce the mean wind direction from the turbulent fluctuations in temperature. Within the atmospheric boundary-layer, temperature records show characteristic ramp-cliff structures, and insects flying downwind would move through these ramps whilst those flying crosswind would not. However, analysis of vertical-looking radar data on the common orientations of nocturnally migrating insects in the UK produced no evidence that the migrants actually use temperature ramps as orientation cues. This suggests that insects rely on turbulent velocity and acceleration cues, and refocuses attention on how these can be detected, especially as small-scale turbulence is usually held to be directionally invariant (isotropic). In the second part of the paper we present a theoretical analysis and simulations showing that velocity fluctuations and accelerations felt by an insect are predicted to be anisotropic even when the small-scale turbulence (measured at a fixed point or along the trajectory of a fluid-particle) is isotropic. Our results thus provide further evidence that insects do indeed use turbulent velocity and acceleration cues as indicators of the mean wind direction.     

Resolving the heading‐direction ambiguity in vertical‐beam radar observations of migrating insects

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WSR-88D doppler radar detection of corn earworm moth migration

Corn earworm (Lepidoptera: Noctuidae) (CEW) populations infesting one crop production area may rapidly migrate and infest distant crop production areas. Although entomological radars have detected corn earworm moth migrations, the spatial extent of the radar coverage has been limited to a small horizontal view above crop production areas. The Weather Service Radar (version 88D) (WSR-88D) continuously monitors the radar-transmitted energy reflected by, and radial speed of, biota as well as by precipitation over areas that may encompass crop production areas. We analyzed data from the WSR-88D radar (S-band) at Brownsville, Texas, and related these data to aerial concentrations of CEW estimated by a scanning entomological radar (X-band) and wind velocity measurements from rawinsonde and pilot balloon ascents. The WSR-88D radar reflectivity was positively correlated (r ²?=?0.21) with the aerial concentration of corn earworm-size insects measured by a scanning X-band radar. WSR-88D radar constant altitude plan position indicator estimates of wind velocity were positively correlated with wind speed (r ²?=?0.56) and wind direction (r ²?=?0.63) measured by pilot balloons and rawinsondes. The results reveal that WSR-88D radar measurements of insect concentration and displacement speed and direction can be used to estimate the migratory flux of corn earworms and other nocturnal insects, information that could benefit areawide pest management programs. In turn, identification of the effects of spatiotemporal patterns of migratory flights of corn earworm-size insects on WSR-88D radar measurements may lead to the development of algorithms that increase the accuracy of WSR-88D radar measurements of reflectivity and wind velocity for operational meteorology.     

Convergent patterns of long-distance nocturnal migration in noctuid moths and passerine birds

Vast numbers of insects and passerines achieve long-distance migrations between summer and winter locations by undertaking high-altitude nocturnal flights. Insects such as noctuid moths fly relatively slowly in relation to the surrounding air, with airspeeds approximately one-third of that of passerines. Thus, it has been widely assumed that windborne insect migrants will have comparatively little control over their migration speed and direction compared with migrant birds. We used radar to carry out the first comparative analyses of the flight behaviour and migratory strategies of insects and birds under nearly equivalent natural conditions. Contrary to expectations, noctuid moths attained almost identical ground speeds and travel directions compared with passerines, despite their very different flight powers and sensory capacities. Moths achieved fast travel speeds in seasonally appropriate migration directions by exploiting favourably directed winds and selecting flight altitudes that coincided with the fastest air streams. By contrast, passerines were less selective of wind conditions, relying on self-powered flight in their seasonally preferred direction, often with little or no tailwind assistance. Our results demonstrate that noctuid moths and passerines show contrasting risk-prone and risk-averse migratory strategies in relation to wind. Comparative studies of the flight behaviours of distantly related taxa are critically important for understanding the evolution of animal migration strategies.     

