Pollinator Abundance Research Articles

Flower richness is key to pollinator abundance: The role of garden features in cities

Urban areas can be both detrimental for pollinators or function as suitable habitats, depending on the land-use type, the urban context and the pollinator group in focus. Urban green spaces, including gardens, parks or cemeteries can provide essential resources for a wide range of pollinator groups, like wild bees, hoverflies and beetles. Urban community gardens can be particularly structurally complex and harbour a diverse range of nesting and food resources for pollinators. However, we know little about how garden features may vary with the urban context of gardens and which specific garden features can increase the abundance of pollinators in general and of different pollinator groups.Over two summer seasons, we recorded garden features and pollinators using flower observations in 33 urban community gardens in Munich and Berlin, Germany. We examined how garden features differ amongst urban community gardens from three urbanisation categories, and analysed the effects of garden features such as floral and nesting resources and landscape imperviousness (as indicator of urbanisation) on pollinator abundance, richness and diversity.In more urbanised gardens, flower richness and bare substrate were less prevalent. Flower richness was positively correlated with overall pollinator abundance, richness and diversity as well as with the abundances of all pollinator taxa excluding beetles. Landscape imperviousness was negatively correlated with hoverfly and beetle abundances. Hoverflies also decreased with increasing bare substrate and wasp abundance decreased with increasing deadwood availability. Our findings highlight the important role of flower richness for insect conservation in urban management and show that pollinator taxa react differently to garden features and urbanisation. To support pollinating insects, gardeners can increase flower richness, especially in highly urbanised areas.

Linked spatial and temporal success of urban growth boundaries to preserve ecosystem services

Urban expansion and sprawl lead to loss of green space. This has the potential to degrade natural capital and associated ecosystem services. Urban growth boundaries (UGBs) are a planning tool to delineate where growth may or may not occur as a strategy to protect green and open space.However, how these policies impact ecosystem services is unknown, particularly across multiple years. Here we compare pairs of cities: one of which has a UGB and one that does not.Specifically, we analyzed the following city pairs: (1) Lexington, KY: Huntsville, AL and (2) Portland, OR: Denver, CO. We modeled the ecosystem services provided to each city, quantifying carbon storage, pollinator abundance, urban flood risk, and urban cooling. Our results show that UGBs succeed in preserving the ecosystem services, over time, at a higher and more predictable rate than cities that do not have a UGB. Change over time highlights the effectiveness of UGBs in preserving ecosystem services overall and concentrating loss of ecosystem service delivery within highly urbanized areas. We discuss how the data necessitates analyzing spatial and temporal trends together to incorporate starting values of ecosystem service function for comparison between case studies. Natural capital and its associated ecosystem services should be key criteria for assessing policies for urban planning and used to further implement laws and policies to enhance environmental and human health within urban areas.

Entomofauna presente en refugios vegetales en un campo de vid var. Crimson Seedless en Ica-Perú

The use of chemical pesticides to control pests also affects beneficial insects, so it is necessary to implement mechanisms that allow them to be protected and promote their development. In the present investigation, three plant shelters were installed to identify their entomofauna and determine the plant species with the potential to host biological controllers of grapevine pests. The study was carried out in the 2020-21 growing season, with seven plant species to make up three plant shelters (A, B, and C) that were installed on the edges of a vineyard of the Crimson Seedless variety in Ica, Peru. In total, 1,209 insects were reported, in six orders, nine families, and sixteen species; the most abundant were pollinators, followed by phytophagous, predators, and some parasitoids. There were no statistical differences between the shelters in terms of the abundance of parasitoids and pollinators, but there were in predators and phytophagous specifically between shelters A and B with C. Shelters A and B, which included the fennel Foeniculum vulgare Mill., stood out for having a larger population of predators, including Chrysoperla externa (Hagen), the main controller of the “vine mealybug” (Planococcus spp.). The importance of plant shelters was demonstrated and their implementation in vineyards is recommended to promote biological control and contribute to integrated pest management in this crop. Keywords: biodiversity, natural enemies, conservation biological control.

