The evolution of floral sonication, a pollen foraging behavior used by bees (Anthophila)

Turgor pressure affects transverse stiffness and resonant frequencies of buzz-pollinated poricidal anthers

Several agriculturally valuable plants store their pollen in tube-like poricidal anthers, which release pollen through buzz pollination. In this process, bees rapidly vibrate the anther using their indirect flight muscles. The stiffness and resonant frequency of the anther are crucial for effective pollen release, yet the impact of turgor pressure on these properties is not well understood. Here, we performed three-point flexure tests and experimental modal analysis to determine anther transverse stiffness and resonant frequency, respectively. Dynamic nanoindentation was used to identify the anther storage modulus as a function of excitation frequency. We subsequently developed mathematical models to estimate how turgor pressure changes after the anther is removed from a flower, thereby emulating zero water availability. We found that anther stiffness decreased by 60% at 30 min post-ablation and anther resonant frequency decreased by 20% at 60 min post-ablation. Models indicated that turgor pressure in the fresh anther was ~0.2-0.3 MPa. Our findings suggest that natural fluctuations in turgor pressure due to environmental factors such as temperature and light intensity may require bees to adjust their foraging behaviors. Interestingly, the anther storage modulus increased with excitation frequency, underscoring the need for more sophisticated mechanical models that consider viscous fluid transport through plant tissue.

Wilting may leave bees wanting: drops in turgor pressure may reduce viability of buzz-pollinated flowers

This article comments on:

Alvord M, McNally J, Casey C, Jankauski M. 2025. Turgor pressure affects transverse stiffness and resonant frequencies of buzz-pollinated poricidal anthers. Journal of Experimental Botany 76, 1784–1794

Vibration mechanics involved in buzz pollination lead to size-dependent associations between bumblebees and Pedicularis flowers

Floral traits modify pollinator behavior and shape the plant-pollinator interaction pattern at ecological and evolutionary levels. Biomechanical traits are important in mediating interactions between flowers and their pollinators in some cases, such as in buzz pollination. During buzz pollination, a bee produces vibrations using its thoracic muscles and transfers these vibrations primarily through its mandibles as it bites the flower. The interaction between buzz-pollinated flowers and their pollinators is influenced by their physical size relative to each other, but the drivers of these size-dependent associations remain unclear. Using eight beaked louseworts (Pedicularis) as a model system, we combined behavioral observations, biomechanical analyses, and pollinator network analyses to test the hypothesis that the location of where a bee bites should constrain the interaction between Pedicularis and bumblebees during buzz pollination. We found that bumblebees always chose to bite the same site at the base of the floral beak when buzzing Pedicularis, and this site is optimal for transferring vibrations from the bee to release pollen from the anthers. Bee bodies must be long enough for the mandibles to clamp onto the same optimal site on the floral beak, while its pollen-collecting abdomen is positioned at the opening of the floral beak where pollen grains are ejected. Our pollination networks showed size matching between the floral beak length of each Pedicularis species and the body length of individual bumblebees regardless of bee species. These results suggest that the optimal excitation point on the Pedicularis flower links a suite of floral traits to its pollinators' dimensions, potentially contributing to prezygotic isolation among co-flowering, sympatric Pedicularis species.

Effects of the insecticide flupyradifurone and the fungicides pyraclostrobin and fluxapyroxad on behavior and morphophysiology in Melipona scutellaris

Native stingless bees are important for natural ecosystems and human nutrition. However, they may be exposed to pesticides used in agriculture. Pesticides are sold as commercial formulations, either with a single active ingredient (e.g., flupyradifurone insecticide) or multiple ones (e.g., pyraclostrobin and fluxapyroxad fungicide). Considering the impact of pesticides on non-target organisms, this study aimed to evaluate the effects of these isolated and combined formulated products on the survival, behavior, and morphophysiology of the midgut and Malpighian tubules of Melipona scutellaris foragers. Sampled bees were divided into the following experimental groups: insecticide (6 ng/μL of flupyradifurone), fungicide (0.1 ng/μL of pyraclostrobin and 0.05 ng/μL of fluxapyroxad), and a combination of both solutions (flupyradifurone: 3 ng/μL, pyraclostrobin: 0.05 ng/μL, and fluxapyroxad: 0.025 ng/μL). Individuals were chronically exposed to pesticides orally to record the survival probability. According to the result, a new bioassay was performed to evaluate their behavior and organ lesion indexes. Exposed bees exhibited high mortality compared to the control experimental group. The insecticide group showed significant alterations in mobility over the course of the experiment, and all experimental groups demonstrated impaired behavior. Histological images also revealed the presence of three levels of injury in the midgut (cell elimination, apocrine secretion, spherocrystals, vacuolization and pycnotic nuclei) and Malpighian tubules (spherocrystals, vacuolization and pycnotic nuclei) following a brief exposure period. The data demonstrate that, even in the short term, both formulated products impair the health and survival of the species, disrupting the internal dynamics of the colony and consequently lead to its weakening.

Strategic honey bee hive placement improves honey bee visitation but not pollination in northern highbush blueberry

Commercial blueberry Vaccinium spp. (Ericales: Ericaceae) production relies on insect-mediated pollination. Pollination is mostly provided by rented honey bees, Apis mellifera L. (Hymenoptera: Apidae), but blueberry crop yields can be limited due to pollination deficits. Various hive placement strategies have been recommended to mitigate pollination shortfalls, but the effect of hive placement has received limited formal investigation. This study explores the effects of clumped and dispersed hive placement strategies on honey bee visitation and pollination outcomes in "Bluecrop" and "Duke" fields over 2 years (2021 and 2022) within 2 economically important regions of production in the United States-the Midwest (Michigan) and Pacific Northwest (Oregon and Washington). Clumping hives consistently increased honey bee visitation rate but did not result in higher fruit set, fruit weight, or seed count. Increases in honey bee visitation through clumping could perhaps improve pollination outcomes in more pollination-limited blueberry cultivars and other pollination-dependent crops. Clumping hives is substantially more efficient and cost-effective for beekeepers due to fewer drop locations and could lead to cost savings for both beekeepers and blueberry growers without growers sacrificing pollination levels and crop yields.

Buzz pollination: investigations of pollen expulsion using the discrete element method

Buzz pollination involves the release of pollen from, primarily, poricidal anthers through vibrations generated by certain bee species. Despite previous experimental and numerical studies, the intricacies of pollen dynamics within vibrating anthers remain elusive due to the challenges in observing these small-scale, opaque systems. This research employs the discrete element method to simulate the pollen expulsion process in vibrating anthers. By exploring various frequencies and displacement amplitudes, a correlation between how aggressively the anther shakes and the initial rate of pollen expulsion is observed under translating oscillations. This study highlights that while increasing both the frequency and displacement of vibration enhances pollen release, the rate of release does not grow linearly with their increase. Our findings also reveal the significant role of pollen-pollen interactions, which account for upwards of one-third of the total collisions. Comparisons between two types of anther exits suggest that pore size and shape also influence expulsion rates. This research provides a foundation for more comprehensive models that can incorporate additional factors such as cohesion, adhesion and Coulomb forces, paving the way for deeper insights into the mechanics of buzz pollination and its variability across different anther types and vibration parameters.

Buzz pollination: A theoretical analysis via scaling invariance

Nearly half of the bee species can perform a fascinating stereotyped behavior to collect pollen grains by vibrating flowers, known as buzz pollination. During the floral visit, these bees mechanically transfer the vibrations produced by their thoracic indirect flight muscles to the flower anther, inducing the movement of the pollen grains and leading them to be released through a small pore or slit placed at the tip of the anther in poricidal flowers. In such flowers, pollen release is affected by the vibrational behavior of buzzing bees, primarily their duration and velocity amplitude. However, we know little about how poricidal anther morphology may influence it. In this work, we investigated through a theoretical and numerical point of view the buzz pollination process considering a typical poricidal anther of a tomato flower (Solanum lycopersicum), which in our work will be approached by a rectangular billiard, experiencing vibrations applied by a bumblebee (Bombus terrestris). Our primary goals in this paper are (i) to understand the mechanism behind the pollen release in this model, (ii) to observe some scale effects associated with morphological variations of the anther (as pore size and anther shape), and (iii) analyze how these results are related to natural buzz pollination systems.