Environmental effects on flying migrants revealed by radar

Migratory animals are affected by various factors during their journeys, and the study of animal movement by radars has been instrumental in revealing key influences of the environment on flying migrants. Radars enable the simultaneous tracking of many individuals of almost all sizes within the radar range during day and night, and under low visibility conditions. We review how atmospheric conditions, geographic features and human development affect the behavior of migrating insects and birds as recorded by radars. We focus on flight initiation and termination, as well as in‐flight behavior that includes changes in animal flight direction, speed and altitude. We have identified several similarities and differences in the behavioral responses of aerial migrants including an overlooked similarity in the use of thermal updrafts by very small (e.g. aphids) and very large (e.g. vultures) migrants. We propose that many aerial migrants modulate their migratory flights in relation to the interaction between atmospheric conditions and geographic features. For example, aerial migrants that encounter crosswind may terminate their flight or continue their migration and may also drift or compensate for lateral displacement depending on their position (over land, near the coast or over sea). We propose several promising directions for future research, including the development and application of algorithms for tracking insects, bats and large aggregations of animals using weather radars. Additionally, an important contribution will be the spatial expansion of aeroecological radar studies to Africa, most of Asia and South America where no such studies have been undertaken. Quantifying the role of migrants in ecosystems and specifically estimating the number of departing birds from stopover sites using low‐elevation radar scans is important for quantifying migrant–habitat relationships. This information, together with estimates of population demographics and migrant abundance, can help resolve the long‐term dynamics of migrant populations facing large‐scale environmental changes.     

To what extent can the tiny parasitoid wasps,Eretmocerus mundus,fly upwind?

Body miniaturization in insects is predicted to result in decreased flight speed and therefore limited ability of these insects to fly upwind. Therefore, tiny insects are often regarded as relying on passive dispersal by winds. We tested this assumption in a wind tunnel by measuring the burst speed of Eretmocerus mundus (Mercet), a beneficial parasitoid wasp with body length <1 mm. Insects were filmed flying upwind towards a UV light source in a range of wind speed 0–0.5 m/s. The Insects flew towards the UV light in the absence and presence of wind but increased their flight speed in the presence of wind. They also changed flight direction to be directly upwind and maintained this body orientation even while drifted backwards relative to the ground by stronger winds. Field measurements showed that the average flight speed observed in the wind tunnel (0.3 m/s) is sufficient to allow flying between plants even when the wind speed above the vegetation was 3–5 folds higher. A simulation of the ability of the insects to control their flight trajectory towards a visual target (sticky traps) in winds show that the insects can manipulate their progress relative to the ground even when the wind speed exceeds their flight speed. The main factors determining the ability of the insects to reach the trap were trap diameter and the difference between insect flight speed and wind speed. The simulation also predicts the direction of arrival to the sticky target showing that many of the insects reach the target from the leeward side (i.e. by flight upwind). In light of these results, the notion that miniature insects passively disperse by winds is misleading because it disregards the ability of the insects to control their drift relative to the ground in winds that are faster than their flight speed.     

迁飞过程中昆虫的行为:对风温场的适应与选择

本文综述了昆虫在迁飞过程中对大气物理环境的各种行为反应,有边界层气象的理论重新审视迁飞种群的时空分布,提出了“边界层顶现象”的概念。即边界层顶的低空逆温和低空急流为迁飞种群提供了最适宜的风温场,迁飞种群在边界层顶集聚成层,并通过定向理一步修饰其位移方位,表现出对风温场的主动选择能力和对大气结构和运动的高度复杂的适应性反应。进一步深化对“边界层顶现象”的认识,对迁飞性害虫的异地预测具有重要的理论意义     

