A novel method to measure hairiness in bees and other insect pollinators

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

Flower-bee versus pollen-bee metanetworks in fragmented landscapes

Understanding the organization of mutualistic networks at multiple spatial scales is key to ensure biological conservation and functionality in human-modified ecosystems. Yet, how changing habitat and landscape features affect pollen-bee interaction networks is still poorly understood. Here, we analysed how bee-flower visitation and bee-pollen-transport interactions respond to habitat fragmentation at the local network and regional metanetwork scales, combining data from 29 fragments of calcareous grasslands, an endangered biodiversity hotspot in central Europe. We found that only 37% of the total unique pairwise species interactions occurred in both pollen-transport and flower visitation networks, whereas 28% and 35% were exclusive to pollen-transport and flower visitation networks, respectively. At local level, network specialization was higher in pollen-transport networks, and was negatively related to the diversity of land cover types in both network types. At metanetwork level, pollen transport data revealed that the proportion of single-fragment interactions increased with landscape diversity. Our results show that the specialization of calcareous grasslands' plant-pollinator networks decreases with landscape diversity, but network specialization is underestimated when only based on flower visitation information. Pollen transport data, more than flower visitation, and multi-scale analyses of metanetworks are fundamental for understanding plant-pollinator interactions in human-dominated landscapes.

Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas

The western honey bee (Apis mellifera L.) is the most globally used managed pollinator species, but it can have limited pollinating activity on nectariferous crops displaying anthers isolated from stigmas, i.e., when anthers are spatially or temporally separated from stigma within or between flowers. We supplemented honey bee colonies with pollen in the combs or in paste form laid on top of the hive frames to test if these treatments could reduce their pollen foraging and increase their pollinating activity in a monoecious and nectariferous cultivar of cantaloupe melon (Cucumis melo L.), in comparison with control colonies not supplemented. We recorded the pollen forager density per flower, the number of pollen grains deposited per stigma and their resulting fruit set, seed set and fruit mass, before and after the colony pollen supplementations. The number of pollen grains deposited by honey bees on stigmas increased gradually after pollen supplementation in the combs. But pollen foraging decreased only moderately, and no effect could be observed on any yield component except the seed set. On the other hand, there was no effect of the pollen paste laid on top of the frames either on stigmatic pollen loads, on colony pollen foraging or on any yield component. Supplementing honey bee colonies with pollen in the combs can therefore be an effective means for increasing their pollinating activity in nectariferous crops displaying anthers isolated from stigmas, e.g., Amaryllidaceae, Apiaceae, Cucurbitaceae, avocado, all hybrid seed productions. The context for the potential use of pollen substitutes is discussed.

Honeybee cluster-not insulation but stressful heat sink

Since the early twentieth century, the outer layer (mantle) of honeybees (Apis mellifera) in the winter cluster has been said to insulate the cluster core. This has encouraged enforced clustering, by the beekeepers' dominant use of inadequately insulated hives and, in North America, refrigeration. This is often seen as a benign or even a necessary process, with beekeeping and academic research considering these conditions of extreme heat loss, compared with the honeybee's natural habitat, as natural and normal. By using porous material correlations, analysis of previous findings and a model of a cluster within a hive in a landscape that implements convection, conduction and radiation, we show that a honeybee colony increases in thermal conductivity, on transition from pre-cluster to dense mantle, by a factor of approximately 2, and insulation R-value can decrease by more than 11. These results show that the mantle does not act like insulation and that clustering is not benign, but instead is an evolutionary behavioural reaction to an existential threat that results in increased cold and exertion stress. Thus the attitude to forced clustering, i.e. deliberately provoking a stressful survival behaviour, needs revision as avoidable forced stress upon animals may be regarded as cruel.

Pollen morphology for successful pollination dependent on pollinator taxa in a generalist plant: relationship with foraging behavior

Pollen morphology varies at inter- and intraspecific levels. Its interaction with pollinator behavior and morphology determines the probability of successful pollination. We tested whether pollen morphology promoting successful pollination differs depending on pollinator taxa in a generalist shrub, Weigela hortensis (Caprifoliaceae). We identified flower visitors carrying pollen from anthers to stigmas and compared the spine length and diameter of the pollen grains they carried. We found that pollen on the bodies of bumble bees and hunch-back flies and the scopae of small bees (including andrenid bees) contributed to seed production. Pollen grains on the bodies of bumble bees had longer spines than those on the scopae of andrenid bees or the bodies of hunch-back flies. Pollen grains on the bodies of bumble bees and the scopae of andrenid bees had larger diameters than those on hunch-back flies. Bumble bees collected pollen grains with shorter spines and larger diameters on their corbiculae while andrenid bees collected pollen grains with shorter spines and intermediate diameters on their scopae. The differences in morphology of pollen carried by pollinators reflected the tendency of bees to collect pollen with specific morphology into corbiculae/scopae. Our findings suggest that pollen morphology has diversified to facilitate successful pollination by pollinating partners.

