Wild Bee Populations Research Articles

Bringing population ecology back to wild bees

AbstractIn recent years, motivated by widespread declines in wild bees, ecologists have prioritized learning about patterns of wild bee communities across the landscape at the expense of learning about the population‐level mechanisms driving those patterns. In this essay, we seek to revitalize the tradition of studying wild bee populations in a way that both contributes key knowledge for bee conservation and builds a strong conceptual understanding of the processes underpinning bee populations. We address two widespread concerns about investing in population‐level research. First, that population‐level studies are too conceptually narrow to provide broad inference. If population‐level studies are couched in general ecological theory, then findings from a single species can be generalized to many. We highlight how wild bees would make excellent candidates for exploring five areas of general ideas in population ecology, including nutritional ecology, drivers of vital rates, phenology and voltinism, habitat selection, and movement. Second, we address the concern that methods for studying bees at the population level are too difficult to implement. Methods for conducting population‐level studies of bees—specifically, identifying living bees in the field and studying individuals throughout their life cycles—are feasible to implement at the scales appropriate for answering population‐level questions, for example, a few species at a few sites. To facilitate adoption of these ideas, we developed an online field guide (www.watchingbees.com) and a detailed methods manual. More generally, we emphasize the value of linking data‐rich pattern‐oriented approaches in ecology with an understanding of the basic biology and mechanisms that generate those patterns.

Osmia3DNest—Novel designed 3D printed artificial nest for solitary cavity‐nesting bees

Abstract The availability and appropriateness of nesting sites significantly influence the reproductive success and overall welfare of wild bees. Human‐induced factors contribute to the destruction of natural nesting habitats. To address these limitations, innovative solutions such as the development of artificial nests, offer alternative nest sites to support wild bee populations. We designed the Osmia3DNest, a 3D printed standardized nest tube for solitary cavity‐nesting bees, aiming to provide a safe for the environment, long‐life, time‐saving and biodegradable product that anyone can print. We proudly present the two Osmia3DNest models for mason bees—closed and open—using polylactic acid filament. We demonstrate the effectiveness of Osmia3DNest on mason bee reproduction parameters compared with traditional reed nests. Osmia3DNest can be an alternative to the other artificial nests, which people can customize for their necessity depending on their place of living (rural or urban area), and they can also be washed and reused several times and then decomposed. Osmia3DNest holds potential for wildlife biologists, management of pollinators, and educational outreach, offering adaptability for different bee species and experimental needs.

Estimating bee distributions and their functional range to map important areas for protecting bee species and their functions

The decline of wild bee populations causes the decline of bee-pollinated plant populations through the deterioration of pollination services. Since high bee species richness generally involves high functional group diversity, protecting areas of high bee species richness will help to maintain pollination services for plants. However, those areas do not always include the habitats of bee species with specialized functions that expand the range of plants being pollinated. To map important areas for protecting native bee species and their functions, we estimated the distributions and functional range of 13 bumble bee species and 1 honey bee species in Japan. The distributions were estimated from an ensemble of six species distribution models using bee occurrence data and environmental data. The functional range of bee species was estimated by combining the estimated distributions and proboscis length, which frequently corresponds to the floral shape of the plant species they pollinate. The estimated species richness was high in western Hokkaido and the estimated functional range was wide in central Honshu. Our method is useful to see whether areas important for high species richness of pollinators differ from those for rare species or their functions.

Advancing bee conservation in the US: gaps and opportunities in data collection and reporting

