Gradual pollen presentation in Vaccinium corymbosum 'Bluecrop': an adaptive mechanism to improve pollination efficiency and outcrossing.

Gradual pollen presentation is a plant reproductive mechanism to improve pollination efficiency and accuracy and promote outcrossing. Vaccinium corymbosum 'Bluecrop' has a typical gradual pollen presentation mechanism. 'Bluecrop' exhibits an inverted bell-shaped flower with a white coloration. By investigating the flower syndrome, pollination characteristics, pollination efficiency, and breeding system of 'Bluecrop', this study aims to explore the adaptive significance of these traits. The results showed 'Bluecrop' released pollen gradually through anther poricidal dehiscence. Among different pollinators, Apis mellifera and Bombus can pollinate effectively, and the mechanism of gradual pollen presentation significantly improved the efficiency of pollen transfer. This characteristic limits the amount of pollen removed by the pollinators and prolongs pollen presentation, thus attracting more pollinators and thereby increasing male fitness. The nectar secretion of 'Bluecrop' is gradual, with a large nectar production and a long phase of nectar secretion, enhance visitation frequencies and the chances of successful pollination. At the same time, campanulate corolla can protect pollen as well as nectar from waste due to environmental factors and other effects. The breeding system of 'Bluecrop' relies mainly on outcrossing because of its low affinity for self-fertilization and good interaction with pollinating insects. Thus, the special floral syndrome and the mechanism of secondary pollen presentation are significant in improving pollination efficiency and promoting the reproductive success of 'Bluecrop' by outcrossing. It can provide a certain theoretical basis for the future propagation breeding of 'Bluecrop'.

Evidence for socially influenced and potentially actively coordinated cooperation by bumblebees.

Cooperation is common in animals, yet the specific mechanisms driving collaborative behaviour in different species remain unclear. We investigated the proximate mechanisms underlying the cooperative behaviour of bumblebees in two different tasks, where bees had to simultaneously push a block in an arena or a door at the end of a tunnel for access to reward. In both tasks, when their partner's entry into the arena/tunnel was delayed, bees took longer to first push the block/door compared with control bees that learned to push alone. In the tunnel task, just before gaining access to reward, bees were more likely to face towards their partner than expected by chance or compared with controls. These results show that bumblebees' cooperative behaviour is not simply a by-product of individual efforts but is socially influenced. We discuss how bees' turning behaviours, e.g. turning around before first reaching the door when their partner was delayed and turning back towards the door in response to seeing their partner heading towards the door, suggest the potential for active coordination. However, because these behaviours could also be interpreted as combined responses to social and secondary reinforcement cues, future studies are needed to help clarify whether bumblebees truly use active coordination.

First large-scale study reveals important losses of managed honey bee and stingless bee colonies in Latin America.

Over the last quarter century, increasing honey bee colony losses motivated standardized large-scale surveys of managed honey bees (Apis mellifera), particularly in Europe and the United States. Here we present the first large-scale standardized survey of colony losses of managed honey bees and stingless bees across Latin America. Overall, 1736 beekeepers and 165 meliponiculturists participated in the 2-year survey (2016-2017 and 2017-2018). On average, 30.4% of honey bee colonies and 39.6% of stingless bee colonies were lost per year across the region. Summer losses were higher than winter losses in stingless bees (30.9% and 22.2%, respectively) but not in honey bees (18.8% and 20.6%, respectively). Colony loss increased with operation size during the summer in both honey bees and stingless bees and decreased with operation size during the winter in stingless bees. Furthermore, losses differed significantly between countries and across years for both beekeepers and meliponiculturists. Overall, winter losses of honey bee colonies in Latin America (20.6%) position this region between Europe (12.5%) and the United States (40.4%). These results highlight the magnitude of bee colony losses occurring in the region and suggest difficulties in maintaining overall colony health and economic survival for beekeepers and meliponiculturists.

Current honey bee stressor investigations and mitigation methods in the United States and Canada.

Honey bees are the most important managed insect pollinators in the US and Canadian crop systems. However, the annual mortality of colonies in the past 15 years has been consistently higher than historical records. Because they are eusocial generalist pollinators and amenable to management, honey bees provide a unique opportunity to investigate a wide range of questions at molecular, organismal, and ecological scales. Here, the American Association of Professional Apiculturists (AAPA) and the Canadian Association of Professional Apiculturists (CAPA) created 2 collections of articles featuring investigations on micro and macro aspects of honey bee health, sociobiology, and management showcasing new applied research from diverse groups studying honey bees (Apis mellifera) in the United States and Canada. Research presented in this special issue includes examinations of abiotic and biotic stressors of honey bees, and evaluations and introductions of various stress mitigation measures that may be valuable to both scientists and the beekeeping community. These investigations from throughout the United States and Canada showcase the wide breadth of current work done and point out areas that need further research.

