The effect of surface topography on the ball-rolling ability of Kheper lamarcki (Scarabaeidae).

The most effective way to avoid intense inter- and intra-specific competition at the dung source, and to increase the distance to the other competitors, is to follow a single straight bearing. While ball-rolling dung beetles manage to roll their dung balls along nearly perfect straight paths when traversing flat terrain, the paths that they take when traversing more complex (natural) terrain are not well understood. In this study, we investigate the effect of complex surface topographies on the ball-rolling ability of Kheper lamarcki. Our results reveal that ball-rolling trajectories are strongly influenced by the characteristic scale of the surface structure. Surfaces with an increasing similarity between the average distance of elevations and the ball radius cause progressively more difficulties during ball transportation. The most important factor causing difficulties in ball transportation appears to be the slope of the substrate. Our results show that, on surfaces with a slope of 7.5 deg, more than 60% of the dung beetles lose control of their ball. Although dung beetles still successfully roll their dung ball against the slope on such inclinations, their ability to roll the dung ball sideways diminishes. However, dung beetles do not seem to adapt their path on inclines such that they roll their ball in the direction against the slope. We conclude that dung beetles strive for a straight trajectory away from the dung pile, and that their actual path is the result of adaptations to particular surface topographies.

Bumblebee thermoregulation at increasing temperatures is affected by behavioral state.

Over the past decades, increasing environmental temperatures have been identified as one of the causes of major insect population declines and biodiversity loss. However, it is unclear how these rising temperatures affect endoheterothermic insects, like bumblebees, that have evolved thermoregulatory capacities to exploit cold and temperate habitats. To investigate this, we measured head, thoracic, and abdominal temperature of bumblebee (Bombus terrestris) workers across a range of temperatures (24 °C-32 °C) during three distinct behaviors. In resting bumblebees, the head, abdomen, and thorax conformed to the environmental temperature. In pre-flight bumblebees, the head and abdominal temperatures were elevated with respect to the environmental temperature, while the thoracic temperature was maintained, indicating a pre-flight muscle warming stage. In post-flight bumblebees, abdominal temperature increased at the same rate as environmental temperature, but the head and the thoracic temperature did not. By calculating the excess temperature ratio, we show that thermoregulation in bumblebees during flight is partially achieved by the active transfer of heat produced in the thorax to the abdomen, where it can more easily be dissipated. These results provide the first indication that the thermoregulatory abilities of bumblebees are plastic and behavior dependent. We also show that the flight speed and number of workers foraging increase with increasing temperature, suggesting that bees do not avoid flying at these temperatures despite its impact on behavioral performance.

Shining a light on species coexistence: visual traits drive bumblebee communities.

Local coexistence of bees has been explained by flower resource partitioning, but coexisting bumblebee species often have strongly overlapping diets. We investigated if light microhabitat niche separation, underpinned by visual traits, could serve as an alternative mechanism underlying local coexistence of bumblebee species. To this end, we focused on a homogeneous flower resource-bilberry-in a heterogeneous light environment-hemi-boreal forests. We found that bumblebee communities segregated along a gradient of light intensity. The community-weighted mean of the eye parameter-a metric measuring the compromise between light sensitivity and visual resolution-decreased with light intensity, showing a higher investment in light sensitivity of communities observed in darker conditions. This pattern was consistent at the species level. In general, species with higher eye parameter (larger investment in light sensitivity) foraged in dimmer light than those with a lower eye parameter (higher investment in visual resolution). Moreover, species realized niche optimum was linearly related to their eye parameter. These results suggest microhabitat niche partitioning to be a potential mechanism underpinning bumblebee species coexistence. This study highlights the importance of considering sensory traits when studying pollinator habitat use and their ability to cope with changing environments.

Airborne! UAV delivery of blood products and medical logistics for combat zones.