IntroductionBee conservation in the US is currently hindered by challenges associated with assessing the status and trends of a diverse group of >3000 species, many of which are rare, endemic to small areas, and/or exhibit high inter-annual variationin population size. Fundamental information about the distribution of most species across space and time, thus, is lacking yet urgently needed to assess population status, guide conservation plans, and prioritize actions among species and geographies.MethodsUsing wild bee data from two public data repositories representing the contiguous US, we evaluated the availability and sufficiency of data for use in species assessments of wild bees. We also examined the number of bee species recorded in each US state and the proportion of species with recent records (2012–2021).ResultsAlthough efforts to monitor bees continue to grow, there remains a massive paucity of data. Exceedingly few records (0.04%)reported both sampling protocol and effort, greatly limiting the usefulness of the data. Few species or locations have adequate publicly available data to support analyses of population status or trends, and fewer than half of species have sufficient data to delineate geographic range. Despite an exponential increase in data submissions since the 2000s, only 47% of species were reported within the last decade, which may be driven by how data are collected, reported, and shared, or may reflect troubling patterns of local or large-scale declines and extirpations.DiscussionBased on our analysis, we provide recommendations to improve the quality and quantity of data that can be used to detect, understand, and respond to changes in wild bee populations.

Ecological and social factors influence interspecific pathogens occurrence among bees

The interspecific transmission of pathogens can occur frequently in the environment. Among wild bees, the main spillover cases are caused by pathogens associated with Apis mellifera, whose colonies can act as reservoirs. Due to the limited availability of data in Italy, it is challenging to accurately assess the impact and implications of this phenomenon on the wild bee populations. In this study, a total of 3372 bees were sampled from 11 Italian regions within the BeeNet project, evaluating the prevalence and the abundance of the major honey bee pathogens (DWV, BQCV, ABPV, CBPV, KBV, Nosema ceranae, Ascosphaera apis, Crithidia mellificae, Lotmaria passim, Crithidia bombi). The 68.4% of samples were positive for at least one pathogen. DWV, BQCV, N. ceranae and CBPV showed the highest prevalence and abundance values, confirming them as the most prevalent pathogens spread in the environment. For these pathogens, Andrena, Bombus, Eucera and Seladonia showed the highest mean prevalence and abundance values. Generally, time trends showed a prevalence and abundance decrease from April to July. In order to predict the risk of infection among wild bees, statistical models were developed. A low influence of apiary density on pathogen occurrence was observed, while meteorological conditions and agricultural management showed a greater impact on pathogen persistence in the environment. Social and biological traits of wild bees also contributed to defining a higher risk of infection for bivoltine, communal, mining and oligolectic bees. Out of all the samples tested, 40.5% were co-infected with two or more pathogens. In some cases, individuals were simultaneously infected with up to five different pathogens. It is essential to increase knowledge about the transmission of pathogens among wild bees to understand dynamics, impact and effects on pollinator populations. Implementing concrete plans for the conservation of wild bee species is important to ensure the health of wild and human-managed bees within a One-Health perspective.

Fewer bowl traps and more hand netting can increase effective number of bee species and reduce excessive captures.

Reports increasingly point to substantial declines in wild bee abundance and diversity, yet there is uncertainty about how best to measure these attributes in wild bee populations. Two commonly used methods are passive trapping with bee bowls or active netting of bees on flowers, but each of these has drawbacks. Comparing the outcomes of the two methods is complicated by their uncomparable units of effort. The abundance distribution of bee species is also typically highly skewed, making it difficult to accurately assess diversity when rarer species are unlikely to be caught. The effective number of species, or Hill numbers, provides a way forward by basing the response metric on the number of equally abundant species. Our goal is to compare the effective number of bee species captured between hand netting and bowl trapping in wheatgrass prairie in South Dakota and tallgrass prairie in Minnesota, USA. Species overlap between the two methods ranged from ~40% to ~60%. Emphasis placed on rare species was important, so that 95% confidence limits overlapped between the two methods for species richness but netting exceeded trapping for Shannon's and Simpson's diversities. Netting always captured more bee species with fewer bee individuals than trapping. In most cases, the number of bees captured in bowl traps indicated substantial over-sampling, with little increase in bee species detected. Correlations between bee and floral abundance, richness, and diversity differed between netted and trapped samples. We conclude that netting and trapping together produce a more complete account of species richness, but shifting sampling emphasis from trapping to netting will result in fewer bees, but more bee species captured. Due to the different relationships between bee and floral diversities that depended on sampling method, it is unwise to compare habitat associations determined by netting with those determined by trapping.

