Honey Bee Abundance Research Articles

Relation between honey bee abundance and wild bee communities in Moroccan agro-ecosystems

Relation between honey bee abundance and wild bee communities in Moroccan agro-ecosystems

Biodiversity measures of a grassland plant-pollinator community are resilient to the introduction of honey bees (Apis mellifera).

The prairies of Canada support a diversity of insect pollinators that contribute pollination services to flowering crops and wild plants. Habitat loss and use of managed pollinators has increased conservation concerns for wild pollinators, as mounting evidence suggests that honey bees (Apis mellifera) may reduce their diversity and abundance. Plant-pollinator community analyses often omit non-bee pollinators, which can be valuable contributors to pollination services. Here, we experimentally introduced honey bees to examine how their abundance affects the species richness, diversity, abundance, species composition, interaction richness, and interaction diversity of all wild pollinators, and of four higher taxa separately. We identified all insect pollinators and analyzed how honey bee abundance affected the above biodiversity metrics, controlling for flower abundance and flower species richness. Even with high honey bee densities, there was no change to any of these variables, except that beetle species diversity increased. All other taxa had no significant relationship to honey bee abundance. Considering the widespread use of managed honey bees, the effect they have on wild pollinators should be firmly established. Our results suggest that honey bees have little to no short-term impact on the wild pollinator community or its interactions with plants in this native grassland.

Evidence of introduced honeybees (Apis mellifera) as pollen wasters in orchid pollination

Biological invasions threaten global biodiversity, altering landscapes, ecosystems, and mutualistic relationships like pollination. Orchids are one of the most threatened plant families, yet the impact of invasive bees on their reproduction remains poorly understood. We conduct a global literature survey on the incidence of invasive honeybees (Apis mellifera) on orchid pollination, followed by a study case on Australian orchids. Our literature survey shows that Apis mellifera is the primary alien bee visiting orchids worldwide. However, in most cases, introduced honeybees do not deposit orchid pollen. We also test the extent to which introduced honeybees affect orchid pollination using Diuris brumalis and D. magnifica. Diuris brumalis shows higher fruit set and pollination in habitats with both native and invasive bees compared to habitats with only introduced bees. Male and female reproductive success in D. magnifica increases with native bee abundance, while conversely pollinator efficiency decreases with honeybee abundance and rises with habitat size. Our results suggest that introduced honeybees are likely involved in pollen removal but do not effectively deposit orchid pollen, acting as pollen wasters. However, Apis mellifera may still contribute to pollination of Diuris where native bees no longer exist. Given the global occurrence of introduced honeybees, we warn that certain orchids may suffer from pollen depletion by these invaders, especially in altered habitats with compromised pollination communities.

Managed honeybee hives negatively affect the reproduction of native plants in a dryland nature reserve

Abstract The honeybee, Apis mellifera, stands out for its positive image due to its contribution to crop pollination and honey production, which facilitated its widespread distribution. However, large apiaries resulting in high honeybee densities could increase pollination frequency while increasing competition for floral resources, ultimately affecting native plant fitness. We studied the impact of managed honeybee hives on pollination and reproductive success of native plants in Villavicencio Nature Reserve, Mendoza, Argentina. During the flowering peak, we studied pollination and reproduction of three native plant species (Larrea divaricata, L. cuneifolia and Zuccagnia punctata) near and far from the hives. We estimated pollen deposition on flower stigmas, pollen tubes developed in flower pistils, fruit set, seed set and seed viability. We found that the honeybee hives had a positive effect on the reproduction of the self‐compatible species, L. divaricata. For the self‐incompatible species, results differed among species: Hives had positive effects on the pollination and negative effects on the reproduction of L. cuneifolia, while they had negative effects on the reproduction of Z. punctata. Synthesis and applications. Beekeeping is increasingly turning to natural areas in search of better quality honey; however, increased honeybee abundance in the field could influence the reproduction of native plants. Our results show that the introduction of managed hives negatively affected the reproduction of self‐incompatible native plants. This result allows us to make several recommendations for conservation and management actions concerning beekeeping in natural areas, regarding the among‐year rotation of the location of hives, the number of hives per site, and the need to monitor the reproduction of self‐incompatible species.

