Pollen Availability Research Articles

Landscape heterogeneity correlates with bee and pollen diversity while size and specialization degree explain species-specific responses of wild bees to the environment

Access to adequate pollen sources in agricultural landscapes is critical for the nutrition and development of bees. The type and quantity of pollen available to bees and may be determined by local plant diversity, land-use intensity and landscape structure but different bee species likely respond differently to these parameters. Identifying community and specific responses is therefore imperative to understand pollinator population dynamics in agricultural landscapes. We sampled bees in 36 plots along a land-use gradient at 4 sites in Belgium and Germany over two years. We collected 1821 bees from 100 bee species and constructed a pollen foraging network with 36 common wild bee species based on pollen metabarcoding. We investigated differences in community responses and species-specific responses to environmental variables.Landscape heterogeneity positively correlated with bee species richness, diversity and functional richness, and significantly explained bee community composition per plot. Bee collected pollen diversity correlated with bee species diversity. Furthermore, landscape heterogeneity positively correlated with bee collected pollen diversity when pooling abundant bee species, while it did not correlate with pollen diversity of the most abundant generalists. Land-use intensity and local plant diversity had no significant effect on bee diversity. Larger bees showed negative responses to increasing land-use intensity and bees with more specialized diets showed positive correlations with landscape heterogeneity. Our study goes beyond mere floral diversity and provides new insight into the responses of wild bee communities to landscape structure and regional pollen availability, as well as the interplay between bee abundance and pollen foraging traits. Our results highlight the importance of determining species-specific nutritional needs and considering landscape level structure in pollinator conservation programs.

Influence of temperature conditions of the environment on the dynamics of collecting bee pollen and flower pollen by honey bees

The study conducted at the apiary of the National Scientific Center «P.I. Prokopovych Institute of Beekeeping» in Hadiach, Poltava region, from 2021 to 2023 investigates the dynamics of bee pollen collecting by honey bees of the Ukrainian steppe breed of the Hadiach type. This research focuses on understanding how weather conditions in the forest-steppe zone impact the mass, volume, and size of bee pollen, as well as the botanical composition of the collected pollen. The primary objective of this research is to analyze how different weather conditions influence the collection of bee pollen by honey bees. Specifically, the study aims to assess how variations in temperature, humidity, and other weather factors affect the quantity and quality of pollen collected, and how these factors interact with the flowering periods of key nectar plants. The study utilized hanging pollen collectors to gather pollen from bee colonies between 8 AM and 2 PM. The botanical origin of the pollen was determined through microscopic analysis and international palynological databases. The research focused on several common nectar plants, including red clover (Trifolium pratense), common primrose (Primula vulgaris), cornflower (Centaurea cyanus), common agrimony (Agrimonia eupatoria), field thistle (Cirsium arvense), and common burdock (Carduus acanthoides). Weather conditions were classified into favorable (temperatures of 18–25°C and relative humidity of 57–72%) and unfavorable (cloudy days with northern winds, temperatures below 15°C or above 28°C, and humidity levels outside the 57–72% range). The research revealed that the average mass of bee pollen collected per season varied between 6.3 and 6.6 kg per bee colony. The study found that different plants responded differently to weather condi­tions. For instance, the mass of pollen from red clover ranged from 8.3 to 12.0 mg under favorable conditions, while field thistle showed a decrease in pollen mass during unfavorable conditions. Pollen collection began in mid-April and continued until mid-August. During unfavorable weather conditions, there was a noticeable reduction in pollen mass, which was attributed to lower pollen availability. However, some plants showed better pollen production under adverse conditions. The spring peak in pollen collection, associated with active colony growth, was also influenced by the less diverse summer flora. Temperature data for 2021–2023 indicated that the most favorable conditions for pollen collection varied annually. For example, the cool spring of 2021 delayed bee colony development, while 2022 experienced normal weather conditions. In contrast, 2023 saw active pollen collection during acacia blooming but a reduction duringlime blooming due to insufficient pollen. The study underscores the importance of considering a comprehensive range of weather conditions when evaluating bee colony productivity. The findings highlight that both temperature and humidity significantly impact pollen collection. The results suggest that beekeepers need to account for these variables in their management practices to optimize pollen collection. Further research should explore the interactions between different weather factors and their combined effects on bee foraging behavior and pollen production. Additionally, studies could investigate how changes in climate over longer periods affect bee colony performance and pollen dynamics, providing insights for developing adaptive strategies in beekeeping.