Host species and geography impact bee-associated RNA virus communities with evidence for isolation by distance in viral populations.

Virus symbionts are important mediators of ecosystem function, yet we know little of their diversity and ecology in natural populations. The alarming decline of pollinating insects in many regions of the globe, especially the European honey bee, Apis mellifera, has been driven in part by worldwide transmission of virus pathogens. Previous work has examined the transmission of known honey bee virus pathogens to wild bee populations, but only a handful of studies have investigated the native viromes associated with wild bees, limiting epidemiological predictors associated with viral pathogenesis. Further, variation among different bee species might have important consequences in the acquisition and maintenance of bee-associated virome diversity. We utilized comparative metatranscriptomics to develop a baseline description of the RNA viromes associated with wild bee pollinators and to document viral diversity, community composition, and structure. Our sampling includes five wild-caught, native bee species that vary in social behavior as well as managed honey bees. We describe 26 putatively new RNA virus species based on RNA-dependent RNA polymerase phylogeny and show that each sampled bee species was associated with a specific virus community composition, even among sympatric populations of distinct host species. From 17 samples of a single host species, we recovered a single virus species despite over 600km of distance between host populations and found strong evidence for isolation by distance in associated viral populations. Our work adds to the small number of studies examining viral prevalence and community composition in wild bees.

The effects of meliponicultural use of Tetragonula laeviceps on other bee pollinators and pollination efficacy of lemon.

The augmentation of pollination success in lemon (Citrus limon Eureka) flowers remains contingent on the involvement of bee pollinators. With wild bee pollinator populations declining in agroecosystems, meliponiculture has emerged as a potential option in Indonesia. This study aimed to investigate the effects of meliponicultural use of Tetragonula laeviceps on diversity, foraging behavior, and monthly population of bee pollinators, as well as lemon pollination efficacy with and without meliponiculture treatment during two periods. Using scan and focal sampling methods in first and second periods, the study found that the diversity of wild bee pollinators was six species (Apis cerana, Lasioglossum albescens, Megachile laticeps, Xylocopa confusa, Xylocopa latipes, and Xylocopa caerulea), and T. laeviceps when using meliponiculture. The relative abundance and daily foraging activity of wild bee pollinators were initially reduced in the first period (March-June) and then maintained in the second period (July-October). T. laeviceps foraged on the flowers, involving specific sequences for 72 s with highest visitation rate of 0.25 flowers/h from 10:00-13:00. Light intensity was observed to be the most influential factor for bee pollinator density. Pollination efficacy results showed that meliponiculture usage has greater benefit compared to meliponiculture absence across various parameters, including fruit sets, fruit weight, yield, and estimated productivity. The effects of meliponicultural use of T. laeviceps can enhance lemon pollination efficacy while preserving the diversity of wild insect pollinators. This suggests that meliponiculture stingless bees could be a beneficial practice in agroecosystems, especially in tropical regions where wild bee populations and diversity are declining.

Bee Assemblage in the Southern Chihuahuan Desert: The Role of Season, Year, and Trap Color in Abundance.

Recognizing how populations fluctuate over time is a crucial factor in determining the environmental elements affecting population persistence. However, the limited information on wild bee populations complicates the estimation of the impact of anthropogenic threats leading to changes in population size. To address this, we conducted a study capturing and monitoring nine species of wild bees through monthly samplings over four years. Tray traps were placed in permanent plots, and capture records were used to determine population size (N) and density (D). A generalized linear model (GLM) was employed to determine how the use of traps affected bee species captures. The families Apidae and Halictidae represented the most captures. Apis mellifera, the Lasioglossum (Dialictus spp.) complex, and Macrotera sinaloana exhibited the largest number of captures and highest population density. Most species (77.7%) showed a tendency to remain constant over the years and to have a higher number of captures in the spring months. Moreover, yellow traps were the most effective in capturing bee individuals. We suggest that the availability of essential resources and the reduction in environmental stressors positively affected the capture of wild bee populations.

Honeybee visitation to shared flowers increases Vairimorpha ceranae prevalence in bumblebees.

