Floral Resources Research Articles

Native bee habitat restoration: key ecological considerations from recent North American literature

Habitat loss is a primary driver of global biodiversity decline, negatively impacting many species, including native bees. One approach to counteract the consequences of habitat loss is through restoration, which includes the transformation of degraded or damaged habitats to increase biodiversity. In this review, we survey bee habitat restoration literature over the last 14 years to provide insights into how best to promote bee diversity and abundance through the restoration of natural landscapes in North America. We highlight relevant questions and concepts to consider throughout the various stages of habitat restoration projects, categorizing them into pre-, during-, and post-restoration stages. We emphasize the importance of planning species- and site-specific strategies to support bees, including providing floral and non-floral resources and increasing nest site availability. Lastly, we underscore the significance of conducting evaluations and long-term monitoring following restoration efforts. By identifying effective restoration methods, success indicators, and areas for future research, our review presents a comprehensive framework that can guide land managers during this urgent time for bee habitat restoration.

An evaluation of ‘pollinator-friendly’ wildflower seed mixes in Italy: are they potential vectors of alien plant species?

Wildflower areas are increasingly used in both urban and rural settings to enhance landscape aesthetics and help the conservation of pollinators, whose dramatic decline threatens both ecosystem functioning and agricultural production. Consequently, today many ‘pollinator-friendly’ wildflower seed mixes can be found on the market. Criteria for the design of these mixes are focused on the ability of the plants to attract pollinators, whereas the identity of the plants themselves in terms of their alien or native status is often not adequately considered. Moreover, seed mixes often lack sufficient floral resources in the early spring and late-season months, which are important to sustain pollinators throughout their whole life cycle. In this study, we analyzed 36 ‘pollinator-friendly’ wildflower seed mixes commercially available in Italy in terms of (1) the abundance of native and alien species, (2) the occurrence of locally alien species with reference to three Italian geographic areas (northern, peninsular, and insular Italy), and (3) the flowering period of native and alien species. Most (83%) of the analyzed seed mixes contain species alien to Italy, with three of them also including invasive alien species. Among native species, many (41%) are locally alien to at least one of the geographic areas. Overall, native species provide earlier blooms than alien species and around 35% of the seed mixes lack blooms in early-spring (March) or prolonged throughout autumn (September-November). These findings highlight the widespread use of alien plant species in ‘pollinator-friendly’ wildflower mixes, which poses serious risks for biodiversity and habitat conservation, especially when sown in agricultural areas. We suggest a more careful design and use of such wildflower mixes, promoting a wider adoption of native seeds of local origin and a greater attention to the blooming period. If properly designed, wildflower mixes can represent an effective strategy for biodiversity conservation in both urban and rural areas.

Semi-natural habitats mitigate the impact of food shortage on honey bees in farmlands

Landscape simplification and the loss of semi-natural habitats are identified as important drivers of insect pollinator decline in farmlands, by disrupting the availability of floral resources and facilitating the occurrence of food shortages. Food shortages can lead to accelerated behavioral maturation in honey bees, with potential consequences for colony survival. However, little is known about the magnitude of behavioral maturation mediated by to food shortage under real field conditions, and whether it could be mitigated by the presence of semi-natural habitats. Here, we monitored the lifespan (LSP), age at first exit (AFE), foraging tenure, and foraging intensity of 1035 honey bees along a landscape gradient of semi-natural habitats in farmlands. We found a clear acceleration of behavioral maturation of bees during the food shortage season, with precocity in AFE between 6 and 10 days earlier and reduced LSP by 5 to 9 days, with no effect on foraging tenure or foraging intensity. We also found that higher proportions of semi-natural habitats mitigated behavioral maturation of bees by up to 6 days. Beyond the direct effects on adult bees, we found no delayed effect of larval feeding status on adult life-history traits or foraging behavior. Nevertheless, our results strongly advocate the implementation of policies aimed at increasing the coverage of semi-natural environments (e.g., grasslands, forests, hedgerows) in intensive agricultural landscapes to support honey bee survival and pollinator conservation.

