Nectar Solutions Research Articles

Interaction of Capnodium alfenasii with extrafloral nectaries of Azadirachta indica.

Sooty moulds are saprophytic epiphytic fungi that grow mostly on insect secretions, but they can also be associated with plant secretions. In this study, we aimed to describe de interaction of Capnodium alfenasii sooty mould with the extrafloral shoot nectaries of Azadirachta indica. Anatomical and histochemical studies were carried out on serial sections of extrafloral shoot nectaries of A. indica without and with C. alfenasii infestation. The total soluble sugar content of the secreted nectar was determined, and the conidial germination of the fungus in distilled water and in dextrose and nectar solutions was evaluated. The shoot nectaries of A. indica are elongated structures that occur in pairs near the base of the petiole. The exuded nectar contains an average of 534.8µg of total soluble sugars per µL of nectar and provides ideal conditions for conidial germination and fungal growth. C. alfenasii hyphae grow on the nectary, penetrate through breaks in the cuticle, travel under the cuticle and penetrate the secretory tissue by inter- and intracellular routes. The present report is the first to describe the interaction of C. alfenasii with the A. indica nectary, including the penetration of hyphae into nectariferous tissues and the plant defence mechanisms.

Plant secondary metabolite has dose‐dependent effects on bumblebees

The presence of secondary metabolites in flower nectar can mediate interactions between plants, pollinators, herbivores, and microbes. Milkweeds range in concentrations of cardenolides in flower nectar from ~ 1 to 100 ng μl–1. Using three different behavioral assays with bumblebees Bombus impatiens, we examined the impacts of the commercially available cardenolide ouabain at the range of concentrations at which cardenolides naturally occur in milkweeds. We show that after four days of exposure bees in consumption assays drank more of a nectar solution with a low ouabain concentration of 10 ng μl–1 than the control sucrose nectar, and over the course of the experiment bees consumed less of the 100 ng μl–1 ouabain solution than the control. Bee activity levels in Petri dish arena assays were not impacted by ouabain consumption, even at the highest concentrations; however, in free‐flying choice assays, bees preferentially visited artificial flowers containing 10 ng μl–1 ouabain more than flowers with sucrose control, or flowers with 100 ng μl–1 of ouabain. We therefore conclude that cardenolides may provide plants advantages to pollination at the low end of the naturally occurring range of concentrations for cardenolides, but may be costly to plants at the high end of the range. This research highlights that secondary metabolites in nectar may be under selection to be maintained at low concentrations, and species with high concentrations of secondary metabolites may be under conflicting selection pressures to maintain high circulating levels to deter herbivores at the cost of reduced pollination.

Adult monarch butterflies show high tolerance to neonicotinoid insecticides

Abstract Numerous studies have documented the negative effects of neonicotinoids on bees; it remains crucial to examine how neonicotinoids affect other non‐target nectar‐feeding insects, such as the monarch butterfly, Danaus plexippus. Wildflowers growing near agricultural areas can be contaminated with neonicotinoids that affect survival or cause sublethal changes to behaviours of nectar‐feeding insects. Nectar residues of imidacloprid and clothianidin found in milkweeds and wildflowers adjacent to agricultural field range from 0 to 72.8 ng/mL. At field‐relevant doses, two neonicotinoids (imidacloprid and clothianidin) were studied for their effects on adult monarch survival, reproduction, flight and behaviour. First, we fed adult monarchs artificial nectar solutions ranging from 15 to 386 ng/mL of imidacloprid and 19 to 531 ng/mL of clothianidin. Neonicotinoid ingestion slightly reduced monarch reproduction but had no significant effects on survival, weight change, or activity levels. Second, we fed monarchs higher clothianidin doses (909 and 4030 ng/mL), that exceed field‐relevant levels by 22 and 99 times. These higher doses reduced monarch nectar consumption, survival, flight performance and reaction time in response to a drop test. Results show that adult monarchs tolerate field‐relevant doses as high as 54 ng/mL for imidacloprid and 75 ng/mL for clothianidin, with minimal lethal or sub‐lethal effects until much higher doses are supplied. We conclude that adult monarchs are more tolerant of ingested clothianidin and imidacloprid than indicated by previous research.