Maintaining habitat diversity at small scales benefits wild bees and pollination services in mountain apple orchards

Abstract Landscape context influences wild bee abundance and diversity, alongside pollination‐related services. Growing evidence supports the positive effects of landscape heterogeneity on bee diversity and fruit production for pollination‐dependent crops in flatlands. However, little remains known about these relationships in mountainous environments where the landscape matrix surrounding crops is often more complex than in lowlands. We conducted our study in apple orchards in South Tyrol, an Alpine region in Italy, using pan‐traps, direct observations of visitation frequency and a pollinator exclusion experiment. We investigated the scale‐dependent effects of landscape heterogeneity and other parameters on wild bee assemblages and the related pollination service they provide at five spatial scales (radius 100–2000 m). We found that landscape heterogeneity positively affected the abundance and richness of wild bees, with the strongest effect at 500 m. We calculated a multidiversity index, reflecting the land‐use intensity based on the species richness of vascular plants, grasshoppers, butterflies, birds and bats. We identified a positive relationship between this multidiversity index and wild bee richness. Additionally, we found that visitation rate of wild bees was negatively affected by crop cover and that abundance of honeybees did not influence wild bee visitation rate or reproductive success. Finally, reproductive success was positively related to semi‐natural habitat cover. Landscape heterogeneity should be maintained in apple orchards to continue to reap the benefits of vital pollination‐related services. Diversification strategies should be implemented to promote habitat diversity at small scales, even in regions with more than 80% of (semi‐)natural habitats.

Understanding how environmental degradation, microclimate, and management shape honey production across different spatial scales.

Although the abundance, survival, and pollination performance of honeybees are sensitive to changes in habitat and climate conditions, the processes by which these effects are transmitted to honey production and interact with beekeeping management are not completely understood. Climate change, habitat degradation, and beekeeping management affect honey yields, and may also interact among themselves resulting in indirect effects across spatial scales. We conducted a 2-year, multi-scale study on Chiloe Island (northern Patagonia), where we evaluated the most relevant environmental and management drivers of honey produced by stationary beekeepers. We found that the effects of microclimate, habitat, and management variables changed with the spatial scale. Among the environmental variables, minimum temperature, and cover of the invasive shrub, gorse (Ulex europaeus) had the strongest detrimental impacts on honey production at spatial scales finer than 4km. Specialized beekeepers who adopted conventional beekeeping and had more mother colonies were more productive. Mean and minimum temperatures interacted with the percentage of mother colonies, urban cover, and beekeeping income. The gorse cover increased by the combination of high temperatures and the expansion of urban lands, while landscape attributes, such as Eucalyptus plantation cover, influenced beekeeping management. Results suggest that higher temperatures change the available forage or cause thermal stress to honeybees, while invasive shrubs are indicators of degraded habitats. Climate change and habitat degradation are two interrelated environmental phenomena whose effects on beekeeping can be mitigated through adaptive management and habitat restoration.

Landscape structure and farming management interacts to modulate pollination supply and crop production in blueberries

Abstract Pollination services are affected by landscape context, farming management and pollinator community structure, all of which impact flower visitation rates, pollen deposition and final production. We studied these processes in Argentina for highbush blueberry crops, which depend on pollinators to produce marketable yields. We studied how land cover and honeybee stocking influence the abundance of wild and managed pollinators in blueberry crops, using structural equation modelling to disentangle the cascading effects through which pollinators contribute to blueberry fruit number, size, nutritional content and overall yield. All pollinator functional groups responded to landscape changes at a spatial scale under 1000 m, and the significance or direction of the effects were modulated by the field‐level deployment of honeybee hives. Fruit diameter increased with pollen deposited, but decreased with honeybee abundance, which, had indirect effects on fruit acidity. Honeybees had a positive effect on the number of fruit produced by the plants and also benefited the overall yield (kg plant−1) through independent effects on both the quality and quantity components of fruit production. Synthesis and applications. Deployment of beehives in blueberry fields can buffer, but not compensate for the negative effects on honeybee abundance produced by surrounding large scale none‐flowering crops. Such compensation would require high‐quality beehives by monitoring their health and strength. The contribution of honeybees to crop production is not equal across production metrics. That is, higher abundance of honeybees increases the number of berries produced but at the cost of smaller and more acidic fruits, potentially reducing their market value. Growers must consider this trade‐off between fruit quantity and quality when actively managing honeybee abundance.

