Decline of six native mason bee species following the arrival of an exotic congener

Standardising bee sampling: A systematic review of pan trapping and associated floral surveys

The use of coloured pan traps (bee bowls, Moericke traps) for sampling bees (and other pollinators) has continuously increased over the last two decades. Although a number of methodological studies and conceptual frameworks offer guidance on standardised sampling, pan trap setups vary widely in characteristics even when optimised for capturing bees. Moreover, some uncertainty persists as to how local flower abundance and diversity influence sampling. We systematically reviewed peer-reviewed studies that used pan traps for bee collection and that were listed in the Web of Science core collection. To gauge methodological variation, we identified a set of relevant methodological criteria and assessed the studies accordingly. For obtaining evidence that pan trap samples and floral environment around traps are correlated, we screened the relevant studies for such correlations. While some aspects of pan trapping (e.g., trap coloration and elevation) were similar in the majority of studies, other aspects varied considerably (e.g., trap volume/diameter and sampling duration). Few studies used floral abundance and/or diversity as an explanatory variable in their analyses of bee samples. Among these studies, we found a considerable variation in key aspects of floral survey methods, such as time and space between vegetation surveys and pan trap sampling, abundance measures (quantitative, semi-quantitative and presence-absence), and processing of raw data prior to analysis. Often studies did not find any correlation between the floral environment and bee samples. Reported correlations varied markedly across studies, even within groups of studies applying a similar method or analysing a similar group of bees. Our synthesis helps to identify key issues of further standardisation of pan trap methodology and of associated floral surveys. In addition to the few aspects that have been standardised over the past decades, we suggest methodological direction for future research using pan traps as a better standardised method for the collection of wild bees. We encourage further studies to illuminate if and how varying floral resources around traps bias bee samples from pan traps. More generally, our synthesis shows that trapping methodologies should be reviewed regularly when their use increases to ensure standardisation.

Optical multiband polarimetric modulation sensing for gender and species identification of flying native solitary pollinators

Native pollinators are crucial to local ecosystems but are under threat with the introduction of managed pollinators, e.g., honeybees (Apis mellifera). We explored the feasibility of employing the entomological lidar technique in native pollinator abundance studies. This study included individuals of both genders of three common solitary bee species, Osmia californica, Osmia lignaria, and Osmia ribifloris, native to North America. Properties including optical cross-section, degree of linear polarization, and wingbeat power spectra at all three wavelengths have been extracted from the insect signals collected by a compact stand-off sensing system. These properties are then used in the classification analysis. For species with temporal and spatial overlapping, the highest accuracies of our method exceed 96% (O. ribifloris & O. lignaria) and 93% (O. lignaria & O. californica). The benefit of employing the seasonal activity and foraging preference information in enhancing identification accuracy has been emphasized.

A checklist of the bees (Hymenoptera: Apoidea) of Minnesota

Research studies and conservation actions aimed at improving conditions for bees require a basic understanding of which species are present in a given region. The US state of Minnesota occupies a unique geographic position at the confluence of eastern deciduous forests, northern boreal forests, and western tallgrass prairie, which has led to a diverse and unique bee fauna. In recent years there have been multiple ongoing bee-focused inventory and research projects in Minnesota. Combined with the historic specimens housed in the University of Minnesota Insect Collection and other regional collections, these furnished a wealth of specimens available to form the basis of a statewide checklist. Here, we present the first comprehensive checklist of Minnesota bee species, documenting a total of 508 species in 45 genera. County-level occurrence data is included for each species, and further information on distribution and rarity is included for species of regional or national interest. Some species have their taxonomy clarified, with Perdita citrinella Graenicher, 1910 syn. nov. recognized as a junior synonym of Perdita perpallida Cockerell, 1901, P. bequaerti syn. nov. recognized as a junior synonym of P. pallidipennis Graenicher, 1910 stat. nov., Anthidiellum boreale (Robertson, 1902) stat. nov. recognized as a full species, and Anthidiellium beijingense Portman & Ascher nom. nov. is proposed for A. boreale Wu to resolve the homonymy with A. boreale (Robertson). We further include a list of species that may occur in Minnesota and highlight 11 species occurring in the state that are considered non-native. Recent collecting efforts, as well as increased taxonomic attention paid to Minnesota bees, have resulted in 66 species that have only been documented in the last 10 years. As a first step in determining native bees of conservation concern, we document 38 species that have not been detected in the state during the last 50 years and discuss their conservation status, along with other species for which evidence of decline exists. The checklist of Minnesota bees will continue to grow and change with additional surveys and research studies. In particular, recent surveys have continued to detect new bee species, and many bee groups are in need of taxonomic revision, with the most recent revisions for many genera occurring decades ago. Overall, this checklist strengthens our understanding of the bees of Minnesota and the broader region, informs conservation assessments, and establishes a baseline for faunal change.

