Artificial light at night has increased significantly in recent decades, profoundly impacting moths, which are key contributors to pollination networks. The global shift to light‐emitting diode (LED) streetlights has further transformed the nocturnal light environment, especially because of their high variability in spectrum and intensity. However, the impact on moths' mating success remains poorly understood, highlighting the urgent need to investigate their behavioural responses. We recorded the flight behaviour of male moths ( Sphinx ligustri L.) using a symmetrical flight tunnel. Two different light environments, homogeneous and heterogeneous, with a female positioned on one side of the tunnel, were used to test in different combinations the effect of LEDs (Amber, Warm white and Neutral white) and intensities (0.05, 150, 370 and 590 lux) on arrival location, flight duration and direction changes of males. In a homogeneous light environment, all tested LEDs significantly reduced the arrival frequency of males at the females compared with a dim light condition, demonstrating that streetlight negatively affects encounter rates. However, neither flight duration nor direction changes were significantly affected. In a heterogeneous light environment, the highest proportion of males was able to reach the females in the presence of Warm white (2200 K), indicating that Amber (1800 K) may not be a universal solution for mitigating the negative effects of artificial light. Both flight duration and direction changes were significantly reduced for Neutral white (3900 K) compared with Warm white, concluding that this LED type induced fast and directed flights towards the light source. Interestingly, light intensity did not significantly affect any of the analysed parameters. Statement of significance: The presence of light drastically reduced the probability of males reaching the females. Furthermore, LEDs with the lowest correlated colour temperature (CCT) were not the ones leading to the highest promise of mating success, indicating that the spectrum of an LED might have an optimum. As LED efficiency decreases with lower CCT values this finding is of crucial importance when considering the indirect effects of light pollution, such as the CO 2 footprint, when developing lighting strategies as minimally disruptive as possible.

One of the most dramatic changes occurring on our planet is the ever-increasing extensive use of artificial light at night, which drastically altered the environment to which nocturnal animals are adapted. Such light pollution has been identified as a driver in the dramatic insect decline of the past years. One nocturnal species group experiencing marked declines are moths, which play a key role in food webs and ecosystem services such as plant pollination. Moths can be easily monitored within the illuminated area of a streetlight, where they typically exhibit disoriented behavior. Yet, little is known about their behavior beyond the illuminated area. Harmonic radar tracking enabled us to close this knowledge gap. We found a significant change in flight behavior beyond the illuminated area of a streetlight. A detailed analysis of the recorded trajectories revealed a barrier effect of streetlights on lappet moths whenever the moon was not available as a natural celestial cue. Furthermore, streetlights increased the tortuosity of flights for both hawk moths and lappet moths. Surprisingly, we had to reject our fundamental hypothesis that most individuals would fly toward a streetlight. Instead, this was true for only 4% of the tested individuals, indicating that the impact of light pollution might be more severe than assumed to date. Our results provide experimental evidence for the fragmentation of landscapes by streetlights and demonstrate that light pollution affects movement patterns of moths beyond what was previously assumed, potentially affecting their reproductive success and hampering a vital ecosystem service.

SummaryOne of the most dramatic changes occurring on our planet in recent decades is the ever-increasing extensive use of artificial light at night, which drastically altered the environment nocturnal animals are adapted to 1,2. One nocturnal species group experiencing marked declines are moths, which are not only of great importance for species conservation, but also for their key role in food webs and in ecosystem services such as nocturnal plant pollination 3,4. Light pollution has been identified as a driver in the dramatic insect decline of the past years 5–7, yet little is known about its impact on natural insect orientation behaviour. Using harmonic radar tracking, we show that the orientation of several species of moths is significantly affected by streetlights, although only 4 % of individuals showed flight-to-light behaviour. We reveal a species-specific barrier effect of streetlights on lappet moths whenever the moon was not available as a natural celestial cue. Furthermore, streetlights increased the tortuosity of flight trajectories for both hawk moths and lappet moths. Our results provide the first spatially resolved experimental evidence for the fragmentation of landscapes by streetlights and demonstrate that light pollution affects movement patterns of moths beyond previously assumed extend, potentially affecting their reproductive success and hampering a vital ecosystem service.