Effects of Different Pollen Substitute Diets on the Survival Rate and Diet Preference of Foraging Honey Bees (Apis mellifera L.)

Honey bee is an eusocial insect from class Insecta. The potential for thriving honey bee colonies hinges on the availability of an effective pollen substitute, particularly during periods of scarcity when natural pollen supply is limited. Numerous beekeepers provide their bees with various pollen substitutes to ensure they receive adequate nutrition during periods of insufficient pollen quantity or quality. For Methodology transparent boxes were made and each artificial diet were kept in each box for each ten replicas of Honey Bees. The experiment was based on Artificial diets as pollen substitutes. For experiment Honey Bee, Apis mellifera was taken and feed with five different diets and data was analysed with test significance level is 0.001.

The Development of an Improved Medium for the In Vitro Germination of Corylus avellana L. Pollen

The European hazelnut (Corylus avellana L.) is a self-incompatible, wind-pollinated species of significant economic-productive interest, mainly cultivated between the Mediterranean basin and the Black Sea. Hazelnut breeding programs and high cropping in commercial orchards are necessarily linked to the availability of fertile pollen with wide germinability and high viability. The objective was to develop an improved method to determine the germinability of pollen, comparing the results with those found in the literature. Pollen germinability was firstly evaluated on a wild-type accession using boric acid (H3BO3), calcium nitrate (Ca(NO3)2), magnesium sulfate (MgSO4), potassium nitrate (KNO3), casein hydrolysate and different concentrations of sugars, including sucrose (10, 15 and 25%) and two monosaccharides, glucose (15%) and fructose (15%). The optimal composition included 15% sucrose in a semi-solid medium composed of 1% animal gelatin, containing collagen. This formulation was then tested on three cultivars of commercial interest, evaluating the effect of different concentrations of sucrose. The comparison between different in vitro germination methods showed that the hanging drop technique in a semi-solid medium provides a statistically higher germination index compared to the liquid and solid/agarized techniques. This study proposes an easy-to-use medium for the in vitro germination of Corylus avellana L. pollen.

To move or not to move: Dispersal of Orius insidiosus in strawberry plants

AbstractSpatial and temporal distribution of food resources influences predatory insects' foraging and dispersal behavior. Orius insidiosus (Say) (Hemiptera: Anthocoridae) is a good biological control agent of western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in the strawberry crop and consumes two‐spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae), and pollen as well. Augmentative biological control programs may fail if, following release, predators disperse from the crop. We studied the dispersal of O. insidiosus as a function of pollen availability, density of their main prey WFT, and the presence of the alternative prey TSSM, within and between strawberry plants. We found that O. insidiosus remained on the flowers during the 24 h of the assay. The dispersal of predators to a neighboring flower with thrips was approximately six times greater from a flower without pollen than from a flower with pollen. When TSSM was the only prey available, O. insidiosus colonized the leaves, and its dispersal within the plant was greater. At the plot scale, the predator dispersal from the release plant to other plants also depended on the presence of flowering plants and prey. Our results highlight the importance of flowering plants and pollen availability in enhancing the persistence of O. insidiosus in strawberry plants. Releases of this predator in the strawberry crop should be after the beginning of flowering, even at low WFT densities.