Doppler radar detection of exceptional mass-migration of aphids into Finland

Our objective was to detect mass migrations of insects of economic significance by insect traps and a Doppler weather radar. Migrants were sampled by suction traps, tow nets and light traps in the Helsinki region. We used radar to observe the migrating insects, and trajectories to backtrack mass migrations of aphids (Homoptera, Aphididae) in spring 1988. The aphid migrations were clearly observed in trap catches and by radar. The first migration, mainly involving Euceraphis betulae, occurred on 18 May and was tracked back to northern Poland. The second migration, mainly of Rhopalosiphum padi (a serious pest of small-grain cereals), occurred 3 days later and was tracked back to a large area covering Latvia and western Russia south of St Petersburg. The third migration included both E. betulae and R. padi, and took place on 30 May. It originated from Estonia. Neither trap nor radar data provide exact quantitative information on migrations. Trapping efficiency depends strongly on wind speed and insect size. Radar echo intensity is very strongly related to the sizes of insects in the large volume of air measured, and the sizes are not known accurately. Weather data, especially temperature, can be used in predicting the development of aphids, and air-parcel trajectories in estimating the source areas of migrants. These methods for forecasting aphid migrations, combined with radar observations, are useful for warning purposes and to intensify insect trapping. This would contribute to more efficient agricultural pest management. Received: 11 March 2000 / Revised: 24 April 2000 / Accepted: 26 April 2000     

Application of lidar remote sensing of insects in agricultural entomology on the Chinese scene

Insect pest management is a very important aspect for plant protection in crops production. Remote sensing provides a large number of techniques that are beneficial in entomological research. Although entomological radars have been used for studying migrations of insects for many years, most of entomological radar studies have been vertically tracing high-altitude migration behaviour of insects. Light detection and ranging (lidar) is a counterpart to radar, now operating in the optical part of the electromagnetic spectrum, which has been recently applied for monitoring of insects at low altitude. Such techniques, in particular low-cost continuous-wave (CW) bi-static systems based on the Scheimpflug arrangement, have been rapidly developing during the last decade. As a result, optical methods present new and fascinating possibilities. Based on experience from a 2-week field campaign in rice paddy fields, we here present an overview of lidar remote sensing applied to the Chinese scene. The capability of a CW Scheimpflug lidar system in monitoring the insects was studied. We present results on insect abundance in relation to time of the day and weather conditions. We also identified insect species by analysing wing-beat frequencies and studied their attraction to ultraviolet (UV) lamp located close to the horizontal laser sampling path during night time. Results showed that the insect species were abundant, that insects detected by the lidar system were attracted to light and that light rain increased the insect activity. The lidar detection system had a high read-out frequency, enabling the estimation of insect wing-beat frequencies.     

迁飞过程中昆虫的行为

根据国内外对昆虫迁飞的雷达观测结果,综述了迁飞过程中昆虫的成层、定向和集聚行为及其生态学意义。昆虫在迁飞过程中不完全是被动地随风飘流,而是在一定程度上自主地选择了自己的运行轨迹。它们选择在气温最高、风力最大和风向最适的高度成层,并通过定向进一步修饰位移方位,从而可最大限度地利用空气动力到达新的栖息地。同时,不同尺度的大气辐合过程使得迁飞昆虫集聚成足以在某种条件下引起局地爆发的高密度种群,而地面大发生种群形成与否取决于大气辐合的发生频率、强度和寿命,以及集聚起来的昆虫是否降落,在何时何地降落,是否还会再迁出等。阐明昆虫在迁飞过程中的各种行为机制是迁飞性害虫测报和防治的关键所在。     

The influence of the atmospheric boundary layer on nocturnal layers of noctuids and other moths migrating over southern Britain