The importance of shrubland and local agroecological practices for pumpkin production in sub-Saharan smallholdings

Land-use and local field management affect pollinators, pest damage and ultimately crop yields. Agroecology is implemented as a sustainable alternative to conventional agricultural practices, but little is known about its potential for pollination and pest management. Sub-Saharan Africa is underrepresented in studies investigating the relative importance of pests and pollinators for crop productivity and how this might be influenced by surrounding landscapes or agroecological practices. In Malawi, we selected 24 smallholder farms differing in landscape-scale shrubland cover, implementation of manual pest removal as an indicator of an agroecological pest management practice, and the number of agroecological soil practices employed at the household level, such as mulching, intercropping and soil conservation tillage. We established pumpkin plots and assessed the abundance and richness of flower visitors and damage of flowers (florivory) caused by pest herbivores on flowers. Using a full-factorial hand pollination and exclusion experiment on each plot, we investigated the relative contribution of pollination and florivory to pumpkin yield. Increasing shrubland cover decreased honeybee abundance but increased the abundance and richness of non-honeybee visitors. Manual removal of herbivores considered to be pests reduced flower visitors, whereas more agroecological soil management practices increased flower visitors. Neither shrubland cover nor agroecological management affected florivory. Pollinator limitation, but not florivory, constrained pumpkin fruit set, and increasing visitor richness decreased the relative differences between hand- and animal-pollinated flowers. We recommend improved protection of shrubland habitats and increasing agroecological soil practices to promote pollinator richness on smallholder farms.

Diversity and Abundance of Insect Pollinators of Cucurbits at Mid-Hills of Meghalaya, India

The current research was carried out at the ICAR-Research Complex for the North Eastern Hill Region (NEH) in Umiam, Meghalaya to investigate the diversity and abundance of insect pollinators of cucurbits at mid-hills of Meghalaya. Ridge gourd, sponge guard, pumpkin, teasel gourd, chow-chow, bottle guard and cucumber were taken as a target crop to observe the data on diversity and abundance. Total twenty-five (25) pollinators were observed in different cucurbits belongs to order Hymenoptera, Diptera and Lepidoptera which represents that mid-hills of Meghalaya have rich pollinator fauna. Out of 25 insect pollinators 3 pollinators identified from ridge gourd, 6 from sponge gourd, 4 from pumpkin, 3 from bottle gourd, 4 from cucumber, 3 from chow-chow and 2 from teasel gourd. Efficient pollinator was nominated on the basis of their abundance. During investigation it was found that bumble bee emerged as the most abundant pollinator in ridge gourd, pumpkin and sponge gourd. In sponge gourd carpenter bee also showed almost equal abundance. Indian honey bee abundance was high in cucumber and in chow-chow. Among collected pollinators, hymenopterans were the abundant with 80% relative abundance. It is clear from the recorded observation that native bees are equally contributing in pollination service so conservation of these bees is also a demand of nature. Activity time period of pollinators on flowers guided the farmers to avoid pesticide spray during particular time period.

