Generation, degradation mechanism, and toxicity evaluation of pigmented compounds in Leucosceptrum canum nectar

Leucosceptrum canum nectar (LCN) emerges as a novel food resource, distinguished by its unique dark brown hue. This study delves into the composition and toxicity assessment of novel pigments within LCN. Through liquid chromatography-tandem mass spectrometry (LC-MS/MS) and chemical synthesis, seventeen 2,5-di-(N-(-)-prolyl)-para-benzoquinone (DPBQ) analogs in LCN were identified. These compounds are synthesized in LCN via the Michael addition reaction, utilizing p-benzoquinone (BQ), derived from phenol metabolism, and amino acids as substrates in an alkaline environment (pH = 8.47 ± 0.06) facilitated by dissolved ammonia and the presence of alkaloids. Analytical techniques, including principal component analysis (PCA), orthogonal partial least squares discrimination analysis (OPLS-DA), and volcano plot analysis, were employed to investigate DPBQ analog degradation within the nectar and honey's unique environments. Toxicity assays revealed that DPBQ analogs exhibited no toxicity, displaying a significant difference in toxicity compared to the precursor compound BQ at concentrations exceeding 25 μM.

An updated review of functional ingredients of Manuka honey and their value-added innovations

Manuka honey (MH) is a highly prized natural product from the nectar of Leptospermum scoparium flowers. Increased competition on the global market drives MH product innovations. This review updates comparative and non-comparative studies to highlight nutritional, therapeutic, bioengineering, and cosmetic values of MH. MH is a good source of phenolics and unique chemical compounds, such as methylglyoxal, dihydroxyacetone, leptosperin glyoxal, methylsyringate and leptosin. Based on the evidence from in vitro, in vivo and clinical studies, multifunctional bioactive compounds of MH have exhibited anti-oxidative, anti-inflammatory, immunomodulatory, anti-microbial, and anti-cancer activities. There are controversial topics related to MH, such as MH grading, safety/efficacy, implied benefits, and maximum levels of contaminants concerned. Artificial intelligence can optimize MH studies related to chemical analysis, toxicity prediction, multi-functional mechanism exploration and product innovation.

Pesticide residues in ornamental plants marketed as bee friendly: Levels in flowers, leaves, roots and soil

Ornamental plants rich in pollen and nectar are often marketed as "pollinator-friendly" by flower retailers. However, even though the plants are attractive from a foraging perspective, i.e pollen and nectar rich, bees and other pollinating insects could be at risk from exposure of pesticide residues on the plants or from pesticide used during production. Pesticides used in ornamental plant production could lead to environmental emissions both during cultivation, at retailer displays and when planted in gardens by the consumers. This study aims to investigate what pesticides that are used in the production of perennial ornamental plants sold in Sweden and if the residues could pose a risk for wild pollinators. We analyze an array of 536 pesticides in whole flowers, leaves, roots and soil of 54 individual (46 had flowers) perennial plants specifically marketed as "bee friendly". In addition, seeds from 65 seed bags were analyzed for the same pesticides. Our result show for the first time the distribution of pesticide residues between flowers, leaves, roots and soils of ornamental plants. We also show that all ornamental plants analyzed contained at least one pesticide, and that some samples contained up to 19 different substances.

Residue dynamics of a contact and a systemic fungicide in pollen, nectar, and other plant matrices of courgette (Cucurbita pepo L.)

Pollen and nectar can be contaminated with a range of pesticides, including insecticides, fungicides, and herbicides. Since these matrices are important food sources for pollinators and other beneficial insects, their contamination can represent a key route of exposure. However, limited knowledge exists with respect to pesticide residue levels and their dynamics in these matrices for many crops and active ingredients (AIs). We used controlled glasshouse studies to investigate the residue dynamics of a systemic (cyprodinil) and a contact (fludioxonil) fungicide in the floral matrices and other plant parts of courgette/zucchini (Cucurbita pepo L.). We aimed to better understand the processes behind residue accumulation and decline in pollen and nectar. Each AI was applied to plants, either by spraying whole plants or by targeted spraying onto leaves only. Samples of pollen, nectar, anthers, flowers, and leaves were taken on the day of application and each subsequent morning for up to 13 days and analysed for residues using LC-MS/MS. Significant differences in residue levels and dynamics were found between AIs and floral matrices. The present study allowed for the identification of potential routes by which residues translocate between tissues and to link those to the physicochemical properties of each AI, which may facilitate the prediction of residue levels in pollen and nectar. Residues of the contact AI declined more quickly than those of the systemic AI in pollen and nectar. Our results further suggest that the risk of oral exposure for pollinators may be considerably reduced by using contact AIs during the green bud stage of plants, but application of systemic compounds could still result in a low, but continuous long-term exposure for pollinators with limited decline.

Land use influences the nutrient concentration and composition of pollen and nectar rewards of wildflowers in human-dominated landscapes

Plant biodiversity is crucial to satisfy the trophic needs of pollinators, mainly through nectar and pollen rewards. However, a few studies have been directed to ascertain the intraspecific variation of chemical features and the nutritional value of nectar and pollen floral rewards in relation to the alteration of landscapes due to human activities. In this study, by using an existing scenario of land use gradients as an open air laboratory, we tested the variation in pollen and nectar nutrient profiles along gradients of urbanization and agriculture intensity, by focusing on sugar, aminoacids of nectar and phytochemicals of pollen from local wild plants. We also highlighted bioactive compounds from plants primary and secondary metabolism due to their importance for insect wellbeing and pollinator health. We surveyed 7 different meadow species foraged by pollinators and common in the main land uses studied. The results indicated that significant variations of nutritional components occur in relation to different land uses, and specifically that the agricultural intensification decreases the sugars and increases the antioxidant content of flower rewards, while the urbanization is positively associated with the total flavonoid content in pollen. These effects are more evident in some species than in others, such as Lotus corniculatus L. (Fabaceae) and Malva sylvestris L. (Malvaceae), as shown by the untargeted metabolomic investigation. This study is crucial for understanding the nutritional landscape quality for pollinators in association to different land uses and sets a base for landscape management and planning of pollinator-friendly strategies by improving the quality of plant rewards to provide benefits to pollinator health in various environmental contexts.

A critical review on the accumulation of neonicotinoid insecticides in pollen and nectar: Influencing factors and implications for pollinator exposure

Neonicotinoids are a class of neuro-active insecticides widely used to protect major crops, primarily because of their broad-spectrum insecticidal activity and low vertebrate toxicity. Owing to their systemic nature, plants readily take up neonicotinoids and translocate them through roots, leaves, and other tissues to flowers (pollen and nectar) that serve as a critical point of exposure to pollinators foraging on treated plants. The growing evidence for potential adverse effects on non-target species, especially pollinators, and persistence has raised serious concerns, as these pesticides are increasingly prevalent in terrestrial and aquatic systems. Despite increasing research efforts, our understanding of the potential toxicity of neonicotinoids and the risks they pose to non-target species remains limited. Therefore, this critical review provides a succinct evaluation of the uptake, translocation, and accumulation processes of neonicotinoids in plants and the factors that may affect the eventual build-up of neonicotinoids in pollen and nectar. The role of plant species, as well as the physicochemical properties and application methods of neonicotinoids is discussed. Potential knowledge gaps are identified, and questions meriting future research are suggested for improving our understanding of the relationship between neonicotinoid residues in plants and exposure to pollinators.

Global assessment of honeybee exposure to pesticides through guttation consumption: An indicator approach

Guttation consumption is a potential pathway of pesticide residue exposure in honeybees. However, modeling tools for assessing honeybee exposure to pesticide residues in guttation drops are lacking. In this study, we propose an indicator-based approach for qualitatively or quantitatively analyzing the guttation-based exposure pathway, allowing us to conduct region-specific pesticide residue exposure assessments for honeybees. Exposure scores (the product of guttation production and residue level scores) were established to compare or rank honeybee exposure to pesticide residues via guttation intake across locations using three specified indicators (i.e., air temperature, relative humidity, and precipitation intensity). Warm, dry regions had high residue level scores (indicating high residue levels in guttation), whereas cold, wet regions had high guttation production scores (indicating high possibilities of guttation formation on leaf surfaces); their exposure scores were a combination of these two values. We evaluated and ranked honeybee exposure to imidacloprid residue across regions in Brazil, China, the United States, and selected European Union member states, revealing that pesticide application in many Brazilian federative units may raise honeybee risks due to high exposure scores. We also compared the guttation pathway to other common exposure pathways (nectar and pollen), suggesting that for some moderately lipophilic compounds, the guttation exposure pathway may not be ignored and should be further evaluated.

