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Many insects depend on high-altitude, migratory movements during part of their life cycle. The daily timing of these migratory movements is not random, e.g. many insect species show peak migratory flight activity at dawn, noon or dusk. These insects provide essential ecosystem services such as pollination but also contribute to crop damage. Quantifying the diel timing of their migratory flight and its geographical and seasonal variation, are hence key towards effective conservation and pest management. Vertical-looking radars provide continuous and automated measurements of insect migration, but large-scale application has not been possible because of limited availability of suitable devices. Here, we quantify patterns in diel flight periodicity of migratory insects between 50 and 500 m above ground level during March-October 2021 using a network of 17 vertical-looking radars across Europe. Independent of the overall daily migratory movements and location, peak migratory movements occur around noon, during crepuscular evening and occasionally the morning. Relative daily proportions of insect migration intensity and traffic during the diel phases of crepuscular-morning, day, crepuscular-evening and night remain largely equal throughout May-September and across Europe. These findings highlight, extend, and generalize previous regional-scale findings on diel migratory insect movement patterns to the whole of temperate Europe. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'. [ABSTRACT FROM AUTHOR]

Despite mass movements of insects being documented for decades, whether dragonflies migrate in Europe has not yet been experimentally tested. Similarly, little is known about the influence of weather on the movement decisions and intensity of dragonflies. Taking advantage of large movements of dragonflies along the Baltic Sea coast of Latvia, we investigated whether European dragonflies showed directed movements indicative of migratory behaviour and how weather influences their movements. First, we performed orientation tests with individual dragonflies of two commonly captured species, Aeshna mixta and Sympetrum vulgatum , to determine whether dragonflies showed directed flight and whether flight direction differed from wind direction. Both A. mixta and S. vulgatum displayed a uniform mean southward orientation, which differed from the prevailing overhead wind direction, indicating migratory behaviour. Second, we investigated the influence of weather conditions on the abundance of dragonflies captured. Differences in flight behaviour in relation to weather conditions were observed between A. mixta and the two smaller Sympetrum species (S. vulgatum and S. sanguineum). Generally, temperature, cloud cover and wind direction were the most important predictors for dragonfly abundance, with temperature positively, and cloud cover negatively, influencing abundance. Aeshna mixta appeared to select favourable tail winds (northerlies), whereas abundance of Sympetrum increased with more easterly winds. Our results provide important information on the influence of local weather conditions on the flight behaviour of dragonflies, as well as evidence of dragonfly migration along the Baltic coast. • Evidence for dragonfly migration along the Baltic coast in Europe. • Aeshna mixta and Sympetrum vulgatum show directed southward flight. • Temperature, cloud cover and wind direction predict migration intensity. • Migratory Aeshna and Sympetrum species respond differently to local weather. • The migrant hawker A. mixta selects for favourable tail winds. [ABSTRACT FROM AUTHOR]