Local and landscape context affects bee communities in mixed fruit orchards in Southern Thailand

Abstract Bees play an important role by contributing to the pollination of a diverse range of crops and wild plants. However, bees are threatened by deforestation and habitat degradation caused by urbanization and agricultural intensification, which reduce floral and nesting resources. In this study, the effects of local (orchard size, flowering plant abundance and richness and floral abundance) and landscape factors (surrounding agricultural, forest and urban cover) on bee richness and abundance in mixed fruit orchards were determined from 28 mature orchards interspersed along a gradient of landscape complexity. Bees were observed for 15 min in 2 × 2 m plots. We categorized all bees into one of the three groups: (a) honey bees, (b) solitary bees and (c) stingless bees. Several local and landscape factors were found to influence bee richness and abundance. Honey bee abundance was positively affected by orchard size, whereas honey bee richness was not. Stingless bee richness and abundance were positively correlated with floral abundance. Forest cover within a 3‐km radius positively affected solitary bee richness. Solitary bee abundance was positively affected by forest cover within a 3‐km radius and negatively impacted by urban cover within a 1.5‐km radius. In our study area, small forest patches are found in abundance; thus, the high proportion of forest edge, relative to the forest interior, greatly supports solitary bee abundance and richness in this landscape. Moreover, most solitary bees are soil‐nesting species that may be excluded from environments that are converted from natural to anthropogenically developed areas. Recommendations to protect pollinators included conserving existing forest patches, especially forest margins; restoring forest patches within farmland landscapes; maintaining a diversity of herbs and grasses within mixed fruit orchards; establishing live fences composed of diverse plant species and retaining dead trees within farmland. For urban areas, augmenting floral resources in green spaces is suggested.

Honey bees (Apis mellifera) modify plant-pollinator network structure, but do not alter wild species' interactions.

Honey bees (Apis mellifera) are widely used for honey production and crop pollination, raising concern for wild pollinators, as honey bees may compete with wild pollinators for floral resources. The first sign of competition, before changes appear in wild pollinator abundance or diversity, may be changes to wild pollinator interactions with plants. Such changes for a community can be measured by looking at changes to metrics of resource use overlap in plant-pollinator interaction networks. Studies of honey bee effects on plant-pollinator networks have usually not distinguished whether honey bees alter wild pollinator interactions, or if they merely alter total network structure by adding their own interactions. To test this question, we experimentally introduced honey bees to a Canadian grassland and measured plant-pollinator interactions at varying distances from the introduced hives. We found that honey bees increased the network metrics of pollinator and plant functional complementarity and decreased interaction evenness. However, in networks constructed from just wild pollinator interactions, honey bee abundance did not affect any of the metrics calculated. Thus, all network structural changes to the full network (including honey bee interactions) were due only to honey bee-plant interactions, and not to honey bees causing changes in wild pollinator-plant interactions. Given widespread and increasing use of honey bees, it is important to establish whether they affect wild pollinator communities. Our results suggest that honey bees did not alter wild pollinator foraging patterns in this system, even in a year that was drier than the 20-year average.

Mason bees and honey bees synergistically enhance fruit set in sweet cherry orchards

AbstractMason bees (Osmia spp.) are efficient fruit tree pollinators that can be encouraged to occupy and breed in artificial nesting material. In sweet cherry orchards, they are occasionally used as an alternative managed pollinator as a replacement for or in addition to honey bees (Apis mellifera). Yet, the lack of practical guidelines on management practices, for example optimal stocking rates, for both mason bee nesting material and honey bees might compromise pollination service provision. In this study, we assessed the relationship between stocking rates (honey bee hives and mason bee nesting material) and the abundance of honey bees and mason bees in 17 sweet cherry (Prunus avium) orchards in Central Germany. We furthermore performed a pollination experiment to explore the interactive effect of mason bees and honey bees on sweet cherry fruit set. In the orchards, both honey bee and mason bee abundance increased with increasing stocking rates of hives or nesting material, respectively. Honey bee abundance increased linearly with stocking rates. In contrast, mason bee abundance asymptoted at 2–3 nesting boxes per ha, beyond which more boxes resulted in little increase in visitation rate. Our pollination experiment demonstrated that orchards were pollen limited, with only 28% of insect‐pollinated flowers setting fruit versus 39% of optimally hand‐pollinated flowers. Honey bees and mason bees enhanced sweet cherry fruit set, but only when both were present and not when either was present alone in an orchard. Our findings demonstrate that offering nesting material for mason bees and employing honey bee hives can enhance bee abundance in sweet cherry orchards. By increasing honey bee abundance in combination with enhanced mason bee abundance, farmers can substantially boost fruit set and potentially sweet cherry yield. To enhance pollination services, farmers should consider the benefits of increasing pollinator biodiversity as an immediate benefit to improve crop yields.