BACKGROUND: Innovative solutions to resupply critical medical logistics and blood products may be required in future near-peer conflicts. Unmanned aerial vehicles (UAVs) are increasingly being used in austere environments and may be a viable platform for medical resupply and the transport of blood products. METHODS: A literature review on PubMed and Google Scholar up to March of 2022 yielded a total of 27 articles that were included in this narrative review. The objectives of this article are to discuss the current limitations of prehospital blood transfusion in military settings, discuss the current uses of UAVs for medical logistics, and highlight the ongoing research surrounding UAVs for blood product delivery. DISCUSSION: UAVs allow for the timely delivery of medical supplies in numerous settings and have been utilized for both military and civilian purposes. Investigations into the effects of aeromedical transportation on blood products have found minimal blood product degradation when appropriately thermoregulated and delivered in a manner that minimizes trauma. UAV delivery of blood products is now actively being explored by numerous entities around the globe. Current limitations surrounding the lack of high-quality safety data, engineering constraints over carrying capacity, storage capability, and distance traveled, as well as air space regulations persist. CONCLUSION: UAVs may offer a novel solution for the transport of medical supplies and blood products in a safe and timely manner for the forward-deployed setting. Further research on optimal UAV design, optimal delivery techniques, and blood product safety following transport should be explored prior to implementation.

Elevated developmental temperatures impact the size and allometry of morphological traits of the bumblebee Bombus terrestris.

The impact of global warming on wild bee decline threatens the pollination services they provide. Exposure to temperatures above optimal during development is known to reduce adult body size but how it affects the development and scaling of body parts remains unclear. In bees, a reduction in body size and/or a reduction in body parts, such as the antennae, tongue and wings, and how they scale with body size (i.e. their allometry) could severely affect their fitness. To date, it remains unclear how temperature affects body size and the scaling of morphological traits in bees. To address this knowledge gap, we exposed both males and workers of Bombus terrestris to elevated temperature during development and assessed the effects on (i) the size of morphological traits and (ii) the allometry between these traits. Colonies were exposed to optimal (25°C) or stressful (33°C) temperatures. We then measured the body size, wing size, antenna and tongue length, as well as the allometry between these traits. We found that workers were smaller and the antennae of both castes were reduced at the higher temperature. However, tongue length and wing size were not affected by developmental temperature. The allometric scaling of the tongue was also affected by developmental temperature. Smaller body size and antennae could impair both individual and colony fitness, by affecting foraging efficiency and, consequently, colony development. Our results encourage further exploration of how the temperature-induced changes in morphology affect functional traits and pollination efficiency.

Visual guidance of honeybees approaching a vertical landing surface.

Landing is a critical phase for flying animals, whereby many rely on visual cues to perform controlled touchdown. Foraging honeybees rely on regular landings on flowers to collect food crucial for colony survival and reproduction. Here, we explored how honeybees utilize optical expansion cues to regulate approach flight speed when landing on vertical surfaces. Three sensory-motor control models have been proposed for landings of natural flyers. Landing honeybees maintain a constant optical expansion rate set-point, resulting in a gradual decrease in approach velocity and gentile touchdown. Bumblebees exhibit a similar strategy, but they regularly switch to a new constant optical expansion rate set-point. In contrast, landing birds fly at a constant time to contact to achieve faster landings. Here, we re-examined the landing strategy of honeybees by fitting the three models to individual approach flights of honeybees landing on platforms with varying optical expansion cues. Surprisingly, the landing model identified in bumblebees proved to be the most suitable for these honeybees. This reveals that honeybees adjust their optical expansion rate in a stepwise manner. Bees flying at low optical expansion rates tend to increase their set-point stepwise, while those flying at high optical expansion rates tend to decrease it stepwise. This modular landing control system enables honeybees to land rapidly and reliably under a wide range of initial flight conditions and visual landing platform patterns. The remarkable similarity between the landing strategies of honeybees and bumblebees suggests that this may also be prevalent among other flying insects. Furthermore, these findings hold promising potential for bioinspired guidance systems in flying robots.