An analysis of time-varying dynamics in electrically sensitive arthropod hairs to understand real-world electrical sensing

With increasing evidence of electroreception in terrestrial arthropods, an understanding of receptor level processes is vital to appreciating the capabilities and limits of this sense. Here, we examine the spatio-temporal sensitivity of mechanoreceptive filiform hairs in detecting electrical fields. We first present empirical data, highlighting the time-varying characteristics of biological electrical signals. After which, we explore how electrically sensitive hairs may respond to such stimuli. The main findings are: (i) oscillatory signals (elicited by wingbeats) influence the spatial sensitivity of hairs, unveiling an inextricable spatio-temporal link; (ii) wingbeat direction modulates spatial sensitivity; (iii) electrical wingbeats can be approximated by sinusoidally modulated DC signals; and (iv) for a moving point charge, maximum sensitivity occurs at a faster timescale than a hair's frequency-based tuning. Our results show that electro-mechanical sensory hairs may capture different spatio-temporal information, depending on an object's movement and wingbeat and in comparison with aero-acoustic stimuli. Crucially, we suggest that electrostatic and aero-acoustic signals may provide distinguishable channels of information for arthropods. Given the pervasiveness of electric fields in nature, our results suggest further study to understand electrostatics in the ecology of arthropods and to reveal unknown ecological relationships and novel interactions between species.

Functional Traits in Bees: the Role of Body Size and Hairs in the Pollination of a Passiflora Crop

Pollination is a vitally important function in nature and becomes an ecosystem service because it influences the food and nutritional security for people. However, the contribution of different functional traits of insects for pollen transport of plants is still poorly known. We explore the relationship between pollinator insect functional traits and the transport of pollen of sweet granadilla (Passiflora ligularis Juss) in eight crops. We sampled flower-visiting insects of this crop and recorded 10 functional traits (five by direct measurements and five from the literature) that were related to the amount of pollen carried by each insect. Bees (Apidae) were not only the most abundant insects but also the ones that loaded the highest amounts of pollen. Within these, the most abundant species was the exotic common honeybee (Apis mellifera (Linnaeus)) making up almost half of the specimens collected; however, this bee carried less pollen grains than other native bees. Bombus hortulanus (Smith) was one of the large-bodied native bees that carried more sweet granadilla pollen, despite not being an abundant species in the community. Body size was the most important trait determining the transport of sweet granadilla pollen, while the traits related to body hairs were not significant for the body's pollen load. None of the functional traits evaluated was influenced by taxonomy at species-level. Our results suggest that large body sizes in bees are the most important traits in granadilla pollen transport, regardless of other changes in composition and structure of pollinating insect assemblages in the crop.

Mobile samplers of particulate matter - Flying omnivorous insects in detection of industrial contamination

Flying insects are potential mobile samplers of airborne particulate matter (PM). However, current knowledge on their susceptibility to PM is limited to pollinators. Insects' capacity for particle surface accumulation depends on the lifestyle, structure of the body integuments, and behavioral patterns. Here, we investigate how two species of flying omnivorous insects from the genus Vespula, possessing direct interactions with air, soil, plants, and herbivores, indicate industrial pollution by accumulating coarse (PM₁₀) and fine (PM_2.5) particles on their bodies. The internal accumulation of particles in wasps' gut tissues is assessed considering heavy metals exposure to reveal and discuss the potential magnitude of ecotoxicological risks. Female individuals of Vespula vulgaris and V. germanica were sampled with a hand-netting near to Harjavalta Cu-Ni smelter and in the control areas in southwestern Finland. They were analyzed with light microscopy (LM), electron microscopy (SEM, TEM), and energy-dispersive X-ray spectroscopy (EDX) methods. Near to the smelter, wasps trapped significantly more particles, which were of bigger size and their surface optical density was higher. Vespula vulgaris accumulated larger particles than V. germanica, but that wasn't associated with morphological characteristics such as body size or hairiness. In both areas, accumulated surface PM carried clays and silicates. Only in polluted environments PM consistently contained metallic and nonmetallic particles (from high to moderate weight %) of Fe, Ni, Cu, and S - major pollutants emitted from the smelter. Wasps from industrially polluted areas carried significantly more granules in the columnar epithelial midgut cells. TEM-EDX analyses identified those structures were associated with metal ions such as Cr, Cu, Ni, and Fe. As epithelial gut cells accumulated metal particles, midgut confirmed as a barrier for metal exposure in wasps. External PM contamination in wasps is suggested as a qualitative, yet a natural and simple descriptor of local industrial emissions.