Evidence of exploitative competition between honey bees and native bees in two California landscapes.

Human-mediated species introductions provide real-time experiments in how communities respond to interspecific competition. For example, managed honey bees Apis mellifera (L.) have been widely introduced outside their native range and may compete with native bees for pollen and nectar. Indeed, multiple studies suggest that honey bees and native bees overlap in their use of floral resources. However, for resource overlap to negatively impact resource collection by native bees, resource availability must also decline, and few studies investigate impacts of honey bee competition on native bee floral visits and floral resource availability simultaneously. In this study, we investigate impacts of increasing honey bee abundance on native bee visitation patterns, pollen diets, and nectar and pollen resource availability in two Californian landscapes: wildflower plantings in the Central Valley and montane meadows in the Sierra. We collected data on bee visits to flowers, pollen and nectar availability, and pollen carried on bee bodies across multiple sites in the Sierra and Central Valley. We then constructed plant-pollinator visitation networks to assess how increasing honey bee abundance impacted perceived apparent competition (PAC), a measure of niche overlap, and pollinator specialization (d'). We also compared PAC values against null expectations to address whether observed changes in niche overlap were greater or less than what we would expect given the relative abundances of interacting partners. We find clear evidence of exploitative competition in both ecosystems based on the following results: (1) honey bee competition increased niche overlap between honey bees and native bees, (2) increased honey bee abundance led to decreased pollen and nectar availability in flowers, and (3) native bee communities responded to competition by shifting their floral visits, with some becoming more specialized and others becoming more generalized depending on the ecosystem and bee taxon considered. Although native bees can adapt to honey bee competition by shifting their floral visits, the coexistence of honey bees and native bees is tenuous and will depend on floral resource availability. Preserving and augmenting floral resources is therefore essential in mitigating negative impacts of honey bee competition. In two California ecosystems, honey bee competition decreases pollen and nectar resource availability in flowers and alters native bee diets with potential implications for bee conservation and wildlands management.

Exploring relationships between time of day and pollinator activity in the context of pesticide use

Pesticide exposure can be harmful to insect pollinators and the ecosystem services they provide. As many pesticide guidelines warn against applying such products when pollinators are active, it is important to evaluate how pollinator activity changes with time of day to determine the most appropriate time to spray.We walked transects from sunrise to sunset in oilseed rape (Brassica napus L.) fields in Ireland to capture the abundance of honeybees, bumblebees, solitary bees, and hoverflies across daylight hours. We also recorded the activity of representative species from the three bee groups at their nests across similar time periods to compare with field observations.Peak pollinator abundance was in the mid-afternoon with fewer individuals in the early morning and late evening for all groups. At the nest we observed patterns of activity that broadly reflected field abundance but indicated that bees are active earlier and later than observed on the crop. However, there were differences between pollinator groups. Overall, honeybee and solitary bee abundance and activity were found to peak in the middle of the day, while bumblebee abundance and activity was more consistent throughout daylight hours. Hoverflies were relatively abundant in the morning and increased in number towards the late afternoon and early evening.Our results confirm current recommendations that pesticide application should be avoided in the middle of the day when pollinators are most active. However, the diversity of responses within and between pollinator groups to time of day should be accounted for when shaping guidelines, and clearly defining optimal pesticide application timings for end users is difficult and needs further consideration as it will vary between regions and crops. Further research should also explore how time impacts both pesticide efficacy and exposure of pollinators to residues post-application to allow full evaluation of how practical and beneficial timing of application may be when aiming to protect pollinators from pesticide exposure.