Migratory insects may move in large numbers, even surpassing migratory vertebrates in biomass. Long-distance migratory insects complete annual cycles through multiple generations, with each generation's reproductive success linked to the resources available at different breeding grounds. Climatic anomalies in these grounds are presumed to trigger rapid population outbreaks. Here, we infer the origin and track the multigenerational path of a remarkable outbreak of painted lady (Vanessa cardui) butterflies that took place at an intercontinental scale in Europe, the Middle East, and Africa from March 2019 to November 2019. Using metabarcoding, we identified pollen transported by 264 butterflies captured in 10 countries over 7 months and modeled the distribution of the 398 plants detected. The analysis showed that swarms collected in Eastern Europe in early spring originated in Arabia and the Middle East, coinciding with a positive anomaly in vegetation growth in the region from November 2018 to April 2019. From there, the swarms advanced to Northern Europe during late spring, followed by an early reversal toward southwestern Europe in summer. The pollen-based evidence matched spatiotemporal abundance peaks revealed by citizen science, which also suggested an echo effect of the outbreak in West Africa during September-November. Our results show that population outbreaks in a part of species' migratory ranges may disseminate demographic effects across multiple generations in a wide geographic area. This study represents an unprecedented effort to track a continuous multigenerational insect migration on an intercontinental scale., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Modelling ecological niches of migratory animals requires incorporating a temporal dimension, in addition to space. Here, we introduce an approach to model multigenerational migratory insects using time-partitioned environmental variables (by months and years) and time- and behaviour-partitioned records (breeding records to model reproductive habitat). We apply this methodology to modelling the Palearctic-African migratory cycle of the Painted Lady butterfly (Vanessa cardui), based on data encompassing 36 years (646 breeding sites from 30 countries). Each breeding record is linked to a particular time (month and year), and the associated values of the bioclimatic variables are used for an ensemble modelling strategy, to finally obtain monthly projections. The results show obligated movements, mostly latitudinal, for the species' successive generations across the overall range, and only scattered locations show high probabilities of reproduction year-round. The southernmost reproductive areas estimated for the Palearctic-African migratory pool reach equatorial latitudes from December to February. We thus propose a potential distribution for the winter 'missing generations' that would expand the V. cardui migration cycle to encompass about 15 000 km in latitude, from northernmost Europe to equatorial Africa. In summer, Europe represents the major temporary resource for V. cardui, while January and February show the lowest overall suitability values, and they are potentially the most vulnerable period for the species to suffer yearly bottlenecks. In summary, we demonstrate the potential of the proposed niche modelling strategy to investigate migratory movements of insects. [ABSTRACT FROM AUTHOR]

Large parts of the continents are continuously scanned by terrestrial weather radars to monitor precipitation and wind conditions. These systems also monitor the mass movements of bird, bat, and insect migration, but it is still unknown how many of these systems perform with regard to detection and quantification of migration intensities of the different groups. In this study that was undertaken within five regions across Europe and the Middle East we examined to what extent bird migration intensities derived from different weather radars are comparable between each other and relate to intensities measured by local small‐scaled radars, some of them specifically developed to monitor birds. Good correspondence was found for the relative day‐to‐day pattern in migration intensities among most radar systems that were compared. Absolute intensities varied between different systems and regions. The findings of this study can be used to infer about absolute bird migration intensities measured by different radar systems and consequently help resolving methodological issues regarding the estimation of migrant numbers in the Western‐Palearctic region. It further depicts a scientific basis for the future monitoring of migratory bird populations across a large spatio‐temporal scale, predicting their movements and studying its consequences on ecological systems and human lives. [ABSTRACT FROM AUTHOR]

Migratory insects are key players in ecosystem functioning and services, but their spatiotemporal distributions are typically poorly known. Ecological niche modeling (ENM) may be used to predict species seasonal distributions, but the resulting hypotheses should eventually be validated by field data. The painted lady butterfly ( Vanessa cardui ) performs multigenerational migrations between Europe and Africa and has become a model species for insect movement ecology. While the annual migration cycle of this species is well understood for Europe and northernmost Africa, it is still unknown where most individuals spend the winter. Through ENM, we previously predicted suitable breeding grounds in the subhumid regions near the tropics between November and February. In this work, we assess the suitability of these predictions through i) extensive field surveys and ii) two-year monitoring in six countries: a large-scale monitoring scheme to study butterfly migration in Africa. We document new breeding locations, year-round phenological information, and hostplant use. Field observations were nearly always predicted with high probability by the previous ENM, and monitoring demonstrated the influence of the precipitation seasonality regime on migratory phenology. Using the updated dataset, we built a refined ENM for the Palearctic-African range of V. cardui . We confirm the relevance of the Afrotropical region and document the missing natural history pieces of the longest migratory cycle described in butterflies.