Flowering areas enhance insect pollinators and biological control agents in wheat intensive agro‐ecosystems

Abstract This 4‐year study (2018–2021) aimed at investigating the effects of flowering areas inserted at the margin of soft wheat fields (Triticum aestivum L.) in comparison with spontaneous field margins. The action formed part of a multidisciplinary initiative promoted by the Barilla food company, aimed at promoting the sustainable production of soft wheat. Specific aims were to study the effects of flowering areas on (i) the abundance and species richness of insect pollinators, including wild bees, syrphids and butterflies; (ii) the levels of wheat aphid and bug infestations and (iii) the assemblages of biological control agents of aphids (coccinellids and aphid mummies as a result of parasitization). Insect surveys were carried out on 61 wheat‐growing farms located in Northern Italy. Insect pollinators were sampled on all farms, whereas wheat aphids, wheat bugs and aphid biological control agents were investigated in a sub‐sample of 20 farms. Results generally indicated a positive impact of flowering areas on multiple taxa in comparison with spontaneous field margins. The abundance of pollinators and coccinellids was significantly enhanced by the flowering areas. Aphid mummies showed an interaction between strategies and distances with more mummies at 5 m in wheat plots close to flowering areas and at 50 m in the plots close to spontaneous field margin (control). Flowering areas were validated as an important tool for promoting beneficial taxa in agro‐ecosystems. However, the successful establishment of this ecological infrastructure was suggested to rely on several factors, which included both the selection of suitable flowering plant species and the implementation of appropriate management practices.

Forest pollinator richness declines with distance into burned areas

The effects of prescribed fire on forest pollinator communities are complex and incompletely understood. One of the least-studied questions concerns how these organisms are affected by the size, or spatial scale, of fire. We sought to address this by sampling bees (Hymenoptera: Apoidea), butterflies (Lepidoptera), and hover flies (Diptera: Syrphidae) at different distances along 500 m transects into forests burned every three years in the southeastern United States. We found combined pollinator richness to decline significantly with distance, being about 23.9 % lower near the centers of burn units than near the edges, and this did not change with time since fire. These patterns held true when small and large pollinators were analyzed separately, as well as for the richness of bees and butterflies (but not hover flies), and regardless of bee nesting guild. We found no relationship between the abundance of all pollinators and distance. However, the abundance of small pollinators decreased with distance whereas that of large pollinators increased. A competing model provided no support for the alternative hypothesis that the observed effects of distance can be explained by the length of road edges nearby as opposed to distance from unburned habitat. The richness and abundance of all pollinators combined and most taxonomic groups and species analyzed separately increased with increasing canopy openness as well as with increasing plant richness. Although pollinator richness declined with distance into large burns and small species appear to be particularly sensitive, we also found the richness and abundance of pollinators to decrease with time since fire. Our results show that fire can improve local conditions for pollinators but that unburned habitats serve as important refugia or sources of flowers following fire, underscoring the importance of pyrodiversity in managed landscapes.

Pollinator abundance, not the richness, benefits from urban green spaces in intensive agricultural land

Pollinator abundance, not the richness, benefits from urban green spaces in intensive agricultural land

Body-size-dependent effects of landscape-level resource energetics on pollinator abundance in woodland remnants.

Land use change alters floral resource availability, thereby contributing to declines in important pollinators. However, the severity of land use impact varies by species, influenced by factors such as dispersal ability and resource specialization, both of which can correlate with body size. Here. we test whether floral resource availability in the surrounding landscape (the 'matrix') influences bee species' abundance in isolated remnant woodlands, and whether this effect varies with body size. We sampled quantitative flower-visitation networks within woodland remnants and quantified floral energy resources (nectar and pollen calories) available to each bee species both within the woodland and the matrix. Bee abundance in woodland increased with floral energy resources in the surrounding matrix, with strongest effects on larger-bodied species. Our findings suggest important but size-dependent effects of declining matrix floral resources on the persistence of bees in remnant woodlands, highlighting the need to incorporate landscape-level floral resources in conservation planning for pollinators in threatened natural habitats.