Heightened sensitivity in high-grooming honey bees (Hymenoptera: Apidae).

Honey bees use grooming to defend against the devastating parasite Varroa destructor Anderson and Trueman. We observed the grooming responses of individual bees from colonies previously chosen for high- and low-grooming behavior using a combination of mite mortality and mite damage. Our aim was to gain insight into specific aspects of grooming behavior to compare if high-grooming bees could discriminate between a standardized stimulus (chalk dust) and a stimulus of live Varroa mites and if bees from high-grooming colonies had greater sensitivity across different body regions than bees from low-grooming colonies. We hypothesized that individuals from high-grooming colonies would be more sensitive to both stimuli than bees from low-grooming colonies across different body regions and that bees would have a greater response to Varroa than a standardized irritant (chalk dust). Individuals from high-grooming colonies responded with longer bouts of intense grooming when either stimulus was applied to the head or thorax, compared to sham-stimulated controls, while bees from low-grooming colonies showed no differences between stimulated and sham-stimulated bees. Further, high-grooming bees from colonies with high mite damage exhibited greater grooming to Varroa than high-grooming colonies with only moderate mite damage rates. This study provides new insights into Varroa-specific aspects of grooming, showing that although a standardized stimulus (chalk dust) may be used to assess general grooming ability in individual bee grooming assays, it does not capture the same range of responses as a stimulus of Varroa. Thus, continuing to use Varroa mites in grooming assays should help select colonies with more precise sensitivity to Varroa.

Indoor tent management for extending honey bee research season: benefits and caveats.

Honey bees are important organisms for research in many fields, including physiology, behavior, and ecology. Honey bee colonies are relatively easy and affordable to procure, manage, and replace. However, some difficulties still exist in honey bee research, specifically that honey bee colonies have a distinct seasonality, especially in temperate regions. Honey bee colonies transition from a large society in which workers have a strict temporal division of labor in the summer, to a group of behaviorally flexible workers who manage the colony over winter. Furthermore, opening colonies or collecting bees when they are outside has the potential to harm the colony because of the disruption in thermoregulation. Here, we present a simple and affordable indoor management method utilizing a mylar tent and controlled environmental conditions that allows bees to freely fly without access to outdoor space. This technique permits research labs to successfully keep several colonies persistently active during winter at higher latitudes. Having an extended research period is particularly important for training students, allowing preliminary experiments to be performed, and developing methods. However, we find distinct behavioral differences in honey bees managed in this situation. Specifically learning and thermoregulatory behaviors were diminished in the bees managed in the tent. Therefore, we recommend caution in utilizing these winter bees for full experiments until more is known. Overall, this method expands the research potential on honey bees, and calls attention to the additional research that is needed to understand how indoor management might affect honey bees.

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.

Local and landscape factors shape alpha and beta trophic interaction diversity in urban gardens.

Promoting urban green spaces is an effective strategy to increase biodiversity in cities. However, our understanding of how local and landscape factors influence trophic interactions in these urban contexts remains limited. Here, we sampled cavity-nesting bees and wasps and their natural enemies within 85 urban gardens in Zurich (Switzerland) to identify factors associated with the diversity and dissimilarity of antagonistic interactions in these communities. The proportions of built-up area and urban green area at small landscape scales (50 m radius), as well as the management intensity, sun exposure, plant richness and proportion of agricultural land at the landscape scale (250 m radius), were key drivers of interaction diversity. This increased interaction diversity resulted not only from the higher richness of host and natural enemy species, but also from species participating in more interactions. Furthermore, dissimilarity in community structure and interactions across gardens (beta-diversity) were primarily influenced by differences in built-up areas and urban green areas at the landscape scale, as well as by management intensity. Our study offers crucial insights for urban planning and conservation strategies, supporting sustainability goals by helping to understand the factors that shape insect communities and their trophic interactions in urban gardens.

Systems theory: A novel approach for understanding how stressors affect honey bee health 'all at once'.

A new study showcases the usefulness of systems theory and network analyses for understanding how dozens of stressors can act concomitantly to affect managed honey bee health. Interestingly, the most influential stressors are not those currently being addressed by beekeepers.

Bumble Bee Watch community science program increases scientific understanding of an important pollinator group across Canada and the USA.