Insects migrating at high altitude over southern Britain have been continuously monitored by automatically operating, vertical-looking radars over a period of several years. During some occasions in the summer months, the migrants were observed to form well-defined layer concentrations, typically at heights of 200-400 m, in the stable night-time atmosphere. Under these conditions, insects are likely to have control over their vertical movements and are selecting flight heights that are favourable for long-range migration. We therefore investigated the factors influencing the formation of these insect layers by comparing radar measurements of the vertical distribution of insect density with meteorological profiles generated by the UK Meteorological Office's (UKMO) Unified Model (UM). Radar-derived measurements of mass and displacement speed, along with data from Rothamsted Insect Survey light traps, provided information on the identity of the migrants. We present here three case studies where noctuid and pyralid moths contributed substantially to the observed layers. The major meteorological factors influencing the layer concentrations appeared to be: (a) the altitude of the warmest air, (b) heights corresponding to temperature preferences or thresholds for sustained migration and (c) on nights when air temperatures are relatively high, wind-speed maxima associated with the nocturnal jet. Back-trajectories indicated that layer duration may have been determined by the distance to the coast. Overall, the unique combination of meteorological data from the UM and insect data from entomological radar described here show considerable promise for systematic studies of high-altitude insect layering.     

Perspectives and challenges for the use of radar in biological conservation

Radar is at the forefront for the study of broad‐scale aerial movements of birds, bats and insects and related issues in biological conservation. Radar techniques are especially useful for investigating species which fly at high altitudes, in darkness, or which are too small for applying electronic tags. Here, we present an overview of radar applications in biological conservation and highlight its future possibilities. Depending on the type of radar, information can be gathered on local‐ to continental‐scale movements of airborne organisms and their behaviour. Such data can quantify flyway usage, biomass and nutrient transport (bioflow), population sizes, dynamics and distributions, times and dimensions of movements, areas and times of mass emergence and swarming, habitat use and activity ranges. Radar also captures behavioural responses to anthropogenic disturbances, artificial light and man‐made structures. Weather surveillance and other long‐range radar networks allow spatially broad overviews of important stopover areas, songbird mass roosts and emergences from bat caves. Mobile radars, including repurposed marine radars and commercially dedicated ‘bird radars’, offer the ability to track and monitor the local movements of individuals or groups of flying animals. Harmonic radar techniques have been used for tracking short‐range movements of insects and other small animals of conservation interest. However, a major challenge in aeroecology is determining the taxonomic identity of the targets, which often requires ancillary data obtained from other methods. Radar data have become a global source of information on ecosystem structure, composition, services and function and will play an increasing role in the monitoring and conservation of flying animals and threatened habitats worldwide.     

昆虫雷达让我们看到了什么?

昆虫雷达的应用深化了人们对昆虫迁飞行为机制的认识。昆虫雷达让我们看到了弱小的昆虫主动起飞 ,以一定的速度爬升到巡航高度乘风远行 ,并对大气风温场表现出令人难以置信的适应和选择能力 ,通过成层 (边界层顶现象 )、定向和集聚等主动行为 ,最大限度地利用空气动力到达新的栖息地。这些全新的画面展示出远迁的昆虫并非完全被动的随风飘流者 ,而是一个个驾舟中流击水的舵手。     

Visual ground pattern modulates flight speed of male Oriental fruit moth Grapholita molesta

Insects flying in a horizontal pheromone plume must attend to visual cues to ensure that they make upwind progress. Moreover, it is suggested that flying insects will also modulate their flight speed to maintain a constant retinal angular velocity of terrestrial contrast elements. Evidence from flies and honeybees supports such a hypothesis, although tests with male moths and beetles flying in pheromone plumes are not conclusive. These insects typically fly faster at higher elevations above a high‐contrast ground pattern, as predicted by the hypothesis, although the increase in speed is not sufficient to demonstrate quantitatively that they maintain constant visual angular velocity of the ground pattern. To test this hypothesis more rigorously, the flight speed of male oriental fruit moths (OFM) Grapholita molesta Busck (Lepidoptera: Tortricidae) flying in a sex pheromone plume in a laboratory wind tunnel is measured at various heights (5–40 cm) above patterns of different spatial wavelength (1.8–90°) in the direction of flight. The OFM modulate their flight speed three‐fold over different patterns. They fly fastest when there is no pattern in the tunnel or the contrast elements are too narrow to resolve. When the spatial wavelength of the pattern is sufficiently wide to resolve, moths fly at a speed that tends to maintain a visual contrast frequency of 3.5 ± 3.2 Hz rather than a constant angular velocity, which varies from 57 to 611° s^?1. In addition, for the first time, it is also demonstrated that the width of a contrast pattern perpendicular to the flight direction modulates flight speed.     