Long-range, seasonal migration is a widespread phenomenon among insects, allowing them to track and exploit abundant but ephemeral resources over vast geographical areas. However, the basic patterns of how species shift across multiple locations and seasons are unknown in most cases, even though migrant species comprise an important component of the temperate-zone biota. The painted lady butterfly Vanessa cardui is such an example; a cosmopolitan continuously-brooded species which migrates each year between Africa and Europe, sometimes in enormous numbers. The migration of 2009 was one of the most impressive recorded, and thousands of observations were collected through citizen science programmes and systematic entomological surveys, such as high altitude insect-monitoring radar and ground-based butterfly monitoring schemes. Here we use V. cardui as a model species to better understand insect migration in the Western Palaearctic, and we capitalise on the complementary data sources available for this iconic butterfly. The migratory cycle in this species involves six generations, encompassing a latitudinal shift of thousands of kilometres (up to 60 degrees of latitude). The cycle comprises an annual poleward advance of the populations in spring followed by an equatorward return movement in autumn, with returning individuals potentially flying thousands of kilometres. We show that many long-distance migrants take advantage of favourable winds, moving downwind at high elevation (from some tens of metres from the ground to altitudes over 1000 m), pointing at strong similarities in the flight strategies used by V. cardui and other migrant Lepidoptera. Our results reveal the highly successful strategy that has evolved in these insects, and provide a useful framework for a better understanding of long-distance seasonal migration in the temperate regions worldwide. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This note is based on a literature search and a recent review of bat mortality data from wind farms in Europe (published elsewhere). We suggest that mortality of bats at wind turbines may be linked to high-altitude feeding on migrating insects that accumulate at the turbine towers. Modern wind turbines seem to reach high enough into the airspace to interfere with the migratory movements of insects. The hypothesis is consistent with recent observations of bats at wind turbines. It is supported by the observation that mortality of bats at wind turbines is highly seasonal (August-September) and typically peaks during nights with weather conditions known to trigger large-scale migratory movements of insects (and songbirds). We also discuss other current hypotheses concerning the mortality of bats at wind turbines. [ABSTRACT FROM AUTHOR]

The continuous operation of insect-monitoring radars in the UK has permitted, for the first time, the characterization of various phenomena associated with highaltitude migration of large insects over this part of northern Europe. Previous studies have taken a case-study approach, concentrating on a small number of nights of particular interest. Here, combining data from two radars, and from an extensive suction- and light-trapping network, we have undertaken a more systematic, longer-term study of diel flight periodicity and vertical distribution of macro-insects in the atmosphere. Firstly, we identify general features of insect abundance and stratification, occurring during the 24-hour cycle, which emerge from four years' aggregated radar data for the summer months in southern Britain. These features include mass emigrations at dusk and, to a lesser extent, at dawn and daytime concentrations associated with thermal convection. We then focus our attention on the well-defined layers of large nocturnal migrants that form in the early evening, usually at heights of 200-500m above ground. We present evidence from both radar and trap data that these nocturnal layers are composed mainly of noctuid moths, with species such as Noctua pronuba, Autographa gamma, Agrotis exclamationis, A. segetum, Xestia c-nigrum and Phlogophora meticulosa predominating. [ABSTRACT FROM AUTHOR]

When honeybee, Apis mellifera, swarms lift off to fly to their new nest site, only a small proportion of individuals know the location of the new site, yet these few individuals must guide the entire swarm to the correct place. How do scouts transfer directional information to their swarm-mates? The vision hypothesis proposes that scout bees fly rapidly through swarms ‘pointing’ in the direction of travel. We examined the vision hypothesis by exposing flying swarms to a large number of fast-moving bees headed in the wrong direction. These bees mimicked scouts and created conflicting directional information. Swarms that were exposed to conflicting information from fast-moving bees showed clear evidence of disrupted guidance including splitting and failure to reach the nestbox. We discuss the implications of our findings for hypotheses about the mechanisms of swarm guidance, and for our knowledge of how collectively moving groups deal with conflicting information. [Copyright &y& Elsevier]