Shared use of a mass‐flowering crop drives dietary niche overlap between managed honeybees and bumblebees

Abstract Resource competition between wild pollinators and managed honeybees (Apis mellifera) has the potential to detrimentally impact insect biodiversity as well as wild plant and crop pollination. As honeybees are central place foragers, their competitive impact on wild bees is expected to be structured by hive proximity, in conjunction with foraging decisions related to landscape‐level resource availability. Yet, how these factors structure dietary niche overlap between wild bees and managed honeybees remains unclear. We conducted a field experiment in seminatural grasslands, where honeybee foraging densities and niche overlap with buff‐tailed bumblebees (Bombus terrestris) were measured at four distances (<100, 500, 1000 and 2000 m) from experimentally placed apiaries, during and after the blooming period of mass‐flowering oilseed rape (Brassica napus). We measured honeybee foraging densities using standardized transect surveys, and quantified species diet composition and dietary niche overlap from pollen samples collected from both bee species. Honeybee foraging densities were highest near apiaries and declined sharply beyond 500 m from the apiaries. However, niche overlap was unrelated to hive proximity but positively related to the availability of oilseed rape. Furthermore, there were significant inter‐ and intraspecific differences in pollen diet composition and breadth throughout the season. Synthesis and applications: Niche overlap between honeybees and bumblebees in agricultural environments was due to resource sharing of mass‐flowering oilseed rape. When both honeybees and bumblebees predominantly forage on wild plants, they maintain distinct pollen diets, suggesting there is a low risk of resource competition between these generalist taxa. Conservation actions that promote floral resource availability and diversity in agricultural landscapes are crucial to maintain niche differentiation between managed honeybees and wild bees.

Close to the edge: Spatial variation in plant diversity, biomass and floral resources in conventional and agri‐environment cereal fields

Abstract Non‐crop (segetal) plants in arable systems are commonly perceived simply as ‘weeds’, that is, harmful at worst and undesirable at best. The increase in management intensity in European arable systems has vastly reduced the populations of all but the most disturbance‐tolerant plant species, negatively impacting the whole agricultural food web. In recent years, efforts have been made to promote agricultural biodiversity through measures such as flower strips and unsprayed field margins. However, studies of their impacts on the arable flora have rarely considered their spatial variation within the crop field. We investigated the spatial distribution of vascular plant species richness and their contribution to the food web via biomass and flower units in conventional and agri‐environment cereal fields in six regions of Germany. We studied two types of in‐crop measures (extensive cereals without pesticides or fertiliser, and with or without intercropping with flowering species) and one adjacent measure (neighbouring flower strip), recording at 1‐m intervals from the field edge to the interior. These results were then extrapolated to illustrate the effects of these measures on resource provision at the field scale. Species richness and plant biomass dropped off sharply after the first metre in the conventional treatments, regardless of the adjacent habitat. The ‘extensive’ treatments maintained a much higher level of diversity and resource provision in the field interior. At the field level, this can mean more than a 60‐fold difference in the provision of flowering resources between conventional management (1900 flower units/ha) and agri‐environment measures (AEMs) (127,000 units/ha for extensive cereals). Synthesis and applications. The strong edge effects we found in conventional cultivation support the premise that reducing field sizes could play a role in promoting in‐crop biodiversity. However, incorporating extensive field margins as an AEM would be more efficient at maximising the diversity of generalists whilst maintaining high yields.

Agricultural specialisation increases the vulnerability of pollination services for smallholder farmers

Abstract Smallholder farms make up 84% of all farms worldwide and feed 2 billion people. These farms are heavily reliant on ecosystem services and vulnerable to environmental change, yet under‐represented in the ecological literature. The high diversity of crops in these systems makes it challenging to identify and manage the best providers of an ecosystem service, such as the best pollinators to meet the needs of multiple crops. It is also unclear whether ecosystem service requirements change as smallholders transition towards more specialised commercial farming—an increasing trend worldwide. Here, we present a new metric for predicting the species providing ecosystem services in diverse multi‐crop farming systems. Working in 10 smallholder villages in rural Nepal, we use this metric to test whether key pollinators, and the management actions that support them, differ based on a farmers' agricultural priority (producing nutritious food to feed the family vs. generating income from cash crops). We also test whether the resilience of pollination services changes as farmers specialise on cash crops. We show that a farmers' agricultural priority can determine the community of pollinators they rely upon. Wild insects including bumblebees, solitary bees and flies provided the majority of the pollination service underpinning nutrient production, while income generation was much more dependent on a single species—the domesticated honeybee Apis cerana. The significantly lower diversity of pollinators supporting income generation leaves cash crop farmers more vulnerable to pollinator declines. Regardless of a farmers' agricultural priority, the same collection of wild plant species (mostly herbaceous weeds and shrubs) were important for supporting crop pollinators with floral resources. Promoting these wild plants is likely to enhance pollination services for all farmers in the region. Synthesis and applications. We highlight the increased vulnerability of pollination services when smallholders transition to specialised cash crop farming and emphasise the role of crop, pollinator and wild plant diversity in mitigating this risk. The method we present could be readily applied to other smallholder settings across the world to help characterise and manage the ecosystem services underpinning the livelihoods and nutritional health of smallholder families.