Floral scent changes in response to pollen removal are rare in buzz-pollinated Solanum

Main conclusionOne of seven Solanum taxa studied displayed associations between pollen presence and floral scent composition and volume, suggesting buzz-pollinated plants rarely use scent as an honest cue for foraging pollinators.Floral scent influences the recruitment, learning, and behaviour of floral visitors. Variation in floral scent can provide information on the amount of reward available or whether a flower has been visited recently and may be particularly important in species with visually concealed rewards. In many buzz-pollinated flowers, tubular anthers opening via small apical pores (poricidal anthers) visually conceal pollen and appear similar regardless of pollen quantity within the anther. We investigated whether pollen removal changes floral scent composition and emission rate in seven taxa of buzz-pollinated Solanum (Solanaceae). We found that pollen removal reduced both the overall emission of floral scent and the emission of specific compounds (linalool and farnesol) in S. lumholtzianum. Our findings suggest that in six out of seven buzz-pollinated taxa studied here, floral scent could not be used as a signal by visitors as it does not contain information on pollen availability.

BRAIN - Holocene archaeo-data for assessing plant-cultural diversity in Italy and other Mediterranean regions

In the field of botany applied to archaeological and palaeoecological studies, the multi- and inter-disciplinary nature of this research produces a lack of data sharing and scattered articles in the specialty literature or in national and international journals. The vast production of archaeobotany and palynology data makes it necessary to develop a tool for the availability, accessibility, and dissemination of existing research. Many databases exist on palaeoecology, archaeobotany or pollen data. There are no collections focused on archaeological sites and human-induced environments and centred on Southern Europe and the Mediterranean. BRAIN - Botanical Records of Archaeobotany Italian Network is the first database listing sites from which all types of plant records are available in Italy and nearby Mediterranean regions. BRAIN represents the largest integrated collection of archaeo/palaeo-botanical data and a range of descriptive information that makes data recovery FAIR ready. This unique network hosts data on the availability of anthropogenic pollen, palynomorphs and plant macroremains in the same database, and experts of different research fields may contribute to it.

Influence of Vineyard Inter-Row Management on Grapevine Leafhoppers and Their Natural Enemies.

Inter-row management in vineyards can influence the abundance of grapevine pests and their natural enemies. In 2013-2015, in a vineyard in northeastern Italy, the influence of two vineyard inter-row management strategies (i.e., alternate mowing, AM, and periodical tillage, PT) on the population dynamics of grapevine leafhoppers Hebata vitis and Zygina rhamni and their natural enemies, the mymarid Anagrus atomus and spiders (Araneae), and other hymenopteran parasitoids, were studied with different survey approaches. The infestations of both leafhoppers were lower in AM than PT due to the reduced leafhopper oviposition and higher nymph mortality in AM. This occurred although leafhopper egg parasitization by A. atomus was greater in PT than AM according to a density-dependent relationship with the leafhopper egg amount. Hymenopteran parasitoids other than A. atomus were the most abundant in AM, probably due to the higher availability of nectar and pollen than in PM. The significantly higher population densities of hunting spiders in AM than PT can be associated with the higher predation of leafhopper nymphs. Therefore, the study demonstrated that the alternate mowing of vineyard inter-rows enhances the abundance of natural enemies, such as spiders and hymenopteran parasitoids, and can contribute to grapevine leafhopper pest control.

Fields of flowers with few strikes: how oligolectic bees manage their foraging behavior on Calibrachoa elegans (Solanaceae).