Buzz-pollinating bees deliver thoracic vibrations to flowers through periodic biting

Pollinator behavior is vital to plant-pollinator interactions, affecting the acquisition of floral rewards, patterns of pollen transfer, and plant reproductive success. During buzz pollination, bees produce vibrations with their indirect flight muscles to extract pollen from tube-like flowers. Vibrations can be transmitted to the flower via the mandibles, abdomen, legs, or thorax directly. Vibration amplitude at the flower determines the rate of pollen release and should vary with the coupling of bee and flower. This coupling often occurs through anther biting, but no studies have quantified how biting affects flower vibration. Here, we used high-speed filmography to investigate how flower vibration amplitude changes during biting in Bombus terrestris visiting two species of buzz-pollinated flowering plants: Solanum dulcamara and Solanum rostratum (Solanaceae). We found that floral buzzing drives head vibrations up to 3 times greater than those of the thorax, which doubles the vibration amplitude of the anther during biting compared with indirect vibration transmission when not biting. However, the efficiency of this vibration transmission depends on the angle at which the bee bites the anther. Variation in transmission mechanisms, combined with the diversity of vibrations across bee species, yields a rich assortment of potential strategies that bees could employ to access rewards from buzz-pollinated flowers.

Buzz pollination: Bee bites and floral vibrations

Certain bees bite tubular anthers while contracting their flight muscles. This floral sonication ejects pollen grains that the bees collect as larval food. Bees bite and buzz simultaneously. A new study shows that where and how they bite is essential for efficient pollen collection.

Evolution of odorant receptor repertoires across Hymenoptera is not linked to the evolution of eusociality

Communication is essential for social organisms. In eusocial insects, olfaction facilitates communication and recognition between nestmates. The study of certain model organisms has led to the hypothesis that odorant receptors are expanded in eusocial Hymenoptera. This has become a widely mentioned idea in the literature, albeit with conflicting reports, and has not been tested with a broad comparative analysis. Here we combined existing genomic and new neuroanatomical data, including from an approximately 100 Myr old fossil ant, across a phylogenetically broad sample of hymenopteran lineages. We find no evidence that variation in the size and evolutionary tempo of odorant receptor repertoires is related to eusociality. Post hoc exploration of our data hinted at loss of flight as a possible factor shaping some of the variation in OR repertoires in Hymenoptera. Nevertheless, our analyses revealed a complex pattern of evolutionary variation, and raise new questions about the ecological, behavioural and social factors that shape olfactory abilities.

Global patterns and drivers of buzzing bees and poricidal plants

Foraging behavior frequently plays a major role in driving the geographic distribution of animals. Buzzing to extract protein-rich pollen from flowers is a key foraging behavior used by bee species across at least 83 genera (these genera comprise ∼58% of all bee species). Although buzzing is widely recognized to affect the ecology and evolution of bees and flowering plants (e.g., buzz-pollinated flowers), global patterns and drivers of buzzing bee biogeography remain unexplored. Here, we investigate the global species distribution patterns within each bee family and how patterns and drivers differ with respect to buzzing bee species. We found that both distributional patterns and drivers of richness typically differed for buzzing species compared with hotspots for all bee species and when grouped by family. A major predictor of the distribution, but not species richness overall for buzzing members of four of the five major bee families included in analyses (Andrenidae, Halictidae, Colletidae, and to a lesser extent, Apidae), was the richness of poricidal flowering plant species, which depend on buzzing bees for pollination. Because poricidal plant richness was highest in areas with low wind and high aridity, we discuss how global hotspots of buzzing bee biodiversity are likely influenced by both biogeographic factors and plant host availability. Although we explored global patterns with state-level data, higher-resolution work is needed to explore local-level drivers of patterns. From a global perspective, buzz-pollinated plants clearly play a greater role in the ecology and evolution of buzzing bees than previously predicted.

Extensive loss of forage diversity in social bees owing to flower constancy in simulated environments

Many bees visit just one flower species during a foraging trip, i.e. they show flower constancy. Flower constancy is important for plant reproduction but it could lead to an unbalanced diet, especially in biodiversity-depleted landscapes. It is assumed that flower constancy does not reduce dietary diversity in social bees, such as honeybees or bumblebees, but this has not yet been tested. We used computer simulations to investigate the effects of flower constancy on colony diet in plant species-rich and species-poor landscapes. We also explored if communication about food sources, which is used by many social bees, further reduces forage diversity. Our simulations reveal an extensive loss of forage diversity owing to flower constancy in both species-rich and species-poor environments. Small flower-constant colonies often discovered only 30-50% of all available plant species, thereby increasing the risk of nutritional deficiencies. Communication often interacted with flower constancy to reduce forage diversity further. Finally, we found that food source clustering, but not habitat fragmentation impaired dietary diversity. These findings highlight the nutritional challenges flower-constant bees face in different landscapes and they can aid in the design of measures to increase forage diversity and improve bee nutrition in human-modified landscapes.

Biomechanical properties of non-flight vibrations produced by bees

Bees use thoracic vibrations produced by their indirect flight muscles for powering wingbeats in flight, but also during mating, pollination, defence and nest building. Previous work on non-flight vibrations has mostly focused on acoustic (airborne vibrations) and spectral properties (frequency domain). However, mechanical properties such as the vibration's acceleration amplitude are important in some behaviours, e.g. during buzz pollination, where higher amplitude vibrations remove more pollen from flowers. Bee vibrations have been studied in only a handful of species and we know very little about how they vary among species. In this study, we conducted the largest survey to date of the biomechanical properties of non-flight bee buzzes. We focused on defence buzzes as they can be induced experimentally and provide a common currency to compare among taxa. We analysed 15,000 buzzes produced by 306 individuals in 65 species and six families from Mexico, Scotland and Australia. We found a strong association between body size and the acceleration amplitude of bee buzzes. Comparison of genera that buzz-pollinate and those that do not suggests that buzz-pollinating bees produce vibrations with higher acceleration amplitude. We found no relationship between bee size and the fundamental frequency of defence buzzes. Although our results suggest that body size is a major determinant of the amplitude of non-flight vibrations, we also observed considerable variation in vibration properties among bees of equivalent size and even within individuals. Both morphology and behaviour thus affect the biomechanical properties of non-flight buzzes.

Floral scent changes in response to pollen removal are rare in buzz-pollinated Solanum

MAIN CONCLUSION

One of seven Solanum taxa studied displayed associations between pollen presence and floral scent composition and volume, suggesting buzz-pollinated plants rarely use scent as an honest cue for foraging pollinators. Floral scent influences the recruitment, learning, and behaviour of floral visitors. Variation in floral scent can provide information on the amount of reward available or whether a flower has been visited recently and may be particularly important in species with visually concealed rewards. In many buzz-pollinated flowers, tubular anthers opening via small apical pores (poricidal anthers) visually conceal pollen and appear similar regardless of pollen quantity within the anther. We investigated whether pollen removal changes floral scent composition and emission rate in seven taxa of buzz-pollinated Solanum (Solanaceae). We found that pollen removal reduced both the overall emission of floral scent and the emission of specific compounds (linalool and farnesol) in S. lumholtzianum. Our findings suggest that in six out of seven buzz-pollinated taxa studied here, floral scent could not be used as a signal by visitors as it does not contain information on pollen availability.

