As some insect groups are declining at alarming rates, accurate and automated insect monitoring is needed to prioritize habitats for conservation. The dual-band entomological Scheimpflug lidar technique is a promising candidate method for real-time insect monitoring: it allows the detection of thousands of flying insects per day at high temporal and spatial resolutions. The signals contain a plethora of properties which can be assigned to flight heading- and species-specific clues which may improve classification. Here, we introduce a systematic approach to robust dimensionality reduction of entomological lidar range-time intensity matrices (time and range, 2D) of observations, into time dependent vectors (1D) and scalar values (0D) which encode features related to the flight heading and species characteristics. Using this single-night dataset as a case study, we show that dual-band parameters not only confirm expected patterns of average insect melanization but also enable exploration of signal diversity such as insects that display distinct spectral signatures.

Abstract Nocturnal migration is a remarkable phenomenon observed in many insect species, including moths. Migratory moths are capable of maintaining precise directional orientation during migration, as demonstrated in both laboratory and field studies, suggesting that they use multiple environmental cues for orientation and navigation. Recent studies on Australian Bogong moths revealed that these animals can use stellar cues and likely the geomagnetic field (in conjunction with local visual cues) to select and maintain population-specific migratory direction. However, the underlying orientation mechanisms used by most other migratory moths are still largely unresolved. Further, it remains unclear whether migratory moths can adjust their orientation using Earth’s magnetic field parameters for determining their position relative to the goal (i.e. location or map information) – an ability clearly shown in some migratory birds which respond to virtual magnetic displacements by correcting their orientation (experiments when animals are exposed to magnetic cues corresponding to other geographic locations). Here, we present results from virtual magnetic displacement experiments conducted on red underwings ( Catocala nupta ). In addition, we tested their orientation under simulated overcast conditions and in a vertical magnetic field to get indications whether this species relies on geomagnetic or celestial cues to maintain its population-specific migratory direction. Our results show that (1) red underwings did not compensate for virtual magnetic displacement, indicating the absence of a magnetic map; (2) they remained significantly oriented in the absence of geomagnetic information, suggesting the use of a stellar compass; and (3) there was no evidence of magnetic compass orientation in absence of any visual cues.

Bogong moths (Agrotis infusa) migrate biannually up to 1,000 km between their breeding areas and geographically restricted aestivation sites in the Australian Alps 1,2 . These moths navigate towards their distant goal using the stars as a compass 3 but navigate correctly even when the stars are obscured by clouds 3 , suggesting that their magnetic sense 4 likely harnesses the Earth’s magnetic field as a compass. However, the nature of this compass, and of the magnetic sense underlying it, remain unknown. Here we show that Bogong moths, tethered in a flight arena under a full-spectrum randomised starry night sky, navigate in their inherited migratory direction using the geomagnetic field alone. If both field inclination and polarity are turned by 180°, or if inclination is turned alone, moths fly in the opposite direction. If polarity is turned alone, moths fail to turn. Furthermore, if violet-blue light (380 nm < λ < 500 nm) is removed from the illumination spectrum, or if tethered moths are exposed to weak broadband radiofrequency fields (150 kHz – 60 MHz), magnetic orientation is abolished. Our results indicate that Bogong moths use the geomagnetic field as an inclination compass for long-distance navigation at night and possess a light-dependent radical-pair-based magnetic sense 5 .

Each spring, billions of Bogong moths escape hot conditions across southeast Australia by migrating up to 1,000 km to a place that they have never previously visited—a limited number of cool caves in the Australian Alps, historically used for aestivating over summer 1,2 . At the beginning of autumn, the same individuals make a return migration to their breeding grounds to reproduce and die. Here we show that Bogong moths use the starry night sky as a compass to distinguish between specific geographical directions, thereby navigating in their inherited migratory direction towards their distant goal. By tethering spring and autumn migratory moths in a flight simulator 3–5 , we found that, under naturalistic moonless night skies and in a nulled geomagnetic field (disabling the moth’s known magnetic sense 4 ), moths flew in their seasonally appropriate migratory directions. Visual interneurons in different regions of the moth’s brain responded specifically to rotations of the night sky and were tuned to a common sky orientation, firing maximally when the moth was headed southwards. Our results suggest that Bogong moths use stellar cues and the Earth’s magnetic field to create a robust compass system for long-distance nocturnal navigation towards a specific destination.