Nocturnal migration of dragonflies over the Bohai Sea in northern China

Abstract.  1. A sudden increase and subsequent sharp decrease of catches of dragonflies in a searchlight trap, with Pantala flavescens Fabricius (Odonata: Libellulidae) predominating, observed at Beihuang Island in the centre of the Bohai Gulf, in 2003 and 2004, indicated a seasonal migration of these insects over the sea during the night in China. The movements were associated with the onset of fog.
2. Simultaneous radar observations indicated that the nocturnally migrating dragonflies generally flew at altitudes of up to 1000 m above sea level, with high density concentrations at about 200–300 or 500 m; these concentrations were coincident with the temperature inversion.
3. During early summer, the dragonflies oriented in a downwind direction, so that the displacement direction varied between different altitudes. In contrast, during late summer, the dragonflies were able to compensate for wind drift, even headwind drift, so as to orient south-westward no matter how the wind changed, and thus the displacement direction was towards the south-west.
4. The duration of flight, estimated from the variation of area density derived from radar data and hourly catches in the searchlight trap through the night, was about 9–10 h. The displacement speed detected using radar was ≈5–11 m s⁻¹. Therefore, the dragonflies might migrate 150–400 km in a single flight.
5. The dragonflies were thought to originate in Jiangsu province and they migrated into north-east China to exploit the temporary environment of paddy fields in early summer. Their offspring probably migrated back south during late summer and autumn.     

A New Approach to Quantify Semiochemical Effects on Insects Based on Energy Landscapes

Introduction

Our ability to document insect preference for semiochemicals is pivotal in pest control as these agents can improve monitoring and be deployed within integrated pest management programmes for more efficacious control of pest species. However, methods used to date have drawbacks that limit their utility. We present and test a new concept for determining insect motivation to move towards, or away from, semiochemicals by noting direction and speed of movement as animals work against a defined energy landscape (environmentally dependent variation in the cost of transport) requiring different powers to negotiate. We conducted trials with the pine weevils Hylobius abietis and peach-potato aphids Myzus persicae exposed to various attractants and repellents and placed so that they either moved up defined slopes against gravity or had to travel over variously rough surfaces.

Results

Linear Mixed Models demonstrated clear reductions in travel speed by insects moving along increasingly energetically taxing energy landscapes but also that responses varied according to different semiochemicals, thus highlighting the value of energy landscapes as a new concept to help measure insect motivation to access or avoid different attractants or repellents across individuals.

Conclusions

New sensitive, detailed indicators of insect motivation derived from this approach should prove important in pest control across the world.     

Quantifying interspecific variation in dispersal ability of noctuid moths using an advanced tethered flight technique

Dispersal plays a crucial role in many aspects of species' life histories, yet is often difficult to measure directly. This is particularly true for many insects, especially nocturnal species (e.g. moths) that cannot be easily observed under natural field conditions. Consequently, over the past five decades, laboratory tethered flight techniques have been developed as a means of measuring insect flight duration and speed. However, these previous designs have tended to focus on single species (typically migrant pests), and here we describe an improved apparatus that allows the study of flight ability in a wide range of insect body sizes and types. Obtaining dispersal information from a range of species is crucial for understanding insect population dynamics and range shifts. Our new laboratory tethered flight apparatus automatically records flight duration, speed, and distance of individual insects. The rotational tethered flight mill has very low friction and the arm to which flying insects are attached is extremely lightweight while remaining rigid and strong, permitting both small and large insects to be studied. The apparatus is compact and thus allows many individuals to be studied simultaneously under controlled laboratory conditions. We demonstrate the performance of the apparatus by using the mills to assess the flight capability of 24 species of British noctuid moths, ranging in size from 12–27 mm forewing length (~40–660 mg body mass). We validate the new technique by comparing our tethered flight data with existing information on dispersal ability of noctuids from the published literature and expert opinion. Values for tethered flight variables were in agreement with existing knowledge of dispersal ability in these species, supporting the use of this method to quantify dispersal in insects. Importantly, this new technology opens up the potential to investigate genetic and environmental factors affecting insect dispersal among a wide range of species.     