Unraveling habitat-driven shifts in alpha, beta, and gamma diversity of hummingbirds and their floral resource.

Biodiversity, crucial for understanding ecosystems, encompasses species richness, composition, and distribution. Ecological and environmental factors, such as habitat type, resource availability, and climate conditions, play pivotal roles in shaping species diversity within and among communities, categorized into alpha (within habitat), beta (between habitats), and gamma (total regional) diversity. Hummingbird communities are influenced by habitat, elevation, and seasonality, making them an ideal system for studying these diversities, shedding light on mutualistic community dynamics and conservation strategies. Over a year-long period, monthly surveys were conducted to record hummingbird species and their visited flowering plants across four habitat types (oak forest, juniper forest, pine forest, and xerophytic shrubland) in Tlaxcala, Mexico. Three locations per habitat type were selected based on conservation status and distance from urban areas. True diversity measures were used to assess alpha, beta, and gamma diversity of hummingbirds and their floral resources. Environmental factors such as altitude and bioclimatic variables were explored for their influence on beta diversity. For flowering plants, gamma diversity encompassed 34 species, with oak forests exhibiting the highest richness, while xerophytic shrublands had the highest alpha diversity. In contrast, for hummingbirds, 11 species comprised the gamma diversity, with xerophytic shrublands having the highest richness and alpha diversity. Our data reveal high heterogeneity in species abundance among habitats. Notably, certain floral resources like Loeselia mexicana and Bouvardia ternifolia emerge as key species in multiple habitats, while hummingbirds such as Basilinna leucotis, Selasphorus platycercus, and Calothorax lucifer exhibit varying levels of abundance and habitat preferences. Beta diversity analyses unveil habitat-specific patterns, with species turnover predominantly driving dissimilarity in composition. Moreover, our study explores the relationships between these diversity components and environmental factors such as altitude and climate variables. Climate variables, in particular, emerge as significant contributors to dissimilarity in floral resource and hummingbird communities, highlighting the influence of environmental conditions on species distribution. Our results shed light on the complex dynamics of hummingbird-flower mutualistic communities within diverse habitats and underscore the importance of understanding how habitat-driven shifts impact alpha, beta, and gamma diversity. Such insights are crucial for conservation strategies aimed at preserving the delicate ecological relationships that underpin biodiversity in these communities.

How many animal-pollinated angiosperms are nectar-producing?

The diversity of plant-pollinator interactions is grounded in floral resources, with nectar considered one of the main floral rewards plants produce for pollinators. However, a global evaluation of the number of animal-pollinated nectar-producing angiosperms and their distribution world-wide remains elusive. We compiled a thorough database encompassing 7621 plant species from 322 families to estimate the number and proportion of nectar-producing angiosperms reliant on animal pollination. Through extensive sampling of plant communities, we also explored the interplay between nectar production, floral resource diversity, latitudinal and elevational gradients, contemporary climate, and environmental characteristics. Roughly 223 308 animal-pollinated angiosperms are nectar-producing, accounting for 74.4% of biotic-pollinated species. Global distribution patterns of nectar-producing plants reveal a distinct trend along latitudinal and altitudinal gradients, with increased proportions of plants producing nectar in high latitudes and altitudes. Conversely, tropical communities in warm and moist climates exhibit greater floral resource diversity and a lower proportion of nectar-producing plants. These findings suggest that ecological trends driven by climate have fostered the diversification of floral resources in warmer and less seasonal climates, reducing the proportion of solely nectar-producing plants. Our study provides a baseline for understanding plant-pollinator relationships, plant diversification, and the distribution of plant traits.