The seasonal migrations of insects involve a substantial displacement of biomass with significant ecological and economic consequences for regions of departure and arrival. Remote sensors have played a pivotal role in revealing the magnitude and general direction of bioflows above 150 m. Nevertheless, the takeoff and descent activity of insects below this height is poorly understood. Our lidar observations elucidate the low-height dusk movements and detailed information of insects in southern Sweden from May to July, during the yearly northward migration period. Importantly, by filtering out moths from other insects based on optical information and wingbeat frequency, we have introduced a promising new method to monitor the flight activities of nocturnal moths near the ground, many of which participate in migration through the area. Lidar thus holds the potential to enhance the scientific understanding of insect migratory behavior and improve pest control strategies.

Introduction: The Bogong moth Agrotis infusa is well known for its remarkable annual round-trip migration from its breeding grounds across eastern and southern Australia to its aestivation sites in the Australian Alps, to which it provides an important annual influx of nutrients. Over recent years, we have benefited from a growing understanding of the navigational abilities of the Bogong moth. Meanwhile, the population of Bogong moths has been shrinking. Recently, the ecologically and culturally important Bogong moth was listed as endangered by the IUCN Red List, and the establishment of a program for long-term monitoring of its population has been identified as critical for its conservation.Methods: Here, we present the results of two years of monitoring of the Bogong moth population in the Australian Alps using recently developed methods for automated wildlife-camera monitoring of flying insects, named Camfi. While in the Alps, some moths emerge from the caves in the evening to undertake seemingly random flights, filling the air with densities in the dozens per cubic metre. The purpose of these flights is unknown, but they may serve an important role in Bogong moth navigation.Results: We found that these evening flights occur throughout summer and are modulated by daily weather factors. We present a simple heuristic model of the arrival to and departure from aestivation sites by Bogong moths, and confirm results obtained from fox-scat surveys which found that aestivating Bogong moths occupy higher elevations as the summer progresses. Moreover, by placing cameras along two elevational transects below the summit of Mt. Kosciuszko, we found that evening flights were not random, but were systematically oriented in directions relative to the azimuth of the summit of the mountain. Finally, we present the first recorded observations of the impact of bushfire smoke on aestivating Bogong moths - a dramatic reduction in the size of a cluster of aestivating Bogong moths during the fire, and evidence of a large departure from the fire-affected area the day after the fire.Discussion: Our results highlight the challenges of monitoring Bogong moths in the wild and support the continued use of automated camera-based methods for that purpose.

Many species of insects undertake long-range, seasonally reversed migrations, displaying sophisticated orientation behaviors to optimize their migratory trajectories. However, when invasive insects arrive in new biogeographical regions, it is unclear if migrants retain (or how quickly they regain) ancestral migratory traits, such as seasonally preferred flight headings. Here we present behavioral evidence that an invasive migratory pest, the fall armyworm moth (Spodoptera frugiperda), a native of the Americas, exhibited locally adaptive migratory orientation less than three years after arriving on a new continent. Specimens collected from China showed flight orientations directed north-northwest in spring and southwest in autumn, and this would promote seasonal forward and return migrations in East Asia. We also show that the driver of the seasonal switch in orientation direction is photoperiod. Our results thus provide a clear example of an invasive insect that has rapidly exhibited adaptive migratory behaviors, either inherited or newly evolved, in a completely alien environment.

The ability to measure flying insect activity and abundance is important for ecologists, conservationists and agronomists alike. However, existing methods are laborious and produce data with low temporal resolution (e.g. trapping and direct observation), or are expensive, technically complex, and require vehicle access to field sites (e.g. radar and lidar entomology). We propose a method called "Camfi" for long-term non-invasive population monitoring and high-throughput behavioural observation of low-flying insects using images and videos obtained from wildlife cameras, which are inexpensive and simple to operate. To facilitate very large monitoring programs, we have developed and implemented a tool for automatic detection and annotation of flying insect targets in still images or video clips based on the popular Mask R-CNN framework. This tool can be trained to detect and annotate insects in a few hours, taking advantage of transfer learning. Our method will prove invaluable for ongoing efforts to understand the behaviour and ecology of declining insect populations and could also be applied to agronomy. The method is particularly suited to studies of low-flying insects in remote areas, and is suitable for very large-scale monitoring programs, or programs with relatively low budgets.