In specialized plant-pollinator associations, partners may exhibit adaptive traits, which favor the maintenance of the interaction. The association between Calibrachoa elegans (Solanaceae) and its oligolectic bee pollinator, Hexantheda missionica (Colletidae), is mutualistic and forms a narrowly specialized pollination system. Flowers of C. elegans are pollinated exclusively by this bee species, and the bees restrict their pollen resources to this plant species. The pollen presentation schedules of C. elegans were evaluated at the population level to test the hypothesis that H. missionica females adjust their foraging behavior to the resource offering regime of C. elegans plants. For this, the number of new flowers and anthers opened per hour (as a proxy for pollen offering) was determined, and pollen advertisement was correlated with the frequency of flower visits during the day. Preferences of female bees for flowers of different stages were also investigated, and their efficiency as pollinators was evaluated. Pollen offering by C. elegans was found to be partitioned throughout the day through scattered flower openings. Females of H. missionica indeed adjusted their foraging activity to the most profitable periods of pollen availability. The females preferred new, pollen-rich flowers over old ones and gathered pollen and nectar selectively according to flower age. Such behaviors must optimize female bee foraging efficiency on flowers. Female bees set 93% of fruit after a single visit. These findings guarantee their importance as pollinators and the persistence of the specialized plant-pollinator association.

Quantifying the production of plant pollen at the farm scale.

Plant pollen is rich in protein, sterols and lipids, providing crucial nutrition for many pollinators. However, we know very little about the quantity, quality and timing of pollen availability in real landscapes, limiting our ability to improve food supply for pollinators. We quantify the floral longevity and pollen production of a whole plant community for the first time, enabling us to calculate daily pollen availability. We combine these data with floral abundance and nectar measures from UK farmland to quantify pollen and nectar production at the landscape scale throughout the year. Pollen and nectar production were significantly correlated at the floral unit, and landscape level. The species providing the highest quantity of pollen on farmland were Salix spp. (38%), Filipendula ulmaria (14%), Rubus fruticosus (10%) and Taraxacum officinale (9%). Hedgerows were the most pollen-rich habitats, but permanent pasture provided the majority of pollen at the landscape scale, because of its large area. Pollen and nectar were closely associated in their phenology, with both peaking in late April, before declining steeply in June and remaining low throughout the year. Our data provide a starting point for including pollen in floral resource assessments and ensuring the nutritional requirements of pollinators are met in farmland landscapes.

Evaluating the role of social context and environmental factors in mediating overwintering physiology in honey bees (Apis mellifera).

In temperate climates, honey bees show strong phenotypic plasticity associated with seasonal changes. In summer, worker bees typically only survive for about a month and can be further classified as young nurse bees (which feed the developing brood) and older forager bees. In winter, brood production and foraging halt and the worker bees live for several months. These differences in task and longevity are reflected in their physiology, with summer nurses and long-lived winter bees typically having large fat bodies, high expression levels of vitellogenin (a longevity-, nutrition- and immune-related gene), and large provisioning glands in their head. The environmental factors (both within the colony and within the surrounding environment) that trigger this transition to long-lived winter bees are poorly understood. One theory is that winter bees are an extended nurse bee state, brought on by a reduction in nursing duties in autumn (i.e. lower brood area). We examined that theory here by assessing nurse bee physiology in both the summer and autumn, in colonies with varying levels of brood. We found that season is a better predictor of nurse bee physiology than brood area. This suggests that seasonal factors beyond brood area, such as pollen availability and colony demography, may be necessary for inducing the winter bee phenotype. This finding furthers our understanding of winter bee biology, which could have important implications for colony management for winter, a critical period for colony survival.

Nurse bees regulate the larval nutrition of developing workers (Apis mellifera) when feeding on various pollen types.

Nutrition has been identified as a key driver of colony health and productivity. Yet, in honey bees, relatively little is known about how the vast variety of natural pollen sources impact larval development. The impact of the nutritional quality of 4 naturally occurring pollen sources, of importance to the Western Australian beekeeping industry, was tested on honey bee (Apis mellifera L.) development. Bee packages consisting of 800 g of bees and a mated sister queen were assigned to 40 nucleus hives and randomly allocated to one of the 4 feed treatments (10 colonies each) of marri (Corymbia calophylla Lindl.), jarrah (Eucalyptus marginata Sm.), clover (Trifolium repens L.), and canola (Brassica napus L.) pollen. Emerging bees were collected once the first bees started hatching on the assigned feed sources. Newly emerging bees were weighed individually, and body composition was measured in batches according to the feed treatment groups. Food consumption was recorded for the duration of the experiment. Nurse bees successfully raised young adult workers from the larval stage until emergence when fed with one of 4 pollen patties with different nutritional qualities. There was no difference in the body composition or weight of emerging bees fed on the different pollen types. However, the body weight of bees increased over time, most likely related to colony size and structure. With the type of pollen patties having little impact on larval development, the availability of pollen may be more important than its composition, providing bees have access to all essential nutrients.