Residues of sulfoxaflor and its metabolites in floral and extrafloral nectar from Hibiscus rosa-sinensis L. (Malvaceae) with or without co-application of tebuconazole

Systemic pesticide exposure through nectar is a growing global concern linked to loss of insect diversity, especially pollinators. The insecticide sulfoxaflor and the fungicide tebuconazole are currently widely used systemic pesticides which are toxic to certain pollinators. However, their metabolisms in floral or extrafloral nectar under different application methods have not yet been well studied. Hibiscus rosa-sinensis was exposed to sulfoxaflor and tebuconazole via soil drenching and foliar spraying. Sulfoxaflor, tebuconazole, and their main metabolites in floral and extrafloral nectar, soil, and leaves were identified and quantified using liquid chromatography coupled with triple quadrupole mass spectrometry (LC-QqQ MS). The chemical compositions of unexposed and contaminated H. rosa-sinensis floral nectar or extrafloral nectar were compared using regular biochemical methods. The activities of two pesticide detoxifying enzymes, glutathione-s-transferase and nitrile hydratase, in H. rosa-sinensis nectar were examined using LC-MS and spectrophotometry. The floral nectar proteome of H. rosa-sinensis was analysed using high-resolution orbitrap-based MS/MS analysis to screen for sulfoxaflor and tebuconazole detoxifying enzymes. H. rosa-sinensis can absorb sulfoxaflor and tebuconazole through its roots or leaf surfaces and secrete them into floral nectar and extrafloral nectar. Both sulfoxaflor and tebuconazole and their major metabolites were present at higher concentrations in extrafloral nectar than in floral nectar. X11719474 was the dominant metabolite of sulfoxaflor in the nectars we studied. Compared with soil application, more sulfoxaflor and tebuconazole remained in their original forms in floral nectar and extrafloral nectar after foliar application. Sulfoxaflor and tebuconazole exposure did not modify the chemical composition of floral or extrafloral nectar. No active components, including proteins in the nectar, were detected to be able to detoxify sulfoxaflor.

Diversity of staminal nectariferous appendages in disymmetric and zygomorphic flowers of Fumarioideae (Papaveraceae)

Staminal nectaries show diversity in their position, size, shape, color, and number in Ranunculales. In Papaveraceae, nectaries only appear at the base of stamen in these lineages with disymmetric and zygomorphic flowers. However, the diversity of the staminal nectaries' developmental characteristics and structure is unknown. The diversity of staminal nectaries of Hypecoum erectum, Ichtyoselmis macrantha, Adlumia asiatica, Dactylicapnos torulosa, Corydalis edulis, and Fumaria officinalis (six species belonging to six genera, respectively) in the Fumarioideae was investigated under scanning electron microscopy, light microscopy, and transmission electron microscopy. In all species studied, according to the developmental characteristics of the nectaries, four developmental stages can be divided into initiation, enlargement, differentiation, and maturation, and the number of nectaries can be determined at the stage of initiation (stage 1), and morphological differentiation occurs at the developmental stage 3. The staminal nectaries consist of secretory epidermis, parenchyma tissue, and phloem with some sieve tube elements reaching the secretory parenchyma cells; however, the number of cell layers of parenchyma can vary from 30 to 40 in I. macrantha and D. torulosa, to only 5 to 10 like in F. officinalis. Secretory epidermis cells are larger than secretory parenchyma cells with abundant microchannels on the outer cell wall. There were abundant mitochondria, Golgi bodies, rough endoplasmic reticulum, and plastids in secretory parenchyma cells. Nectar is stored in the intercellular space and exuded to the exterior via microchannels. In A. asiatica, according to the evidence of small secretory cell characteristics such as dense cytoplasm, and numerous mitochondria, together with the filamentous secretions present on the surface of epidermal cells on groove, it can be inferred that the U-shaped sulcate which is located in the white projection formed at the filament of triplets in A. asiatica is nectariferous.

Nectar compounds impact bacterial and fungal growth and shift community dynamics in a nectar analog

Floral nectar is frequently colonised by microbes. However, nectar microbial communities are typically species-poor and dominated by few cosmopolitan genera. One hypothesis is that nectar constituents may act as environmental filters. We tested how five non-sugar nectar compounds as well as elevated sugar impacted the growth of 12 fungal and bacterial species isolated from nectar, pollinators, and the environment. We hypothesised that nectar isolated microbes would have the least growth suppression. Additionally, to test if nectar compounds could affect the outcome of competition between microbes, we grew a subset of microbes in co-culture across a subset of treatments. We found that some compounds such as H2 O2 suppressed microbial growth across many but not all microbes tested. Other compounds were more specialised in the microbes they impacted. As hypothesised, the nectar specialist yeast Metschnikowia reukaufii was unaffected by most nectar compounds assayed. However, many non-nectar specialist microbes remained unaffected by nectar compounds thought to reduce microbial growth. Our results show that nectar chemistry can influence microbial communities but that microbe-specific responses to nectar compounds are common. Nectar chemistry also affected the outcome of species interactions among microbial taxa, suggesting that non-sugar compounds can affect microbial community assembly in flowers.

How can structure and nectar composition explain the secretory process in super productive nuptial nectaries of Mabea fistulifera Mart. (Euphorbiaceae)?

Mabea fistulifera, a species pollinated mainly by diurnal and nocturnal vertebrates, presents pendulous inflorescences with approximately 70 pairs of nuptial nectaries (NNs). These NNs exude voluminous nectar drops that defy gravity, remaining exposed at the inflorescence for more than a day. We aimed to investigate the NN secretory process and the unique nectar presentation of M. fistulifera. NNs and their exudate were collected at different secretory stages and submitted to structural studies and chemical analysis. The epidermis is devoid of stomata and constitutes the main site of synthesis for non-sugar metabolites found on nectar and nectar-coating film. Nectary parenchyma presents few small starch grains, and vascular strands are distributed until the nectary parenchyma cells close to the epidermis. Vascular tissues at the nectary parenchyma seem to provide sugar and water for the nectar. A film composed of lipids, alkaloids, and proteins covers the nectar drops. The film guarantees the nectar offering for several hours, as it minimizes water loss and prevents falls by gravitational action. The release of large nectar drops is intrinsically linked to the NN anatomical traits and the exudate composition. Low sugar concentration and predominance of hexoses in M. fistulifera nectar are essential for maintaining nectar exudation for many hours, which results in the visitation of a broad spectrum of pollinators.

A conserved hymenopteran-specific family of cytochrome P450s protects bee pollinators from toxic nectar alkaloids

Many plants produce chemical defense compounds as protection against antagonistic herbivores. However, how beneficial insects such as pollinators deal with the presence of these potentially toxic chemicals in nectar and pollen is poorly understood. Here, we characterize a conserved mechanism of plant secondary metabolite detoxification in the Hymenoptera, an order that contains numerous highly beneficial insects. Using phylogenetic and functional approaches, we show that the CYP336 family of cytochrome P450 enzymes detoxifies alkaloids, a group of potent natural insecticides, in honeybees and other hymenopteran species that diverged over 281 million years. We linked this function to an aspartic acid residue within the main access channel of CYP336 enzymes that is highly conserved within this P450 family. Together, these results provide detailed insights into the evolution of P450s as a key component of detoxification systems in hymenopteran species and reveal the molecular basis of adaptations arising from interactions between plants and beneficial insects.

Structure of the nectary in Chaenomeles japonica (Thunb.) Lindl. ex Spach. in different stages of flowering with focus on nectar secretion

Chaenomeles japonica is an attractive ornamental shrub flowering in spring. It is also a valuable source of nectar and pollen for entomofauna. The study was carried out to investigate the structure of hypanthial nectaries present in the flowers of this species with the use of light and scanning electron microscopy. Nectary tissues were examined in three stages of flowering, with special focus placed on changes occurring in the epidermis and nectariferous parnechyma. Long-styled flowers, which produce nectar abundantly, were selected for the study. The nectary parenchyma was shown to consist of multiple cell layers (up to 20). The epidermis was initially single-layered, but the number of layers gradually increased to 2-3 during the following days of flowering. The outer walls of epidermis cells were covered by a strongly undulating cuticle with massive striae. Cracks and perforations, which are probably nectar release sites, were visible between the striae. The presence of the secretion in the intercellular spaces between the parenchyma layer and the epidermis may indicate apoplastic nectar transport. The presence of stomata, as well as pores in the cuticle layer of the nectary epidermis, suggests that C. japonica nectar is secreted in two ways: (i) through the nectarostomata and (ii) ordinary epidermis cells with the involvement of the cuticle.