The Diversity of pollinator insects in vegetable gardens, Kabawo District, Muna Regency

Pollinator insects play an important role in pollination to increase the productivity of flowering plants. The aim of this study was to analyze the abundance, diversity, and specific taxon of insect pollinators among different vegetable crops in local farmers' gardens. Insects were sampled from four gardens, namely polyculture long bean (KKP), eggplant polyculture (KT), curly chili monoculture (KCK), and Indofood chili monoculture (KCI) used nets and light traps. The results showed that the abundance and diversity of pollinator insects varied between gardens. The pollinator insect community in KCI was most similar to that in KCK; KT was similar to the KCI and KCK groups, while KKP were separate from the KT, KCK and KCI groups. The richest genus occurs in KKP, while chili plantations are the poorest. The apis genus in KKP and KT, and the Nomina genus in KCK and KCI were dominant. The specific pollinator insect genus in KKP is the richest. It concluded that plant species and cropping patterns contribute to the composition and diversity of the pollinator insect community.

Co-occurrence and abundance of pollinators and pests in horticultural systems in Africa using an integrated Earth observation-based approach

ABSTRACT Flower-visiting insects that are pollinators play a critical role in promoting biodiversity in agroecosystems and agricultural food production through their pollination ecosystem service. However, several factors affect the survival of these pollinators and flower visitors, including the heavy and indiscriminate application of agrochemicals to control crop insect pests, which is impacted by various cropping patterns in a landscape and by shifting environmental conditions. Thus, this study focused on investigating the influence of cropping patterns on the spatial distribution of pollinators (Apis mellifera, Hymenoptera other than A. mellifera, and Syrphidae), flower visitors (Calliphoridae), and pests, i.e. fruit fly (Bactrocera dorsalis) and false codling moth (Thaumatotibia leucotreta) of the avocado, a pollinator-dependent crop. Cropping patterns, earth observation data and relevant environmental variables were used as the predictor variables for modeling the potential distribution and abundance of avocado pollinators, flower visitors and pests in one of the leading regions in avocado production in Kandara, Maragua, and Gatanga sub-Counties in Murang’a County, Kenya. In specific, species distribution modeling (SDM) and species abundance modeling (SAM) techniques, i.e. the maximum entropy (MaxEnt) model (presence-only data) and negative binomial (NB) distribution in a generalized linear model (GLM) (abundance data) were used, respectively. Additionally, the spatial distribution probability of the co-occurrence of the pollinators, flower visitors and pests was also analyzed. This study revealed that cropping patterns was the most consistent influential predictor variables for the distribution of avocado pollinators, flower visitors and pests. A large area of Kandara and some parts of Maragua and Gatanga sub-Counties showed a high spatial distribution probability of the studied avocado pollinators, flower visitors and pests. However, only the majority of Kandara sub-County had a high spatial distribution probability score of the potential co-occurrence of the avocado pollinators, flower visitors and pests. Further, A. mellifera was the most abundant flower-visiting pollinator compared with the other studied pollinators, while B. dorsalis was the most abundant avocado pest compared with T. leucotreta. In addition, GLM analysis indicated that no environmental variable was significant in explaining the abundance of the studied avocado pollinators, whereas precipitation and elevation derivatives of aspect and hillshade were statistically significant (p ≤ 0.05) in explaining the abundance of B. dorsalis. Solar radiation was significant in explaining only the abundance of T. leucotreta. Our study revealed that SDM and SAM modeling outputs can be used to inform decision-making for the implementation of sustainable management efforts regarding pollinators, flower visitors, and insect pests.

Strong habitat and seasonal phenology effects on the evolution of self-compatibility, clonality and pollinator shifts in Lachenalia (Asparagaceae: Scilloideae).