Novel ollusvirus detected in a solitary wild bee species (Osmia taurus) in Japan

Pathogens of wild bees in Japan remain largely unknown. We examined viruses harbored by solitary wild Osmia bees, including Osmia cornifrons and Osmia taurus. Interestingly, the full-length genome of a novel virus (designated as "Osmia-associated bee chuvirus", OABV) was identified in three Osmia taurus bees collected in Fukushima prefecture. The sequences and genomic features are similar to those of Scaldis River bee virus. Phylogenetic analysis based on RNA-dependent RNA polymerase, glycoprotein, and nucleoprotein sequences showed that OABV formed a subcluster within ollusviruses and was closely related to strains identified in European countries. This study extends our knowledge of wild bee parasites in Japan.

Minimal Sharing of Nosematid and Trypanosomatid Parasites between Honey Bees and Other Bees, but Extensive Sharing of Crithidia between Bumble and Mason Bees

We document gut parasites in co-occurring Apis, Bombus, and Osmia spp. in the Northern Virginia region, USA. Trypanosomatidea occurred in sixty percent of specimens and 13% carried Nosematidae. We found strong host partitioning: Lotmaria passim and Vairimorpha (Nosema) ceranae predominated in Apis, and Crithidia bombi and V. bombi in Bombus. We did not detect pathogen spread from Apis to Bombus but did detect sharing of C. bombi between Bombus and Osmia, higher parasite levels in Apis at sites with apiaries, and clustering of Vairimopha infection. Given the presence of C. bombi in Osmia, we suggest disease sharing across taxa be monitored.

Osmia taurus (Hymenoptera: Megachilidae): A Non-native Bee Species With Invasiveness Potential in North America

Bees are important pollinators and are essential for the reproduction of many plants in natural and agricultural ecosystems. However, bees can have adverse ecological effects when introduced to areas outside of their native geographic ranges. Dozens of non-native bee species are currently found in North America and have raised concerns about their potential role in the decline of native bee populations. Osmia taurus Smith (Hymenoptera: Megachilidae) is a mason bee native to eastern Asia that was first reported in the United States in 2002. Since then, this species has rapidly expanded throughout the eastern part of North America. Here, we present a comprehensive review of the natural history of O. taurus, document its recent history of spread through the United States and Canada, and discuss the evidence suggesting its potential for invasiveness. In addition, we compare the biology and history of colonization of O. taurus to O. cornifrons (Radoszkowski), another non-native mason bee species now widespread in North America. We highlight gaps of knowledge and future research directions to better characterize the role of O. taurus in the decline of native Osmia spp. Panzer and the facilitation of invasive plant-pollinator mutualisms.

Solitary bee larvae modify bacterial diversity of pollen provisions in the stem-nesting bee, Osmia cornifrons (Megachilidae)

Microbes, including diverse bacteria and fungi, play an important role in the health of both solitary and social bees. Among solitary bee species, in which larvae remain in a closed brood cell throughout development, experiments that modified or eliminated the brood cell microbiome through sterilization indicated that microbes contribute substantially to larval nutrition and are in some cases essential for larval development. To better understand how feeding larvae impact the microbial community of their pollen/nectar provisions, we examine the temporal shift in the bacterial community in the presence and absence of actively feeding larvae of the solitary, stem-nesting bee, Osmia cornifrons (Megachilidae). Our results indicate that the O. cornifrons brood cell bacterial community is initially diverse. However, larval solitary bees modify the microbial community of their pollen/nectar provisions over time by suppressing or eliminating rare taxa while favoring bacterial endosymbionts of insects and diverse plant pathogens, perhaps through improved conditions or competitive release. We suspect that the proliferation of opportunistic plant pathogens may improve nutrient availability of developing larvae through degradation of pollen. Thus, the health and development of solitary bees may be interconnected with pollen bacterial diversity and perhaps with the propagation of plant pathogens.