In a time of increasing threats to bumble bees (Hymenoptera: Apidae: Bombus), it is important to understand their ecology and distribution. As experts are limited in resources to conduct field surveys, there is potential for community scientists to help. The Bumble Bee Watch (BBW) community science program involves volunteers taking photos of bumble bees in Canada and the USA and submitting them, along with geographic and optional plant information, to a website or through an app. Taxon experts then verify the bee species identification. The Bumble Bees of North America database (BBNA) stores data (no photographs) collected and identified by more traditional scientific methods over the same range. Here we compared BBW data to BBNA data over all years and just 2010-2020 to understand the scientific contribution of community scientists to the state of the knowledge about native bumble bees. We found that BBW had similar geographic and species coverage as BBNA. It had records from all 63 provinces, states, and territories where bumble bees occur (including four more than BBNA in 2010-2020), and represented 41 of the 48 species in BBNA (with ten more species than BBNA in 2010-2020). While BBW contributed only 8.50% of records overall, it contributed 25.06% of all records over 2010-2020. BBW confirmed the persistence of species and identified new locations of species, both inside and outside of the previously known extent of occurrences. BBW also contributed a wealth of ecological information, such as unique plant genera and species data for almost all the bee species. Thus, while BBW had fewer bee records than the BBNA database overall, it helped to fill in data gaps and provided novel information, complementing the traditional methods. This community science program is valuable in helping to inform conservation management for bumble bee species.

Regulatory roles of long non-coding RNAs in short-term heat stress in adult worker bees.

Long non-coding RNAs (lncRNAs) are crucial modulators of post-transcriptional gene expression regulation, cell fate determination, and disease development. However, lncRNA functions during short-term heat stress in adult worker bees are poorly understood. Here, we performed deep sequencing and bioinformatic analyses of honeybee lncRNAs. RNA interference was performed by using siRNA targeting the most highly expressed lncRNA. The silencing effect on lncRNA and the relative expression levels of seven heat shock protein (HSP) genes, were subsequently examined. Overall, 7,842 lncRNAs and 115 differentially expressed lncRNAs (DELs) were identified in adult worker bees following heat stress exposure. Structural analysis revealed that the overall expression abundance, length of transcripts, exon number, and open reading frames of lncRNAs were lower than those of mRNAs. GO analysis revealed that the target genes were mainly involved in "metabolism," "protein folding," "response to stress," and "signal transduction" pathways. KEGG analysis indicated that the "protein processing in endoplasmic reticulum" and "longevity regulating pathway-multiple species" pathways were most enriched. Quantitative real-time polymerase chain reaction (qRT-PCR) detection of the selected DELs confirmed the reliability of the sequencing data. Moreover, the siRNA experiment indicated that feeding siRNA yielded a silencing efficiency of 77.51% for lncRNA MSTRG.9645.5. Upon silencing this lncRNA, the expression levels of three HSP genes were significantly downregulated (p < 0.05), whereas those of three other HSP genes were significantly upregulated (p < 0.05). Our results provide a new perspective for understanding the regulatory mechanisms of lncRNAs in adult worker bees under short-term heat stress.

Collective behaviour: Stingless bees are self-organised nest builders.

A new study compiles compelling evidence that stingless bees construct their brood combs in a self-organised manner in which local modification of a structure stimulates further modifications, a process known as stigmergy.

Telomere length is longer following diapause in two solitary bee species.

The mechanisms that underlie senescence are not well understood in insects. Telomeres are conserved repetitive sequences at chromosome ends that protect DNA during replication. In many vertebrates, telomeres shorten during cell division and in response to stress and are often used as a cellular marker of senescence. However, little is known about telomere dynamics across the lifespan in invertebrates. We measured telomere length in larvae, prepupae, pupae, and adults of two species of solitary bees, Osmia lignaria and Megachile rotundata. Contrary to our predictions, telomere length was longer in later developmental stages in both O. lignaria and M. rotundata. Longer telomeres occurred after emergence from diapause, which is a physiological state with increased tolerance to stress. In O. lignaria, telomeres were longer in adults when they emerged following diapause. In M. rotundata, telomeres were longer in the pupal stage and subsequent adult stage, which occurs after prepupal diapause. In both species, telomere length did not change during the 8 months of diapause. Telomere length did not differ by mass similarly across species or sex. We also did not see a difference in telomere length after adult O. lignaria were exposed to a nutritional stress, nor did length change during their adult lifespan. Taken together, these results suggest that telomere dynamics in solitary bees differ from what is commonly reported in vertebrates and suggest that insect diapause may influence telomere dynamics.

Bee and butterfly records indicate diversity losses in western and southern North America, but extensive knowledge gaps remain.