Identification and quantitation of the novel insecticide sulfoxaflor and its metabolites in floral nectar from Salvia splendens Ker Gawl. (Lamiaceae)

Sulfoxaflor is a new systemic insecticide developed as a replacement for older neonicotinoids which are known to be toxic to pollinators. However, its metabolism in nectar and effect on nectar biosynthesis have not been investigated. After soil and foliar application, sulfoxaflor and its main metabolites in soil, leaf and Salvia splendens nectar, were measured by liquid chromatography coupled with triple quadrupole mass spectrometer (LC-MS/MS). The chemical composition between the clean and sulfoxaflor spiked nectar were also compared. The activities of two possible sulfoxaflor detoxifying enzymes in S. splendens nectar, nitrile hydratase and glutathione-s-transferase, were measured by LC-MS and spectrophotometry. S. splendens nectar proteome was investigated by high-resolution orbitrap-based MS/MS to screen for sulfoxaflor detoxifying relevant proteins. S. splendens could absorb sulfoxaflor through root or leaf surface and secrete a proportion of sulfoxaflor along with its metabolites into the nectar. After soil application, sulfoxaflor's low toxic metabolite X11719474 was dominant in the nectar and reached an average concentration of 8905 ppb. However, after foliar application, sulfoxaflor was dominant over its metabolites in the nectar. S. splendens nectar has no nitrile hydratase and glutathione-s-transferase activity and none of the 106 proteins identified in the nectar were predicted to function in detoxifying sulfoxaflor. Soil and foliar sulfoxaflor application can result in different profiles of sulfoxaflor and its metabolites presented in the nectar. However, sulfoxaflor had no effects on S. splendens nectar secretion and chemical composition and cannot be directly detoxified by components in the nectar.

Floral nectaries and pseudonectaries in Eranthis (Ranunculaceae): petal development, micromorphology, structure and ultrastructure

Flowers are an innovative characteristic of angiosperms, and elaborate petals usually have highly specialized structures to adapt to different living environments and pollinators. Petals of Eranthis have complex bilabiate structures with nectaries and pseudonectaries; however, the diversity of the petal micromorphology and structure is unknown. Petal development, micromorphology, structure and ultrastructure in four Eranthis species were investigated under SEM, TEM and LM. The results show that petals undergo 5 developmental stages, and accessory structure formation (stage 4) mainly determines the diversity of final mature petal morphology and pseudonectaries; the central depression formed in stage 2 will develop into nectary tissues. Petals are bilabiate and have hidden nectaries in nectary grooves; they consist of one layer of rounded and raised secretory epidermal cells and 3-14 layers of secretory cells with abundant plasmodesmata between cells. A large number of sieve tubes are distributed between the cells and extend to the epidermis; in addition, the vessel elements are located below the secretory area. Nectar is stored in the intercellular space between secretory parenchyma cells and escapes through microchannels or cell rupture. Pseudonectaries in all species of Eranthis except for E. hyemalis consist of smooth, ornamented epidermal cells and 9-12 layers of parenchyma cells with sparse cytoplasm, which may have the function of attracting pollinators.

Sweet solutions: nectar chemistry and quality

Nectar, the main floral reward for pollinators, varies greatly in composition and concentration. The assumption that nectar quality is equivalent to its sugar (energy) concentration is too simple. Diverse non-sugar components, especially amino acids and secondary metabolites, play various roles in nutrition and health of pollinators. Many nectar compounds have indirect effects by altering the foraging behaviour of pollinators or protecting them from disease. This review also emphasizes the water component of nectar, often ignored because of evaporative losses and difficulties in sampling small nectar volumes. Nectar properties vary with environmental factors, pollinator visits and microbial contamination. Pollination mutualisms depend on the ability of insect and vertebrate pollinators to cope with and benefit from the variation and diversity in nectar chemistry. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Modeling pesticide residues in nectar and pollen in support of pesticide exposure assessment for honeybees: A generic modeling approach

Pesticide residues in nectar and pollen of plants can damage honeybees; however, few modeling approaches have simulated residue levels in nectar and pollen in support of exposure assessment for honeybees. This study introduced a generic modeling approach based on plant uptake models and simple partitioning rules that specifies soil incorporation and foliar spray application scenarios of pesticides and is flexible for conducting variability analysis for various environmental conditions, pesticide application patterns, chemical individuals, and plant varieties. The results indicated that, in general, systemic or moderate lipophilicity (log K_OW of ~2.5) pesticides have relatively high simulated residue levels in nectar and pollen because of the enhanced residue uptake process from soil. For non-systemic or highly lipophilic pesticides, the residue uptake via leaf surface deposition pathway can be enhanced, and more residues will be bioaccumulated in pollen than nectar due to a relatively high lipid content of pollen (as compared to nectar), but the overall residue levels in nectar and pollen are lower than systemic or moderately lipophilic pesticides. The variability analysis showed that environmental conditions, pesticide application patterns, chemical properties, and plant varieties cause considerable variations in simulated residue levels in nectar and pollen, indicating that spatiotemporal, chemical, and plant-related factors must be considered in pesticide exposure assessment for honeybees. Moreover, the comparison between the simulated and measured data showed a high degree of consistency, indicating that the proposed model could be used to conduct a screening-level pesticide exposure assessment for honeybees.

Is there a risk to honeybees from use of thiamethoxam as a sugar beet seed treatment?

The ban imposed by the European Union on the use of neonicotinoids as sugar beet seed treatments was based on the exposure of bees to residues of neonicotinoids in pollen and nectar of succeeding crops. To address this concern, residues of thiamethoxam (TMX) and clothianidin (CTD) were analyzed in soil collected from fields planted in at least the previous year with thiamethoxam-treated sugar beet seed. This soil monitoring program was conducted at 94 sites across Germany in two separate years. In addition, a succeeding crop study assessed residues in soil, guttation fluid, pollen, and nectar sampled from untreated succeeding crops planted in the season after thiamethoxam seed-treated sugar beet at eight field sites across five countries. The overall mean residues observed in soil monitoring were 8.0 ± 0.5 µg TMX + CTD/kg in the season after the use of treated sugar beet seed. Residue values decreased with increasing time interval between the latest thiamethoxam or clothianidin application before sugar beet drilling and with lower application frequency. Residues were detected in guttation fluid (2.0-37.7 µg TMX/L); however, the risk to pollinators from this route of exposure is likely to be low, based on the reported levels of consumption. Residues of thiamethoxam and clothianidin in pollen and nectar sampled from the succeeding crops were detected at or below the limit of quantification (0.5-1 µg a.i./kg) in 86.7% of pollen and 98.6% of nectar samples and, unlike guttation fluid residues, were not correlated with measured soil residues. Residues in pollen and nectar are lower than reported sublethal adverse effect concentrations in studies with honeybee and bumble bee individuals and colonies fed only thiamethoxam-treated sucrose, and are lower than those reported to result in no effects in honeybees, bumble bees, and solitary bees foraging on seed-treated crops. Integr Environ Assess Manag 2022;18:709-721. © 2021 SYNGENTA. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Pesticide residues in honeybee-collected pollen: does the EU regulation protect honeybees from pesticides?

Researchers globally identify pesticides as one of the main reasons for pollinator decline. In the European Union (EU), extensive legislation is implemented to protect pollinators from harmful pesticide exposure. The aim of our study was to discover whether the pesticide residue levels in honeybee matrices, such as nectar and pollen, exceeded the chronic or acute toxicity levels when beehives were located next to fields treated with specific insecticides. The insecticides were used according to the EU legislation and its national implementation. The experiments were conducted in turnip rape, oilseed rape, and caraway fields in southern Finland during the years 2019 and 2020. The pesticides used in the experiments contained the active substances lambda-cyhalothrin (2019), esfenvalerate (2020), and tau-fluvalinate (2020). However, the honeybee-collected pollen and nectar were analyzed for residues of more than 100 active substances. The results showed that the pesticide residue levels clearly remained under the oral acute toxicity for honeybees, although we found high levels of thiacloprid residues in the pollen collected in 2019. The pesticide residues in nectar were below LOQ values, which was most likely due to the rainy weather conditions together with the chosen sampling method. No statistically significant differences were observed between the insecticide-treated and untreated fields. In light of our research, the EU legislation protected honeybees from oral acute toxicity during the years 2019 and 2020. However, potential sublethal effects of thiacloprid and other pesticide compounds found in the collected pollen cannot be ruled out. In the future, constant monitoring of pesticide exposure of honeybees and wild pollinators should be established to ensure that pesticide legislation, and its implementation across the EU successfully protects pollinators and their services in agricultural environments.