Plants employ a diversity of reproductive safeguarding strategies to circumvent the challenge of pollen limitation. Focusing on southern African Lachenalia (Asparagaceae: Scilloideae), we test the hypothesis that the evolution of reproductive safeguarding traits (self-compatibility, autonomous selfing, bird pollination and clonal propagation) is favoured in species occupying conditions of low insect abundance imposed by critically infertile fynbos heathland vegetation and by flowering outside the austral spring insect abundance peak. We trace the evolution of these traits and selective regimes on a dated, multi-locus phylogeny of Lachenalia and assess their evolutionary associations using ordinary and phylogenetic regression. Ancestral state reconstructions identify an association with non-fynbos vegetation and spring flowering as ancestral in Lachenalia, the transition to fynbos vegetation and non-spring flowering taking place multiple times. They also show that self-compatibility, autofertility, bird pollination and production of multiple clonal offsets have evolved repeatedly. Regression models suggest that bird pollination and self-compatibility are selected for in fynbos and in non-spring flowering lineages, with autofertility being positively associated with non-spring flowering. These patterns support the interpretation of these traits as reproductive safeguarding adaptations under reduced insect pollinator abundance. We find no evidence to support the interpretation of clonal propagation as a reproductive safeguarding strategy.

Landscape simplification leads to loss of plant–pollinator interaction diversity and flower visitation frequency despite buffering by abundant generalist pollinators

AbstractAimGlobal change, especially landscape simplification, is a main driver of species loss that can alter ecological interaction networks, with potentially severe consequences to ecosystem functions. Therefore, understanding how landscape simplification affects the rate of loss of plant–pollinator interaction diversity (i.e., number of unique interactions) compared to species diversity alone, and the role of persisting abundant pollinators, is key to assess the consequences of landscape simplification on network stability and pollination services.LocationFrance, Germany, and Switzerland.MethodsWe analysed 24 landscape‐scale plant–pollinator networks from standardised transect walks along landscape simplification gradients in three countries. We compared the rates of species and interaction diversity loss along the landscape simplification gradient and then stepwise excluded the top 1%–20% most abundant pollinators from the data set to evaluate their effect on interaction diversity, network robustness to secondary loss of species, and flower visitation frequencies in simplified landscapes.ResultsInteraction diversity was not more vulnerable than species diversity to landscape simplification, with pollinator and interaction diversity showing similar rates of erosion with landscape simplification. We found that 20% of both species and interactions are lost with an increase of arable crop cover from 30% to 80% in a landscape. The decrease in interaction diversity was partially buffered by persistent abundant generalist pollinators in simplified landscapes, which were nested subsets of pollinator communities in complex landscapes, while plants showed a high turnover in interactions across landscapes. The top 5% most abundant pollinator species also contributed to network robustness against secondary species loss but could not prevent flowers from a loss of visits in simplified landscapes.Main ConclusionsAlthough persistent abundant pollinators buffered the decrease in interaction diversity in simplified landscapes and stabilised network robustness, flower visitation frequency was reduced, emphasising potentially severe consequences of further ongoing land‐use change for pollination services.

Intercropping Industrial Hemp and Cowpea Enhances the Yield of Squash—A Pollinator-Dependent Crop

Cultural crop-production practices are not only engineered to minimize pest incidence but also improve resource use efficiency and increase the diversity of habitat for beneficial insects that provide pollination services. With the increasing cultivation of industrial hemp and the benefits associated with the cultivation of multiple crops, its integration into a polyculture cropping system remains to be evaluated. We intercropped two pollinator-attractive crops, hemp and cowpea, with squash, a pollinator-dependent crop, to evaluate the impact of pollinator abundance and diversity on crop yield. Intercropping significantly increased the overall abundance of pollinators with 79.1% recorded from the intercropping systems compared to 21.9% in the monocropping systems. Sweat bees and bumble bees were the most abundant bees, and Squash+Cowpea was the most diverse cropping system. Intercropping significantly increased the yield of squash with higher squash yield (155%) in Hemp+Squash and (161%) in Squash+Cowpea than in squash monocrop. Also, intercropping resulted in higher hemp yield (64%) in Hemp+Cowpea and (165%) in Hemp+Squash compared to hemp monocrop. This study demonstrated that agricultural systems such as intercropping that are designed to attract pollinators are much more productive by not only improving crop yield but also growers’ returns on investments.