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub

Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient. Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes. Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude. The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

Smaller, lighter coloured and less hairy Procladius (Diptera, Chironomidae) in warmer climate

The relationship between body size, colour and hairiness of Procladius of the Diptera family Chironomidae and climate measured as annual mean air temperature was analysed. The study was based on 453 males representing 31 species from 253 localities in 27 countries in Europe and six elsewhere. Wing length as well as three other characters reflecting body size showed significant decrease with warmer climate conditions. The results are in line with several other studies of insects concluding that adult insects are smaller in warmer climate, also considering the implications of global warming. Likewise, all five characters representing colour lightness showed significantly lighter coloured Procladius specimens with warmer climate. The relationship between hairiness and annual mean air temperature was weaker than that of size or colour and temperature, but all five characters studied showed a statistically significant decrease in hairiness with warmer climate. The biological relevance of smaller size, lighter colour and less hairiness in warmer climate can be related to several factors regulating flight and swarming, including less need of protection against cold weather, overheating avoidance, mating success agility and predator escape.

Passive electrolocation in terrestrial arthropods: Theoretical modelling of location detection

The recent discovery that some terrestrial arthropods can detect, use, and learn from weak electrical fields adds a new dimension to our understanding of how organisms explore and interact with their environments. For bees and spiders, the filiform mechanosensory systems enable this novel sensory modality by carrying electric charge and deflecting in response to electrical fields. This mode of information acquisition opens avenues for previously unrealised sensory dynamics and capabilities. In this paper, we study one such potential: the possibility for an arthropod to locate electrically charged objects. We begin by illustrating how electrostatic interactions between hairs and surrounding electrical fields enable the process of location detection. After which we examine three scenarios: (1) the determination of the location and magnitude of multiple point charges through a single observation, (2) the learning of electrical and mechanical sensor properties and the characteristics of an electrical field through several observations, (3) the possibility that an observer can infer their location and orientation in a fixed and known electrical field (akin to "stellar navigation"). To conclude, we discuss the potential of electroreception to endow an animal with thus far unappreciated sensory capabilities, such as the mapping of electrical environments. Electroreception by terrestrial arthropods offers a renewed understanding of the sensory processes carried out by filiform hairs, adding to aero-acoustic sensing and opening up the possibility of new emergent collective dynamics and information acquisition by distributed hair sensors.

The diversity, evolution, and development of setal morphologies in bumble bees (Hymenoptera: Apidae: Bombus spp.)

Bumble bees are characterized by their thick setal pile that imparts aposematic color patterns often used for species-level identification. Like all bees, the single-celled setae of bumble bees are branched, an innovation thought important for pollen collection. To date no studies have quantified the types of setal morphologies and their distribution on these bees, information that can facilitate understanding of their adaptive ecological function. This study defines several major setal morphotypes in the common eastern bumble bee Bombus impatiens Cresson, revealing these setal types differ by location across the body. The positions of these types of setae are similar across individuals, castes, and sexes within species. We analyzed the distribution of the two most common setal types (plumose and spinulate) across the body dorsum of half of the described bumble bee species. This revealed consistently high density of plumose (long-branched) setae across bumble bees on the head and mesosoma, but considerable variation in the amount of metasomal plumosity. Variation on the metasoma shows strong phylogenetic signal at subgeneric and smaller group levels, making it a useful trait for species delimitation research, and plumosity has increased from early Bombus ancestors. The distribution of these setal types suggests these setae may serve several functions, including pollen-collecting and thermoregulatory roles, and probable mechanosensory functions. This study further examines how and when setae of the pile develop, evidence for mechanosensory function, and the timing of pigmentation as a foundation for future genetic and developmental research in these bees.

Changes in bee functional traits at community and intraspecific levels along an elevational gradient in a Mexical-type scrubland

Understanding the causes of morphological variation of organisms along climatic gradients has been a central challenge in ecological research. We studied the variation of community weighted mean (CWM) and two functional diversity metrics (Rao-Q and functional richness) computed for five morphological traits of wild bees (Hymenoptera: Apoidea) related to thermal performance (namely body size, relative appendage length and hairiness), at community and interspecific levels, along an elevation gradient in a Mexical-type scrubland. At the community level we found a decreasing CWM of body size pattern with increasing elevation which is consistent with the species-energy theory (and contrary to Bergmann's rule). We also found an increase in the CWM of relative tibia length, which is contrary to Allen's rule. Additionally, we found an increase in the CWM of relative hair length towards high levels of elevation, which would be consistent with the hypothesis that hairiness plays an important role as thermal insulation. We found that functional diversity was larger at low elevations with respect to high elevation for body size and hair length, which could imply that highland communities were more sensitive towards environmental changes than lowland communities. Overall, at intraspecific level, most of species showed no pattern for any of the traits along the elevation gradient. Future research should provide further evidence on the possible behavioral or physiological mechanisms behind it.