A chemometric approach for the differentiation of 15 monofloral honeys based on physicochemical parameters

BACKGROUND

Although the main method for authentication of monofloral honey is pollen analysis, other classification approaches have been also applied. However, the majority of the existing classification models so far have utilized a few honey types or a few honey samples of each honey type, which can lead to inaccurate results. Aiming at addressing this, the goal of the present study was to create a classification model by analysing in total 250 honey samples from 15 different monofloral honey types in ten physicochemical parameters and then, multivariate analysis [multivariate analysis of variance (MANOVA), principal component analysis (PCA) and multi-discriminant analysis (MDA)] was applied in an effort to distinguish and classify them.

RESULTS

Electrical conductivity and colour were found to have the highest discriminative power, allowing the classification of monofloral honey types, such as oak, knotgrass and chestnut honey, as well as the differentiation between honeydew and nectar honeys. The classification model had a high predictive power, as the 84.4% of the group cases was correctly classified, while for the cases of chestnut, strawberry tree and sunflower honeys the respective prediction was correct by 91.3%, 95% and 100%, allowing further determination of unknown honey samples.

CONCLUSION

It seems that the characterization of monofloral honeys based on their physicochemical parameters through the proposed model can be achieved and further applied on other honey types. The results could contribute to the development of methodologies for the determination of honey's botanical origin, based on simple techniques, so that these can be applied for routine analysis. © 2021 Society of Chemical Industry.

Nectaries in ferns: their taxonomic distribution, structure, function, and sugar composition

PREMISE

Extrafloral nectaries have mainly been studied in angiosperms, but have also been reported in 39 fern species. Here we provide a global review of nectaries in ferns and examined their structure, function, and nectar sugar composition in two genera.

METHODS

We searched in the literature and living plant collections of botanical gardens for indications of fern nectaries, observed nectar-feeding animals, studied the morphoanatomy in the two genera Aglaomorpha and Campyloneurum, and analyzed the total sugar concentrations and ratios of 16 species. Diurnal nectar release was observed with time-lapse photography.

RESULTS

We found evidence for nectaries in 101 species of ferns from 11 genera and 6 families. Most of the nectary-bearing species were tree ferns (Cyatheaceae) and epiphytic ferns of the family Polypodiaceae. Nectaries consisted of cytoplasm-rich parenchyma with large nuclei and an epidermis with or without stomata, were attached to amphiphloic vascular bundles, and released nectar on the lower leaf surface mainly on expanding leaves during the night. Sugar concentrations varied between species (3.8-15.3%) but not between genera, and were sucrose-dominant (3 spp.), sucrose-rich (7), or hexose-rich (3). In the greenhouse, introduced ants, scale insects, and snails fed on the nectar.

CONCLUSIONS

The wide taxonomic distribution, variable morphology, locations, and sugar compositions point to multiple evolutionary origins of fern nectaries. Nectar release in young leaves might attract mutualistic ants to protect leaves against herbivores only during this most vulnerable developmental stage. Even ex-situ, fern nectar is a valuable food source because it attracted several opportunistic animal species.

Nectar Chemistry or Flower Morphology-What Is More Important for the Reproductive Success of Generalist Orchid Epipactis palustris in Natural and Anthropogenic Populations?

The aim of this study was to determine the level of reproductive success (RS) in natural and anthropogenic populations of generalist orchid Epipactis palustris and its dependence on flower structure and nectar composition, i.e., amino acids and sugars. We found that both pollinaria removal and female reproductive success were high and similar in all populations, despite differences in flower traits and nectar chemistry. Flower structures were weakly correlated with parameters of RS. Nectar traits were more important in shaping RS; although, we noted differentiated selection on nectar components in distinct populations. Individuals in natural populations produced nectar with a larger amount of sugars and amino acids. The sucrose to (fructose and glucose) ratio in natural populations was close to 1, while in anthropogenic ones, a clear domination of fructose and glucose was noted. Our results indicate that the flower traits and nectar composition of E. palustris reflect its generalist character and meet the requirements of a wide range of pollinators, differing according to body sizes, mouth apparatus, and dietary needs. Simultaneously, differentiation of nectar chemistry suggests a variation of pollinator assemblages in particular populations or domination of their some groups. To our knowledge, a comparison of nectar chemistry between natural and anthropogenic populations of orchids is reported for the first time in this paper.

Foliar herbivory increases sucrose concentration in bracteal extrafloral nectar of cotton

Cultivated cotton, such as Gossypium hirsutum L., produces extrafloral (EF) nectar on leaves (foliar) and reproductive structures (bracteal) as an indirect anti-herbivore defense. In exchange for this carbohydrate-rich substance, predatory insects such as ants protect the plant against herbivorous insects. Some EF nectar-bearing plants respond to herbivory by increasing EF nectar production. For instance, herbivore-free G. hirsutum produces more bracteal than foliar EF nectar, but increases its foliar EF nectar production in response to herbivory. This study is the first to test for systemically induced changes to the carbohydrate composition of bracteal EF nectar in response to foliar herbivory on G. hirsutum. We found that foliar herbivory significantly increased the sucrose content of bracteal EF nectar while glucose and fructose remained unchanged. Sucrose content is known to influence ant foraging behavior and previous studies of an herbivore-induced increase to EF nectar caloric content found that it led to increased ant activity on the plant. As a follow-up to our finding, ant recruitment to mock EF nectar solutions that varied in sucrose content was tested in the field. The ants did not exhibit any preference for either solution, potentially because sucrose is a minor carbohydrate component in G. hirsutum EF nectar: total sugar content was not significantly affected by the increase in sucrose. Nonetheless, our findings raise new questions about cotton’s inducible EF nectar responses to herbivory. Further research is needed to determine whether an herbivore-induced increase in sucrose content is typical of Gossypium spp., and whether it constitutes a corollary of systemic sucrose induction, or a potentially adaptive mechanism which enhances ant attraction to the plant

Within-Body Distributions and Feeding Effects of the Neonicotinoid Insecticide Clothianidin in Bumblebees (Bombus terrestris)

Bumblebees can be exposed to neonicotinoid pesticides through nectar and pollen collected from treated crops, which can cause lethal and sublethal effects in these nontarget pollinators. However, the body distribution of the compound after exposure to neonicotinoids in bumblebees is not well studied. Bumblebee colonies (Bombus terrestris, n = 20) were exposed to field-realistic concentrations of clothianidin through artificial nectar (3.6-13 µg/L) for 9 d. Comparison of the nominal with the measured exposure in nectar indicated good compliance, confirming the applicability of the method. When quantified, clothianidin showed a concentration-dependent occurrence in the head and body of workers (head: <0.2-2.17 µg/kg; body: <0.2-3.17 µg/kg), and in the body of queens (<0.2-2.49 µg/kg), although concentrations were below those measured in the nectar (bioaccumulation factor = 0.2). Exposure to clothianidin did not affect mortality nor brood production, nor did it have a statistically significant effect on nectar consumption and size of food storage. However, visual inspection suggests higher nectar consumption of nectar with low clothianidin content compared with nectar with no or high clothianidin content. Our results show that dietary clothianidin is taken up in bumblebees, but does not bioaccumulate to elevated levels compared with exposure. Still, clothianidin may elicit responses that affect feeding behavior of the pollinator B. terrestris, although our endpoints were not significantly affected. Environ Toxicol Chem 2021;40:2781-2790. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Yeast-nectar interactions: metacommunities and effects on pollinators

About 90% of all flowering plant species are pollinated by animals. Animals are attracted to flowers because they often provide food in the form of nectar and pollen. While floral nectar is assumed to be initially sterile, it commonly becomes colonized by yeasts after animals have visited the flowers. Although yeast communities in floral nectar appear simple, community assembly depends on a complex interaction between multiple factors. Yeast colonization has a significant effect on the scent of floral nectar, foraging behavior of insects and nectar consumption. Consumption of nectar colonized by yeasts has been shown to improve bee fitness, but effects largely depended on yeast species. Altogether, these results indicate that dispersal, colonization history and nectar chemistry strongly interact and have pronounced effects on yeast metacommunities and, as a result, on bee foraging behavior and fitness. Future research directions to better understand the dynamics of plant-microbe-pollinator interactions are discussed.