Ten‐a‐day: Bumblebee pollen loads reveal high consistency in foraging breadth among species, sites and seasons

Abstract Pollen and nectar are crucial resources for bees but vary greatly among plant species in their quantity, nutritional quality and timing of availability. This makes it challenging to identify an appropriate range of plants to meet the nutritional needs of bees throughout the year, though this information is important in the design of pollinator conservation schemes. Using DNA metabarcoding of pollen loads, we record the floral resource use of UK farmland bumblebees at different stages of their colony lifecycle, and compare this with null models of ‘expected’ resource use based on landscape‐scale resource availability (pollen and nectar), to identify foraging priorities and preferences. We use this approach to ask three main questions: (i) what is the foraging breadth of individual bumblebees?; (ii) do bumblebees utilise a greater or lesser diversity of plant species than expected if they foraged in proportion to resource availability?; (iii) which plant species do bumblebees preferentially utilise? Individual bumblebees foraged from a highly consistent number of different plant taxa (mean: 10 ± 0.37 SE per bee), regardless of their species, sampling site or time of year. This high consistency in foraging breadth, despite large changes in the quantity, identity and diversity of resource availability, implies a strong behavioural tendency towards a fixed range of foraging resources. This effect was most striking in April when foraging diversity was maintained despite very low landscape‐level resource diversity. Bumblebees used some plant taxa significantly more than predicted from their landscape‐level floral abundance, nectar or pollen supply, implying certain desirable characteristics beyond the mere quantity of resource. These included Allium spp. and Vicia spp. in April; Trifolium repens and Lotus corniculatus in July and Cardueae spp. (thistles) and Taraxacum officinale in September. Practical implication: Our results strongly indicate that resource quantity is not the only factor driving bumblebee foraging patterns and that resource diversity and quality are also important factors. Thus, in addition to providing large quantities of floral resources, we recommend that pollinator conservation schemes also focus on providing a sufficient diversity of preferred floral resources, enabling pollinators to self‐select a diverse and nutritious diet.

Elucidating dietary secrets of the Blue‐headed Macaw, Primolius couloni (Sclater, 1876), through citizen‐sourced photographs

AbstractDietary data are vital for understanding species' resource requirements and ecological roles and supporting conservation efforts. The Blue‐headed Macaw, Primolius couloni, is a vulnerable and endemic species in the Amazon. Due to their rarity, elusive nature, complex forest canopy habitat, and occurrence in remote areas, we minimally know their dietary habits. To address this gap, we analysed photographs of Blue‐headed Macaws posted on wildlife‐focused social media platforms, specifically targeting images that capture foraging behaviour on plants. Photographs depicting the same foraging were included only once, and those where the plants were not identified were discarded. By doing so, we identified 36 distinct foraging events (or photos), primarily taken between July and October, concentrated in specific locations in Peru and Brazil, a potential seasonality in foraging. We documented 27 food plant species and items such as nectar (n = 9 photos), pulp (8), seeds (7), buds, bark (5 each), aril, and leaves (n = 1 photo each). Notably, floral resources, including nectar, are a potentially important food in the driest months. Using Levin's Index (Ba), we identified a broad dietary niche, indicating a generalist feeding strategy with a wide variety of plant species (Ba = 0.69) and food items (Ba = 0.88). Additionally, the study revealed interactions such as florivory, seed predation, bark consumption, and potential mutualistic roles like pollination and seed dispersal. Our photo‐centric approach here expanded the known dietary spectrum of the Blue‐headed Macaw from four to 31 plant species, offering new insights for conservation strategies. We recommend the preservation of identified food plants and suggest using these data to inform habitat restoration efforts that support the macaws' dietary needs and ecological functions. Future research should focus on continuous monitoring of these food plants to deepen our understanding of seasonal foraging trends and ecological interactions and refine conservation approaches.

A bee's-eye view of landscape change: differences in diet of 2 Andrena species (Hymenoptera: Andrenidae) between 1943 and 2021.

Declines in pollinating insects have been linked to changes in land cover, affecting the availability of nesting sites and floral resources. Our study is the first analysis of changes in pollen load composition of 2 mining bees, Andrena barbilabris (Kirby) and Andrena flavipes (Panzer) (Hymenoptera: Andrenidae), at the same sites in central England, over 75 years. This provides a unique opportunity to remove spatial variation and review temporal changes in pollen diet within the context of landscape change. We analyzed modern-day pollen load composition for these species and compared it with historical data from the same sites. We then examined potential links between land-use change and the bees' diets. Both bees showed dietary flexibility and lower diet breadth for A. barbilabris, and the bees' foraging strategies appear to have changed. Andrena flavipes collected more pollen taxa in a single load, while A. barbilabris appeared to source pollen from greater distances. Landscape changes at the studied sites have affected the nutritional environment for these bees. Our findings are supported by an existing assessment of floral resources, which found floral diversity has decreased overall in both the habitats used by these bees. However, more research is needed on the nutritional content of pollens used by these bees, both now and historically, to estimate how pollen diversity has changed. The bee's-eye view underlines the importance of understanding how species respond to local changes so that effective conservation strategies can be developed.