The pollinator conservation approach “Farming with Alternative Pollinators”: Success and drivers

Global food security is heavily reliant on crop pollination. However, evidence on pollinator decline has been reported in all continents. Globally affordable conservation strategies need to be developed, as high-cost measures like European agri-environment schemes are not scalable in all countries. Here, we test, if a low-cost conservation approach named “Farming with Alternative Pollinators” (FAP) can benefit wild pollinator abundance and richness in agro-ecosystems and in crops, through establishment of marketable habitat enhancement plants (MHEP). The study was carried out in four Moroccan agro-climatic regions, during two years, using 6 main crops (pumpkin, zucchini, faba bean, tomato, eggplant and apple) and 201 sites. Additionally, we investigated how crop type, crop-MHEP composition (i.e. phylogenetic distances among crop and MHEP) and local climate can drive the success of the approach in comparison to monocultural fields. Based on 7097 recorded specimens, our results show that the wild pollinators of the entire FAP fields (i.e. 75% main crop and 25% MHEP) were significantly more abundant and species-rich than those of control fields (i.e. 100% main crop). Considering the main crop wild pollinators, FAP did not display any significant effect either on wild pollinator abundance or on pollinator richness. The mean phylogenetic distance between the main crop and MHEP, and climatic variables were not correlated with increase in wild pollinator abundance and richness in FAP fields. The crop type was found to influence the effect of the FAP approach. Our study provides strong evidence that FAP constitutes a relevant method for wild pollinator conservation in agro-ecosystems. Further research on additional environmental factors is necessary to outline the circumstances under which the FAP approach can positively affect wild pollinator communities.

The effect of global change on the expression and evolution of floral traits.

Pollinators impose strong selection on floral traits. Indeed, pollinator syndromes are the result of these strong selective forces, but other abiotic and biotic agents also drive the evolution of floral traits and influence plant reproduction. Global change is expected to have widespread effects on biotic and abiotic systems resulting in novel selection on floral traits under future conditions. Global change has depressed pollinator abundance and altered abiotic conditions, thereby exposing flowering plant species to novel suites of selective pressures. Here we consider how biotic and abiotic factors interact to shape the expression and evolution of various floral characteristics (the targets of selection), including floral size, color, physiology, reward quantity and quality, and longevity amongst other traits. We examine cases in which selection imposed by climatic factors conflicts with pollinator-mediated selection. Additionally, we explore how floral traits respond to environmental changes through phenotypic plasticity and how that can alter plant fecundity. In this review, we evaluate how global change may shift the expression and evolution of floral phenotypes. Floral traits evolve in response to multiple interacting agents of selection. Different agents can sometimes exert conflicting selection. For example, pollinators often prefer large flowers, but drought stress can favor the evolution of smaller flowers, and the size of floral organs can evolve as a trade-off between selection mediated by these opposing actors. Nevertheless, few studies have factorially manipulated abiotic and biotic agents of selection to disentangle their relative strengths and directions of selection. The literature has more often evaluated plastic responses of floral traits to stressors than it has considered how abiotic factors alter selection on these traits. Furthermore, global change will likely alter the selective landscape through changes in the abundance and community compositions of mutualists and antagonists and novel abiotic conditions. We encourage future work to consider a more holistic model of floral evolution, which will enable more robust predictions about floral evolution and plant reproduction as global change progresses.

Konservasi Kupu-Kupu Penting Sebagai Penyerbuk di Kampung Wisata Isyo Hills Rhepang Muaif Nimbokrang, Kabupaten Jayapura