The role of alanine synthesis and nitrate-induced nitric oxide production during hypoxia stress in Cucurbita pepo nectaries

Floral nectar is a sugary solution produced by nectaries to attract and reward pollinators. Nectar metabolites, such as sugars, are synthesized within the nectary during secretion from both pre-stored and direct phloem-derived precursors. In addition to sugars, nectars contain nitrogenous compounds such as amino acids; however, little is known about the role(s) of nitrogen (N) compounds in nectary function. In this study, we investigated N metabolism in Cucurbita pepo (squash) floral nectaries in order to understand how various N-containing compounds are produced and determine the role of N metabolism in nectar secretion. The expression and activity of key enzymes involved in primary N assimilation, including nitrate reductase (NR) and alanine aminotransferase (AlaAT), were induced during secretion in C. pepo nectaries. Alanine (Ala) accumulated to about 35% of total amino acids in nectaries and nectar during peak secretion; however, alteration of vascular nitrate supply had no impact on Ala accumulation during secretion, suggesting that nectar(y) amino acids are produced by precursors other than nitrate. In addition, nitric oxide (NO) is produced from nitrate and nitrite, at least partially by NR, in nectaries and nectar. Hypoxia-related processes are induced in nectaries during secretion, including lactic acid and ethanolic fermentation. Finally, treatments that alter nitrate supply affect levels of hypoxic metabolites, nectar volume and nectar sugar composition. The induction of N metabolism in C. pepo nectaries thus plays an important role in the synthesis and secretion of nectar sugar.

Altered feeding behavior and immune competence in paper wasps: A case of parasite manipulation?

Paper wasps (Polistes dominula), parasitized by the strepsipteran Xenos vesparum, are castrated and desert the colony to gather on plants where the parasite mates and releases primary larvae, thus completing its lifecycle. One of these plants is the trumpet creeper Campsis radicans: in a previous study the majority of all wasps collected from this plant were parasitized and focused their foraging activity on C. radicans buds. The unexpected prevalence and unusual feeding strategy prompted us to investigate the influence of this plant on wasp behavior and physiology through a multidisciplinary approach. First, in a series of laboratory bioassays, we observed that parasitized wasps spent more time than non-parasitized ones on fresh C. radicans buds, rich of extra-floral nectaries (EFNs), while the same wasps ignored treated buds that lacked nectar drops. Then, we described the structure and ultra-structure of EFNs secreting cells, compatible with the synthesis of phenolic compounds. Subsequently, we analysed extracts from different bud tissues by HPLC-DAD-MS and found that verbascoside was the most abundant bioactive molecule in those tissues rich in EFNs. Finally, we tested the immune-stimulant properties of verbascoside, as the biochemical nature of this compound indicates it might function as an antibacterial and antioxidant. We measured bacterial clearance in wasps, as a proxy for overall immune competence, and observed that it was enhanced after administration of verbascoside-even more so if the wasp was parasitized. We hypothesize that the parasite manipulates wasp behavior to preferentially feed on C. radicans EFNs, since the bioactive properties of verbascoside likely increase host survival and thus the parasite own fitness.

Herbivory and Time Since Flowering Shape Floral Rewards and Pollinator-Pathogen Interactions

Herbivory can induce chemical changes throughout plant tissues including flowers, which could affect pollinator-pathogen interactions. Pollen is highly defended compared to nectar, but no study has examined whether herbivory affects pollen chemistry. We assessed the effects of leaf herbivory on nectar and pollen alkaloids in Nicotiana tabacum, and how herbivory-induced changes in nectar and pollen affect pollinator-pathogen interactions. We damaged leaves of Nicotiana tabacum using the specialist herbivore Manduca sexta and compared nicotine and anabasine concentrations in nectar and pollen. We then pooled nectar and pollen by collection periods (within and after one month of flowering), fed them in separate experiments to bumble bees (Bombus impatiens) infected with the gut pathogen Crithidia bombi, and assessed infections after seven days. We did not detect alkaloids in nectar, and leaf damage did not alter the effect of nectar on Crithidia counts. In pollen, herbivory induced higher concentrations of anabasine but not nicotine, and alkaloid concentrations rose and then fell as a function of days since flowering. Bees fed pollen from damaged plants had Crithidia counts 15 times higher than bees fed pollen from undamaged plants, but only when pollen was collected after one month of flowering, indicating that both damage and time since flowering affected interaction outcomes. Within undamaged treatments, bees fed late-collected pollen had Crithidia counts 10 times lower than bees fed early-collected pollen, also indicating the importance of time since flowering. Our results emphasize the role of herbivores in shaping pollen chemistry, with consequences for interactions between pollinators and their pathogens.

Comparison of Biochemical Constituents and Contents in Floral Nectar of Castanea spp

Pollination is essential for efficient reproduction in pollinator-dependent crops that rely on the attraction of pollinators to flowers. Especially, floral nectar is considered to be an important factor attracting pollinator like honey bees, but differences among major chestnut species (Castanea crenata, C. mollissima, C. dentata, and C. sativa) are still little explored. This study aims to evaluate the value of honey source by analyzing floral nectar characteristics and comparing the composition of volatile organic compounds (VOCs) that mediate plant-pollinator interaction. In this study, we analyzed nectar samples obtained from male flowers using HPLC and HS-SPME/GC-MS. The five chestnuts showed significant differences between the volume of secreted nectar, free sugar composition, amino acid content and VOCs composition. Furthermore, C. crenata (Japanese cultivar 'Ungi') was revealed to emit the highest total amounts of VOCs and high levels of benzenoid compounds that are generally associated with flower-visiting insects. The sugar content per catkin, which is used to determine the honey yield, was the highest in C. crenata, suggesting that C. crenata 'Ungi' can be highly valued as a honey tree. Therefore, a better understanding of the relationship between pollinator and nectar characteristics of C. crenara could contribute to a prospective honey plant.

Reduced Water Negatively Impacts Social Bee Survival and Productivity Via Shifts in Floral Nutrition

Pollinators provide a key ecosystem service vital for the survival and stability of the biosphere. Identifying factors influencing the plant-pollinator mutualism and pollinator management is necessary for maintaining a healthy ecosystem. Since healthy beehives require substantial amounts of carbohydrates (nectar) and protein (pollen) from forage plants such as clover, we must assess how resources offered by plants change under limited water conditions in order to fully understand how drought modifies the pollination mutualism. Here we document how reduced water availability leads to decreased nectar quality and quantity and decreased protein quality of pollen. Furthermore, we provide conclusive evidence that these lower quality resources lead to decreased survival and productivity in both developing honey bees (Hymenoptera: Apidae) and bumble bees (Hymenoptera: Apidae). The results emphasize the importance of the nutritional effects of reduced water on bees when predicting shifts of pollination mutualisms under climate change.

Influence of light, dark, temperature and drought on metabolite and ion composition in nectar and nectaries of an epiphytic bromeliad species (Aechmea fasciata)

Research into the influence of stress factors, such as drought, different temperatures and/or varied light conditions, on plants due to climate changes is becoming increasingly important. Epiphytes, like many species of the Bromeliaceae, are particularly affected by this, but little is known about impacts on nectar composition and nectary metabolism. We investigated the influence of drought, different temperatures and light-dark regimes on nectar and nectaries of the epiphytic bromeliad species, Aechmea fasciata, and also the influence of drought with the terrestrial bromeliad, Billbergia nutans. The content of sugars, amino acids and ions in nectar and nectaries was analysed using HPLC. In addition, the starch content and the activities of different invertases in nectaries were determined. Compositions of nectar and nectaries were hardly influenced, neither by light nor dark, nor by different temperatures. In contrast, drought revealed changes in nectar volumes and nectar sugar compositions in the epiphytic bromeliad as well as in the terrestrial bromeliad. In both species, the sucrose-to-hexose ratio in nectar decreased considerably during the drought period. These changes in nectar sugar composition do not correlate with changes in the nectaries. The total sugar, amino acid and ion concentrations remained constant in nectar as well as in nectaries during the drought period. Changes in nectar composition or in the production of floral pollinator rewards are likely to affect plant-pollinator interactions. It remains questionable how far the adaptations of the bromeliads to drought and diverse light or temperature conditions are still sufficient.