Sodium-enriched nectar shapes plant-pollinator interactions in a subalpine meadow.

Many plants have evolved nutrient rewards to attract pollinators to flowers, but most research has focused on the sugar content of floral nectar resources. Concentrations of sodium in floral nectar (a micronutrient in low concentrations in nectar) can vary substantially both among and within co-occurring species. It is hypothesized that sodium concentrations in floral nectar might play an important and underappreciated role in plant-pollinator interactions, especially because many animals, including pollinators, are sodium limited in nature. Yet, the consequences of variation in sodium concentrations in floral nectar remain largely unexplored. Here, we investigate whether enriching floral nectar with sodium influences the composition, diversity, and frequency of plant-pollinator interactions. We experimentally enriched sodium concentrations in four plant species in a subalpine meadow in Colorado, USA. We found that flowers with sodium-enriched nectar received more visits from a greater diversity of pollinators throughout the season. Different pollinator species foraged more frequently on flowers enriched with sodium and showed evidence of other changes to foraging behavior, including greater dietary evenness. These findings are consistent with the "salty nectar hypothesis," providing evidence for the importance of sodium limitation in pollinators and suggesting that even small nectar constituents can shape plant-pollinator interactions.

Manipulating the community structure of arthropods in rice fields with floral resources plants

Abstract Conservation biological control encourages natural enemies to suppress target pests through manipulation of environmental factors that influence natural enemy survival and effectiveness, including microclimates, availability of food for adults and alternative prey, and shelter from adverse environmental conditions. This study aimed to identify selective flowering plants that could be used to manipulate the arthropod community structure in rice fields. Three rice fields (a field without resources of flowering plants, a field with vegetable crop, and a field with ornamental plant) were used in this experiment. The flowering plants included Helianthus sp., Catharanthus roseus, and Cosmos sulphureus while the vegetable plants included eggplant, cucumber, and long beans. Arthropod recording was carried out by direct observation and yellow pan traps from 14 to 98 days after planting. We recorded 33,728 arthropods representing 153 species in 68 families, 13 orders, and 2 classes. The presence of flowering plant significantly affects abundance, species richness, diversity index, and evenness of arthropods both in dry and wet seasons. The rice field surrounded with ornamental plants or vegetables showed the lowest abundance of phytophagous arthropods, the highest abundance of parasitoid and predatory arthropods. Therefore, vegetable crops such as cucumber, long beans and eggplant have great opportunities as refugia in rice fields.

Foraging task specialization in honey bees (Apis mellifera): the contribution of floral rewards on the learning performance of pollen and nectar foragers.

Social insects live in communities where cooperative actions heavily rely on the individual cognitive abilities of their members. In the honey bee (Apis mellifera), the specialization in nectar or pollen collection is associated with variations in gustatory sensitivity, affecting both associative and non-associative learning. Gustatory sensitivity fluctuates as a function of changes in motivation for the specific floral resource throughout the foraging cycle, yet differences in learning between nectar and pollen foragers at the onset of food collection remains unexplored. Here, we examined nectar and pollen foragers captured upon arrival at food sources. We subjected them to an olfactory PER conditioning using a 10% sucrose solution paired (S10%+P) or unpaired (S10%) with pollen as a co-reinforcement. For non-associative learning, we habituated foragers with S10%+P or S10%, followed by dishabituation tests with either a 50% sucrose solution paired (S50%+P) or unpaired (S50%) with pollen. Our results indicate that pollen foragers show lower performance than nectar foragers when conditioned with S10%. Interestingly, performance improves to levels similar to those of nectar foragers when pollen is included as a rewarding stimulus (S10%+P). In non-associative learning, pollen foragers tested with S10%+P displayed a lower degree of habituation than nectar foragers and a higher degree of dishabituation when pollen was used as the dishabituating stimulus (S10%+P). Altogether, our results support the idea that pollen and nectar honey bee foragers differ in their responsiveness to rewards, leading to inter-individual differences in learning that contribute to foraging specialization.