Vairimorpha (=Nosema) ceranae is a widespread pollinator parasite that commonly infects honeybees and wild pollinators, including bumblebees. Honeybees are highly competent V. ceranae hosts and previous work in experimental flight cages suggests V. ceranae can be transmitted during visitation to shared flowers. However, the relationship between floral visitation in the natural environment and the prevalence of V. ceranae among multiple bee species has not been explored. Here, we analyzed the number and duration of pollinator visits to particular components of squash flowers-including the petals, stamen, and nectary-at six farms in southeastern Michigan, USA. We also determined the prevalence of V. ceranae in honeybees and bumblebees at each site. Our results showed that more honeybee flower contacts and longer duration of contacts with pollen and nectar were linked with greater V. ceranae prevalence in bumblebees. Honeybee visitation patterns appear to have a disproportionately large impact on V. ceranae prevalence in bumblebees even though honeybees are not the most frequent flower visitors. Floral visitation by squash bees or other pollinators was not linked with V. ceranae prevalence in bumblebees. Further, V. ceranae prevalence in honeybees was unaffected by floral visitation behaviors by any pollinator species. These results suggest that honeybee visitation behaviors on shared floral resources may be an important contributor to increased V. ceranae spillover to bumblebees in the field. Understanding how V. ceranae prevalence is influenced by pollinator behavior in the shared floral landscape is critical for reducing parasite spillover into declining wild bee populations.

Stand stage affects wild bee communities in working pine forests

Wild bees provide critical pollination services to both crops and native forest plants. Evidence suggests that wild bees are declining due to factors such as habitat loss, disease, pesticide use, and climate change. Privately owned, working loblolly pine (Pinus taeda L.) forest landscapes cover a large area in the southeastern U.S. and may be important for wild bee conservation. However, there is little research on wild bees in private, working forests. Hence, our research objectives were to compare wild bee populations and communities among different stages within working, loblolly pine forest landscapes and assess stand structure and composition effects on wild bees. We sampled bees and forest attributes in four stages [0–3 years (recently established), 4–7 years (pre-thinned, closing canopy), 8–13 years (pre-thinned, closed canopy), and 14–20 years (post-thinned)] of privately owned, working pine forests in the Southeastern Plains Ecoregion of Georgia. We collected 5,933 bees from 88 species in two years. Wild bees were 2–5 times more abundant in recently established stages, and more diverse in recently established and post-thinned stages. Functional dispersion, a measure of beta diversity, was also greater in recently established and post-thinned stages. Canopy openness, percent of plants flowering, and percent cover of minimally decayed woody debris were important variables driving the bee community composition in recently established stages. Number of snags and litter layer depth were important variables driving the bee community composition in older stages with a closing or closed canopy. Working pine forests support a diverse community of wild bees and have high conservation value for these pollinators. Overall, wild bees appear to benefit from various stand stages, especially open canopy stands with a diverse structure. Promoting and maintaining open canopy conditions in managed pine landscapes may assist with conserving wild bee communities in this region. This can be achieved by planting trees at wider spacing, thinning as early as possible, and supporting fewer trees per hectare or a lower basal area.

Environmental variables and species traits as drivers of wild bee pollination in intensive agroecosystems—A metabarcoding approach