Reduced Water Negatively Impacts Social Bee Survival and Productivity Via Shifts in Floral Nutrition

Pollinators provide a key ecosystem service vital for the survival and stability of the biosphere. Identifying factors influencing the plant-pollinator mutualism and pollinator management is necessary for maintaining a healthy ecosystem. Since healthy beehives require substantial amounts of carbohydrates (nectar) and protein (pollen) from forage plants such as clover, we must assess how resources offered by plants change under limited water conditions in order to fully understand how drought modifies the pollination mutualism. Here we document how reduced water availability leads to decreased nectar quality and quantity and decreased protein quality of pollen. Furthermore, we provide conclusive evidence that these lower quality resources lead to decreased survival and productivity in both developing honey bees (Hymenoptera: Apidae) and bumble bees (Hymenoptera: Apidae). The results emphasize the importance of the nutritional effects of reduced water on bees when predicting shifts of pollination mutualisms under climate change.

Microstructure of floral nectaries in Robinia viscosa var. hartwigii (Papilionoideae, Fabaceae)-a valuable but little-known melliferous plant

Floral nectaries are important components of floral architecture and significant taxonomic traits facilitating assessment of relationships between taxa and can contribute substantially to studies on the ecology and evolution of a particular genus. Knowledge of nectary structure and functioning allows better understanding of the mutualistic interactions between the pollinator and the plant. Robinia viscosa var. hartwigii (Hartweg's locust), planted in many European countries as an ornamental plant and used for recovery of degraded areas and urban arborisation, is a valuable melliferous species often visited by honeybees and bumblebees. The aim of this study was to investigate the microstructure of the floral nectaries of R. viscosa var. hartwigii with the use of light, fluorescence, scanning, and transmission electron microscopes. The photosynthetic nectaries were located on the inner surface of the cup-like receptacle. The components of pre-nectar were synthesised in the chloroplasts of the glandular parenchyma and transported via the conducting elements of the phloem. Nectar was released through modified nectarostomata. Nectar secretion presumably proceeded in the eccrine mode, whereas nectar transport represented the symplastic and apoplastic types. The cuticle on the nectary epidermis surface contained lipids, essentials oils, and flavonoids, while proteins and flavonoids were present in the glandular parenchyma cells. Idioblasts containing phenolic compounds, tannins, and polysaccharides were observed between the glandular parenchyma cells. The location of the nectaries and the mode of nectar production in the flowers of the Hartweg's locust follow the common location and structure pattern characteristic for the nectaries in some members of the subfamily Papilionoideae and can be a significant taxonomic trait for the genus Robinia and the tribe Robinieae.

Flowers and climate change: a metabolic perspective

Adverse climatic conditions at the time of flowering severely hinder crop yields and threaten the interactions between plants and their pollinators. These features depend on a common trait: the metabolism of flowers. In this Viewpoint article, we aim to provide insight into the metabolic changes that occur in flowers in response to changes in climate and emphasize that these changes severely impact the fitness of autogamous and allogamous species, plant-pollinator interactions, and overall ecosystem health. We review the biochemical processes that lead to failure of gamete development and to alterations of color, scent and nectar secretion. Then, making use of open access expression data, we examine the expression of genes that may drive these changes in response to heat and drought. Finally, we present measurements of metabolites from flowers exposed to a heat wave and discuss how the results of this short-term experiment may give rise to misleading conclusions regarding the positive effect of heat on flower fitness. We hope this article draws attention to this often-neglected dynamic and its important consequences.

Combined nutritional stress and a new systemic pesticide (flupyradifurone, Sivanto®) reduce bee survival, food consumption, flight success, and thermoregulation

Flupyradifurone (FPF, Sivanto®) is a new butenolide insecticide that, like the neonicotinoids, is a systemic nicotinic acetylcholine receptor (nAChR) agonist. However, FPF is considered bee-safe (according to standard Risk Assessment tests), and is thus a potential solution to the adverse effects of other pesticides on beneficial insects. To date, no studies have examined the impact of nutritional stress (decreased food diversity and quality) and FPF exposure on bee health although both stressors can occur, especially around agricultural monocultures. We therefore tested the effects of a field-realistic FPF concentration (4 ppm, FPF_{daily dose} = 241 ± 4 ng/bee/day, 1/12 of LD₅₀) and nutritional stress (nectar with low-sugar concentrations) on honey bee (Apis mellifera L.) mortality, food consumption, thermoregulation, flight success (unsuccessful vs. successful), and flight ability (duration, distance, velocity). Flight and thermoregulation are critical to colony health: bees fly to collect food and reproduce, and they thermoregulate to increase flight efficiency and to rear brood. We studied the effects across seasons because seasonality can influence bee sensitivity to environmental stress. We demonstrate that, depending upon season and nutritional stress, FPF can reduce bee survival (-14%), food consumption (-14%), thermoregulation (-4%, i.e. hypothermia), flight success (-19%), and increase flight velocity (+13%). Because pesticide exposure and nutritional stress can co-occur, we suggest that future studies and pesticide risk assessments consider both seasonality and nutritional stress when evaluating pesticide safety for bees.

Analysis on safety assessment of Tephrosia vogelii Hook to Apis cerana cerana

Tephrosia vogelii Hook was excellent insecticidal plant, it was introduced into China and planted over a large area in Guangdong province. The main active components of T. vogelii was rotenone and it widely found in leaves and pods of T. vogelii. This paper study of the safety assessment of T. vogelii flowers to worker bees. In this paper, the content of rotenone in T. vogelii petal, nectar, pollen, pistil, and stamen samples were investigated by HPLC, and tested the toxicity of T. vogelii flowers for Apis cerana cerana during 24 h. The dissipation and dynamic of rotenone in A. c. cerana different biological compartments were investigated under indoor conditions during 24 h. The results showed, The LT₅₀ of T. vogelii flowers to worker bees were collected from the eastern, western, southern, northern and top were 13.95, 24.17, 12.55, 26.48, and 18.84 h, the haemolymph of worker bees have the highest content of rotenone, the least accumulation of rotenone in workers bee's thorax, and the rate of dissipation was slowly during the whole study. In conclusion, the results showed the T. vogelii create security risks to worker bees under some ecosystems.

Floral micromorphology and nectar composition of the early evolutionary lineage Utricularia (subgenus Polypompholyx, Lentibulariaceae)

Utricularia (Lentibulariaceae) is a genus comprising around 240 species of herbaceous, carnivorous plants. Utricularia is usually viewed as an insect-pollinated genus, with the exception of a few bird-pollinated species. The bladderworts Utricularia multifida and U. tenella are interesting species because they represent an early evolutionary Utricularia branch and have some unusual morphological characters in their traps and calyx. Thus, our aims were to (i) determine whether the nectar sugar concentrations and composition in U. multifida and U. tenella are similar to those of other Utricularia species from the subgenera Polypompholyx and Utricularia, (ii) compare the nectary structure of U. multifida and U. tenella with those of other Utricularia species, and (iii) determine whether U. multifida and U. tenella use some of their floral trichomes as an alternative food reward for pollinators. We used light microscopy, histochemistry, and scanning and transmission electron microscopy to address those aims. The concentration and composition of nectar sugars were analysed using high-performance liquid chromatography. In all of the examined species, the floral nectary consisted of a spur bearing glandular trichomes. The spur produced and stored the nectar. We detected hexose-dominated (fructose + glucose) nectar in U. multifida and U. tenella as well as in U. violacea. In both U. multifida and U. tenella, there were trichomes that blocked the entrance into the throat and spur. Because these trichomes were rich in chromoplasts and contained lipid droplets, they may form an additional visual attractant. Bearing in mind the phylogenetic hypothesis for the genus, we suggest that an early ancestor of Utricularia had a nectariferous spur flower with a lower lip that formed a wide landing platform for bee pollinators.