Phylogenomic analysis of Stylops reveals the evolutionary history of a Holarctic Strepsiptera radiation parasitizing wild bees

Holarctic Stylops is the largest genus of the enigmatic insect order Strepsiptera, twisted winged parasites. Members of Stylops are obligate endoparasites of Andrena mining bees and exhibit extreme sexual dimorphism typical of Strepsiptera. So far, molecular studies on Stylops have focused on questions on species delimitation. Here, we utilize the power of whole genome sequencing to infer the phylogeny of this morphologically challenging genus from thousands of loci. We use a species tree method, concatenated maximum likelihood analysis and Bayesian analysis with a relaxed clock model to reconstruct the phylogeny of 46 Stylops species, estimate divergence times, evaluate topological consistency across methods and infer the root position. Furthermore, the biogeographical history and coevolutionary patterns with host species are assessed. All methods recovered a well resolved topology with close to all nodes maximally supported and only a handful of minor topological variations. Based on the result, we find that included species can be divided into 12 species groups, seven of them including only Palaearctic species, three Nearctic and two were geographically mixed. We find a strongly supported root position between a clade formed by the spreta, thwaitesi and gwynanae species groups and the remaining species and that the sister group of Stylops is Eurystylops or Eurystylops + Kinzelbachus. Our results indicate that Stylops originated in the Western Palaearctic or Western Palaearctic and Nearctic in the early Neogene or late Paleogene, with four independent dispersal events to the Nearctic. Cophylogenetic analyses indicate that the diversification of Stylops has been shaped by both significant coevolution with the mining bee hosts and host-shifting. The well resolved and strongly supported phylogeny will provide a valuable phylogenetic basis for further studies into the fascinating world of Strepsipterans.

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'.

High floral disparity without pollinator shifts in buzz-bee-pollinated Melastomataceae

Shifts among functional pollinator groups are commonly regarded as sources of floral morphological diversity (disparity) through the formation of distinct pollination syndromes. While pollination syndromes may be used for predicting pollinators, their predictive accuracy remains debated, and they are rarely used to test whether floral disparity is indeed associated with pollinator shifts. We apply classification models trained and validated on 44 functional floral traits across 252 species with empirical pollinator observations and then use the validated models to predict pollinators for 159 species lacking observations. In addition, we employ multivariate statistics and phylogenetic comparative analyses to test whether pollinator shifts are the main source of floral disparity in Melastomataceae. We find strong support for four well-differentiated pollination syndromes ('buzz-bee', 'nectar-foraging vertebrate', 'food-body-foraging vertebrate', 'generalist'). While pollinator shifts add significantly to floral disparity, we find that the most species-rich 'buzz-bee' pollination syndrome is most disparate, indicating that high floral disparity may evolve without pollinator shifts. Also, relatively species-poor clades and geographic areas contributed substantially to total disparity. Finally, our results show that machine-learning approaches are a powerful tool for evaluating the predictive accuracy of the pollination syndrome concept as well as for predicting pollinators where observations are missing.

Harvesting pollen with vibrations: towards an integrative understanding of the proximate and ultimate reasons for buzz pollination

Buzz pollination, a type of interaction in which bees use vibrations to extract pollen from certain kinds of flowers, captures a close relationship between thousands of bee and plant species. In the last 120 years, studies of buzz pollination have contributed to our understanding of the natural history of buzz pollination, and basic properties of the vibrations produced by bees and applied to flowers in model systems. Yet, much remains to be done to establish its adaptive significance and the ecological and evolutionary dynamics of buzz pollination across diverse plant and bee systems. Here, we review for bees and plants the proximate (mechanism and ontogeny) and ultimate (adaptive significance and evolution) explanations for buzz pollination, focusing especially on integrating across these levels to synthesize and identify prominent gaps in our knowledge. Throughout, we highlight new technical and modelling approaches and the importance of considering morphology, biomechanics and behaviour in shaping our understanding of the adaptive significance of buzz pollination. We end by discussing the ecological context of buzz pollination and how a multilevel perspective can contribute to explain the proximate and evolutionary reasons for this ancient bee-plant interaction.

Lessons from assembling UCEs: A comparison of common methods and the case of Clavinomia (Halictidae)

Sequence data assembly is a foundational step in high-throughput sequencing, with untold consequences for downstream analyses. Despite this, few studies have interrogated the many methods for assembling phylogenomic UCE data for their comparative efficacy, or for how outputs may be impacted. We study this by comparing the most commonly used assembly methods for UCEs in the under-studied bee lineage Nomiinae and a representative sampling of relatives. Data for 63 UCE-only and 75 mixed taxa were assembled with five methods, including ABySS, HybPiper, SPAdes, Trinity and Velvet, and then benchmarked for their relative performance in terms of locus capture parameters and phylogenetic reconstruction. Unexpectedly, Trinity and Velvet trailed the other methods in terms of locus capture and DNA matrix density, whereas SPAdes performed favourably in most assessed metrics. In comparison with SPAdes, the guided-assembly approach HybPiper generally recovered the highest quality loci but in lower numbers. Based on our results, we formally move Clavinomia to Dieunomiini and render Epinomia once more a subgenus of Dieunomia. We strongly advise that future studies more closely examine the influence of assembly approach on their results, or, minimally, use better-performing assembly methods such as SPAdes or HybPiper. In this way, we can move forward with phylogenomic studies in a more standardized, comparable manner.

Comparative analyses of mitogenomes in the social bees with insights into evolution of long inverted repeats in the Meliponini

The insect mitogenome is typically a compact circular molecule with highly conserved gene contents. Nonetheless, mitogenome structural variations have been reported in specific taxa, and gene rearrangements, usually the tRNAs, occur in different lineages. Because synapomorphies of mitogenome organizations can provide information for phylogenetic inferences, comparative analyses of mitogenomes have been given increasing attention. However, most studies use a very few species to represent the whole genus, tribe, family, or even order, overlooking potential variations at lower taxonomic levels, which might lead to some incorrect inferences. To provide new insights into mitogenome organizations and their implications for phylogenetic inference, this study conducted comparative analyses for mitogenomes of three social bee tribes (Meliponini, Bombini, and Apini) based on the phylogenetic framework with denser taxonomic sampling at the species and population levels. Comparative analyses revealed that mitogenomes of Apini and Bombini are the typical type, while those of Meliponini show diverse variations in mitogenome sizes and organizations. Large inverted repeats (IRs) cause significant gene rearrangements of protein coding genes (PCGs) and rRNAs in Indo-Malay/Australian stingless bee species. Molecular evolution analyses showed that the lineage with IRs have lower d N/ d S ratios for PCGs than lineages without IRs, indicating potential effects of IRs on the evolution of mitochondrial genes. The finding of IRs and different patterns of gene rearrangements suggested that Meliponini is a hotspot in mitogenome evolution. Unlike conserved PCGs and rRNAs whose rearrangements were found only in the mentioned lineages within Meliponini, tRNA rearrangements are common across all three tribes of social bees, and are significant even at the species level, indicating that comprehensive sampling is needed to fully understand the patterns of tRNA rearrangements, and their implications for phylogenetic inference.

A supermatrix phylogeny of the world's bees (Hymenoptera: Anthophila)

The increasing availability of large molecular phylogenies has provided new opportunities to study the evolution of species traits, their origins and diversification, and biogeography; yet there are limited attempts to synthesise existing phylogenetic information for major insect groups. Bees (Hymenoptera: Anthophila) are a large group of insect pollinators that have a worldwide distribution, and a wide variation in ecology, morphology, and life-history traits, including sociality. For these reasons, as well as their major economic importance as pollinators, numerous molecular phylogenetic studies of family and genus-level relationships have been published, providing an opportunity to assemble a bee 'tree-of-life'. We used publicly available genetic sequence data, including phylogenomic data, reconciled to a taxonomic database, to produce a concatenated supermatrix phylogeny for the Anthophila comprising 4,586 bee species, representing 23% of species and 82% of genera. At family, subfamily, and tribe levels, support for expected relationships was robust, but between and within some genera relationships remain uncertain. Within families, sampling of genera ranged from 67 to 100% but species coverage was lower (17-41%). Our phylogeny mostly reproduces the relationships found in recent phylogenomic studies with a few exceptions. We provide a summary of these differences and the current state of molecular data available and its gaps. We discuss the advantages and limitations of this bee supermatrix phylogeny (available online at beetreeoflife.org), which may enable new insights into long standing questions about evolutionary drivers in bees, and potentially insects more generally.