Within-bloom shift in abundance of a wild pollinator mediates pollen deposition rates to blueberry

Intra-seasonal variation in abiotic and biotic conditions can have profound consequences for pollinator community compositions and foraging movement, with flow-on effects upon pollination services. Yet, few studies have related such variations to pollination services in crop systems. In a cultivated highbush blueberry system with two primary pollinators — the managed European honey bee and a wild stingless bee species — we investigated how pollinator abundances, bee foraging behaviour, and con- and heterospecific stigmatic pollen loads changed over early, mid, and late blueberry blooming. Both con- and heterospecific stigmatic pollen loads declined following early bloom. This shift was associated with a decline in the abundance of stingless bees, whereas the abundance of honey bees only declined during late bloom. Simultaneously, honey bees were more likely to forage for blueberry pollen, and stigmatic pollen loads, relative to bee abundance, increased during late bloom. Although mixed pollen loads were common on pollinator bodies, especially on pollen foraging honey bees, heterospecific pollen deposition on blueberry stigmas was low. Given the similar effectiveness of honey bees and stingless bees as pollinators of blueberries, we contend that the observed seasonal variation in pollen deposition is likely caused by the decline in stingless bee abundances, as honey bees were not able to fully compensate for the loss of stingless bees during late bloom. Greater consideration of seasonal heterogeneity of pollinator abundance and behaviour, as part of pollination management plans, may aid in ensuring high pollination services throughout the entirety of crop bloom.

Overlapping exposure effects of pathogen and dimethoate on honeybee (Apis mellifera Linnaeus) metabolic rate and longevity.

Introduction: Declines in honeybee abundance have been observed worldwide during last decades. This is partly due to plant protection agents used in intensive farming, landscaping and infrastructure maintenance. Another type of factors negatively affecting honeybees is the spread of diseases caused by different pathogens and pests. Lately, more focus has been paid to the interactions between different overlapping stressors affecting honeybee health, the combination of these often being more detrimental compared to individual stressors. The most widely used stress-evaluating methods take into account lethal- or motorial changes of the individuals or colonies. Comparatively little honeybee research has examined changes in initial recovery potential and physiological symptoms of toxification. The aim of this study was to examine the combined effect of Nosema apis and N. ceranae (according to a newer classification Vairimorpha apis and V. ceranae), the common causes of nosemosis in the honeybee Apis mellifera L., with the insecticide dimethoate. Methods: In this study, honeybee mortality and metabolic rate were used to assess the combined effects interactions of Nosema ssp. and dimethoate. Results: Our results showed that exposure to the low concentration of either dimethoate, either one or both species of Nosema ssp as single factors or in the combination had no significant effect on honeybee metabolic rate. The mortality increased with the two Nosema spp., as well as with infection by N. ceranae alone. The effect of dimethoate was observed only in combination with N. apis infection, which alone had no effect on individual honeybee mortality. Conclusion: This study demonstrates that the overlapping exposure to a non-lethal concentration of a pesticide and a pathogen can be hidden by stronger stressor but become observable with milder stressors.

Native and introduced pollinators vary in their seasonal floral resource visitation and selection between native and exotic plant species

Abstract Anthropogenic pressures on native ecosystems have resulted in numerous functional and compositional changes, creating novel ecosystems with new interactions between native and exotic species. How native species utilize these resources is crucial for their management in altered landscapes and the promotion of their essential ecosystem services. We compared seasonal floral selection between European honey bees and their most phylogenetically similar native component in our study region, bumble bees, in North American grasslands with high densities of exotic plant species. Additionally, we determined whether floral species richness, total flowering density, native floral density or exotic floral density best explained the abundance of both groups. Selection analyses revealed that honey bees and native bumble bees differed in selection between native and non‐native floral resource availability, with any significant selection of honey bees being for exotic plants while native bumble bees selected for native plants. Native forb presence and floral richness best explained the variation in bumble bee abundance, while honey bee abundance was associated with flowering densities in the early and mid‐seasons and floral richness in both the early and late seasons. Despite their generalist diets, we emphasize the importance of native floral availability for bumble bee foraging in novel grassland landscapes and the importance of exotic plants to support honey bee production. Synthesis and applications. Our results indicate that pollinator forage management should differ for non‐native and native species, despite morphological and life‐history similarities. However, greater floral diversity provides a common management focus that can benefit honey bees and bumble bees in particular seasonal periods. Our results suggest that management actions promoting resource diversity can benefit functionally different species. In grasslands, implementing disturbance processes that can favour floral expression (e.g. fire; grazing) can support bumble bees of conservation concern and agriculturally important bees simultaneously.