Extra-stigmatic pollen germination and pistil elongation: a novel strategy towards reproductive assurance in Dodonaea viscosa subsp. angustifolia

Context Reproductive success in dioecious plant species may be limited by severe pollen limitation owing to their separate sexes and pollination barriers. Aims Dodonaea viscosa subsp. angustifolia (Jacq.) (Sapindaceae) is a dioecious and wind-pollinated species that has a long flowering period. This study sought to determine the relationship between its reproductive behaviour and pollen availability during different flowering phases. Methods Extra-stigmatic pollen germination and reproductive performance during different phases of flowering were investigated and correlated with pistil elongation under natural conditions. Results The species offers whole stigmatic and stylar surfaces for pollen to land and germinate under natural conditions. During pollen-limiting conditions, the length of the pistil increases significantly to enhance pollen capture. Depending on where on the pistil pollen lands, the timing of pollen tube arrival at the ovary varies. Conclusions Dodonaea viscosa subsp. angustifolia is the first reported wild species in the Sapindaceae where pistil elongation is regulated by pollination conditions and extra-stigmatic pollen germination ensures reproduction during phases of differing pollen availability. Our results indicated that the flexibility of female function and reproductive behaviour in Dodonaea viscosa subsp. angustifolia adds to the evolutionary possibilities to overcome pollination constraints. Implications This unique strategy for increasing female fitness through pollen presentation in D. viscosa subsp. angustifolia could be explored in other subspecies of D. viscosa on the Australian subcontinent.

Agents of Pollination on Fruit Set of Piper nigrum L.

The role of agents on pollination and fruit set of Piper nigrum L. was carried out in the Department of Plantation Crops and Spices, College of Agriculture, Vellayani, Thiruvantha puram during 2017-2019. The role of wind, gravity, rain and dew were investigated and the data was analyzed on twenty-five inflorescences of field grown black pepper plants and twenty-five inflorescences of pot grown bush pepper plants. The fruit set was superior due to the influence of wind and gravity (95.99%) in pot grown bush pepper and it was 91.98 per cent in field grown black pepper vines. The percentage of fruit set due to wind in field grown black pepper and potted bush pepper was 77.67% and 59.39 % respectively. The role of rain water in the pollination also revealed higher fruit set of 92.76% under natural conditions. Insects which visited black pepper spike were foraging nectar and common visitors were yellow crazy ant, black garden ant and pollu beetle with visit rates of 1.79, 1.41 and 0.45 respectively. The small size of pollen with high pollen availability makes it suitable to be carried away by wind. The pendulous nature of the spike, the shedding of pollen, the pollen carried by the rainwater or dew down the spike can all contributed to pollination. Integration of more factors resulted in more fruit set. Characteristics of black pepper flowers studied revealed their adaptation for wind pollination and the pendulous nature of the spike makes it efficient to carry the pollen due to gravity as well as rain and dew for pollination. The role of insects in pollination in black pepper was precluded.