Pollinator losses threaten ecosystems and food security, diminishing gene flow and reproductive output for ecological communities and impacting ecosystem services broadly. For four focal families of bees and butterflies, we constructed over 1400 ensemble species distribution models over two time periods for North America. Models indicated disproportionally increased richness in eastern North America over time, with decreases in richness over time in the western US and southern Mexico. To further pinpoint geographic areas of vulnerability, we mapped records of potential pollinator species of conservation concern and found high concentrations of detections in the Great Lakes region, US East Coast, and southern Canada. Finally, we estimated asymptotic diversity indices for genera known to include species that visit flowers and may carry pollen for ecoregions across two time periods. Patterns of generic diversity through time mirrored those of species-level analyses, again indicating a decline in pollinators in the western U.S. Increases in generic diversity were observed in cooler and wetter ecoregions. Overall, changes in pollinator diversity appear to reflect changes in climate, though other factors such as land use change may also explain regional shifts. While statistical methods were employed to account for unequal sampling effort across regions and time, improved monitoring efforts with rigorous sampling designs would provide a deeper understanding of pollinator communities and their responses to ongoing environmental change.

Brood indicators are an early warning signal of honey bee colony loss-a simulation-based study.

Honey bees (Apis mellifera) are exposed to multiple stressors such as pesticides, lack of forage, and diseases. It is therefore a long-standing aim to develop robust and meaningful indicators of bee vitality to assist beekeepers While established indicators often focus on expected colony winter mortality based on adult bee abundance and honey reserves at the beginning of the winter, it would be useful to have indicators that allow detection of stress effects earlier in the year to allow for adaptive management. We used the established honey bee simulation model BEEHAVE to explore the potential of different indicators such as population size, number of capped brood cells, flight activity, abundance of Varroa mites, honey stores and a brood-bee ratio. We implemented two types of stressors in our simulations: 1) parasite pressure, i.e. sub-optimal Varroa treatment by the beekeeper (hereafter referred as Biotic stress) and 2) temporal forage gaps in spring and autumn (hereafter referred as Environmental stress). Neither stressor type could be detected by bee abundance or honey reserves at the end of the first year. However, all response variables used in this study did reveal early warning signals during the course of the year. The most reliable and useful measures seem to be related to brood and the abundance of Varroa mites at the end of the year. However, while in the model we have full access to time series of variables from stressed and unstressed colonies, knowledge of these variables in the field is challenging. We discuss how our findings can nevertheless be used to develop practical early warning indicators. As a next step in the interactive development of such indicators we suggest empirical studies on the importance of the number of capped brood cells at certain times of the year on bee population vitality.

Magnetite in the abdomen and antennae of Apis mellifera honeybees.

The detection of magnetic fields by animals is known as magnetoreception. The ferromagnetic hypothesis explains magnetoreception assuming that magnetic nanoparticles are used as magnetic field transducers. Magnetite nanoparticles in the abdomen of Apis mellifera honeybees have been proposed in the literature as the magnetic field transducer. However, studies with ants and stingless bees have shown that the whole body of the insect contain magnetic material, and that the largest magnetization is in the antennae. The aim of the present study is to investigate the magnetization of all the body parts of honeybees as has been done with ants and stingless bees. To do that, the head without antennae, antennae, thorax, and abdomen obtained from Apis mellifera honeybees were analyzed using magnetometry and Ferromagnetic Resonance (FMR) techniques. The magnetometry and FMR measurements show the presence of magnetic material in all honeybee body parts. Our results present evidence of the presence of biomineralized magnetite nanoparticles in the honeybee abdomen and, for the first time, magnetite in the antennae. FMR measurements permit to identify the magnetite in the abdomen as biomineralized. As behavioral experiments reported in the literature have shown that the abdomen is involved in magnetoreception, new experimental approaches must be done to confirm or discard the involvement of the antennae in magnetoreception.

Polyandry may mitigate the negative impact of reproductive interference among bumblebees in Japan.

In social hymenopterans, monandry of the queen is an ancestral trait, and polyandry is a derived trait. Polyandry of the queen is the norm in a limited number of lineages, such as honeybees, leaf-cutting ants, Pogonomyrmex ants, and Vespula wasps, which presumably provide fitness advantages for the whole colony. The queen of the introduced bumblebee, Bombus terrestris, is polyandrous in Japan, whereas it is monandrous in native regions. We hypothesize that polyandry can evolve in a process that avoids the negative impacts of reproductive interference caused by interspecific mating and conducted genetic studies of the invasive species B. terrestris and two native subspecies, Bombus hypocrita sapporoensis and Bombus hypocrita hypocrita, in Japan. Our results revealed that although the native queens of B. hypocrita hypocrita allopatric with B. terrestris were strictly monandrous, the native queens of B. hypocrita sapporoensis sympatric with B. terrestris were polyandrous. These results suggested that the queens of native B. hypocrita sapporoensis do not experience negative impacts on interspecific mating from the invasive B. terrestris. We discuss the possibility that reproductive interference is a driving force in selection for multiple mating through an arms race between sympatric species.