Novel Microsatellite Markers for Osmia lignaria (Hymenoptera: Megachilidae): A North American Pollinator of Agricultural Crops and Wildland Plants

Comprehensive decisions on the management of commercially produced bees, depend largely on associated knowledge of genetic diversity. In this study, we present novel microsatellite markers to support the breeding, management, and conservation of the blue orchard bee, Osmia lignaria Say (Hymenoptera: Megachilidae). Native to North America, O. lignaria has been trapped from wildlands and propagated on-crop and used to pollinate certain fruit, nut, and berry crops. Harnessing the O. lignaria genome assembly, we identified 59,632 candidate microsatellite loci in silico, of which 22 were tested using molecular techniques. Of the 22 loci, 12 loci were in Hardy-Weinberg equilibrium (HWE), demonstrated no linkage disequilibrium (LD), and achieved low genotyping error in two Intermountain North American wild populations in Idaho and Utah, USA. We found no difference in population genetic diversity between the two populations, but there was evidence for low but significant population differentiation. Also, to determine if these markers amplify in other Osmia, we assessed 23 species across the clades apicata, bicornis, emarginata, and ribifloris. Nine loci amplified in three species/subspecies of apicata, 22 loci amplified in 11 species/subspecies of bicornis, 11 loci amplified in seven species/subspecies of emarginata, and 22 loci amplified in two species/subspecies of ribifloris. Further testing is necessary to determine the capacity of these microsatellite loci to characterize genetic diversity and structure under the assumption of HWE and LD for species beyond O. lignaria. These markers will inform the conservation and commercial use of trapped and managed O. lignaria and other Osmia species for both agricultural and nonagricultural systems.

Biology, Genetic Diversity, and Conservation of Wild Bees in Tree Fruit Orchards

Different species of bees provide essential ecosystem services by pollinating various agricultural crops, including tree fruits. Many fruits and nuts depend on insect pollination, primarily by wild and managed bees. In different geographical regions where orchard crops are grown, fruit growers rely on wild bees in the farmscape and use orchard bees as alternative pollinators. Orchard crops such as apples, pears, plums, apricots, etc., are mass-flowering crops and attract many different bee species during their bloom period. Many bee species found in orchards emerge from overwintering as the fruit trees start flowering in spring, and the active duration of these bees aligns very closely with the blooming time of fruit trees. In addition, most of the bees in orchards are short-range foragers and tend to stay close to the fruit crops. However, the importance of orchard bee communities is not well understood, and many challenges in maintaining their populations remain. This comprehensive review paper summarizes the different types of bees commonly found in tree fruit orchards in the fruit-growing regions of the United States, their bio-ecology, and genetic diversity. Additionally, recommendations for the management of orchard bees, different strategies for protecting them from multiple stressors, and providing suitable on-farm nesting and floral resource habitats for propagation and conservation are discussed.

Establishment of the non-native horned-face bee Osmia cornifrons and the taurus mason bee Osmia taurus (Hymenoptera: Megachilidae) in Canada

Established populations of the non-native horned-face bee, Osmia cornifrons (Radoszkowski, 1887), and the taurus mason bee, Osmia taurus Smith, 1873 (Hymenoptera: Megachilidae), have been identified from Canada for the first time. In the US, the importation of O. cornifrons, beginning in the 1970s, led to its release for agricultural crop pollination and spread across the country. In this article, we report on O. cornifrons captured while sampling wild bees in Toronto, Ontario using hand nets, bug vacuums, and vane traps, as well as established populations in trap nests, from 2017-2020. The morphologically similar O. taurus, which was accidentally introduced to the US with shipments of imported O. cornifrons, was also recorded in our samples. Recently, a few individual O. taurus specimens have been identified from Ontario and Quebec; however, the extent of our sampling included nests, indicating it is also established in Canada. Others have shown its population growth to have been associated with concordant declines in abundances of native mason bee species in the US, and similar impacts are possible in Canada if action is not taken. We propose three non-mutually exclusive possible pathways for the arrival of O. cornifrons, as well as O. taurus, in Canada: (1) natural migration northward from non-native populations in the US, (2) international importation in the 1980s-2000s to support agricultural research programs, and (3) unintentional release of mason bee cocoons purchased from non-local vendors. We argue that a focus on enhancing populations of locally occurring native bees and stronger policy on the importation and sale of non-native bees are needed.

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.

The potential consequences of 'bee washing' on wild bee health and conservation

Concern around declining bee populations globally has become an environmental issue of mainstream importance. Policymakers, scientists, environmental non-government organizations, media outlets and the public have displayed great interest in conservation actions to support pollinators. As with many environmental causes, green washing, or in this case ‘bee washing’, has become rampant. Bee washing can lead to multiple negative consequences, including misinformation, misallocation of resources, increasing threats and steering public understanding and environmental policy away from evidence-based decision-making. Here I will discuss the multiple potential consequences of bee washing on efforts to conserve declining wild bees and promote wild bee health.

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Concern around declining bee populations globally has become an environmental issue of mainstream importance.

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Policymakers, scientists, environmental non-government organizations, media outlets and the public have displayed interest in conservation action to support pollinators.

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‘Bee washing’, has become rampant.