Butterflies are an important example of pollinating insects of the Order Lepidoptera. The presence of butterfly pollinating insects in nature is highly dependent or influenced by the availability of flowering plants visited in the ecosystem. The purpose of this study was to determine the diversity and abundance of butterfly pollinator in flowering plants. A direct survey method (visual) with a radius of ± 100-250 m² was done with scan sampling technique. Parameters measured were the abundance and the species richness of butterflies visited flowering plants as well as the species richness of flowering plants visited by butterflies pollinator. The data obtained were analyzed using the the Shannon-Wiener diversity index (H’). The results showed that at study sites in secondary forest habitats and yards, 25 species of butterfly pollinators were found consisting of 5 families with 308 individuals. Nine species of flowering plants visited by butterfly pollinators. The Jatropha integerrima was the most visited by butterfly pollinators with 11 species, followed by Hibiscus rosa-sinensis and Ixora coccinea (9 species), Clerodendron paniculatum (6 species), Mussaenda ralateensis (4 species), Bidens pilosa and Celosia argentea (3 species), Zinnia elegans visited by 2 species and Portulaca oleracea visited by 1 species of butterfly pollinators. Based on the calculation, the value of Shannon-Wiener index (H') is 2.946, which indicates that the level of diversity of butterfly pollinators in the medium category.

Landscape-wide floral resource deficit enhances the importance of diverse wildflower plantings for pollinators in farmlands

Pollinators are declining rapidly, largely due to land conversion and intensification of agriculture. To mitigate their crisis, low-disturbance habitats, such as sown wildflower plantings, could promote pollinators by restoration of their resources. However, comprehensive knowledge is lacking on how landscape context, spatial configuration and age of wildflower plantings, seasonality and flower composition affect pollinator communities, especially from East-Central Europe. To understand these effects, we established diverse native wildflower plantings within heterogeneous and homogeneous agricultural landscapes, by two spatial configurations: one large field or three smaller strips, in Hungary. We sampled floral resources and wild pollinator insects (wild bees, hoverflies, butterflies), in early and mid-summer, for two years after establishment. Flower resources of the sown plant species increased continuously, and were complemented at high rate by flowering plant species from the soil seed bank, especially in the first year. Both flower abundance and diversity increased the abundance of pollinators, highlighting the important role of using diverse seed mixtures. Wild bee abundance and species richness increased year by year and season by season, while butterfly abundance also demonstrated a yearly increase after establishment. Hoverfly abundance and species richness, however, showed an opposite trend, possibly due to the inter-annual variation. Wild bee and butterfly abundance was higher in the heterogeneous than in the homogeneous landscapes. We did not observe any significant local effects of spatial configuration itself on pollinator populations. Wildflower plantings were particularly attractive for wild bees in flower-poor (homogeneous) landscapes during the flower-poor (mid-summer) period of the year. This can be explained by the increased contrast in flower resources between the wildflower plantings and the surrounding landscape, and highlights the importance of wildflower plantings in such conditions. Our results emphasise that to support pollinators effectively, future wildflower plantings should be maintained for multiple years, aim to maximise floral diversity and ensure continuously available flower resources throughout the entire season. They can be facilitated by i) using diverse seed mixtures of native flowering plants, ii) particularly focusing on plants that bloom during the crucial mid-summer period, iii) allowing the plant species to grow and bloom from the soil seed bank, and iv) using management techniques, which help to extend the flowering season. Further results from the upcoming years and similar long-term and landscape-scale experimental studies are needed to understand all the benefits and ecological processes of diverse native wildflower plantings especially in understudied European regions.

Diversity of bumble bees and butterflies in Minnesota roadsides depends on floral diversity and abundance but not floral native status

Abstract Habitat loss is an important driver in the rapid decline of many insects. The restoration of roadside habitat has been touted as an opportunity to support communities of bumble bees and butterflies, two insect groups of conservation concern. However, it is unclear how current roadside restoration methods translate to pollinator abundance and diversity. Here, we ask how the plant communities of roadsides seeded with native and non‐native seed mixes affect bumble bee and butterfly communities 2–20 years after planting. We found that bumble bee and butterfly abundance and diversity were positively correlated with floral abundance and diversity. However, the pollinator community in plots planted with diverse native seed mixes did not differ from that found in plots seeded with species‐poor non‐native mixes, likely because many forbs in the native seed mixes had poor establishment, and all plots were readily colonised by species that were never planted. While plots with more native flowers did not necessarily support higher pollinator diversity, we did find several native plants that established well in roadsides and supported pollinators, including goldenrods (Solidago spp.), milkweeds (Asclepias spp.) and wild bergamot (Monarda fistulosa). Our data suggest that managing a more diverse and abundant floral community will benefit bumble bees and butterflies. Refining the composition of native seed mixes, adding more floral abundance to non‐native mixes and investing in management for native plant communities may increase the habitat value of roadsides for pollinator communities.