During their period of summer dormancy, Australian Bogong moths Agrotis infusa undertake seemingly random evening flights, filling the air with densities in the dozens per cubic metre. The purpose of these flights is unknown, but they may serve an important role in Bogong moth navigation, which remarkably enables them to return to the same exact summer sites— generation after generation—after migrating around 1000 km, and with no opportunity to learn their route or destination from prior generations. The recent development of the camera-based insect monitoring method, Camfi, enables quantitative observations of Bogong moth behaviour at an unprecedented scale. To gain a better understanding of the summer evening flights of Bogong moths, we have extended Camfi to facilitate automated video tracking of flying insects, taking the already-high throughput of the method to a new level. We used this new method to record the evening flight behaviour of Bogong moths in two elevational transects below the summit of Mt. Kosciuszko, NSW, on a single night in February 2021, and found that these flights were not random, but were systematically oriented in directions relative to the azimuth of the summit of the mountain. These results stimulate interesting and plausible hypotheses relating to previously unexplained summer evening flight behaviour of Bogong moths, and the mechanisms of their long-distance navigation.

Insects are well known for their ability to keep track of their heading direction based on a combination of skylight cues and visual landmarks. This allows them to navigate back to their nest, disperse throughout unfamiliar environments, as well as migrate over large distances between their breeding and non-breeding habitats. The monarch butterfly (Danaus plexippus), for instance, is known for its annual southward migration from North America to certain trees in Central Mexico. To maintain a constant flight route, these butterflies use a time-compensated sun compass, which is processed in a region in the brain, termed the central complex. However, to successfully complete their journey, the butterflies' brain must generate a multitude of orientation strategies, allowing them to dynamically switch from sun-compass orientation to a tactic behavior toward a certain target. To study whether monarch butterflies exhibit different orientation modes and if they can switch between them, we observed the orientation behavior of tethered flying butterflies in a flight simulator while presenting different visual cues to them. We found that the butterflies' behavior depended on the presented visual stimulus. Thus, while a dark stripe was used for flight stabilization, a bright stripe was fixated by the butterflies in their frontal visual field. If we replaced a bright stripe with a simulated sun stimulus, the butterflies switched their behavior and exhibited compass orientation. Taken together, our data show that monarch butterflies rely on and switch between different orientation modes, allowing the animal to adjust orientation to its actual behavioral demands.

The Bogong moth Agrotis infusa is well known for its remarkable annual round-trip migration from its breeding grounds across eastern Australia to its aestivation sites in the Australian Alps, to which it provides an important annual influx of nutrients. Over recent years, we have benefited from a growing understanding of the navigational abilities of the Bogong moth. Meanwhile, the population of Bogong moths has been shrinking. Recently, the ecologically and culturally important Bogong moth was listed as endangered by the IUCN Red List, and the establishment of a program for long-term monitoring of its population has been identified as critical for its conservation. Here, we present the results of two years of monitoring of the Bogong moth population in the Australian Alps using a recently developed method for automated monitoring of flying insects, named Camfi. We found that the evening flights of Bogong moths occur throughout summer, and are modulated by daily weather factors. We present a simple heuristic model of the arrival to and departure from aestivation sites by Bogong moths, and confirm results obtained from fox-scat surveys which found that aestivating Bogong moths occupy higher elevations as the summer progresses. We also present the first recorded observations of the impact of bushfire smoke on aestivating Bogong moths. We observed a dramatic reduction in the size of a cluster of aestivating Bogong moths during the fire, and evidence of a large departure from the fire-affected area the day after the fire. Our results highlight the challenges of monitoring Bogong moths in the wild, and support the continued use of automated camera-based methods for that purpose.