Online case-based educational meetings can increase knowledge, skills, and widen access to surgical training:The nationwideVirtualTrauma & Orthopaedic Meetingseries.

BACKGROUND: Access to surgical training is challenging for undergraduate and early postgraduate trainees due to a greater focus on developing generic knowledge and skills, and a drive to recruit greater numbers into internal medicine and primary care. COVID-19 accelerated the declining access to surgical training environments. Our aims were to: 1) establish the feasibility of an online, specialty-specific, case-based surgical training series, and 2) evaluate its suitability for meeting the needs of trainees. METHODS: A nationwide audience of undergraduate and early postgraduate trainees were invited to a series of bespoke online case-based educational meetings in Trauma & Orthopaedics (T&O) over a six month period. The six sessions, which simulated real-world clinical meetings, were constructed by Consultant sub-specialists and involved the presentation of cases by registrars, followed by structured discussion of basic principles, radiological interpretation, and management strategies. Mixed qualitative and quantitative analyses were conducted. RESULTS: There were 131 participants (59.5% male), consisting mostly of doctors in training (58%) and medical students (37.4%). The mean quality rating was 9.0/10 (SD 1.06), further supported by qualitative analysis. 98% enjoyed the sessions, 97% reported improved knowledge of T&O, and 94% reported a direct benefit to clinical practice. There was a significant improvement in knowledge of T&O conditions, management plans, and radiological interpretation (p = <0.05). CONCLUSION: Structured virtual meetings, underpinned by bespoke clinical cases, may widen access to T&O training, increase flexibility and robustness of learning opportunities, and mitigate the effects of reduced exposure on preparation for surgical careers and recruitment.

Exposure to elevated temperature during development affects eclosion and morphology in the temperate Pieris napi butterfly (Lepidoptera: Pieridae).

Global warming has been identified as one of the main drivers of population decline in insect pollinators. One aspect of the insect life cycle that would be particularly sensitive to elevated temperatures is the developmental transition from larva to adult. Temperature-induced modifications to the development of body parts and sensory organs likely have functional consequences for adult behaviour. To date, we have little knowledge about the effect of sub-optimal temperature on the development and functional morphology of different body parts, particularly sensory organs, in ectothermic solitary pollinators such as butterflies. To address this knowledge gap, we exposed the pupae of the butterfly Pieris napi to either 23 °C or 32 °C and measured the subsequent effects on eclosion, body size and the development of the wings, proboscis, eyes and antennae. In comparison to individuals that developed at 23 °C, we found that exposure to 32 °C during the pupal stage increased mortality and decreased time to eclose. Furthermore, both female and male butterflies that developed at 32 °C were smaller and had shorter proboscides, while males had shorter antennae. In contrast, we found no significant effect of rearing temperature on wing and eye size or wing deformity. Our findings suggest that increasing global temperatures and its corresponding co-stressors, such as humidity, will impact the survival of butterflies by impairing eclosion and the proper development of body and sensory organs.

Allometric scaling of a superposition eye optimizes sensitivity and acuity in large and small hawkmoths.

Animals vary widely in body size within and across species. This has consequences for the function of organs and body parts in both large and small individuals. How these scale, in relation to body size, reveals evolutionary investment strategies, often resulting in trade-offs between functions. Eyes exemplify these trade-offs, as they are limited by their absolute size in two key performance features: sensitivity and spatial acuity. Due to their size polymorphism, insect compound eyes are ideal models for studying the allometric scaling of eye performance. Previous work on apposition compound eyes revealed that allometric scaling led to poorer spatial resolution and visual sensitivity in small individuals, across a range of insect species. Here, we used X-ray microtomography to investigate allometric scaling in superposition compound eyes-the second most common eye type in insects-for the first time. Our results reveal a novel strategy to cope with the trade-off between sensitivity and spatial acuity, as we show that the eyes of the hummingbird hawkmoth retain an optimal balance between these performance measures across all body sizes.