Bumblebees mediate landscape effects on a forest herb's population genetic structure in European agricultural landscapes.

Spatially isolated plant populations in agricultural landscapes exhibit genetic responses not only to habitat fragmentation per se but also to the composition of the landscape matrix between habitat patches. These responses can only be understood by examining how the landscape matrix influences among-habitat movements of pollinators and seed vectors, which act as genetic linkers among populations. We studied the forest herb Polygonatum multiflorum and its associated pollinator and genetic linker, the bumblebee Bombus pascuorum, in three European agricultural landscapes. We aimed to identify which landscape features affect the movement activity of B. pascuorum between forest patches and to assess the relative importance of these features in explaining the forest herb's population genetic structure. We applied microsatellite markers to estimate the movement activity of the bumblebee as well as the population genetic structure of the forest herb. We modelled the movement activity as a function of various landscape metrics. Those metrics found to explain the movement activity best were then used to explain the population genetic structure of the forest herb. The bumblebee movement activity was affected by the cover of maize fields and semi-natural grasslands on a larger spatial scale and by landscape heterogeneity on a smaller spatial scale. For some measures of the forest herb's population genetic structure, that is, allelic richness, observed heterozygosity and the F-value, the combinations of landscape metrics, which explained the linker movement activity best, yielded lower AICc values than 95% of the models including all possible combinations of landscape metrics. Synthesis: The genetic linker, B. pascuorum, mediates landscape effects on the population genetic structure of the forest herb P. multiflorum. Our study indicates, that the movement of the genetic linker among forest patches, and thus the pollen driven gene flow of the herb, depends on the relative value of floral resources in the specific landscape setting. Noteworthy, the population genetic structure of the long-lived, clonal forest herb species correlated with recent land-use types such as maize, which have been existing for not more than a few decades within these landscapes. This underscores the short time in which land-use changes can influence the evolutionary potential of long-lived wild plants.

Pollen foraging preferences in honey bees and the nutrient profiles of the pollen

Honey bees are important insect pollinators that provide critical pollination services to fruit and nut crops in the US. They face challenges likely due to pressures associated with agricultural intensification related habitat loss. To better understand this, pollen preferences of foraging bees and the nutritional profile of pollen brought into hives by foraging bees in crop fields and nut orchards can provide valuable information. We trained bees to forage on bee-collected pollen from hives placed for pollination services in almond orchards, sunflower fields, or mixed species from inter-row plantings. Using bees trained to a certain kind of hive pollen, we applied a binary scoring system, to test preferences of these preconditioned foragers. We also performed metabolomic analyses of the hive pollen used for training and testing to elucidate their nutritional content. Irrespective of preconditioning, bees collected all the available choice pollen types, predominantly choosing hive-collected mixed species pollen (MSP), followed by almond orchard pollen. The hive-collected MSP was chemically diverse, richest in cholesterol, vitamins, and phytochemicals quercetin, kaempferol, coumarin, and quinine, but was not consistently high for essential amino acids and polyunsaturated fatty acids. Although diversity in chemical profiles may not directly relate to plant species diversity, our results suggest that foragers collect a variety of pollen types when available reiterating the importance of diverse floral resources.

The effects of plant invasion, floral resources and soil characteristics on ground-nesting bees

Ground-nesting bees are susceptible to disturbances that affect foraging resources, vegetation structure and soil characteristics. We studied the effects of 12 invasive alien plant species on environmental variables and directly on ground-nesting bees to reveal their specific importance. We sampled bees along transects; flowers, vegetation, bare ground and litter in quadrats, as well as soil characteristics. Our results suggested that plant invasion reduced overall and flowering plant richness and positively affected the height of native vegetation. However, this did not affect ground-nesting bees’ abundance or species richness. Although we found invaded plots to have altered soil chemical characteristics compared to control plots, there was no correlation between soil characteristics and ground-nesting bees. The large explanatory potential of the random factors suggests that there were large differences in the abundance and species richness of ground-nesting bee species among the different habitat types and before and during the flowering of the invasive species. Although our study lacked a direct sampling of nesting bees, our results show the adverse effects of plant invasion on foraging and some nesting characteristics of ground-nesting bees. Future studies should put effort into the investigation of the number of nest holes and additional soil characteristics to get a better picture of the effects of plant invasion on ground-nesting activity.