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Narratives and actions tend to focus on low-hanging fruit, actions which are easy to address and/or the selling of commercial items where industry benefits but the species of concern do not.

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Negative consequences include misinformation, misallocation of resources, increasing threats and steering environmental policy away from evidence-based decision-making.

Early-phase colonisation by introduced sculptured resin bee (Hymenoptera, Megachilidae, Megachile sculpturalis) revealed by local floral resource variability

There is a growing interest to document and better understand patterns and processes involved in non-native bee introductions and subsequent colonisation of new areas worldwide. We studied the spread of the East Asian bee Megachile sculpturalis in Serbia and south-eastern Europe; the bee was earlier established in the USA (since 1994) and western Europe (since 2008). Its establishment in Serbia remained dubious throughout most of 2017–2019, following its first detection. We hereby report on its establishment and spreading, which were corroborated in 2019 under specific circumstances. Owing to an exceptionally poor blooming of Styphnolobium japonicum in 2019, we recorded a high activity density of M. sculpturalis concentrated on a scarce key food resource. We present a novel quantitative approach for an improved early detection of M. sculpturalis, based on the interplay between the bee local occurrence pattern and dynamics of key food-plant(s) availability. This approach seems particularly effective during the early-phase colonisation, at initially low population density of introduced bees. We address the importance of integration of the genuine plant usage patterns with context-specific bee assessment options in establishing effective monitoring. The improved understanding of M. sculpturalis local dynamics triggered the questions about possible origin(s) and modes of its dispersal east of the Alps. To explore the possible scenarios of M. sculpturalis introduction(s), we extended the study to a wider spatio-temporal context – the region of SE Europe (2015–2019). The two complementary study approaches (at local and regional scale) provided more comprehensive evidence of bee dispersal history and the detection patterns in varied recording contexts. Based on this two-scale approach, we suggest that a diffusive mode of M. sculpturalis introduction into Serbia now seems to be a more plausible scenario (than a long-distance jump). We argue that the integration of outcomes from the contrasting approaches (a systematic surveillance, based on plant resources and a broad-scale opportunistic recording) could be of great methodological relevance for the development of future monitoring protocols.

Non-Native Non-Apis Bees Are More Abundant on Non-Native Versus Native Flowering Woody Landscape Plants

Simple Summary

Bees and other pollinators play a vital role in food production and natural ecosystems. Native bee populations are declining due in part to habitat loss. Individuals can help bees by landscaping with plants that provide pollen and nectar. Most information on bee-friendly plants concerns herbaceous ornamentals, but flowering trees and shrubs, too, can provide food for urban bees. Conservation organizations recommend landscaping mainly with native plants to support native bees, but some studies suggest that including some non-invasive non-native plants that bloom earlier or later than native plants can help support bees when resources from native plants are scarce. That strategy might backfire, however, if such plants disproportionately host invasive bee species. This study tested that hypothesis by identifying all non-native bees among 11,275 bees previously collected from 45 species of flowering woody plants across hundreds of urban sites. Besides the ubiquitous honey bee, six other non-native bee species comprised 2.9% of the total collection. Two alien species considered to have invasive tendencies by outcompeting native bees were more abundant on non-native plants. Planting their favored hosts might facilitate those bees’ spread in urban areas. Pros and cons of non-native woody landscape plants for urban bee conservation warrant further study.

Abstract

Urban ecosystems can support diverse communities of wild native bees. Because bloom times are conserved by geographic origin, incorporating some non-invasive non-native plants in urban landscapes can extend the flowering season and help support bees and other pollinators during periods when floral resources from native plants are limiting. A caveat, though, is the possibility that non-native plants might disproportionately host non-native, potentially invasive bee species. We tested that hypothesis by identifying all non-native bees among 11,275 total bees previously collected from 45 species of flowering woody landscape plants across 213 urban sites. Honey bees, Apis mellifera L., accounted for 22% of the total bees and 88.6% of the non-native bees in the collections. Six other non-native bee species, accounting for 2.86% of the total, were found on 16 non-native and 11 native woody plant species. Non-Apis non-native bees in total, and Osmia taurus Smith and Megachile sculpturalis (Smith), the two most abundant species, were significantly more abundant on non-native versus native plants. Planting of favored non-native hosts could potentially facilitate establishment and spread of non-Apis non-native bees in urban areas. Our host records may be useful for tracking those bees’ distribution in their introduced geographical ranges.