Negative Effects of Pollen Drought Stress on Floral Volatiles, Floral Nectar, Pollinator Behavior, and Seed Production in Ocimum basilicum Plants

Ocimum basilicum is an aromatic plant belonging to the family of Lamiaceae. Many biotic and abiotic factors particularly drought stress influences its reproduction. Drought stress can harm the pollen grains of O. basilicum plants and disrupt the production of floral volatiles, reduce floral rewards for pollinators, decrease pollinator activity, and ultimately result in a decline in the seed set. These detrimental impacts highlight the importance of sufficient pollen availability for the successful reproduction and survival of plant species. The reproduction in plants is significantly impacted by drought stress, as it can directly or indirectly alter the attraction of pollinators. In this study, the effect of drought stress in O. basilicum plants was investigated by comparing drought- with no drought-stressed plants in order to examine various elements including: (1) nectar quantity and quality (2) pollen production (3) flower volatile emissions (4) pollinator visitation rates from both domesticated and wild species, and (5) the plant’s' reproductive outcomes, which contributes to the knowledge of the relationship between drought stress and pollination on O. basilicum. The planting was done in two different locations within the Saran division of Bihar state in India, first one is Chapra town and second one is Siwan town, in June 2019. The result indicated that plants with drought conditions, in contrast to drought free plants, produced a reduced quantity of pollen and had a decrease of the number of flowers and the volume of nectar produced per flower. Furthermore, drought affected plants produced nectar with a lower percentage of sucrose in relation to the total sugar content. Bees visiting rate was low compared to control plants and plants emitted more Z-3-hexenol, C4H8O, C5H10O, and Isovaleraldehyde. Moreover, this study utilized HPLC analysis to investigate the impact of drought stress on the floral nectar of O. basilicum plants. The findings revealed significant changes in nectar composition, highlighting the susceptibility of plantpollinator interactions and seed production to environmental stress factors.

Effect of climate, anther morphology and pollination syndrome on pollen availability in Penstemon

Traditionally, pollen presentation is thought to be a function of pollinator type and visitation frequency. However, despite the repeated observation that pollen presentation is influenced by flower morphology and abiotic factors, these aspects have been little studied in the wild. Here, we evaluated the effect of climate, anther morphology, and pollination syndrome on anther dehiscence time (the length of time an anther takes to fully dehisce after a flower opens). We recorded anther dehiscence time in twelve species of Penstemon including the four major anther types and the two most common pollination syndromes. We also conducted an experiment to measure the effect of humidity and temperature on anther dehiscence. We found that anther morphology was correlated with anther dehiscence time. Anthers with wide openings take the longest time to dehiscence. These results provide some support for the hypothesis that anther dehiscence time has evolved to decrease pollen wastage. Contrary to the assumption that bird-pollinated species have simultaneous pollen presentation, hummingbird-pollinated species had longer anther dehiscence time than most bee-pollinated species. The experiment revealed that high humidity and low temperature increase anther dehiscence time. Our results suggest that pollen presentation is influenced by anther morphology, pollination syndrome, and the physical environment. Optimal pollen presentation presumably maximizes conspecific pollen transfer and reduces pollen thieving.

A trainable object finder, selector and identifier for pollen, spores and other things: A step towards automated pollen recognition in lake sediments

Pollen records are the most important proxy for reconstructing past terrestrial vegetation. While new approaches for improved quantitative interpretation of pollen data have been developed over the last decades, the availability of pollen records remains mostly limited because pollen samples are still analysed manually, which is a time-consuming task and requires extensive training. Here, we present an approach for automated recognition of pollen and spores from lake sediments using deep convolutional neural networks and machine learning. The approach includes two stages. The detector first locates pollen and spores in the sample matrix, and the classifier then classifies these objects. We have trained the approach on two pollen datasets from two lakes in north-eastern Germany. So far, our approach is able to automatically recognise 10 pollen types and Lycopodium spores with high accuracy. As soon as more training data are available, more pollen and spore types can be added. The preparation of training data, the training of the neural networks and their application are accessible via a freely available, browser-based user interface called TOFSI.