Short-term exposure to heatwave-like temperatures affects learning and memory in bumblebees.

Global warming has been identified as a key driver of bee declines around the world. While it is clear that elevated temperatures during the spring and summer months-the principal activity period of many bee species-is a factor in this decline, exactly how temperature affects bee survival is unknown. In vertebrates, there is clear evidence that elevated ambient temperatures impair cognition but whether and how heat affects the cognitive abilities of invertebrates remains unclear. Cognitive skills in bees are essential for their survival as, to supply the hive with nutrition, workers must be able to learn and remember the location of the most rewarding floral resources. Here, we investigate whether temperature-related cognitive impairments could be a driver of bee declines by exploring the effect of short-term increases in ambient temperature on learning and memory. We found that, in comparison to bees that were tested at 25°C (a temperature that they would typically experience in summer), bees that were exposed to 32°C (a temperature that they will becoming increasingly exposed to during heatwave events) were significantly worse at forming an association between a coloured light and a sucrose reward and that their capacity to remember this association after just 1 h was abolished. This study provides novel experimental evidence that even just a few hours of exposure to heatwave-like temperatures can severely impair the cognitive performance of insects. Such temperature-induced cognitive deficits could play an important role in explaining recent and future bee population declines.

Spatial tuning of translational optic flow responses in hawkmoths of varying body size.

To safely navigate their environment, flying insects rely on visual cues, such as optic flow. Which cues insects can extract from their environment depends closely on the spatial and temporal response properties of their visual system. These in turn can vary between individuals that differ in body size. How optic flow-based flight control depends on the spatial structure of visual cues, and how this relationship scales with body size, has previously been investigated in insects with apposition compound eyes. Here, we characterised the visual flight control response limits and their relationship to body size in an insect with superposition compound eyes: the hummingbird hawkmoth Macroglossum stellatarum. We used the hawkmoths' centring response in a flight tunnel as a readout for their reception of translational optic flow stimuli of different spatial frequencies. We show that their responses cut off at different spatial frequencies when translational optic flow was presented on either one, or both tunnel walls. Combined with differences in flight speed, this suggests that their flight control was primarily limited by their temporal rather than spatial resolution. We also observed strong individual differences in flight performance, but no correlation between the spatial response cutoffs and body or eye size.

Spatial resolution and sensitivity of the eyes of the stingless bee, Tetragonula iridipennis.

Stingless bees are important pollinators in the tropics. The tremendous variation in body size makes them an excellent group to study how miniaturization affects vision and visual behaviours. Using direct measurements and micro-CT, we reconstructed the eye structure, estimated anatomical spatial resolution and optical sensitivity of the stingless bee Tetragonula iridipennis. T. iridipennis is similar in size to the Australian stingless bee Tetragonula carbonaria and is smaller than honeybees. It has correspondingly small eyes (area = 0.56 mm2), few ommatidia (2451 ± 127), large inter-facet (3.0 ± 0.6°) and acceptance angles (2.8°). Theoretical estimates suggest that T. iridipennis has poorer spatial resolution (0.17 cycles degree-1) than honeybees, bumblebees, and T. carbonaria. Its optical sensitivity (0.08 µm2 sr), though higher than expected, is within the range of diurnal bees. This may provide them with greater contrast sensitivity, which is likely more relevant than the absolute sensitivity in this diurnal bee. Behaviourally determined detection thresholds for single targets using y-maze experiments were 11.5° for targets that provide chromatic contrast alone and 9.1° for targets providing chromatic and achromatic contrast. Further studies into microhabitat preferences and behaviour are required to understand how miniaturization influences its visual ecology.

Multimodal cue integration in the dung beetle compass.