Enhanced urban roadside vegetation increases pollinator abundance whereas landscape characteristics drive pollination

Roads cause pollution, habitat degradation and fragmentation, while recent studies report that roadside vegetation can benefit plant and insect diversity. However, the factors that drive effects of roadside vegetation on pollinator abundance and pollination need further attention. Our main interest in this study was to evaluate urban roadside enhancement by identifying direct and indirect effects of local resource availability and landscape characteristics on pollinator abundance and quality of pollination, by using functionally different phytometer plants. Thus, we established 34 species-rich wildflower patches along urban roads, and monitored flowering species and floral density at the local scale. At the landscape scale we measured the amount of impervious surface within a radius of 500 m around the wildflower patches, as well as edge density of all major land-use types, and distance to the city center. As control, we used 34 patches with existing species-poor roadside green. The abundance of pollinators, i.e., honeybees, wild bees, and hoverflies, was sampled with colored pan traps. Pollination was monitored based on fruit number and weight of three phytometer species, i.e., Fragaria × ananassa, Ranunculus acris, and Trifolium pratense, that differ in flower morphology and color, and attract different pollinators. Pollinator abundance was positively related to local richness of flowering plants and floral density. At the landscape scale, pollinator abundance was positively related to the proportion of impervious surface but negatively to edge density. Phytometer-specific effects on pollination were moderated by landscape characteristics: Fruit mass of F. x. ananassa was highest in the inner city, fruit number of R. acris was lower in areas with high edge density, whereas in T. pratense fruit number increased with edge density, and was negatively related with the proportion of impervious surface. There were no indirect effects of local and landscape factors via pollinator abundance on pollination. The study of the three phytometer species revealed that roadside enhancement can directly support fruit production in wild plants and crops in cities. Thereby, different landscape characteristics influenced the quality of fruit set, which also depended on individual plant reproductive adaptations. This stresses the importance of using a set of complementary phytometer species in pollination experiments, especially to gain insights into ecosystem functioning at coarser spatial scales.

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.

Pollination of exotic fruit crops depends more on extant pollinators and landscape structure than on local management of domestic bees

Agricultural globalization has driven the expansion of exotic crops into new agricultural areas. Pollinator-dependent exotic crops not only have to face the abiotic constraints of the new cultivation regions but also deal with local pollinator assemblages, which may or may not fulfill pollination requirements. Here, we studied how three entomophilous exotic crops (kiwifruit, northern highbush blueberry and rabbiteye blueberry) adapt to a common pollination environment in new cultivation areas in Spain. For this, we assessed the pollination limitation of those crops, the contribution of insect assemblages to the pollination service, and the effect of landscape structure and the management of domestic pollinators on these assemblages. The three exotic crops showed large and diverse pollinator assemblages but differed in the assemblage composition and in the identity of the main pollinator species. Honeybee clearly dominated kiwifruit assemblages, representing almost 70 % of visits to flowers. Bumblebees and honeybee fairly equally dominated floral visits in highbush blueberry, and bumblebees accounted for more than 90% of visits in rabbiteye blueberry. Floral morphology partially explained interspecific differences in pollinator assemblages and led to the distinct contributions of the different insects to the different crops. Kiwifruit (but not blueberry) crops experienced pollination limitation that led to, on average, a 7.2 % reduction in fruit weight. This pollination limitation decreased when honeybee abundance rose. In all three crops, the local pollinator assemblages mostly depended on the landscape structure around orchards but were only affected by the management of domestic pollinators in rabbiteye blueberry crops. Our results highlight the importance of understanding the interspecific differences in the pollination ecology of new exotic crops before designing general management recommendations, and also question the use of managed pollinators before making an assessment of the contribution of extant insects to the pollination service.