The mechanics and interactions of electrically sensitive mechanoreceptive hair arrays of arthropods

Recent investigations highlight the possibility of electroreception within arthropods through charged mechanosensory hairs. This discovery raises questions about the influence of electrostatic interaction between hairs and surrounding electrical fields within this sensory modality. Here, we investigate these questions by studying electrostatic coupling in arrays of hairs. We establish the notion of sensitivity contours that indicate regions within which point charges deflect hairs beyond a given threshold. We then examine how the contour’s shape and size and the overall hair behaviour change in response to variations in the coupling between hairs. This investigation unveils synergistic behaviours whereby the sensitivity of hairs is enhanced or inhibited by neighbouring hairs. The hair spacing and ratio of a system’s electrical parameters to its mechanical parameters influence this behaviour. Our results indicate that electrostatic interaction between hairs leads to emergent sensory properties for biologically relevant parameter values. The analysis raises new questions around the impact of electrostatic interaction on the current understanding of sensory hair processes, such as acoustic sensing, unveiling new sensory capabilities within electroreception such as amplification of hair sensitivity and location detection of charges in the environment.

Morphological Structure and Distribution of Hairiness on Different Body Parts of Apis mellifera with an Implication on Pollination Biology and a Novel Method to Measure the Hair Length

Bees play a very important role in pollination, especially western honey bees, which contribute upwards of billions of dollars concerning crop pollination. Hairiness plays an important role in pollination success by transporting pollen, and pollen intake, but there is a lack of detailed studies on the morphological mechanisms. The hairiness trait is barely discussed in pollinator trait analysis because of the lack of systematic techniques used to measure hairiness. This paper reports a novel method that is used to measure the hair length of different body parts of a western honey bee through a stereomicroscope equipped with live measurement module software. Scanning electron microscope (SEM) was used to update the knowledge regarding the hair structure of a western honey bee. We explained different types of hairs, hair branches, and their distributions on different body parts, which are discussed in detail. A positive correlation was found between hair length and the number of branches on all body parts. Five types of branches were observed, and these branches vary with different body parts. Our study provides sufficient details about the hair morphology of the western honey bee and a new methodology for measuring hair length. This methodology will improve the knowledge about understanding the pollination efficiency of the western honey bee.

Honeybees as active samplers for microplastics

Microplastics are ubiquitous and their sampling is a difficult task. Honeybees interact with the environment inside their foraging range and take pollutants with them. In this work, we demonstrated for the first time that worker bees can act as active samplers of microplastics. We collected honeybees from apiaries located in the centre of Copenhagen and from nearby semiurban and rural areas. We showed the presence of microplastics in all sampled locations mostly in the form of fragments (52%) and fibres (38%) with average equivalent diameter of 64 ± 39 μm for fibres and 234 ± 156 μm for fragments. The highest load corresponded to urban apiaries, but comparable number of microplastics was found in hives from suburban and rural areas, which can be explained by the presence of urban settlements inside the foraging range of worker bees and to the easy dispersion of small microplastics by wind. Micro-FTIR analysis confirmed the presence of thirteen synthetic polymers, the most frequently of which was polyester followed by polyethylene and polyvinyl chloride. Our results demonstrated the presence of microplastics attached to the body of the honeybees and opens a new research pathway to their use as active biosamplers for anthropogenic pollution.

Ecological Monitoring with Spy Satellite Images—The Case of Red Wood Ants in Romania

Dynamics of habitat conditions drive important changes in distribution and abundance of animal species making monitoring an important but also a challenging task when data from the past are scarce. We compared the distribution of ant mounds in the 1960s with recent inventories (2018), looking at changes in canopy cover over time, in a managed forest. Both historical and recent sources of information were used. Habitat suitability at present was determined using a Normalized Difference Vegetation Index (NDVI) image as a proxy for stand canopy cover. The NDVI product was obtained using Google Earth Engine and Sentinel 2 repository. For past conditions (no spectral information available), presence of edges and more open canopies was assessed on a Corona spy-satellite image and based on information from old forest management plans. A threshold distance of 30 m was used to assess location of ant nests compared to favorable habitats. Both old and new information sources showed that ants prefer intermediate canopy cover conditions in their vicinity. Nests remained clustered because of the heterogeneous habitat conditions, but spatial distribution has changed due to canopy alteration along time. The analysis on the NDVI was effective for 82% of cases (i.e., nests occurred within 30 m from favorable habitats). For all the remaining nests (18%), the Google Earth high resolution satellite image revealed in their vicinity the presence of small canopy gaps (undetected by the NDVI). These results show that historical satellite images are very useful for explaining the long-term dynamics of ant colonies. In addition, the use of modern remote sensing techniques provides a reliable and expedite method in determining the presence of favorable small-scale habitat, offering a very useful tool for ecological monitoring across large landscapes and in very different areas, especially in the context of ecosystem dynamics driven and exacerbated by climate change.