Flight-induced compass representation in the monarch butterfly heading 1 network 2 3 M. Jerome Beetz 1*, Christian Kraus1, Myriam Franzke1, David Dreyer2, Martin F. Strube-Bloss3, 4 Wolfgang Rössler1, Eric J. Warrant2, Christine Merlin4, Basil el Jundi1* 5 6 Affiliations 7 1Zoology II, Biocenter, University of Würzburg, Würzburg, Germany 8 2Lund Vision Group, Department of Biology, Lund University, Lund, Sweden 9 3Department of Biological Cybernetics, University of Bielefeld, Bielefeld, Germany 10 4Department of Biology and Center for Biological Clocks Research, Texas A&M, College Station, TX, 11 USA 12 13 *Corresponding authors 14

Head direction can be represented in a self-centered egocentric or a viewpoint-invariant allocentric reference frame. Using the most efficient representation is especially crucial for migrating animals, like monarch butterflies (Danaus plexippus) that use the sun for orientation. With tetrode recordings from the brain of tethered flying monarch butterflies, we examined the reference frame in which insects encode heading. We show that compass neurons switch their reference frame in a state-dependent manner. In quiescence, they encode sun-bearing angles, allowing the butterfly to map the environment within an egocentric frame. However, during flight, the same neurons encode heading within an allocentric frame. This switch converts the sun from a local to a global cue, an ideal strategy for maintaining a migratory heading over large distance. One-Sentence Summary Heading information is encoded in different state-dependent reference frames in the monarch butterfly central complex

For navigation, animals use a robust internal compass. Compass navigation is especially crucial for long-distance migrating animals like monarch butterflies, which use a sun compass to navigate every fall over 4,000 km to their overwintering sites. The central complex, a brain region equipped with sun-compass neurons, is proposed to control the butterfly’s heading. Although the activity of central-complex neurons exhibits a locomotor-dependent modulation in many insects, the consequences of such modulations for the coding of heading remain unexplored. Here, we developed tetrode recordings from tethered flying monarch butterflies to reveal how flight modulates heading representation. We found that during flight, heading-direction neurons change their tuning, transforming the central-complex network to function as a global compass. This compass coding is characterized by the dominance of steering feedback and allows for robust heading representation even under unreliable visual scenarios, an ideal strategy for maintaining a migratory heading over enormous distances.

Studying the routes flown by long-distance migratory insects comes with the obvious challenge that the animal’s body size and weight is comparably low. This makes it difficult to attach relatively heavy transmitters to these insects in order to monitor their migratory routes (as has been done for instance in several species of migratory birds. However, the rather delicate anatomy of insects can be advantageous for testing their capacity to orient with respect to putative compass cues during indoor experiments under controlled conditions. Almost 20 years ago, Barrie Frost and Henrik Mouritsen developed a flight simulator which enabled them to monitor the heading directions of tethered migratory Monarch butterflies, both indoors and outdoors. The design described in the original paper has been used in many follow-up studies to describe the orientation capacities of mainly diurnal lepidopteran species. Here we present a modification of this flight simulator design that enables studies of nocturnal long-distance migration in moths while allowing controlled magnetic, visual and mechanosensory stimulation. This modified flight simulator has so far been successfully used to study the sensory basis of migration in two European and one Australian migratory noctuid species.

The ability to measure flying insect activity and abundance is important for ecologists, conservationists and agronomists alike. However, existing methods are laborious and produce data with low temporal resolution (e.g. trapping and direct observation), or are expensive, technically complex, and require vehicle access to field sites (e.g. radar and lidar entomology). We propose a method called “camfi” for long-term non-invasive monitoring of the activity and abundance of low-flying insects using images obtained from inexpensive wildlife cameras, which retail for under USD$100 and are simple to operate. We show that in certain circumstances, this method facilitates measurement of wingbeat frequency, a diagnostic parameter for species identification. To increase usefulness of our method for very large monitoring programs, we have developed and implemented a tool for automatic detection and annotation of flying insect targets based on the popular Mask R-CNN framework. This tool can be trained to detect and annotate insects in a few hours, taking advantage of transfer learning. We demonstrate the utility of the method by measuring activity levels and wingbeat frequencies in Australian Bogong moths Agrotis infusa in the Snowy Mountains of New South Wales, and find that these moths have log-normally distributed wingbeat frequencies (mean = 49.4 Hz, std = 5.25 Hz), undertake dusk flights in large numbers, and that the intensity of their dusk flights is modulated by daily weather factors. Validation of our tool for automatic image annotation gives baseline performance metrics for comparisons with future annotation models. The tool performs well on our test set, and produces annotations which can be easily modified by hand if required. Training completed in less than 2 h on a single machine, and inference took on average 1.15 s per image on a laptop. Our method will prove invaluable for ongoing efforts to understand the behaviour and ecology of the iconic Bogong moth, and can easily be adapted to other flying insects. The method is particularly suited to studies on low-flying insects in remote areas, and is suitable for very large-scale monitoring programs, or programs with relatively low budgets.