To counteract insect decline, it is essential to understand the underlying causes, especially for key pollinators such as nocturnal moths whose ability to orientate can easily be influenced by ambient light conditions. These comprise natural light sources as well as artificial light, but their specific relevance for moth orientation is still unknown. We investigated the influence of moonlight on the reproductive behavior of privet hawkmoths ( Sphinx ligustri ) at a relatively dark site where the Milky Way was visible while the horizon was illuminated by distant light sources and skyglow. We show that male moths use the moon for orientation and reach females significantly faster with increasing moon elevation. Furthermore, the choice of flight direction depended on the cardinal position of the moon but not on the illumination of the horizon caused by artificial light, indicating that the moon plays a key role in the orientation of male moths.

Honeybees, Apis mellifera, perform re-orientation flights to learn about the new surroundings of the hive when their hive is transported to a new location. Since the pattern of re-orientation flights has not yet been studied, we asked whether this form of exploratory behavior differs from the well described exploratory orientation flights performed by young honeybees before they start foraging. We also investigated whether the exploratory components of re-orientation flights differ from foraging flights and if so how. We recorded re-orientation flights using harmonic radar technology and compared the patterns and flight parameters of these flights with the first exploratory orientation flights of young honeybees and foraging flights of experienced foragers. Just as exploratory orientation flights of young honeybees, re-orientation flights can be classified into short- and long-range flights, and most short-range re-orientation flights were performed under unfavorable weather conditions. This indicates that bees adapt the flight pattern of their re-orientation and orientation flights to changing weather conditions in a similar way. Unlike exploratory orientation flights, more than one sector of the landscape was explored during a long-range re-orientation flight, and significantly longer flight durations and flight distances were observed. Thus, re-orienting bees explored a larger terrain than bees performing their first exploratory orientation flight. By displacing some bees after their first re-orientation flight, we could demonstrate that a single re-orientation flight seems to be sufficient to learn the new location of the hive. The flight patterns of re-orientation flights differed clearly from those of foraging flights. Thus, re-orientation flights represent a special exploratory behavior that is triggered by a change in the location of the hive.

Exploration is an elementary and fundamental form of learning about the structure of the world [1-3]. Little is known about what exactly is learned when an animal seeks to become familiar with the environment. Navigating animals explore the environment for safe return to an important place (e.g., a nest site) and to travel between places [4]. Flying central-place foragers like honeybees (Apis mellifera) extend their exploration into distances from which the features of the nest cannot be directly perceived [5-10]. Bees perform short-range and long-range orientations flights. Short-range flights are performed in the immediate surroundings of the hive and occur more frequently under unfavorable weather conditions, whereas long-range flights lead the bees into different sectors of the surrounding environment [11]. Applying harmonic radar technology for flight tracking, we address the question of whether bees learn landscape features during their first short-range or long-range orientation flight. The homing flights of single bees were compared after they were displaced to areas explored or not explored during the orientation flight. Bees learn the landscape features during the first orientation flight since they returned faster and along straighter flights from explored areas as compared to unexplored areas. We excluded a range of possible factors that might have guided bees back to the hive based on egocentric navigation strategies (path integration, beacon orientation, and pattern matching of the skyline). We conclude that bees localize themselves according to learned ground structures and their spatial relations to the hive.

Honeybees, Apis mellifera, perform exploratory orientation flights before they start foraging in order to become familiar with the terrain. To reveal the structure of consecutive orientation flights and hence gain insight into exploratory behaviour, we monitored individual bees from their first flight onwards using harmonic radar technology for flight tracking. We categorized flights into short- and long-range orientation flights. (1) Short-range flights are likely to be related to learning the specific features of the hive's immediate surroundings, and were performed significantly more frequently under unfavourable weather conditions. (2) The duration of long-range orientation flights declined from the first to the fourth flight because the bees spent less time inspecting the immediate surroundings of the hive. (3) Parts of single orientation flights were guided by extended parallel landscape structures on the ground. (4) During consecutive orientation flights bees explored novel sectors of the terrain. (5) Foraging flights performed after orientation flights covered greater distances and may involve a sector of the terrain not explored before, indicating that the acquired visual information plus path integration is sufficient for successful homing even from unfamiliar areas. (6) Exploration may be mixed with foraging flights after the initial orientation flights, sometimes leading to extremely long and elaborate flights. The latter are interpreted as being performed by scout bees. The results are interpreted within the frame of the psychology of exploratory behaviour in animals. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.