Improving the Quality of Honey and Socialitzion of Flora Nectar Producer as Bee Feed in the Bangunkarya Village Langkaplancar District Pangandaran

Honey production depends on the availability of nectar and pollen as bee food. In Bangunkarya Village, this potential is abundant and has not been utilized optimally, which includes yards, gardens, and forest flora. At least fifteen residents have coffee plantations that have started to bear fruit and harvest; these people's coffee plantations are an essential source of nectar and pollen. Currently, only two residents are active in the honey business. The village in Langkaplancar District is currently active in becoming a Tourism Village in support of the Aspiring Geopark Pangandaran. Increasing the quality and production of honey is targeted in community service activities to contribute to advancing geo products. Activities include identifying nectar and pollen-producing flora, socializing nectar-producing flora, educating about hygienic honey products, and making attractive honey packaging. Two types of honey that have been improved in quality and given names to marketers are the name Hani Kuya, given to natural honey from Apis dorsata bees, and Rosisdin Honey for livestock honey from Teuwul bees (Heterotrigona sp.). Quality improvements include improving packaging, filtering techniques, dosage, and providing product name labels. Honey products that have experienced improvements in quality have been exhibited in Forum Group Discussion (FGD) activities at the Pangandaran Tourism office as a promotional step to encourage increased sales and economic value.

Investigating the influence of diet diversity on infection outcomes in a bumble bee (Bombus impatiens) and microsporidian (Nosema bombi) host-pathogen system.

Diet can have an array of both direct and indirect effects on an organism's health and fitness, which can influence the outcomes of host-pathogen interactions. Land use changes, which could impact diet quantity and quality, have imposed foraging stress on important natural and agricultural pollinators. Diet related stress could exacerbate existing negative impacts of pathogen infection. Accounting for most of its nutritional intake in terms of protein and many micronutrients, pollen can influence bee health through changes in immunity, infection, and various aspects of individual and colony fitness. We investigate how adult pollen consumption, pollen type, and pollen diversity influence bumble bee Bombus impatiens survival and infection outcomes for a microsporidian pathogen Nosema (Vairimorpha) bombi. Experimental pathogen exposures of larvae occurred in microcolonies and newly emerged adult workers were given one of three predominantly monofloral, polyfloral, or no pollen diets. Workers were assessed for size, pollen consumption, infection 8-days following adult-eclosion, survival, and the presence of extracellular microsporidian spores at death. Pollen diet treatment, specifically absence of pollen, and infection independently reduced survival, but we saw no effects of pollen, pollen type, or pollen diet diversity on infection outcomes. The latter suggests infection outcomes were likely already set, prior to differential diets. Although infection outcomes were not altered by pollen diet in our study, it highlights both pathogen infection and pollen availability as important for bumble bee health, and these factors may interact at different stages of bumble bee development, at the colony level, or under different dietary regimes.

Specific alien plant species predominantly deliver nectar sugar and pollen but are not preferentially visited by wild pollinating insects in suburban riparian ecosystems.

The invasion of alien plants has been rapidly proceeding worldwide due to urbanisation. This might be beneficial to wild pollinating insects, since some alien plant species have large flowers and/or long flowering periods, which can increase nectar sugar and pollen availability. To determine the relative contribution of alien plants to floral resource supply and whether resource-rich alien plants, if any, serve as an important food source of pollinating insects, we performed year-round field observations in suburban riverbanks. We quantified the per-unit-area availability of nectar sugar and pollen delivered by alien and native flowering species and counted wild flower visitors (bees and wasps, hoverflies and butterflies) per plant species. The available nectar sugar and pollen per area were predominantly delivered by a few specific alien species, and the relative contribution of other species to floral resource provision was low throughout the period that wild flower visitors were observed. Nonetheless, the resource-rich alien plants were not visited by as many insects as expected based on their contribution to resource provision. Rather, on a yearly basis, these plants received equal or even fewer visits than other flowering species, including resource-poor natives. We show that despite their great contribution to the gross floral resource supply, resource-rich alien plants do not serve as a principal food source for wild pollinating insects, and other plants, especially natives, are still needed to satisfy insect demand. For the conservation of pollinating insects in suburban ecosystems, maintaining floral resource diversity would be more beneficial than having an increase in gross floral resources by allowing the dominance of specific alien plants.