Diversity of staminal nectariferous appendages in disymmetric and zygomorphic flowers of Fumarioideae (Papaveraceae)

Staminal nectaries show diversity in their position, size, shape, color, and number in Ranunculales. In Papaveraceae, nectaries only appear at the base of stamen in these lineages with disymmetric and zygomorphic flowers. However, the diversity of the staminal nectaries' developmental characteristics and structure is unknown. The diversity of staminal nectaries of Hypecoum erectum, Ichtyoselmis macrantha, Adlumia asiatica, Dactylicapnos torulosa, Corydalis edulis, and Fumaria officinalis (six species belonging to six genera, respectively) in the Fumarioideae was investigated under scanning electron microscopy, light microscopy, and transmission electron microscopy. In all species studied, according to the developmental characteristics of the nectaries, four developmental stages can be divided into initiation, enlargement, differentiation, and maturation, and the number of nectaries can be determined at the stage of initiation (stage 1), and morphological differentiation occurs at the developmental stage 3. The staminal nectaries consist of secretory epidermis, parenchyma tissue, and phloem with some sieve tube elements reaching the secretory parenchyma cells; however, the number of cell layers of parenchyma can vary from 30 to 40 in I. macrantha and D. torulosa, to only 5 to 10 like in F. officinalis. Secretory epidermis cells are larger than secretory parenchyma cells with abundant microchannels on the outer cell wall. There were abundant mitochondria, Golgi bodies, rough endoplasmic reticulum, and plastids in secretory parenchyma cells. Nectar is stored in the intercellular space and exuded to the exterior via microchannels. In A. asiatica, according to the evidence of small secretory cell characteristics such as dense cytoplasm, and numerous mitochondria, together with the filamentous secretions present on the surface of epidermal cells on groove, it can be inferred that the U-shaped sulcate which is located in the white projection formed at the filament of triplets in A. asiatica is nectariferous.

The evolutionary history of bees in time and space

Bees are the most significant pollinators of flowering plants. This partnership began ca. 120 million years ago, but the uncertainty of how and when bees spread across the planet has greatly obscured investigations of this key mutualism. We present a novel analysis of bee biogeography using extensive new genomic and fossil data to demonstrate that bees originated in Western Gondwana (Africa and South America). Bees likely originated in the Early Cretaceous, shortly before the breakup of Western Gondwana, and the early evolution of any major bee lineage is associated with either the South American or African land masses. Subsequently, bees colonized northern continents via a complex history of vicariance and dispersal. The notable early absences from large landmasses, particularly in Australia and India, have important implications for understanding the assembly of local floras and diverse modes of pollination. How bees spread around the world from their hypothesized Southern Hemisphere origin parallels the histories of numerous flowering plant clades, providing an essential step to studying the evolution of angiosperm pollination syndromes in space and time.

Automatic acoustic recognition of pollinating bee species can be highly improved by Deep Learning models accompanied by pre-training and strong data augmentation

Introduction

Bees capable of performing floral sonication (or buzz-pollination) are among the most effective pollinators of blueberries. However, the quality of pollination provided varies greatly among species visiting the flowers. Consequently, the correct identification of flower visitors becomes indispensable to distinguishing the most efficient pollinators of blueberry. However, taxonomic identification normally depends on microscopic characteristics and the active participation of experts in the decision-making process. Moreover, the many species of bees (20,507 worldwide) and other insects are a challenge for a decreasing number of insect taxonomists. To overcome the limitations of traditional taxonomy, automatic classification systems of insects based on Machine-Learning (ML) have been raised for detecting and distinguishing a wide variety of bioacoustic signals, including bee buzzing sounds. Despite that, classical ML algorithms fed by spectrogram-type data only reached marginal performance for bee ID recognition. On the other hand, emerging systems from Deep Learning (DL), especially Convolutional Neural Networks (CNNs), have provided a substantial boost to classification performance in other audio domains, but have yet to be tested for acoustic bee species recognition tasks. Therefore, we aimed to automatically identify blueberry pollinating bee species based on characteristics of their buzzing sounds using DL algorithms.

Methods

We designed CNN models combined with Log Mel-Spectrogram representations and strong data augmentation and compared their performance at recognizing blueberry pollinating bee species with the current state-of-the-art models for automatic recognition of bee species.

Results and Discussion

We found that CNN models performed better at assigning bee buzzing sounds to their respective taxa than expected by chance. However, CNN models were highly dependent on acoustic data pre-training and data augmentation to outperform classical ML classifiers in recognizing bee buzzing sounds. Under these conditions, the CNN models could lead to automating the taxonomic recognition of flower-visiting bees of blueberry crops. However, there is still room to improve the performance of CNN models by focusing on recording samples for poorly represented bee species. Automatic acoustic recognition associated with the degree of efficiency of a bee species to pollinate a particular crop would result in a comprehensive and powerful tool for recognizing those that best pollinate and increase fruit yields.

Sociality is a key driver of foraging ranges in bees

Bees are important pollinators of wild and agricultural plants^1,2,3,4,5 and there is increasing evidence that many bee populations decline due to a combination of habitat loss, climate change, pesticides, and other anthropogenic effects.^{6,7,8,9,10,11} One trait that shapes both their role in plant reproduction^12,13 and their exposure to anthropogenic stressors is the distance at which bees forage. It has been suggested that bee sociality¹⁴ and diet¹⁵ affect bee foraging ranges, but how these traits and their potential interactions drive foraging ranges remains unclear. We analyzed flight distance data from 90 bee species and developed an agent-based model to test how social, dietary, and environmental factors affect foraging ranges. We confirm that bee sociality is positively associated with foraging range, with average-sized social bees foraging up to 3 times farther from the nest than size-matched solitary bees. A comparative analysis of social bees and computer simulations shows that foraging distances increase with colony size, supporting the hypothesis that greater foraging distances are an emergent property of increasing colony sizes in a food-limited environment. Flower constancy and communication, two traits often found in social bees, synergistically increase foraging distances further in many simulated environments. Diet breadth (oligolectic versus polylectic diet), on the other hand, does not appear to affect foraging ranges in solitary bees. Our findings suggest that multiple traits linked to bee sociality explain why social bees have greater foraging ranges. This has implications for predicting pollination services and for developing effective conservation strategies for bees and isolated plant populations.^{15,16,17,18,19}.

Cryptic Diversity Revealed in A Revision of West Palaearctic Nomiapis and Systropha (Hymenoptera: Halictidae)

Revisionary taxonomic studies of bees from the Old World Mediterranean basin are hindered both by the apparent absence of type material for many taxa and a lack of genetic resources. The discovery of important type materials in combination with the generation of novel DNA barcodes (Cytochrome Oxidase I) has allowed cryptic diversity within the widespread taxa Nomiapis bispinosa (Brullé, 1832) and Systropha planidens Giraud, 1861 to be clarified. Nomiapis bispinosa actually consists of three distinct taxa: Nomiapis bispinosa s. str. from Morocco and Iberia to Central Asia, Nomiapis rufiventris (Spinola, 1838) spec. resurr. from Morocco to Egypt, including Sicily and Nomiapis paulyispec. nov. from Portugal and Spain. A lectotype is designated for Nomia rufiventris Spinola, 1838. Lectotypes are designated for Nomia bispinosa Brullé, 1832 and Nomia albocincta Lucas, 1849, and type material for Nomia perforata Lucas, 1849 is clarified; both Nomiapis albocincta and Nomiapis perforata are synonymised syn. nov. with Nomiapis rufiventris. A lectotype is designated for Nomia ruficornis Spinola, 1838, and this taxon is confirmed as a synonym of Nomiapis bispinosa. Systropha planidens also consists of three distinct taxa: S. planidens from Central Europe to Iran and the European part of Russia, S. grandimargo Pérez, 1905 spec. resurr. from Portugal, Spain, and France, and S. anatolica Warncke, 1977 stat. nov. from Turkey, Syria, and northern Israel. A lectotype is designated for Systropha planidens Giraud, 1861. Systropha chrysura Pérez, 1905 is synonymised syn. nov. with S. grandimargo. These findings illustrate the extent to which our understanding of the taxonomy of Mediterranean bees remains incomplete.