AbstractWild bees are known to be efficient pollinators of wild plants and cultivated crops and they are essential ecosystem service providers. However, wild bee populations have been suffering from significant declines in the last decades mainly due to the use of agrochemicals. Within this framework, we aimed to characterize wild bees' pollination spectrum (i.e., the community of pollinated flowering plants) in intensive agroecosystems, and describe the environmental variables and wild bee species traits influencing the pollination. To do this, we conducted metabarcoding analyses of pollen loads from wild bees collected in sunflower crops in the French region of Nouvelle‐Aquitaine. Our study revealed that wild bees visited flowering plants corresponding to 231 different operational taxonomic units, classified into 38 families of which Asteraceae, Brassicaceae, and Apiaceae were the most visited and more than 90% of the visited taxa turned out to be wildflowers. We also analyzed the potential effect of environmental variables and wild bee species traits in governing their choice of pollinated plants. The community composition of pollinated plants varied depending on the flowering stages of the sunflower and the farming system. Our results also show that pollination niche breadth (alpha diversity) varied depending on the flowering stages of the sunflower but was not different between organic and conventional farming systems. Regarding wild bee species traits, the community composition of pollinated plants varied in relation to wild bees' body sizes and sociality levels. Our results are consistent with previous studies, suggesting that solitary bees are more specialist when it comes to flower selection than social bees, which are more generalist. The metabarcoding of pollen loads enabled us to draw a global picture of plant–wild bee interactions in an intensive agroecosystem. Our findings support the hypothesis that a higher diversity of weeds may increase wild bee diversity in intensive agroecosystems.

Commercial Bombus impatiens colonies function as ecological traps for wild queens

Abstract In response to anthropogenic environmental change, the cues that animals use throughout their lifecycle to optimize fitness may become unreliable, resulting in an ecological trap. Here we investigated whether commercial bumble bee Bombus impatiens colonies managed for early spring crop pollination act as ecological traps for wild nest‐searching Bombus queens by subverting their natural nest usurpation behaviour. An average of 10 dead wild queens were recovered from each standard colony during the 2‐week period of the experiment, but colonies with queen excluders were successful in preventing wild queen deaths. The use of queen excluders did not impact colony performance in terms of resident queen survival, colony reproduction, colony weight gain or worker body size. Sites where wild nest‐searching queens were small had higher rates of failed usurpation, suggesting smaller‐sized queens are disproportionately at risk from failed usurpation. Furthermore, sites where commercial colonies without queen excluders were introduced for spring crop pollination had fewer bumble bee visits to a later‐blooming crop compared to sites without commercial colonies. Synthesis and applications. Our findings reveal a novel mechanism by which commercial colonies can negatively impact wild bumble bee populations and their pollination services. At the same time, we demonstrate a simple and inexpensive risk mitigation tool—a queen excluder—was 100% effective at eliminating this risk without compromising colony performance. Commercial colonies used outdoors during the bumble bee nest‐searching period should be fit with queen excluders to prevent negative impacts on wild pollinator communities and their services.

Decline in wild bee species richness associated with honey bee (Apis mellifera L.) abundance in an urban ecosystem.

The spatial heterogeneity of urban landscapes, relatively low agrochemical use, and species-rich floral communities often support a surprising diversity of wild pollinators in cities. However, the management of Western honey bees (Apis mellifera L.) in urban areas may represent a new threat to wild bee communities. Urban beekeeping is commonly perceived as an environmentally friendly practice or a way to combat pollinator declines, when high-density beekeeping operations may actually have a negative influence on native and wild bee populations through floral resource competition and pathogen transmission. On the Island of Montréal, Canada there has been a particularly large increase in beekeeping across the city. Over the years following a large bee diversity survey ending in 2013, there was an influx of almost three thousand honey bee colonies to the city. In this study, we examined the wild bee communities and floral resources across a gradient of honey bee abundances in urban greenspaces in 2020, and compared the bee communities at the same sites before and after the large influx of honey bees. Overall, we found a negative relationship between urban beekeeping, pollen availability, and wild bee species richness. We also found that honey bee abundance had the strongest negative effect on small (inter-tegular span <2.25 mm) wild bee species richness. Small bee species may be at higher risk in areas with abundant honey bee populations as their limited foraging range may reduce their access to floral resources in times of increased competition. Further research on the influence of urban beekeeping on native and wild pollinators, coupled with evidence-based beekeeping regulations, is essential to ensure cities contain sufficient resources to support wild bee diversity alongside managed honey bees.

Supplementation in vitamin B3 counteracts the negative effects of tryptophan deficiencies in bumble bees.