Do bird captures reflect migration intensity? – Trapping numbers on an Alpine pass compared with radar counts

A limitation of standardized mist netting for monitoring migration is caused by the lack of knowledge about the relationship between trapped birds and birds flying aloft. Earlier studies related nocturnal radar counts with trapping data of the following day. In this study, we compared for the first time data gathered simultaneously by radar and mist netting, separately for diurnal and nocturnal migration. Trapping numbers were strongly correlated with migratory intensities measured by radar (r>0.6). A multiple regression analysis, including wind speed and wind direction explained 61% of variation in the number of captures. During the night, and particularly with favourable winds, birds flew at higher altitudes and hence escaped the nets to a higher proportion. The number of nocturnal migrants trapped during daytime was well correlated with migratory intensities observed by radar in the preceding night. The diurnal time patterns, however, revealed fundamental differences between trapping counts and radar observations. This was mainly due to increasing and decreasing flight altitudes in the course of the night, and by the limitations of the radar technique that underestimates migratory intensities during the day when birds aggregate in flocks. In relation to the migratory intensity recorded by radar, diurnal migrants are trapped in a much higher proportion than nocturnal migrants. Finally, our results confirm that trapping data from a site hardly used for stopover are well suited to represent the ongoing migration during the day and night.     

Slaves of the environment: the movement of herbivorous insects in relation to their ecology and genotype

The majority of insect species do not show an innate behavioural migration, but rather populations expand into favourable new habitats or contract away from unfavourable ones by random changes of spatial scale. Over the past 50 years, the scientific fascination with dramatic long-distance and directed mass migratory events has overshadowed the more universal mode of population movement, involving much smaller stochastic displacement during the lifetime of the insects concerned. This may be limiting our understanding of insect population dynamics. In the following synthesis, we provide an overview of how herbivorous insect movement is governed by both abiotic and biotic factors, making these animals essentially ''slaves of their environment''. No displaced insect or insect population can leave a resource patch, migrate and flourish, leaving descendants, unless suitable habitat and/or resources are reached during movement. This must have constrained insects over geological time, bringing about species-specific adaptation in behaviour and movements in relation to their environment at a micro- and macrogeographical scale. With insects that undergo long-range spatial displacements, e.g. aphids and locusts, there is presumably a selection against movement unless overruled by factors, such as density-dependent triggering, which cause certain genotypes within the population to migrate. However, for most insect species, spatial changes of scale and range expansion are much slower and may occur over a much longer time-scale, and are not innate (nor directed). Ecologists may say that all animals and plants are figuratively speaking ''slaves of their environments'', in the sense that their distribution is defined by their ecology and genotype. But in the case of insects, a vast number must perish daily, either out at sea or over other hostile habitats, having failed to find suitable resources and/or a habitat on which to feed and reproduce. Since many are blown by the vagaries of the wind, their chances of success are serendipitous in the extreme, especially over large distances. Hence, the strategies adopted by mass migratory species (innate pre-programmed flight behaviour, large population sizes and/or fast reproduction), which improve the chances that some of these individuals will succeed. We also emphasize the dearth of knowledge in the various interactions of insect movement and their environment, and describe how molecular markers (protein and DNA) may be used to examine the details of spatial scale over which movement occurs in relation to insect ecology and genotype.