Toward evidence-based decision support systems to optimize pollination and yields in highbush blueberry

Highbush blueberry (Vaccinium spp.) is a globally important fruit crop that depends on insect-mediated pollination to produce quality fruit and commercially viable yields. Pollination success in blueberry is complex and impacted by multiple interacting factors including flower density, bee diversity and abundance, and weather conditions. Other factors, including floral traits, bee traits, and economics also contribute to pollination success at the farm level but are less well understood. As blueberry production continues to expand globally, decision-aid technologies are needed to optimize and enhance the sustainability of pollination strategies. The objective of this review is to highlight our current knowledge about blueberry pollination, where current research efforts are focused, and where future research should be directed to successfully implement a comprehensive blueberry pollination decision-making framework for modern production systems. Important knowledge gaps remain, including how to integrate wild and managed pollinators to optimize pollination, and how to provide predictable and stable crop pollination across variable environmental conditions. In addition, continued advances in pesticide stewardship are required to optimize pollinator health and crop outcomes. Integration of on- and off-farm data, statistical models, and software tools could distill complex scientific information into decision-aid systems that support sustainable, evidence-based pollination decisions at the farm level. Utility of these tools will require multi-disciplinary research and strategic deployment through effective extension and information-sharing networks of growers, beekeepers, and extension/crop advisors.

Heteromorphic stamens are differentially attractive in Swartzia (Fabaceae)

The division of labour hypothesis between stamens has explained the evolution of divergent functions between dimorphic stamens in the same flower. However, little is known about whether the distinct type of stamens differs in attractiveness to pollinators. Therefore, we investigate whether the two types of stamens commonly found in Swartzia have different visual and olfactory attractants. We performed observations of anthesis dynamics, registration and collection of floral visitors, measurements of reflectance of floral parts and chemical analysis of the volatile organic compounds of the floral parts of two species, S. flaemingii and S. simplex. Both species have two distinct sets of stamens: one with smaller and abundant stamens in the centre of the flower and the other with fewer but larger abaxial stamens. The sets differ in UV reflectance (only S. simplex) and exhibit a distinct chromatic contrast. Concerning olfactory attractiveness, aliphatic compounds make up most of the odour of the two species, both whole flowers and most of their floral organs. On the other hand, only S. simplex presented apocarotenoids (as ionones) and benzenoids. Furthermore, there are differences in the proportion of volatiles emitted by the stamen in both cases, as the high proportion of sesquiterpenes among the smaller stamens compared to the larger ones. In conclusion, the two types of stamens found in S. flaemingii and S. simplex show a distinct attractiveness. In addition, our data have demonstrated diverse ways of differential attractiveness both between distinct stamens set per flower and between the two species from the same pollen flowers genus.

Carpenter bee thorax vibration and force generation inform pollen release mechanisms during floral buzzing

Approximately 10% of flowering plant species conceal their pollen within tube-like poricidal anthers. Bees extract pollen from poricidal anthers via floral buzzing, a behavior during which they apply cyclic forces by biting the anther and rapidly contracting their flight muscles. The success of pollen extraction during floral buzzing relies on the direction and magnitude of the forces applied by the bees, yet these forces and forcing directions have not been previously quantified. In this work, we developed an experiment to simultaneously measure the directional forces and thorax kinematics produced by carpenter bees (Xylocopa californica) during defensive buzzing, a behavior regulated by similar physiological mechanisms as floral buzzing. We found that the buzzing frequencies averaged about 130 Hz and were highly variable within individuals. Force amplitudes were on average 170 mN, but at times reached nearly 500 mN. These forces were 30–80 times greater than the weight of the bees tested. The two largest forces occurred within a plane formed by the bees’ flight muscles. Force amplitudes were moderately correlated with thorax displacement, velocity and acceleration amplitudes but only weakly correlated with buzzing frequency. Linear models developed through this work provide a mechanism to estimate forces produced during non-flight behaviors based on thorax kinematic measurements in carpenter bees. Based on the buzzing frequencies, individual bee’s capacity to vary buzz frequency and predominant forcing directions, we hypothesize that carpenter bees leverage vibration amplification to increase the deformation of poricidal anthers, and hence the amount of pollen ejected.

Reduced visitation to buzz-pollinated Cyanella hyacinthoides in the presence of other pollen sources in the hyperdiverse Cape Floristic Region

Many plant species have floral morphologies that restrict access to floral resources, such as pollen or nectar, and only a subset of floral visitors can perform the handling behaviors required to extract restricted resources. Due to the time and energy required to extract resources from morphologically complex flowers, these plant species potentially compete for pollinators with co-flowering plants that have more easily accessible resources. A widespread floral mechanism restricting access to pollen is the presence of tubular anthers that open through small pores or slits (poricidal anthers). Some bees have evolved the capacity to remove pollen from poricidal anthers using vibrations, giving rise to the phenomenon of buzz-pollination. These bee vibrations that are produced for pollen extraction are presumably energetically costly, and to date, few studies have investigated whether buzz-pollinated flowers may be at a disadvantage when competing for pollinators' attention with plant species that present unrestricted pollen resources. Here, we studied Cyanella hyacinthoides (Tecophilaeaceae), a geophyte with poricidal anthers in the hyperdiverse Cape Floristic Region of South Africa, to assess how the composition and relative abundance of flowers with easily accessible pollen affect bee visitation to a buzz-pollinated plant. We found that the number of pollinator species of C. hyacinthoides was not influenced by community composition. However, visitation rates to C. hyacinthoides were reduced when the relative abundances of flowers with more accessible resources were high. Visitation rates were strongly associated with petal color, showing that flower color is important in mediating these interactions. We conclude that buzz-pollinated plants might be at a competitive disadvantage when many easily accessible pollen sources are available, particularly when competitor species share its floral signals.

Phylogenomics and historical biogeography of the cleptoparasitic bee genus Nomada (Hymenoptera: Apidae) using ultraconserved elements

The genus Nomada Scopoli (Hymenoptera: Apidae) is the largest genus of brood parasitic bees with nearly 800 species found across the globe and in nearly all biogeographic realms except Antarctica. There is no previous molecular phylogeny focused on Nomada despite their high species abundance nor is there an existing comprehensive biogeography for the genus. Using ultraconserved element (UCE) phylogenomic data, we constructed the first molecular phylogeny for the genus Nomada and tested the monophyly of 16 morphologically established species groups. We also estimated divergence dates using fossil calibration points and inferred the origin and of this genus around the globe. Our phylogeny recovered 14 of the 16 previously established species groups as monophyletic. The superba and ruficornis groups, however, were recovered as non-monophyletic and need to be re-evaluated using morphology. Divergence dating and historic biogeographic analyses performed on the phylogenetic reconstruction indicates that Nomada most likely originated in the Holarctic ∼65 Mya. Geodispersal into the southern hemisphere occurred three times; once during the Eocene into the Afrotropics, once during the Oligocene into the Neotropics, and once during the Miocene into Australasia. Geodispersal across the Holarctic was most frequent and occurred repeatedly throughout the Cenozoic era, using the De Geer, Thulean, and the Bering Land Bridges. This is the first instance of a bee using both the Thulean and De Geer land bridges and has implications of how early bee species dispersed throughout the Palearctic in the late Cretaceous and early Paleogene.

Structural dynamics of real and modelled Solanum stamens: implications for pollen ejection by buzzing bees

An estimated 10% of flowering plant species conceal their pollen within tube-like anthers that dehisce through small apical pores (poricidal anthers). Bees extract pollen from poricidal anthers through a complex motor routine called floral buzzing, whereby the bee applies vibratory forces to the flower stamen by rapidly contracting its flight muscles. The resulting deformation depends on the stamen's natural frequencies and vibration mode shapes, yet for most poricidal species, these properties have not been sufficiently characterized. We performed experimental modal analysis on Solanum elaeagnifolium stamens to quantify their natural frequencies and vibration modes. Based on morphometric and dynamic measurements, we developed a finite-element model of the stamen to identify how variable material properties, geometry and bee weight could affect its dynamics. In general, stamen natural frequencies fell outside the reported floral buzzing range, and variations in stamen geometry and material properties were unlikely to bring natural frequencies within this range. However, inclusion of bee mass reduced natural frequencies to within the floral buzzing frequency range and gave rise to an axial-bending vibration mode. We hypothesize that floral buzzing bees exploit the large vibration amplification factor of this mode to increase anther deformation, which may facilitate pollen ejection.