Comparative Efficiency of Native Insect Pollinators in Reproductive Performance of Medicago sativa L. in Pakistan

Lucerne (Medicago sativa L.) is a cross-pollinated crop and requires entomophilous pollination for tripping of flowers and subsequent pod and seed set. To discover the best pollinators for lucerne seed production, a two-year field trial was carried out at the research farm of MNS University of Agriculture, Multan, Pakistan. Abundance and diversity of insect pollinators along with the foraging behavior were recorded in terms of tripping efficiency, stay time, visitation rate and pollen harvest. The single-visit efficiency of abundant insect pollinators was also evaluated in terms of number of seeds and seed weight per raceme along with germination percentage. Ten most abundant floral visitors (five solitary bee species, three honeybee species and two syrphid fly species) were tested for their pollination efficiency. Honeybees were most abundant in both the years followed by the solitary bees and syrphid flies. Single-visit efficacy in terms of number of pods per raceme, number of seeds per raceme, 1000 seed weight and germination percentage revealed Megachile cephalotes as the most efficient insect pollinator followed by Megachile hera and Amegilla sp. Future studies should investigate the biology and ecology of these bee species with special emphasis on their nesting behavior and seasonality.

A keystone mutualism promotes resistance to invasion

It is not uncommon for one or a few species, and their interactions, to have disproportionate effects on other species in ecological communities. Such keystone interactions might affect how communities respond to the invasion of non-native species by preventing or inhibiting the establishment, spread or impact of non-native species. We explore whether a keystone mutualism among a hummingbird-mistletoe-marsupial promotes ecological resistance to an invasive pollinator, the bumblebee Bombus terrestris, by comparing data collected at sites prior to bumblebee invasion to data collected 11 years after the invasion in sites with and without the keystone mutualism. We built pollination networks and focused on network motifs, regarded as building blocks of networks, to identify the central pollinators and estimate the change in their interactions after invasion of B. terrestris. We also estimated the interaction rewiring across the season in post-invasion networks and tested it as a possible mechanism explaining how the keystone mutualism increased ecological resistance to invasion. We found two times more species in post-invasion sites with the keystone mutualism than in post-invasion sites without the keystone mutualism. Moreover, we found that invasive bumblebee reduced the strength and interaction niche of the five central pollinator species while increasing its own strength and interaction niche, suggesting a replacement of interactions. Also, we found that the keystone mutualism promoted resistance to B. terrestris invasion by reducing its negative impacts on central species. In the presence of the keystone mutualism, central species had three times more direct interactions than in sites without this keystone mutualism. The higher interaction rewiring, after invasion of B. terrestris, in sites with the keystone mutualism indicates greater chances of central pollinators to form new interactions and reduces their competence for resources with the non-native bumblebee. Our results demonstrate that a keystone mutualism can enhance community resistance against the impacts of a non-native invasive pollinator by increasing species diversity and promoting interaction rewiring in the community. This study suggests that the conservation of mutualisms, especially those considered keystone, could be essential for long-term preservation of natural communities under current and future impacts of global change.

The managed-to-invasive species continuum in social and solitary bees and impacts on native bee conservation

Invasive bee species have negative impacts on native bee species and are a source of conservation concern. The invasion of bee species is mediated by the abiotic environment, biotic communities, and propagule pressure of the invader. Each of these factors is further affected by management, which can amplify the magnitude of the impact on native bee species. The ecological traits and behavior of invasive bees also play a role in whether and to what degree they compete with or otherwise negatively affect native bee species. The magnitude of impact of an invasive bee species relates both to its population size in the introduced habitat and the degree of overlap between its resources and the resources native bees require.

Conservation insights from wild bee genetic studies: Geographic differences, susceptibility to inbreeding, and signs of local adaptation

Conserving bees are critical both ecologically and economically. Genetic tools are valuable for monitoring these vital pollinators since tracking these small, fast-flying insects by traditional means is difficult. By surveying the current state of the literature, this review discusses how recent advances in landscape genetic and genomic research are elucidating how wild bees respond to anthropogenic threats. Current literature suggests that there may be geographic differences in the vulnerability of bee species to landscape changes. Populations of temperate bee species are becoming more isolated and more genetically depauperate as their landscape becomes more fragmented, but tropical bee species appear unaffected. These differences may be an artifact of historical differences in land-use, or it suggests that different management plans are needed for temperate and tropical bee species. Encouragingly, genetic studies on invasive bee species indicate that low levels of genetic diversity may not lead to rapid extinction in bees as once predicted. Additionally, next-generation sequencing has given researchers the power to identify potential genes under selection, which are likely critical to species' survival in their rapidly changing environment. While genetic studies provide insights into wild bee biology, more studies focusing on a greater phylogenetic and life-history breadth of species are needed. Therefore, caution should be taken when making broad conservation decisions based on the currently few species examined.