Many latitudinal insect migrants including agricultural pests, disease vectors, and beneficial species show huge fluctuations in the year-to-year abundance of spring immigrants reaching temperate zones. It is widely believed that this variation is driven by climatic conditions in the winter-breeding regions, but evidence is lacking. We identified the environmental drivers of the annual population dynamics of a cosmopolitan migrant butterfly (the painted lady Vanessa cardui ) using a combination of long-term monitoring and climate and atmospheric data within the western part of its Afro-Palearctic migratory range. Our population models show that a combination of high winter NDVI (normalized difference vegetation index) in the Savanna/Sahel of sub-Saharan Africa, high spring NDVI in the Maghreb of North Africa, and frequent favorably directed tailwinds during migration periods are the three most important drivers of the size of the immigration to western Europe, while our atmospheric trajectory simulations demonstrate regular opportunities for wind-borne trans-Saharan movements. The effects of sub-Saharan vegetative productivity and wind conditions confirm that painted lady populations on either side of the Sahara are linked by regular mass migrations, making this the longest annual insect migration circuit so far known. Our results provide a quantification of the environmental drivers of large annual population fluctuations of an insect migrant and hold much promise for predicting invasions of migrant insect pests, disease vectors, and beneficial species., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Despite the fact that migratory insects dominate aerial bioflows in terms of diversity, abundance, and biomass [ 1–6 ], the migration patterns of most species, and the effects of their annual fluxes between high- and low-latitude regions, are poorly known. One important group of long-range migrants that remain understudied is a suite of highly beneficial species of hoverfly in the tribe Syrphini, which we collectively term "migrant hoverflies." Adults are key pollinators [ 7–10 ] and larvae are significant biocontrol agents of aphid crop pests [ 11 ], and thus, it is important to quantify the scale of their migrations and the crucial ecosystem services they provide with respect to energy, nutrient, and biomass transport; regulation of crop pests; and pollen transfer. Such assessments cannot be made by sporadic observations of mass arrivals at ground level, because hoverflies largely migrate unnoticed high above ground. We used insect-monitoring radars [ 12 ] to show that up to 4 billion hoverflies (80 tons of biomass) travel high above southern Britain each year in seasonally adaptive directions. The long-range migrations redistribute tons of essential nutrients (nitrogen [N] and phosphorus [P]) and transport billions of pollen grains between Britain and Europe, and locally produced populations consume 6 trillion aphids and make billions of flower visits. Migrant hoverfly abundance fluctuated greatly between years, but there was no evidence of a population trend during the 10-year study period. Considering that many beneficial insects are seriously declining [ 7, 10, 13–19 ], our results demonstrate that migrant hoverflies are key to maintaining essential ecosystem services. • Between 1 and 4 billion hoverflies migrate into and out of southern Britain each year • These migrants provide important pest control by consuming 3–10 trillion aphids • They also provide extensive pollination services and long-range pollen transfer • Migrant hoverflies play a vital role due to declines of other beneficial insects Wotton et al. show that hoverflies have seasonally adaptive migration directions, allowing colonization of high-latitude summer breeding areas before their progeny return in autumn. Hoverflies deliver vital biocontrol and pollination services and are increasingly important, as their numbers are stable while other beneficial insects are declining. [ABSTRACT FROM AUTHOR]

Insect migrations are spectacular natural events and resemble a remarkable relocation of biomass between two locations in space. Unlike the well-known migrations of daytime flying butterflies, such as the painted lady ( Vanessa cardui ) or the monarch butterfly ( Danaus plexippus ), much less widely known are the migrations of nocturnal moths. These migrations - typically involving billions of moths from different taxa - have recently attracted considerable scientific attention. Nocturnal moth migrations have traditionally been investigated by light trapping and by observations in the wild, but in recent times a considerable improvement in our understanding of this phenomenon has come from studying insect orientation behaviour, using vertical-looking radar. In order to establish a new model organism to study compass mechanisms in migratory moths, we tethered each of two species of central European Noctuid moths in a flight simulator to study their flight bearings: the red underwing ( Catocala nupta ) and the large yellow underwing ( Noctua pronuba ). Both species had significantly oriented flight bearings under an unobscured view of the clear night sky and in the Earth's natural magnetic field. Red underwings oriented south-southeast, while large yellow underwings oriented southwest, both suggesting a southerly autumn migration towards the Mediterranean. Interestingly, large yellow underwings became disoriented on humid (foggy) nights while red underwings remained oriented. We found no evidence in either species for a time-independent sky compass mechanism as previously suggested for the large yellow underwing., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)