How and why do bees buzz? Implications for buzz pollination

Buzz pollination encompasses the evolutionary convergence of specialized floral morphologies and pollinator behaviour in which bees use vibrations (floral buzzes) to remove pollen. Floral buzzes are one of several types of vibrations produced by bees using their thoracic muscles. Here I review how bees can produce these different types of vibrations and discuss the implications of this mechanistic understanding for buzz pollination. I propose that bee buzzes can be categorized according to their mode of production and deployment into: (i) thermogenic, which generate heat with little mechanical vibration; (ii) flight buzzes which, combined with wing deployment and thoracic vibration, power flight; and (iii) non-flight buzzes in which the thorax vibrates but the wings remain mostly folded, and include floral, defence, mating, communication, and nest-building buzzes. I hypothesize that the characteristics of non-flight buzzes, including floral buzzes, can be modulated by bees via modification of the biomechanical properties of the thorax through activity of auxiliary muscles, changing the rate of activation of the indirect flight muscles, and modifying flower handling behaviours. Thus, bees should be able to fine-tune mechanical properties of their floral vibrations, including frequency and amplitude, depending on flower characteristics and pollen availability to optimize energy use and pollen collection.

Total-evidence dating and morphological partitioning: a novel approach to understand the phylogeny and biogeography of augochlorine bees (Hymenoptera: Apoidea)

Augochlorini comprise 646 described bee species primarily distributed in the Neotropical region. According to molecular and morphological phylogenies, the tribe is monophyletic and subdivided into seven genus groups. Our main objective is to propose a revised phylogeny of Augochlorini based on a comprehensive data set including fossil species as terminals and new characters from the internal skeleton. We also aim to develop a total-evidence framework incorporating a morphological-partitioned homoplasy approach and molecular data and propose a detailed biogeographic and evolutionary scenario based on ancestor range estimation. Our results recovered Augochlorini and most genus groups as monophyletic, despite some uncertainties about monophyly of the Megalopta and Neocorynura groups. The position of the cleptoparasite Temonosoma is still uncertain. All analyses recovered Augochloropsis s.l. as related to the Megaloptidia group. Internal characters from the head, mesosoma and sting apparatus provided important synapomorphies for most internal nodes, genus groups and genera. Augochlorini diversification occurred in the uplands of the Neotropical region, especially the Brazilian Plateau. Multiple dispersals to Amazonia, Central America and North America with returns to the Atlantic endemism area were recovered in our analysis. Total evidence, including morphological partitioning, was shown to be a reliable approach for phylogenetic reconstruction.

The Birth-and-Death Evolution of Cytochrome P450 Genes in Bees

The birth-and-death model of multigene family evolution describes how gene families evolve and diversify through duplication and deletion. The cytochrome P450s are one of the most diverse and well-studied multigene families, involved in both physiological and xenobiotic functions. Extensive studies of insect P450 genes have demonstrated their role in insecticide resistance. Bees are thought to experience toxin exposure through their diet of nectar and pollen, as well as the resin-collecting behavior exhibited by some species. Here, we describe the repertoire of P450 genes in the orchid bee Euglossa dilemma. Male orchid bees form perfume bouquets used in courtship displays by collecting volatile compounds, resulting in exposure to compounds known to be toxic. In addition, we conducted phylogenetic and selection analyses across ten bee species encompassing three bee families. We find that social behavior and resin collection are not correlated with the repertoire of P450 present in a bee species. However, our analyses revealed that P450 clades can be classified as stable and unstable, and that genes involved in xenobiotic metabolism are more likely to belong to unstable clades. Furthermore, we find that unstable clades are under more dynamic evolutionary pressures and exhibit signals of adaptive evolution. This work highlights the complexity of multigene family evolution, revealing that multiple factors contribute to the diversification, stability, and dynamics of this gene family. Furthermore, we provide a resource for future detailed studies investigating the function of different P450s in economically important bee species.

Examining the Role of Buzzing Time and Acoustics on Pollen Extraction of Solanum elaeagnifolium

Buzz pollination is a specialized pollination syndrome that requires vibrational energy to extract concealed pollen grains from poricidal anthers. Although a large body of work has examined the ecology of buzz pollination, whether acoustic properties of buzz pollinators affect pollen extraction is less understood, especially in weeds and invasive species. We examined the pollination biology of Silverleaf nightshade (Solanum elaeagnifolium), a worldwide invasive weed, in its native range in the Lower Rio Grande Valley (LRGV) in south Texas. Over two years, we documented the floral visitors on S. elaeagnifolium, their acoustic parameters (buzzing amplitude, frequency, and duration of buzzing) and estimated the effects of the latter two factors on pollen extraction. We found five major bee genera: Exomalopsis, Halictus, Megachile, Bombus, and Xylocopa, as the most common floral visitors on S. elaeagnifolium in the LRGV. Bee genera varied in their duration of total buzzing time, duration of each visit, and mass. While we did not find any significant differences in buzzing frequency among different genera, an artificial pollen collection experiment using an electric toothbrush showed that the amount of pollen extracted is significantly affected by the duration of buzzing. We conclude that regardless of buzzing frequency, buzzing duration is the most critical factor in pollen removal in this species.

Phylogenetic relationships and the evolution of host preferences in the largest clade of brood parasitic bees (Apidae: Nomadinae)

Brood parasites (also known as cleptoparasites) represent a substantial fraction of global bee diversity. Rather than constructing their own nests, these species instead invade those of host bees to lay their eggs. Larvae then hatch and consume the food provisions intended for the host's offspring. While this life history strategy has evolved numerous times across the phylogeny of bees, the oldest and most speciose parasitic clade is the subfamily Nomadinae (Apidae). However, the phylogenetic relationships among brood parasitic apids both within and outside the Nomadinae have not been fully resolved. Here, we present new findings on the phylogeny of this diverse group of brood parasites based on ultraconserved element (UCE) sequence data and extensive taxon sampling with 114 nomadine species representing all tribes. We suggest a broader definition of the subfamily Nomadinae to describe a clade that includes almost all parasitic members of the family Apidae. The tribe Melectini forms the sister group to all other Nomadinae, while the remainder of the subfamily is composed of two sister clades: a "nomadine line" representing the former Nomadinae sensu stricto, and an "ericrocidine line" that unites several mostly Neotropical lineages. We find the tribe Osirini Handlirsch to be polyphyletic, and divide it into three lineages, including the newly described Parepeolini trib. nov. In addition to our taxonomic findings, we use our phylogeny to explore the evolution of different modes of parasitism, detecting two independent transitions from closed-cell to open-cell parasitism. Finally, we examine how nomadine host-parasite associations have evolved over time. In support of Emery's rule, which suggests close relationships between hosts and parasites, we confirm that the earliest nomadines were parasites of their close free-living relatives within the family Apidae, but that over time their host range broadened to include more distantly related hosts spanning the diversity of bees. This expanded breadth of host taxa may also be associated with the transition to open-cell parasitism.

Bee flowers drive macroevolutionary diversification in long-horned bees

The role of plant–pollinator interactions in the rapid radiation of the angiosperms have long fascinated evolutionary biologists. Studies have brought evidence for pollinator-driven diversification of various plant lineages, particularly plants with specialized flowers and concealed rewards. By contrast, little is known about how this crucial interaction has shaped macroevolutionary patterns of floral visitors. In particular, there is currently no empirical evidence that floral host association has increased diversification in bees, the most prominent group of floral visitors that essentially rely on angiosperm pollen. In this study, we examine how floral host preference influenced diversification in eucerine bees (Apidae, Eucerini), which exhibit large variations in their floral associations. We combine quantitative pollen analyses with a recently proposed phylogenetic hypothesis, and use a state speciation and extinction probabilistic approach. Using this framework, we provide the first evidence that multiple evolutionary transitions from host plants with accessible pollen to restricted pollen from ‘bee-flowers’ have significantly increased the diversification of a bee clade. We suggest that exploiting host plants with restricted pollen has allowed the exploitation of a new ecological niche for eucerine bees and contributed both to their colonization of vast regions of the world and their rapid diversification.