Monarch butterflies (Danaus plexippus) are prominent for their annual long-distance migration from North America to their overwintering area in Central Mexico. To find their way on this long journey, they use a sun compass as their main orientation reference but will also adjust their migratory direction with respect to mountain ranges. This indicates that the migratory butterflies also attend to the panorama to guide their travels. Although the compass has been studied in detail in migrating butterflies, little is known about the orientation abilities of non-migrating butterflies. Here, we investigated whether non-migrating butterflies -which stay in a more restricted area to feed and breed - also use a similar compass system to guide their flights. Performing behavioral experiments on tethered flying butterflies in an indoor LED flight simulator, we found that the monarchs fly along straight tracks with respect to a simulated sun. When a panoramic skyline was presented as the only orientation cue, the butterflies maintained their flight direction only during short sequences, suggesting that they potentially use it for flight stabilization. We further found that when we presented the two cues together, the butterflies incorporate both cues in their compass. Taken together, we show here that non-migrating monarch butterflies can combine multiple visual cues for robust orientation, an ability that may also aid them during their migration.

The Bogong moth Agrotis infusa is well known for its remarkable long‐distance migration – a return journey from the plains of southeast Australia to the Australian Alps – as well as for its cultural significance for Indigenous Australians. Each spring, as many as four billion moths are estimated to arrive in the Australian Alps to aestivate in cool mountain caves and in boulder fields, bringing with them a massive annual influx of energy and nutrients critical for the health of the alpine ecosystem. However, a massive decline in moths present at their aestivation sites has occurred over the past 3 years, with only a few individuals present where hundreds of thousands could earlier be found. In order to understand the possible sources of decline, we analysed historical records of Bogong moth numbers at aestivation sites in the Australian Alps, including observations on Mt. Gingera (NSW) in the early 1950s, observations from 1980 onwards in the Snowy Mountains (NSW) and an almost‐unbroken series of observations each summer over the past 53 years in three caves at different elevations on Mt. Buffalo (Victoria). This analysis shows that moth numbers were probably steady from 1951 until about 1980, fluctuated and slowly fell from then until 2016 and dramatically crashed in 2017. In the Murray–Darling Basin, the main winter breeding ground of Bogong moths, changes in farming practices, such as increasing land clearing for crops (which has removed around a quarter of a billion moths annually from the mountains compared to pre‐European levels), has probably driven some of the decline in Bogong moth numbers observed from 1980 to 2016. The impact of insecticide remains unclear and is in urgent need of further study. Even though we found little evidence that increasing global temperatures per se are responsible for the Bogong moth decline, the Australian climate has nonetheless become drier and warmer over past decades, possibly hampering the survival of immature stages in the breeding areas and confining adult aestivation to gradually higher elevations. The crash in moth numbers from 2017 is most likely due to the recent severe drought in the moth's breeding grounds.

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.

Like many birds [1], numerous species of nocturnal moths undertake spectacular long-distance migrations at night [2]. Each spring, billions of Bogong moths (Agrotis infusa) escape hot conditions in different regions of southeast Australia by making a highly directed migration of over 1,000 km to a limited number of cool caves in the Australian Alps, historically used for aestivating over the summer [3, 4]. How moths determine the direction of inherited migratory trajectories at night and locate their destination (i.e., navigate) is currently unknown [5-7]. Here we show that Bogong moths can sense the Earth's magnetic field and use it in conjunction with visual landmarks to steer migratory flight behavior. By tethering migrating moths in an outdoor flight simulator [8], we found that their flight direction turned predictably when dominant visual landmarks and a natural Earth-strength magnetic field were turned together, but that the moths became disoriented within a few minutes when these cues were set in conflict. We thus conclude that Bogong moths, like nocturnally migrating birds [9], can use a magnetic sense. Our results represent the first reliable demonstration of the use of the Earth's magnetic field to steer flight behavior in a nocturnal migratory insect.