Increasing evidence highlights the importance of diet content in nine essential amino acids for bee physiological and behavioural performance. However, the 10th essential amino acid, tryptophan, has been overlooked as its experimental measurement requires a specific hydrolysis. Tryptophan is the precursor of serotonin and vitamin B3, which together modulate cognitive and metabolic functions in most animals. Here, we investigated how tryptophan deficiencies influence the behaviour and survival of bumble bees (Bombus terrestris). Tryptophan-deficient diets led to a moderate increase in food intake, aggressiveness and mortality compared with the control diet. Vitamin B3 supplementation in tryptophan-deficient diets tended to buffer these effects by significantly improving survival and reducing aggressiveness. Considering that the pollens of major crops and common plants, such as corn and dandelion, are deficient in tryptophan, these effects could have a strong impact on bumble bee populations and their pollination service. Our results suggest planting tryptophan and B3 rich species next to tryptophan-deficient crops could support wild bee populations.

Investigating the effects of glyphosate on the bumblebee proteome and microbiota

Glyphosate is one of the most widely used herbicides globally. It acts by inhibiting an enzyme in an aromatic amino acid synthesis pathway specific to plants and microbes, leading to the view that it poses no risk to other organisms. However, there is growing concern that glyphosate is associated with health effects in humans and an ever-increasing body of evidence that suggests potential deleterious effects on other animals including pollinating insects such as bees. Although pesticides have long been considered a factor in the decline of wild bee populations, most research on bees has focussed on demonstrating and understanding the effects of insecticides. To assess whether glyphosate poses a risk to bees, we characterised changes in survival, behaviour, sucrose solution consumption, the digestive tract proteome, and the microbiota in the bumblebee Bombus terrestris after chronic exposure to field relevant doses of technical grade glyphosate or the glyphosate-based formulation, RoundUp Optima+®. Regardless of source, there were changes in response to glyphosate exposure in important cellular and physiological processes in the digestive tract of B. terrestris, with proteins associated with oxidative stress regulation, metabolism, cellular adhesion, the extracellular matrix, and various signalling pathways altered. Interestingly, proteins associated with endocytosis, oxidative phosphorylation, the TCA cycle, and carbohydrate, lipid, and amino acid metabolism were differentially altered depending on whether the exposure source was glyphosate alone or RoundUp Optima+®. In addition, there were alterations to the digestive tract microbiota of bees depending on the glyphosate source No impacts on survival, behaviour, or food consumption were observed. Our research provides insights into the potential mode of action and consequences of glyphosate exposure at the molecular, cellular and organismal level in bumblebees and highlights issues with the current honeybee-centric risk assessment of pesticides and their formulations, where the impact of co-formulants on non-target organisms are generally overlooked.

Co-benefits from tree planting in a typical English agricultural landscape: Comparing the relative effectiveness of hedgerows, agroforestry and woodland creation for improving crop pollination services

Land use policy in England is encouraging tree planting on farms to meet decarbonisation targets. This could be delivered through woodland creation, hedgerow planting or agroforestry. All three approaches could provide co-benefits for wild bee populations and crop pollination services, by increasing nesting and floral resources, but their relative effectiveness has not been studied at a landscape scale. We simulated six tree planting scenarios and used a validated process-based model to predict their effect on bumblebee abundance and pollination service to two common mass-flowering crops (oilseed rape and field beans) in a representative 10x10km agricultural landscape in England, UK. Two levels of planting intensity were studied: one representing the tree cover that would be achieved by 2035 if the 2020 woodland creation rate continues and another reflecting UK Government ambitions (threefold increase in planting rate). Hedgerow planting and woodland were predicted to give the biggest increase bumblebee abundance. Silvoarable agroforestry using fruit trees or willow was predicted, on average, to give the biggest increase in crop pollination service. However, the magnitude of increase was highly variable and hedgerow creation (which is more dispersed across the landscape) provided a more consistent increase in crop pollination services. Agroforestry with poplar (which offers less floral resource) and woodland creation (which concentrates tree planting in fewer locations) were only effective at enhancing landscape-level crop pollination at high planting intensity. Future land management policy should promote fruit tree and willow-based agroforestry as multifunctional tree planting measures in arable contexts, whilst continuing to encourage hedgerow planting and woodland creation for their role in promoting abundance and diversity of pollinators. Hedgerow planting may be needed alongside agroforestry to help stabilise pollination service through a crop rotation cycle.