South African ball-rolling dung beetles exhibit a unique orientation behavior to avoid competition for food: after forming a piece of dung into a ball, they efficiently escape with it from the dung pile along a straight-line path. To keep track of their heading, these animals use celestial cues, such as the sun, as an orientation reference. Here we show that wind can also be used as a guiding cue for the ball-rolling beetles. We demonstrate that this mechanosensory compass cue is only used when skylight cues are difficult to read, i.e., when the sun is close to the zenith. This raises the question of how the beetles combine multimodal orientation input to obtain a robust heading estimate. To study this, we performed behavioral experiments in a tightly controlled indoor arena. This revealed that the beetles register directional information provided by the sun and the wind and can use them in a weighted manner. Moreover, the directional information can be transferred between these 2 sensory modalities, suggesting that they are combined in the spatial memory network in the beetle's brain. This flexible use of compass cue preferences relative to the prevailing visual and mechanosensory scenery provides a simple, yet effective, mechanism for enabling precise compass orientation at any time of the day.

How Dung Beetles Steer Straight.

Distant and predictable features in the environment make ideal compass cues to allow movement along a straight path. Ball-rolling dung beetles use a wide range of different signals in the day or night sky to steer themselves along a fixed bearing. These include the sun, the Milky Way, and the polarization pattern generated by the moon. Almost two decades of research into these remarkable creatures have shown that the dung beetle's compass is flexible and readily adapts to the cues available in its current surroundings. In the morning and afternoon, dung beetles use the sun to orient, but at midday, they prefer to use the wind, and at night or in a forest, they rely primarily on polarized skylight to maintain straight paths. We are just starting to understand the neuronal substrate underlying the dung beetle's compass and the mystery of why these beetles start each journey with a dance.

The effect of optic flow cues on honeybee flight control in wind.

To minimize the risk of colliding with the ground or other obstacles, flying animals need to control both their ground speed and ground height. This task is particularly challenging in wind, where head winds require an animal to increase its airspeed to maintain a constant ground speed and tail winds may generate negative airspeeds, rendering flight more difficult to control. In this study, we investigate how head and tail winds affect flight control in the honeybee Apis mellifera, which is known to rely on the pattern of visual motion generated across the eye-known as optic flow-to maintain constant ground speeds and heights. We find that, when provided with both longitudinal and transverse optic flow cues (in or perpendicular to the direction of flight, respectively), honeybees maintain a constant ground speed but fly lower in head winds and higher in tail winds, a response that is also observed when longitudinal optic flow cues are minimized. When the transverse component of optic flow is minimized, or when all optic flow cues are minimized, the effect of wind on ground height is abolished. We propose that the regular sidewards oscillations that the bees make as they fly may be used to extract information about the distance to the ground, independently of the longitudinal optic flow that they use for ground speed control. This computationally simple strategy could have potential uses in the development of lightweight and robust systems for guiding autonomous flying vehicles in natural environments.

Laboratory phase-contrast nanotomography of unstained Bombus terrestris compound eyes.

Imaging the visual systems of bumblebees and other pollinating insects may increase understanding of their dependence on specific habitats and how they will be affected by climate change. Current high-resolution imaging methods are either limited to two dimensions (light- and electron microscopy) or have limited access (synchrotron radiation x-ray tomography). For x-ray imaging, heavy metal stains are often used to increase contrast. Here, we present micron-resolution imaging of compound eyes of buff-tailed bumblebees (Bombus terrestris) using a table-top x-ray nanotomography (nano-CT) system. By propagation-based phase-contrast imaging, the use of stains was avoided and the microanatomy could more accurately be reconstructed than in samples stained with phosphotungstic acid or osmium tetroxide. The findings in the nano-CT images of the compound eye were confirmed by comparisons with light- and transmission electron microscopy of the same sample and finally, comparisons to synchrotron radiation tomography as well as to a commercial micro-CT system were done.

Accelerated landing in a stingless bee and its unexpected benefits for traffic congestion.