Machine learning approach for automatic recognition of tomato-pollinating bees based on their buzzing-sounds

Bee-mediated pollination greatly increases the size and weight of tomato fruits. Therefore, distinguishing between the local set of bees–those that are efficient pollinators–is essential to improve the economic returns for farmers. To achieve this, it is important to know the identity of the visiting bees. Nevertheless, the traditional taxonomic identification of bees is not an easy task, requiring the participation of experts and the use of specialized equipment. Due to these limitations, the development and implementation of new technologies for the automatic recognition of bees become relevant. Hence, we aim to verify the capacity of Machine Learning (ML) algorithms in recognizing the taxonomic identity of visiting bees to tomato flowers based on the characteristics of their buzzing sounds. We compared the performance of the ML algorithms combined with the Mel Frequency Cepstral Coefficients (MFCC) and with classifications based solely on the fundamental frequency, leading to a direct comparison between the two approaches. In fact, some classifiers powered by the MFCC–especially the SVM–achieved better performance compared to the randomized and sound frequency-based trials. Moreover, the buzzing sounds produced during sonication were more relevant for the taxonomic recognition of bee species than analysis based on flight sounds alone. On the other hand, the ML classifiers performed better in recognizing bees genera based on flight sounds. Despite that, the maximum accuracy obtained here (73.39% by SVM) is still low compared to ML standards. Further studies analyzing larger recording samples, and applying unsupervised learning systems may yield better classification performance. Therefore, ML techniques could be used to automate the taxonomic recognition of flower-visiting bees of the cultivated tomato and other buzz-pollinated crops. This would be an interesting option for farmers and other professionals who have no experience in bee taxonomy but are interested in improving crop yields by increasing pollination.

Bees are the most important pollinators of cultivated tomatoes. We also know that the distinct species of bees have different performances as pollinators, and these performances are directly related to the size and weight of the fruits. Moreover, the characteristics of the buzzing sounds tend to vary between the bee species. However, the buzzing sounds are complex and can widely vary over time, making the analysis of this data difficult using the usual statistical methods in Ecology. In the face of this problem, we proposed to automatically recognize pollinating bees of tomato flowers based on their buzzing sounds using Machine Learning (ML) tools. In fact, we found that the ML algorithms are capable of recognizing bees just based on their buzzing sounds. This could lead to automating the recognition of flower-visiting bees of the cultivated tomato, which would be a nice option for farmers and other professionals who have no experience in bee taxonomy but are interested in improving crop yields. On the other hand, this encourages the farmer to adopt sustainable agricultural practices for the conservation of native tomato pollinators. To achieve this goal, the next step is to develop applications compatible with smartphones capable of recognizing bees by their buzzing sounds.

Mutualisms and (A)symmetry in Plant-Pollinator Interactions

The majority of flowering plants relies on animal pollinators for sexual reproduction and many animal pollinators rely on floral resources. However, interests of plants and pollinators are often not the same, resulting in an asymmetric relationship that ranges from mutualistic to parasitic interactions. Our understanding of the processes that underlie this asymmetry remains fragmentary. In this Review, we bring together evidence from evolutionary biology, plant chemistry, biomechanics, sensory ecology and behaviour to illustrate that the degree of symmetry often depends on the perspective taken. We also highlight variation in (a)symmetry within and between plant and pollinator species as well as between geographic locations. Through taking different perspectives from the plant and pollinator sides we provide new ground for studies on the maintenance and evolution of animal pollination and on the (a)symmetry in plant-pollinator interactions.

Pollinator effectiveness is affected by intraindividual behavioral variation

Variation in pollinator quality is fundamental to the evolution of plant-pollinator mutualisms and such variation frequently results from differences in foraging behavior. Surprisingly, despite substantial intraindividual variation in pollinator foraging behavior, the consequences for pollen removal and deposition on flowers are largely unknown. We asked how two pollen foraging behaviors of a generalist pollinator (Bombus impatiens) affect removal and deposition of heterospecific and conspecific pollen, key aspects of pollinator quality, for multiple plant species. In addition, we examined how bee body size and pollen placement among body parts shaped pollen movement. We manipulated foraging behavior types using artificial flowers, which donated pollen that captive bees then deposited on three recipient plant species. While body size primarily affected donor pollen removal, foraging behavior primarily affected donor pollen deposition. How behavior affected donor pollen deposition depended on the plant species and the quantity of donor pollen on the bee's abdomen. Plant species with smaller stigmas received significantly less pollen and fewer bees successfully transferred pollen to them. For a single plant species, heterospecific pollen interfered with conspecific pollen deposition, such that more heterospecific pollen on the bee's abdomen resulted in less conspecific pollen deposition on the flower. Thus, intraindividual variation in foraging behavior and its interaction with the amount and placement of acquired pollen and with floral morphology can affect pollinator quality and may shape plant fitness via both conspecific and heterospecific pollen transfer.

Buzz-Pollination in a Tropical Montane Cloud Forest: Compositional Similarity and Plant-Pollinator Interactions

Buzz-pollinated plants are an essential source of pollen for a significant portion of local bee communities. Buzz pollination research has focused on studying the properties of bee buzzes and their implications on pollen release, morphological specialization of flowers, and the reproductive ecology of buzz-pollinated plants. In contrast, diversity patterns and ecological interactions between bees and buzz-pollinated plants have been studied less. This study analyzed the buzzing bee community of twelve tropical buzz-pollinated co-occurring plant species in a tropical montane cloud forest during the flowering periods of two consecutive years, focusing on diversity, compositional similarity, structure, and specialization (H₂´) of the network. Twenty-one bee species belonging to Apidae, Colletidae, and Halictidae were recorded, fifteen species in 2014, and eighteen in 2015. Floral display and visited flowers doubled from first to second year, although the flowering period was 2 months longer in the first year. Bee compositional similarity between plants tended to be low; however, this was due rather to a high nestedness than species replacement. Temporal bee compositional similarity was also low but variable, and different plant species showed the highest similarity between years. The number of bee visits depended significantly on the number of flowers and years. Interactions between bees and plants showed a tendency to generalization. Compared to other buzz-pollinated networks, specialization (H₂´) was similar, but diversity was low and the network small. In endangered ecosystems like the Mexican cloud forest, however, buzzing bees support biodiversity and provide an essential ecological service by pollinating dominant understory flora.

Overview of Bee Pollination and Its Economic Value for Crop Production

Simple Summary

There is a rising demand for food security in the face of threats posed by a growing human population. Bees as an insect play a crucial role in crop pollination alongside other animal pollinators such as bats, birds, beetles, moths, hoverflies, wasps, thrips, and butterflies and other vectors such as wind and water. Bees contribute to the global food supply via pollinating a wide range of crops, including fruits, vegetables, oilseeds, legumes, etc. The economic benefit of bees to food production per year was reported including the cash crops, i.e., coffee, cocoa, almond and soybean, compared to self-pollination. Bee pollination improves the quality and quantity of fruits, nuts, and oils. Bee colonies are faced with many challenges that influence their growth, reproduction, and sustainability, particularly climate change, pesticides, land use, and management strength, so it is important to highlight these factors for the sake of gainful pollination.

Abstract

Pollination plays a significant role in the agriculture sector and serves as a basic pillar for crop production. Plants depend on vectors to move pollen, which can include water, wind, and animal pollinators like bats, moths, hoverflies, birds, bees, butterflies, wasps, thrips, and beetles. Cultivated plants are typically pollinated by animals. Animal-based pollination contributes to 30% of global food production, and bee-pollinated crops contribute to approximately one-third of the total human dietary supply. Bees are considered significant pollinators due to their effectiveness and wide availability. Bee pollination provides excellent value to crop quality and quantity, improving global economic and dietary outcomes. This review highlights the role played by bee pollination, which influences the economy, and enlists the different types of bees and other insects associated with pollination.