Comparative studies on structure of the floral nectaries and the abundance of nectar production of Prunus laurocerasus L

There is very scanty information concerning the floral nectary structure and nectar secretion in Prunus laurocerasus L. Therefore, the aim of the study was to determine the micromorphology, anatomy and ultrastructure of nectaries; the abundance of nectar production; and the quantitative and qualitative composition of sugars contained in the nectar of two P. laurocerasus cultivars: 'Schipkaensis' and 'Zabeliana'. The nectary structure was studied using light, fluorescence, scanning and transmission electron microscopy techniques. The nectar sugars were analysed with HPLC. The 'Schipkaensis' had longer inflorescences with a larger number of flowers and a longer perianth than 'Zabeliana'. The micromorphological structure of the nectaries in 'Schipkaensis' exhibited denser (approx. 39%) and larger (approx. 50%) stomata and thicker (approx. 13%) cuticular striae forming wider bands (approx. 26%) than in 'Zabeliana'. The results provide new data on the micromorphology, anatomy and ultrastructure of these floral nectaries. Nectary cuticle ornamentation as well as the size, type and density of stomata and stomatal complex topography can have a diagnostic value in Prunus. The nectar sugar weight indicates a significant apicultural value of the cherry laurel, especially in the case of 'Schipkaensis'. Cherry laurel is an entomophilous species recommended for cultivation in nectariferous zones and insect pollinator refuges; however, climatic conditions eliminating the invasiveness of these plants should be considered.

Diversity of nectar amino acids in the Fritillaria (Liliaceae) genus: ecological and evolutionary implications

Nectar is considered to be a primary food reward for most pollinators. It mostly contains sugars, but also has amino acids. The significance of the concentration and composition of amino acids in nectar is often less understood than that of its volume, sugar concentration and composition. However, there is a trend towards a broader approach in ecological research, which helps to understand nectar properties in an ecological context. The genus Fritillaria, exhibiting great diversity in flower morphology, nectar composition, and dominant pollinators, allows for the possibility to study some of the above. We studied the concentration and composition of amino acids in the nectar of 38 Fritillaria species attracting different groups of pollen vectors (bees, flies, passerines, and hummingbirds). The flowers of fritillaries produced nectar with a varying composition and concentration of amino acids. These differences were mostly associated with the pollinator type. The nectar of passerine bird-pollinated species was rich in amino acids, whereas humming bird-pollinated produced low amino acid nectar. Contrary to previous reports nectar of the insect-pollinated species did not contain a higher amount of proline. Two non-protein amino acids, sarcosine and norvaline, were detected in the floral nectar for the first time.

Fiber-optic refractometer for in vivo sugar concentration measurements of low-nectar-producing flowers

Sugar concentration in floral nectars is an assessment required in several diverse fields of application. The widely used analysis, consisting of nectar extraction with a microcapillary and sugar concentration measurement with a light refractometer, is not reliable when the nectar is secreted in small quantities, unextractable with a microcapillary. Ancillary methods adopted in such cases are destructive, rather complicated and often provide much less precise and accurate results. The microscopic-size, low cost and biocompatibility of optical fibers were exploited to deliver light directly inside the flower with minimal invasiveness and measure instantaneously the refractometric properties of the nectar without extracting it. After comparing the new and old methods using two known nectariferous species, the new approach was validated on Primula palinuri, whose nectar is unextractable with microcapillaries. The fiber-optic probe was able to measure the nectar refractive index in P. palinuri flowers making it possible to highlight a previously undetected significant trend of the sugar concentration throughout the long anthesis of the single flowers. Changes in nectar concentrations are similar in both longistylous and brevistylous flowers. The fiber-optic refractometer is an advancement of light refractometer analysis. Further customization of the laboratory set-up into portable equipment will boost applications.

Influence of sugar experience during development on gustatory sensitivity of the honey bee

The level of response to sugar plays a role in many aspects of honey bee behavior including age dependent polyethism and division of labor. Bees may tune their sensitivity to sugars so that they maximize collection of high quality nectar, but they must also be able to collect from less profitable sources when high quality food is scarce. However, our understanding of the mechanisms by which bees can change their responsiveness to different sugars remains incomplete. To investigate the plasticity of sensitivity to sugar, bees were raised on different sugars either in vitro or in colonies. Bees raised in the incubator on diets containing mostly either fructose or glucose showed significantly more responsiveness to the majority sugar. In contrast, bees raised in colonies that only foraged on fructose or glucose responded equally well to both sugars. These data suggest that developmental plasticity for responses to sugar is masked by the feeding of worker jelly to larvae and young bees. The production of worker jelly from secretions of the hypopharyngeal and mandibular glands by nurse bees ensures that both glucose and fructose are experienced by young bees so that they respond to both sugars and will be able to exploit all future food sources.

Nectar composition in moth-pollinated Platanthera bifolia and P. chlorantha and its importance for reproductive success

Sugars (glucose, fructose and sucrose), as well as proteogenic and non-proteogenic amino acids, are present in the nectar of Platanthera bifolia and P. chlorantha. Nectar quantity and quality are floral traits that are subjected to pollinator-mediated selection. Nectar sugar and amino acid (AA) composition in two sister species, P. bifolia and P. chlorantha, was analysed and the interspecies differences in nectar and the importance of these nectar characteristics for reproductive success were investigated. Nectar was collected from four P. bifolia and three P. chlorantha populations that exist in different habitats in three regions of NE Poland. Nectar from about 30 flowers (from each population) was sampled and analysed using high-performance liquid chromatography. We found the same primary sugars and AA components in the nectar of both species, although their content varied between the populations according to habitat properties. The nectar of P. bifolia and P. chlorantha both had low sugar concentrations (9.04-20.68%) and were dominated by hexoses, with sucrose:hexoses ratios between 0.03 and 0.31 across the different populations (the average for the P. bifolia populations was 0.17 and the average for the P. chlorantha populations was - 0.05). Total sugar content did not influence reproductive success and we found positive selection on fructose content. In general, 23 different AAs were detected in both Platanthera species. Cysteine and γ-aminobutyric acid were present in only one population of P. chlorantha. Sarcosine dominated among the non-proteogenic AAs. To our knowledge, this is the first report that characterizes the sugar and AA profiles in the nectar of P. bifolia and P. chlorantha in natural populations in the context of effectiveness of reproduction. Total AAs negatively influenced male reproductive success (r = - 0.79). Pollinators of the investigated species were found to be sensitive to the AAs' taste, from taste classes I and IV. Correlation between male reproductive success and the content of AAs from these groups was 0.79 in both cases. In this manuscript, we investigated the characteristics of P. bifolia and P. chlorantha nectar, and compared these characteristics to the available data in the context of their adaptations to the requirements of pollinators and with regard to the importance of nectar quality for reproductive success of the studied species.

A matter of taste: the adverse effect of pollen compounds on the pre-ingestive gustatory experience of sugar solutions for honeybees

In addition to sugars, nectar contains multiple nutrient compounds in varying concentrations, yet little is known of their effect on the reward properties of nectar and the resulting implications for insect behaviour. We examined the pre-ingestive responses of honeybees to sucrose solutions containing a mix of pollen compounds, the amino acids proline or phenylalanine, or known distasteful substances, quinine and salt. We predicted that in taste and learning assays, bees would respond positively to the presence of nutrient compounds in a sucrose solution. However, bees’ proboscis extension responses decreased when their antennae were stimulated with pollen- or amino acid-supplemented sucrose solutions. Compared to pure sucrose, bees exhibited worse acquisition when conditioned to an odour with pollen-supplemented sucrose as the unconditioned stimulus. Such learning impairment was also observed with quinine-containing sucrose solutions. Our results suggest that bees can use their antennae to detect pollen compounds in floral nectars. Depending on the type and concentrations of compounds present, this may result in nectar being perceived as distasteful by bees, making it less effective in reinforcing the learning of floral cues. Such reward devaluation might be adaptive in cases where plants benefit from regulating the frequency of bee visitation.

A review of the factors that influence pesticide residues in pollen and nectar: Future research requirements for optimising the estimation of pollinator exposure

In recent years, the impact of Plant Protection Products (PPPs) on insect pollinator decline has stimulated significant amounts of research, as well as political and public interest. PPP residues have been found in various bee-related matrices, resulting in governmental bodies worldwide releasing guidance documents on methods for the assessment of the overall risk of PPPs to different bee species. An essential part of these risk assessments are PPP residues found in pollen and nectar, as they represent a key route of exposure. However, PPP residue values in these matrices exhibit large variations and are not available for many PPPs and crop species combinations, which results in inaccurate estimations and uncertainties in risk evaluation. Additionally, residue studies on pollen and nectar are expensive and practically challenging. An extrapolation between different cropping scenarios and PPPs is not yet justified, as the behaviour of PPPs in pollen and nectar is poorly understood. Therefore, this review aims to contribute to a better knowledge and understanding of the fate of PPP residues in pollen and nectar and to outline knowledge gaps and future research needs. The literature suggests that four primary factors, the crop type, the application method, the physicochemical properties of a compound and the environmental conditions have the greatest influence on PPP residues in pollen and nectar. However, these factors consist of many sub-factors and initial effects may be disguised by different sampling methodologies, impeding their exact characterisation. Moreover, knowledge about these factors is ambiguous and restricted to a few compounds and plant species. We propose that future research should concentrate on identifying relationships and common features amongst various PPP applications and crops, as well as an overall quantification of the described parameters; in order to enable a reliable estimation of PPP residues in pollen, nectar and other bee matrices.