Determining the plant-pollinator network in a culturally significant food and medicine garden in the Great Lakes region.

Understanding the interactions between plants and pollinators within a system can provide information about pollination requirements and the degree to which species contribute to floral reproductive success. Past research has focused largely on interactions within monocultured agricultural systems and only somewhat on wild pollination networks. This study focuses on the culturally significant Three Sisters Garden, which has been grown and tended by many Indigenous peoples for generations in the Great Lakes Region. Here, the plant-pollinator network of the traditional Three Sisters Garden with the inclusion of some additional culturally significant plants was mapped. Important visitors in this system included the common eastern bumble bee, Bombus impatiens Cresson (Hymenoptera: Apidae), and the hoary squash bee, Xenoglossa pruinosa (Say) (Hymenoptera: Apidae), as determined by their abundances and pollinator service index (PSI) values. Understanding the key pollinators in the Three Sisters Garden links biological diversity to cultural diversity through the pollination of culturally significant plants. Further, this information could be of use in supporting Indigenous food sovereignty by providing knowledge about which wild pollinators could be supported to increase fruit and seed set within the Three Sisters Garden. Our findings can also lead to more effective conservation of important wild pollinator species.

Uncovering hidden dangers: The combined toxicity of abamectin and lambda-cyhalothrin on honey bees.

Studying the toxic effects of pesticides on bees has consistently been a prominent area of interest for researchers. Nonetheless, existing research has predominantly concentrated on individual toxicity assessments, leaving a gap in our understanding of mixed toxicity. This study delves into the individual and combined toxic effects of abamectin (ABA) and lambda-cyhalothrin (LCY) on honey bees (Apis mellifera) in laboratory settings. We discovered that ABA (96 h-LC50 value of 0.079 mg/L) exhibited greater acute toxicity to honey bees compared to LCY (96 h-LC50 value of 9.177 mg/L). Moreover, the mixture of ABA and LCY presented an acute antagonistic effect on honey bees. Additionally, our results indicated that exposure to LCY, at medium concentration, led to a reduction in the abundance of gut core bacterium Snodgrassella. However, an increase in the abundance of Bifidobacterium was noted when exposed to a medium concentration of LCY and its mixture with ABA. Transcriptomic analysis revealed significant regulation of certain genes in the medium concentration of all three treatments compared to the control group, primarily enriching in metabolism and immune-related pathways. Following chronic exposure to field-relevant concentrations of ABA, LCY, and their mixture, there were significant alterations in the activities of immunity-related enzyme polyphenol oxidase (PPO) and detoxification enzymes glutathione S-transferase (GST) and carboxylesterase (CarE). Additionally, the expression of four genes (abaecin, cyp9e2, cyp302a1, and GstD1) associated with immune and detoxification metabolism was significantly altered. These findings suggest a potential health risk posed by the insecticides ABA and LCY to honey bees. Despite exhibiting acute antagonistic effect, mixed exposure still induced damage to bees at all levels. This study advances our knowledge of the potential adverse effects of individual or combined exposure to these two pesticides on non-target pollinators and offers crucial guidance for the use of insecticides in agricultural production.

Towards acoustic monitoring of bees: wingbeat sounds are related to species and individual traits.

Global pollinator decline urgently requires effective methods to assess their trends, distribution and behaviour. Passive acoustics is a non-invasive and cost-efficient monitoring tool increasingly employed for monitoring animal communities. However, insect sounds remain highly unexplored, hindering the application of this technique for pollinators. To overcome this shortfall and support future developments, we recorded and characterized wingbeat sounds of a variety of Iberian domestic and wild bees and tested their relationship with taxonomic, morphological, behavioural and environmental traits at inter- and intra-specific levels. Using directional microphones and machine learning, we shed light on the acoustic signature of bee wingbeat sounds and their potential to be used for species identification and monitoring. Our results revealed that frequency of wingbeat sounds is negatively related with body size and environmental temperature (between-species analysis), while it is positively related with experimentally induced stress conditions (within-individual analysis). We also found a characteristic acoustic signature in the European honeybee that supported automated classification of this bee from a pool of wild bees, paving the way for passive acoustic monitoring of pollinators. Overall, these findings confirm that insect sounds during flight activity can provide insights on individual and species traits, and hence suggest novel and promising applications for this endangered animal group. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'.