Including fossils in phylogeny: a glimpse into the evolution of the superfamily Evanioidea (Hymenoptera: Apocrita) under tip-dating and the fossilized birth–death process

Using a fossilized birth–death model, a new phylogeny of the superfamily Evanioidea (including ensign wasps, nightshade wasps and hatchet wasps) is proposed, with estimates of divergence times for its constitutive families and for corroborating the monophyly of Evanioidea. Additionally, our Bayesian analyses demonstrate the monophyly of †Anomopterellidae, †Othniodellithidae, †Andreneliidae, Aulacidae, Gasteruptiida and Evaniidae, whereas †Praeaulacidae and †Baissidae appear to be paraphyletic. Vectevania vetula and Hyptiogastrites electrinus are transferred to Aulacidae. We estimate the divergence time of Evanioidea to be in the Late Triassic (~203 Mya). Additionally, three new othniodellithid wasps are described and figured from mid-Cretaceous Burmese amber as the new genus Keratodellitha, with three new species: Keratodellitha anubis sp. nov., Keratodellitha basilisci sp. nov. and Keratodellitha kirin sp. nov. We also document a temporal shift in relative species richness between Ichneumonoidea and Evanioidea.

Connective appendages in Huberia bradeana (Melastomataceae) affect pollen release during buzz pollination

Floral structures, such as stamen appendages, play crucial roles in pollinator attraction, pollen release dynamics and, ultimately, the reproductive success of plants. The pollen-rewarding, bee buzz-pollinated flowers of Melastomataceae often bear conspicuous staminal appendages. Surprisingly, their functional role in the pollination process remains largely unclear. We use Huberia bradeana Bochorny & R. Goldenb. (Melastomataceae) with conspicuously elongated, twisted stamen appendages to investigate their functional role in the pollination process. We studied the effect of stamen appendages on pollinator behaviour and reproductive success by comparing manipulated flowers (appendages removed) with unmanipulated flowers. To assess bee pollinator behaviour, we measured three properties of buzzes (vibrations) produced by bees on Huberia flowers: frequency, duration and number of buzzes per flower visit. We measured male and female reproductive success by monitoring pollen release and deposition after single bee visits. Finally, we used artificial vibrations and laser vibrometry to assess how flower vibrational properties change with the removal of stamen appendages. Our results show that the absence of staminal appendages does not modify bee buzzing behaviour. Pollen release was higher in unmanipulated flowers, but stigmatic pollen loads differ only marginally between the two treatments. We also detected lower vibration amplitudes in intact flowers as compared to manipulated flowers in artificial vibration experiments. The presence of connective appendages are crucial in transmitting vibrations and assuring optimal pollen release. Therefore, we propose that the high diversity of colours, shapes and sizes of connective appendages in buzz-pollinated flowers may have evolved by selection through male fitness.

Transmission of bee-like vibrations in buzz-pollinated plants with different stamen architectures

In buzz-pollinated plants, bees apply thoracic vibrations to the flower, causing pollen release from anthers, often through apical pores. Bees grasp one or more anthers with their mandibles, and vibrations are transmitted to this focal anther(s), adjacent anthers, and the whole flower. Pollen release depends on anther vibration, and thus it should be affected by vibration transmission through flowers with distinct morphologies, as found among buzz-pollinated taxa. We compare vibration transmission between focal and non-focal anthers in four species with contrasting stamen architectures: Cyclamen persicum, Exacum affine, Solanum dulcamara and S. houstonii. We used a mechanical transducer to apply bee-like vibrations to focal anthers, measuring the vibration frequency and displacement amplitude at focal and non-focal anther tips simultaneously using high-speed video analysis (6000 frames per second). In flowers in which anthers are tightly arranged (C. persicum and S. dulcamara), vibrations in focal and non-focal anthers are indistinguishable in both frequency and displacement amplitude. In contrast, flowers with loosely arranged anthers (E. affine) including those with differentiated stamens (heterantherous S. houstonii), show the same frequency but higher displacement amplitude in non-focal anthers compared to focal anthers. We suggest that stamen architecture modulates vibration transmission, potentially affecting pollen release and bee behaviour.

Minimum size threshold of visiting bees of a buzz-pollinated plant species: consequences for pollination efficiency

PREMISE

Flowering plants with poricidal anthers are commonly visited by buzzing bees, which vibrate flowers to extract pollen. However, not all flower visitors are in fact pollinators, and features such as body size and duration of flower visits are important factors in determining pollination effectiveness. We tested whether bee-to-flower size relationships predict the pollination effectiveness of flower visitors of a buzz-pollinated species (Chamaecrista ramosa, Fabaceae).

METHODS

We sorted 13 bee taxa into three groups: smaller than, equivalent to ("fit-size"), and larger than flower herkogamy (spatial separation between anthers and stigma). We expected the latter two groups to touch the stigmas, which would be an indicator of pollination effectiveness, more frequently than the first group. To test this hypothesis, we assessed contact with stigmas, foraging behavior, and duration of visits for the three size groups of bees.

RESULTS

Our data reveal that small bees scarcely touched the stigmas, while large and fit-size bees were the most efficient pollinators, achieving high stigma-touching rates, conducting much shorter flower visits, and visiting flowers and conspecific plants at high rates during foraging bouts.

CONCLUSIONS

The results did not show size-matching among bees and flowers, as expected, but rather a minimum size threshold of efficient pollinators. The finding of such a threshold is a nonarbitrary approach to predicting pollination effectiveness of visitors to herkogamous flowers with poricidal anthers.

Pollen dispensing schedules in buzz-pollinated plants: experimental comparison of species with contrasting floral morphologies

PREMISE

Plants can mitigate the fitness costs associated with pollen consumption by floral visitors by optimizing pollen release rates. In buzz-pollinated plants, bees apply vibrations to remove pollen from anthers with small pores. These poricidal anthers potentially function as mechanism staggering pollen release, but this has rarely been tested across plant species differing in anther morphology.

METHODS

In Solanum Section Androceras, three pairs of buzz-pollinated species have undergone independent evolutionary shifts between large- and small-flowers, which are accompanied by replicate changes in anther morphology. We used these shifts in anther morphology to characterize the association between anther morphology and pollen dispensing schedules. We applied simulated bee-like vibrations to anthers to elicit pollen release, and compared pollen dispensing schedules across anther morphologies. We also investigated how vibration velocity affects pollen release.

RESULTS

Replicate transitions in Solanum anther morphology are associated with consistent changes in pollen dispensing schedules. We found that small-flowered taxa release their pollen at higher rates than their large-flowered counterparts. Higher vibration velocities resulted in quicker pollen dispensing and more total pollen released. Finally, both the pollen dispensing rate and the amount of pollen released in the first vibration were negatively related to anther wall area, but we did not observe any association between pore size and pollen dispensing.

CONCLUSIONS

Our results provide the first empirical demonstration that the pollen dispensing properties of poricidal anthers depend on both floral characteristics and bee vibration properties. Morphological modification of anthers could thus provide a mechanism to exploit different pollination environments.

Buzz-Pollinated Crops: A Global Review and Meta-analysis of the Effects of Supplemental Bee Pollination in Tomato

Buzz-pollinated plants require visitation from vibration producing bee species to elicit full pollen release. Several important food crops are buzz-pollinated including tomato, eggplant, kiwi, and blueberry. Although more than half of all bee species can buzz pollinate, the most commonly deployed supplemental pollinator, Apis mellifera L. (Hymenoptera: Apidae; honey bees), cannot produce vibrations to remove pollen. Here, we provide a list of buzz-pollinated food crops and discuss the extent to which they rely on pollination by vibration-producing bees. We then use the most commonly cultivated of these crops, the tomato, Solanum lycopersicum L. (Solanales: Solanaceae), as a case study to investigate the effect of different pollination treatments on aspects of fruit quality. Following a systematic review of the literature, we statistically analyzed 71 experiments from 24 studies across different geopolitical regions and conducted a meta-analysis on a subset of 21 of these experiments. Our results show that both supplemental pollination by buzz-pollinating bees and open pollination by assemblages of bees, which include buzz pollinators, significantly increase tomato fruit weight compared to a no-pollination control. In contrast, auxin treatment, artificial mechanical vibrations, or supplemental pollination by non-buzz-pollinating bees (including Apis spp.), do not significantly increase fruit weight. Finally, we compare strategies for providing bee pollination in tomato cultivation around the globe and highlight how using buzz-pollinating bees might improve tomato yield, particularly in some geographic regions. We conclude that employing native, wild buzz pollinators can deliver important economic benefits with reduced environmental risks and increased advantages for both developed and emerging economies.