Pathogen-induced changes in floral scent may increase honeybee-mediated dispersal of Erwinia amylovora

Honeybees are well recognised for their key role in plant reproduction as pollinators. On the other hand, their activity may vector some pathogens, such as the bacterium Erwinia amylovora, the causative agent of fire blight disease in pomaceous plants. In this research, we evaluated whether honeybees are able to discriminate between healthy and E. amylovora-infected flowers, thus altering the dispersal of the pathogen. For this reason, honeybees were previously trained to forage either on inoculated or healthy (control) apple flower. After the training, the two honeybee groups were equally exposed to inoculated and control flowering apple plants. To assess their preference, three independent methods were used: (1) direct count of visiting bees per time frame; (2) incidence on apple flowers of a marker bacterium (Pantoea agglomerans, strain P10c) carried by foragers; (3) quantification of E. amylovora populations in the collected pollen loads, proportional to the number of visits to infected flowers. The results show that both honeybee groups preferred control flowers over inoculated ones. The characterisation of volatile compounds released by flowers revealed a different emission of several bioactive compounds, providing an explanation for honeybee preference. As an unexpected ecological consequence, the influence of infection on floral scent increasing the visit rate on healthy flowers may promote a secondary bacterial spread.

Thiamethoxam: Long-term effects following honey bee colony-level exposure and implications for risk assessment

Neonicotinoid insecticides have been used in a wide range of crops through seed treatment, soil and foliar applications and a large database exists on both their lethal and sub-lethal effects on honey bees under controlled laboratory conditions. However, colony-level studies on the effects of neonicotinoids in field studies are limited, primarily due to their complexity and the resources required. This paper reports the combined results of two large-scale colony-feeding studies, each with 6 weeks of continuous dosing of 12 colonies per treatment (24 control) to 12.5, 25, 37.5, 50 or 100 ng thiamethoxam/g sucrose solution. Exposure continued beyond dosing with residues present in stored nectar and bee-bread. The studies were conducted in an area with limited alternative forage and colonies were required to forage for pollen and additional nectar The studies provide colony-level endpoints: significant effects (reductions in bees, brood) were observed after exposure to the two highest dose rates, colony loss occurred at the highest dose rate, but colonies were able to recover (2-3 brood cycles after the end of dosing) after dosing with 50 ng thiamethoxam/g sucrose. No significant colony-level effects were observed at lower dose rates. The data reported here support the conclusions of previous colony-level crop-based field studies with thiamethoxam, in which residues in pollen and nectar were an order of magnitude below the colony-level NOEC of 37.5 ng thiamethoxam/g sucrose. The feeding study data are also compared to the outcomes of regulatory Tier 1 risk assessments conducted using guidance provided by the USA, Canada, Brazil and the EU regulatory authorities. We propose an adaptation of the European chronic adult bee risk assessment that takes into account the full dataset generated in laboratory studies while still providing an order of magnitude of safety compared with the colony feeding study NOEC.

Clothianidin seed-treatment has no detectable negative impact on honeybee colonies and their pathogens

Interactions between multiple stressors have been implicated in elevated honeybee colony losses. Here, we extend our landscape-scale study on the effects of placement at clothianidin seed-treated oilseed rape fields on honeybees with an additional year and new data on honeybee colony development, swarming, mortality, pathogens and immune gene expression. Clothianidin residues in pollen, nectar and honeybees were consistently higher at clothianidin-treated fields, with large differences between fields and years. We found large variations in colony development and microbial composition and no observable negative impact of placement at clothianidin-treated fields. Clothianidin treatment was associated with an increase in brood, adult bees and Gilliamella apicola (beneficial gut symbiont) and a decrease in Aphid lethal paralysis virus and Black queen cell virus - particularly in the second year. The results suggest that at colony level, honeybees are relatively robust to the effects of clothianidin in real-world agricultural landscapes, with moderate, natural disease pressure.

Honey bee colony-level exposure and effects in realistic landscapes: An application of BEEHAVE simulating clothianidin residues in corn pollen

Discerning potential effects of insecticides on honey bee colonies in field studies conducted under realistic conditions can be challenging because of concurrent interactions with other environmental conditions. Honey bee colony models can control exposures and other environmental factors, as well as assess links among pollen and nectar residues in the landscape, their influx into the colony, and the resulting exposures and effects on bees at different developmental stages. We extended the colony model BEEHAVE to represent exposure to the insecticide clothianidin via residues in pollen from treated cornfields set in real agricultural landscapes in the US Midwest. We assessed their potential risks to honey bee colonies over a 1-yr cycle. Clothianidin effects on colony strength were only observed if unrealistically high residue levels in the pollen were simulated. The landscape composition significantly impacted the collection of pollen (residue exposure) from the cornfields, resulting in higher colony-level effects in landscapes with lower proportions of semi-natural land. The application of the extended BEEHAVE model with a pollen exposure-effects module provides a case study for the application of a mechanistic honey bee colony model in pesticide risk assessment integrating the impact of a range of landscape compositions. Environ Toxicol Chem 2019;38:423-435. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Endocrine disruption and chronic effects of plant protection products in bees: Can we better protect our pollinators?

Exposure to plant protection products (PPPs) is one of the causes for the population decline of pollinators. In addition to direct exposure, pollinators are exposed to PPPs by pollen, nectar and honey that often contain residues of multiple PPPs. While in legislation PPPs are regarded mainly for their acute toxicity in bees, other effects such as neurotoxicity, immunotoxicity, behavioural changes, stress responses and chronic effects that may harm different physiologically and ecologically relevant traits are much less or not regarded. Despite the fact that endocrine disruption by PPPs is among key effects weakening survival and thriving of populations, pollinators have been poorly investigated in this regard. Here we summarize known endocrine disruptive effects of PPPs in bees and compare them to other chronic effects. Endocrine disruption in honey bees comprise negative effects on reproductive success of queens and drones and behavioural transition of nurse bees to foragers. Among identified PPPs are insecticides, including neonicotinoids, fipronil, chlorantraniliprole and azadirachtin. So far, there exists no OECD guideline to investigate possible endocrine effects of PPPs. Admittedly, investigation of effects on reproduction success of queens and drones is rarely possible under laboratory conditions. But the behavioural transition of nurse bees to foragers could be a possible endpoint to analyse endocrine effects of PPPs under laboratory conditions. We identified some genes, including vitellogenin, which regulate this transition and which may be used as biomarkers for endocrine disruptive PPPs. We plea for a better implementation of the adverse outcome pathway concept into bee's research and propose a procedure for extending and complementing current assessments, including OECD guidelines, with additional physiological and molecular endpoints. Consequently, assessing potential endocrine disruption in pollinators should receive much more relevance.

The effects of iprodione fungicide on survival, behavior, and brood development of honeybees (Apis mellifera L.) after one foliar application during flowering on mustard

A semifield study to assess the effects of iprodione on honeybees at label use rates was conducted on a bloom mustard crop. The present study followed the Organisation for Economic Co-operation and Development guideline 75 tunnel test and consisted of 3 groups: the iprodione-treated group, the untreated control group, and the toxic reference item group. In addition to the tunnels used for biological assessments, a tunnel was set up in the treatment and control groups to determine the level of residues in flowers, nectar, and pollen. The major endpoints to assess the effects of the application of iprodione were mortality, flight intensity, behavior, condition of the colonies, and development of the brood. Residue analysis showed that honeybees were exposed to significant residues of iprodione. However, no adverse effects were observed on overall mortality, flight intensity, behavior, or brood development of honeybees compared to control. It is concluded that iprodione does not adversely affect the health of honeybees when applied in agriculture at commercially relevant rates in a worst-case exposure scenario. Environ Toxicol Chem 2018;37:3086-3094. © 2018 SETAC.