Host plants and landscape predict use of roadside habitat by breeding monarchs

Abstract Vegetation along roadside edges, while posing some risks, can also provide breeding habitat for monarch butterflies. We investigated how landscape and site‐specific factors affect the quality of roadsides as monarch breeding habitat. We surveyed more than 250 sites along roadsides throughout Minnesota for milkweeds, floral resources and monarch eggs and larvae. We found that milkweed distribution was affected by adjacent land use and geography, with milkweeds more likely to be present in roadsides adjacent to crop and grassland and the south and west of the state. The presence and density of monarch eggs and larvae were primarily driven by milkweed density, with the likelihood of monarch presence at each site increasing with milkweed density. The density of monarchs per plant increased in sites with lower densities of milkweed, suggesting that monarch eggs are concentrated more densely on fewer plants where milkweed is scarce and spread more thinly across plants where milkweed is common. Monarch density per milkweed increased as sites were farther from core grasslands, to the south, and on narrower roadsides, also suggesting use may be higher in areas with a scarcity of habitat. The density of monarch eggs and larvae was higher in mowed than unmowed milkweed. Our study suggests that roadside habitats effectively provide breeding locations for monarchs, regardless of adjacent land use type and even when distant to high‐quality natural areas. Our findings assist conservation practitioners in planning and managing roadside habitats for monarchs and other pollinators.

Dietary foundations for pollinators: nutritional profiling of plants for bee health

Human activities, including urban expansion, intensive farming practices, and the application of pesticides have significantly reshaped bee habitats. Understanding the nutritional content of pollen, the primary source of bees’ proteins and lipids, is important for maintaining their diet and health. In this study, we set out to determine the nutritional composition of pollen from various plant families and genera. Our objectives were to analyze the levels of non-esterified fatty acids (NEFAs), amino acids (AAs), protein-to-lipid (P:L) ratios, and omega-6:3 ratios of 57 pollen species native to North America. These data suggest a potential trade-off between NEFA and AA content within pollen, suggesting that a diverse floral diet may benefit bees more than a single pollen source. The AA profiles showed considerable diversity, with all pollen species providing the essential amino acids (EAAs) required for bee health, except for methionine which was lacking in Rhus glabra pollen. The plant family Asteraceae was especially abundant in EAAs. P:L ratios varied widely further emphasizing bees’ need for access to a diverse array of nutritional profiles. There were no overall nutritional differences between pollen from native and introduced plant species. This study highlights the significance of a diverse array of floral resources to meet the comprehensive nutritional needs of bees, contributing to the support of pollinator populations and the broader ecological system.

Pollen morphology and reproductive biology of Calophyllum brasiliense Cambess. (Calophyllaceae)

Pollen morphology and the reproductive biology of Calophyllum brasiliense were investigated in Parque Estadual das Fontes do Ipiranga, São Paulo, Brazil. The study encompassed pollen analyses using light, scanning, and transmission electron microscopy. Additionally, we collected data on reproductive biology, main visitors/pollinators, fruit set, and seed germination. The species exhibits individuals with perfect flowers (hermaphrodites) as well as male individuals with staminate and perfect flowers. Flowering occurs in October and November, and flowers have diurnal anthesis and pollen as a floral resource. Pollen grains are monads of medium size, isopolar, oblate-spheroidal to prolate-spheroidal, 3-(4)-zonocolporate, with exine fossulate-perforate with supratectal microechini. Hermaphrodite individuals have the highest proportion of malformed pollen due to their reduced grain size. The pollen grains from the hermaphrodite individuals displayed a low viability (0.06%), while those from male individuals had higher viability (66.38% and 55.78% for perfect and staminate flowers, respectively). The stigma was receptive throughout the anthesis period. Cross-pollination between perfect flowers of male and hermaphrodite individuals resulted in 8.80% success in fruit set, but led to the development of one abnormal seedling. Cross-pollination between staminate flowers and perfect flowers of hermaphrodite individuals showed a 7.70% success rate and the control group showed an 8.00% success rate, both groups leading to the development of normal seedlings. This tree species shows relatively low reproductive success and relies on pollinators (mainly Apis mellifera, Paratrigona subnuda, Tetragonisca angustula, and Halictidae sp. 1) for the setting of fruits and seeds.