Eat, Drink, Live: Foraging behavior of a nectarivore when relative humidity varies but nectar resources do not

To meet energetic and osmotic demands, animals make dynamic foraging decisions about food quality and quantity. In the wild, foraging animals may be forced to consume a less preferred or sub-optimal food source for long periods of time. Few choice feeding assays in laboratory settings approximate such contingencies. In this study the foraging behaviors of the hawkmoth Manduca sexta were measured when adult moths were placed within different relative humidity (RH) environments (20%, 40%, 60% and 80% RH) and provided with only one of the following experimental nectars: 0% (water), 12% or 24 % w/V sucrose solutions. Overall, ambient humidity influenced survivorship and foraging behaviors. Moth survivorship increased at higher ambient humidity regardless of experimental nectar. Moths that had access to experimental nectar imbibed large volumes of fluid regardless of what nectar was offered when placed at the lowest humidity (20% RH). However, when placed at the highest humidity (80% RH), moths imbibed higher volumes of fluid when given access to experimental nectar with sucrose in comparison with water. RH also influenced daily foraging behaviors: peak nectar consumption occurred earlier at lower RH levels. Consistent with previous studies in which moths could choose among nectar solutions, total energy intake was not affected by ambient RH under no-choice conditions. However, the proportion of time spent foraging and total energy consumption were significantly reduced across all RH levels in no-choice assays, when compared with previous studies of choice assays under the same conditions. Our results show that even when M. sexta moths are presented with limited options, they can alter their foraging behavior in response to environmental changes, enabling them to meet osmotic and/or energetic demands.

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

Associative learning of non-sugar nectar components: amino acids modify nectar preference in a hawkmoth.

ABSTRACTThe nearly ubiquitous presence of amino acids in the nectar of flowering plants has led to significant interest in the relevance of these compounds to pollinator behavior and physiology. A number of flower-visiting animals exhibit behavioral preferences for nectar solutions containing amino acids, but these preferences vary by species and are often context or condition dependent. Furthermore, the relative strength of these preferences and potential influence on the foraging behavior of flower-visiting animals remains unclear. Here, we used innate preference tests and associative learning paradigms to examine the nectar preferences of the flower-visiting hawkmoth Manduca sexta, in relation to both sugar and amino acid content. Manduca sexta exhibited a strong preference for higher sucrose concentrations, while the effect of amino acids on innate feeding preference was only marginally significant. However, with experience, moths were able to learn nectar composition and flower color associations and to forage preferentially (against innate color preference) for nectar with a realistic amino acid composition. Foraging moths responding to learned color cues of nectar amino acid content exhibited a behavioral preference comparable to that observed in response to a 5% difference in nectar sucrose concentration. These results demonstrate that experienced foragers may assess nectar amino acid content in addition to nectar sugar content and caloric value during nectar-foraging bouts.

Retrospective study on admission trends of Californian hummingbirds found in urban habitats (1991-2016).

BackgroundHummingbirds are frequently presented to California wildlife rehabilitation centers for medical care, accounting for approximately 5% of overall admissions. Age, sex, and reason for admission could impact hummingbird survivability, therefore identification of these factors could help maximize rehabilitation efforts.MethodsMixed-effects logistic regression models were used to identify specific threats to the survival of 6908 hummingbirds (1645 nestlings and 5263 non-nestlings) consisting of five species (Calypte anna, Calypte costa, Selasphorus rufus, Selasphorus sasin, Archilochus alexandri), found in urban settings, and admitted to California wildlife rehabilitation centers over 26 years.ResultsIn total, 36% of birds survived and were transferred to flight cage facilities for further rehabilitation and/or release. Nestlings were more likely to be transferred and/or released compared to adult hummingbirds. After accounting for age, birds rescued in spring and summer were twice as likely to be released compared to birds rescued in the fall. A high number of nestlings were presented to the rehabilitation centers during spring, which coincides with the nesting season for hummingbirds in California, with the lowest number of nestlings presented in fall. Reasons for presentation to rehabilitation centers included several anthropogenic factors such as window collisions (9.6%) and interactions with domesticated animals (12.9%). Survival odds were lower if a hummingbird was rescued in a “torpor-like state” and were higher if rescued for “nest-related” reasons. Evaluation of treatment regimens administered at wildlife rehabilitation centers identified supportive care, including providing commercial nutrient-rich nectar plus solution, to significantly increase hummingbird survivability.DiscussionOur results provide evidence of threats to hummingbirds in urban habitats, based on reasons for rescue and presentation to rehabilitation centers. Reasons for hummingbird admissions to three California wildlife rehabilitation centers were anthropogenic in nature (i.e., being associated with domestic animals, window collisions, and found inside a man-made structure) and constituted 25% of total admissions. There was a clear indication that supportive care, such as feeding a commercial nectar solution, and medical treatment significantly increased the odds of survival for rescued hummingbirds.