Influence of flowering red clover on flower visitation in a sweet corn agroecosystem

Agricultural intensification and the conversion of natural landscapes into annual cropping systems have contributed to declines in pollinator abundance and biodiversity. Increasing the abundance of flowering plants within crop fields is an often-overlooked practice that may be used to help sustain and enhance pollinator populations. In this study, the influence of red clover (Trifolium pratense) used as an interplanted living mulch on pollinator richness and visitation rates was evaluated and compared with monoculture sweet corn habitats. Treatments included sweet corn interplanted with red clover or monoculture with or without cover crop residue. Weekly visual observations of foraging floral visitors revealed that multiple species of bumblebees and butterflies, as well as honeybees frequently visited red clover flowers. Observations of visitors foraging on sweet corn tassels during pollen shed revealed distinct insect communities were attracted by sweet corn and red clover plants. Findings provided evidence that the inclusion of red clover in crop fields can increase the diversity and abundance of bees and butterflies on arable lands by serving as an important food source.

Tropical agroforestry supports insect pollinators and improves bean yield

Abstract Pollination services contribute to crop productivity worldwide, but insect pollinators are declining in most agricultural landscapes, mainly due to agricultural expansion and an increase in intensive agricultural practices. To reduce the negative effects of agricultural expansion and intensification, farmers can adopt ecological interventions, such as diversifying agricultural systems through agroforestry. However, there have been variable results on the effectiveness of agroforestry in enhancing pollinators and pollination services. Furthermore, most of the information has been generated in temperate regions, while the impact of agroforestry in tropical East Africa is largely unknown. Using common beans (Phaseolus vulgaris L.) as the focal crop, this study tested whether a tropical agroforestry system called Chagga home gardens supports pollinator communities and improves pollination and crop yield. We examined 16 agroforestry plots paired with 16 non‐agroforestry plots located along a gradient of woody (trees and shrubs) cover within a 1‐km radius to document the abundance, species richness and visitation rates of pollinating insects on bean flowers and how they contributed to bean yield. The beans planted in the agroforestry plots had almost twice the abundance of insect pollinators, three times the richness of the species and almost twice the visitation rates than those planted in non‐agroforestry plots. We also found a significant positive effect of woody cover in the surrounding landscape on insect pollinator abundances, but not on species richness and visitation rates. Additionally, the abundance and richness of insect pollinators increased significantly with flower abundance, while the overall plant richness in a plot significantly increased insect pollinator abundance and their visitation rate. The difference in bean yield between unbagged flowers (in which insect pollinators were allowed to access bean flowers) and bagged flowers and the total yield were higher in agroforestry than in non‐agroforestry plots. Synthesis and applications. This study showed that, compared to monoculture, agroforestry generally promotes pollination services in a tropical context. Furthermore, we found that agroforestry is likely to be particularly helpful for pollinators when it increases flower abundance and plant richness and if it is coordinated so that woody cover also increases at the landscape scale.

How can we enhance crops with flowers to increase pollination services and stop bee decline?

Pollinator populations and diversity are experiencing a dramatic global decline. As a result, the pollination of many crops around the world is threatened. Several empirical studies have shown that the addition of flower patches adjacent to crops can (1) increase crop pollination services and (2) prevent declines in pollinator abundance and diversity. Despite the empirical evidence, the economic profitability and specific characteristics required for the flower patches remain uncertain for farmers. We review theory and experiments, and we classify flower patches into three different types: attractive, composition-complementary, and population-increase. We develop a decision-making scheme that enables us to decide when we should use each type of patch and what are the possible benefits and drawbacks, depending on the characteristics of the crop and surrounding environment. Our work provides guidance to policy makers and consultants working with land managers on how to increase crop pollination services and simultaneously contribute to more ecologically sustainable agriculture around the world.