To land, flying animals must simultaneously reduce speed and control their path to the target. While the control of approach speed has been studied in many different animals, little is known about the effect of target size on landing, particularly for small targets that require precise trajectory control. To begin to explore this, we recorded the stingless bees Scaptotrigona depilis landing on their natural hive entrance-a narrow wax tube built by the bees themselves. Rather than decelerating before touchdown as most animals do, S. depilis accelerates in preparation for its high precision landings on the narrow tube of wax. A simulation of traffic at the hive suggests that this counterintuitive landing strategy could confer a collective advantage to the colony by minimizing the risk of mid-air collisions and thus of traffic congestion. If the simulated size of the hive entrance increases and if traffic intensity decreases relative to the measured real-world values, 'accelerated landing' ceases to provide a clear benefit, suggesting that it is only a useful strategy when target cross-section is small and landing traffic is high. We discuss this strategy in the context of S. depilis' ecology and propose that it is an adaptive behaviour that benefits foraging and nest defence.

Straight-line orientation in the woodland-living beetle Sisyphus fasciculatus.

To transport their balls of dung along a constant bearing, diurnal savannah-living dung beetles rely primarily on the sun for compass information. However, in more cluttered environments, such as woodlands, this solitary compass cue is frequently hidden from view by surrounding vegetation. In these types of habitats, insects can, instead, rely on surrounding landmarks, the canopy pattern, or wide-field celestial cues, such as polarised skylight, for directional information. Here, we investigate the compass orientation strategy behind straight-line orientation in the diurnal woodland-living beetle Sisyphus fasciculatus. We found that, when manipulating the direction of polarised skylight, Si. fasciculatus responded to this change with a similar change in bearing. However, when the apparent position of the sun was moved, the woodland-living beetle did not change its direction of travel. In contrast, the savannah-living beetle Scarabaeus lamarcki responded to the manipulation of the solar position with a corresponding change in bearing. These results suggest that the dominant compass cue used for straight-line orientation in dung beetles may be determined by the celestial cue that is most prominent in their preferred habitat.

Obstacle avoidance in bumblebees is robust to changes in light intensity.

Flying safely and avoiding obstacles in low light is crucial for the bumblebees that forage around dawn and dusk. Previous work has shown that bumblebees overcome the limitations of their visual system-typically adapted for bright sunlight-by increasing the time over which they sample photons. While this improves visual sensitivity, it decreases their capacity to resolve fast motion. This study investigates what effect this has on obstacle avoidance in flight, a task that requires the bees to reliably detect obstacles in the frontal visual field and to make a timely diversion to their flight path. In both bright and dim light, bumblebees avoided the 5 cm diameter obstacle at a consistent distance (22 cm) although in dim light they approached it more slowly from a distance of at least at least 80 cm. This suggests that bumblebees have an effective strategy for avoiding obstacles in all light conditions under which they are naturally active, and it is hypothesised that this is based on a time-to-contact prediction.

A dung beetle that path integrates without the use of landmarks.

Unusual amongst dung beetles, Scarabaeus galenus digs a burrow that it provisions by making repeated trips to a nearby dung pile. Even more remarkable is that these beetles return home moving backwards, with a pellet of dung between their hind legs. Here, we explore the strategy that S. galenus uses to find its way home. We find that, like many other insects, they use path integration to calculate the direction and distance to their home. If they fail to locate their burrow, the beetles initiate a distinct looping search behaviour that starts with a characteristic sharp turn, we have called a 'turning point'. When homing beetles are passively displaced or transferred to an unfamiliar environment, they initiate a search at a point very close to the location of their fictive burrow-that is, a spot at the same relative distance and direction from the pick-up point as the original burrow. Unlike other insects, S. galenus do not appear to supplement estimates of the burrow location with landmark information. Thus, S. galenus represents a rare case of a consistently backward-homing animal that does not use landmarks to augment its path integration strategy.