Sudden collapse of xylophilous bee populations in the mountains of northern Utah (USA): An historical illustration

A scarcity of studies of the dynamics of wild bee populations hampers conservation efforts by bee ecologists and conservationists. Present limited information suggests that bee populations are highly unpredictable from year-to-year. Here we present an historical data set from nine sites replicated in 1984 and 1985 that demonstrates extreme between-year variability in numbers for 19 xylophilous bee species. Sixteen of those species produced far fewer nests in 1985, and 13 species in 1985 produced less than a third the number of nests produced in 1984. We argue that the 1985 collapse was not due to semivoltinism, i.e., the absence of morphs that require two years to mature, or to excessive sampling in 1984, but to a record cold period from January to March 1985 which likely killed most diapausing bees. Such events illustrate the dynamism of wild bee populations and thereby the large number of years needed to establish statistically significant population trends. We suggest that the current emphasis by bee conservationists to promote widespread surveillance monitoring programs is misguided and that funds are more effectively spent on hypothesis-driven targeted monitoring and on actions to actually reclaim degraded wild bee habitat.

Identifying wild bee visitors of major crops in North America with notes on potential threats from agricultural practices

Considering the critical importance of insect pollination to food security and documented declines in wild bee populations, it is imperative to develop effective conservation and management strategies that promote the health of wild bee communities associated with agroecosystems. Identifying wild bee visitors of crops, including crop-flower visitors and species that nest within cropping areas, may prove critical to this endeavor as optimal conservation strategies may differ among bee species and/or guilds, regions, and cropping systems. Although lists of bee species that are associated with North American crops are scattered throughout the literature, there is a need for a comprehensive compilation of those species by crop, region, and nesting guild. Here, we searched the literature to compile a list of wild bee species associated with 33 major crops in North America and assessed the overlap in bee species communities among crops and regions. Of the 739 crop-associated bee species retrieved, 405 species (54.8%) were ground nesters, and 438 species (59.3%) were identified as crop-flower visitors of at least one crop. Because of their nesting and foraging behavior, we argue that these species are more likely to be exposed to agricultural pesticide residues than bee species that do not nest in the ground or feed directly on crop flowers. We further compiled lists of wild bees that have been found to be associated with all of the four most surveyed perennial fruit crops (apple, blueberry, cranberry, strawberry) and all of the three most surveyed cucurbit crops (cucumber, Cucurbita, watermelon) in eastern North America. These lists of bee species can be used to focus attention on species needing better protection strategies within agroecosystems, especially for these two important North American crop groups and can also inform the development of multi-species pesticide risk assessment schemes.

Bee richness and abundance in small fruit farms from semiarid landscape, NE, Brazil

Bee diversity and current status of native populations is barely known in cropland from semiarid Sergipe, where fruit production is a growing activity among small farmers. Psidium guajava L. (Myrtaceae) is spread among small growers in Canindé de São Francisco and Poço Redondo in Sergipe state, Northeastern Brazil, in semiarid Caatinga, causing landscape change and habitat loss. Available evidences support that cross-pollination provided by bees may increase seed set and fruit production, despite self-pollination. We aimed to access bee richness and abundance within Guava orchard and identify landscape parameters important to these patterns. Survey was conducted in ten Guava orchards during the flowering period (n=10) from May to December 2017. Nine bee species were recorded and the high density and generalist bees Trigona spinipes and Apis mellifera comprised 92% of the flower visitors. No other social native bees were found, and solitary bees were scarce. No significant influence of landscape structure was found for bee richness, while bee abundance was affected by environmental diversity, isolation, and distance to caatinga patches and continuous vegetation reserves. Landscape simplification threatened bee diversity and pollination services. These results highlight the importance of providing bee habitat within farmlands, rearing stingless bees and restoring natural habitats along streams to increase wild bee populations within crops.