Microbial metabolites elicit distinct olfactory and gustatory preferences in bumblebees.

Animals such as bumblebees use chemosensory cues to both locate and evaluate essential resources. Increasingly, it is recognized that microbes can alter the quality of foraged resources and produce metabolites that may act as foraging cues. The distinct nature of these chemosensory cues however and their use in animal foraging remain poorly understood. Here, we test the hypothesis that species of nectar-inhabiting microbes differentially influence pollinator attraction and feeding via microbial metabolites produced in nectar. We first examined the electrophysiological potential for bumblebee (Bombus impatiens) antennal olfactory neurons to respond to microbial volatile organic compounds (mVOCs), followed by an olfactory preference test. We also assessed gustatory preferences for microbial-altered nectar through both no-choice and choice feeding assays. Antennal olfactory neurons responded to some mVOCs, and bees preferred nectar solutions inoculated with the bacterium Asaia astilbes over the yeast Metschnikowia reukaufii based on volatiles alone. However, B. impatiens foragers consumed significantly more Metschnikowia-inoculated nectar, suggesting distinct roles for mVOCs and non-volatile metabolites in mediating both attraction and feeding decisions. Collectively, our results suggest that microbial metabolites have significant potential to shape interspecific, plant-pollinator signalling, with consequences for forager learning, economics and floral host reproduction.

Sex-Dependent Variation of Pumpkin (Cucurbita maxima cv. Big Max) Nectar and Nectaries as Determined by Proteomics and Metabolomics.

Nectar is a floral reward that sustains mutualisms with pollinators, which in turn, improves fruit set. While it is known that nectar is a chemically complex solution, extensive identification and quantification of this complexity has been lacking. Cucurbita maxima cv. Big Max, like many cucurbits, is monoecious with separate male and female flowers. Attraction of bees to the flowers through the reward of nectar is essential for reproductive success in this economically valuable crop. In this study, the sex-dependent variation in composition of male and female nectar and the nectaries were defined using a combination of GC-MS based metabolomics and LC-MS/MS based proteomics. Metabolomics analysis of nectar detected 88 metabolites, of which 40 were positively identified, and includes sugars, sugar alcohols, aromatics, diols, organic acids, and amino acids. There are differences in 29 metabolites between male and female nectar. The nectar proteome consists of 45 proteins, of which 70% overlap between nectar types. Only two proteins are unique to female nectar, and 10 are specific to male nectar. The nectary proteome data, accessible at ProteomeXchange with identifier PXD009810, contained 339 identifiable proteins, 71% of which were descriptively annotatable by homology to Plantae. The abundance of 45 proteins differs significantly between male and female nectaries, as determined by iTRAQ labeling. This rich dataset significantly expands the known complexity of nectar composition, supports the hypothesis of H+-driven nectar solute export, and provides genetic and chemical targets to understand plant–pollinator interactions.

Optimization of soymilk, mango nectar and sucrose solution mixes for better quality of soymilk based beverage [pdf

Optimization of soymilk, mango nectar and sucrose solution mixes for better quality of soymilk based beverage [pdf

Acute, Fatal, Presumptive Xylitol Toxicosis in Cape Sugarbirds ( Promerops cafer).

Twenty-nine wild Cape sugarbirds ( Promerops cafer) died acutely after ingestion of a homemade xylitol nectar solution from a bird feeder. The most aggressive feeders were first affected. Most birds showed clinical signs within 15 minutes of nectar ingestion, including incoordination, weakness, falling from perches, collapse, and death. A few birds showing clinical signs seemed to spontaneously recover and fly away. Full necropsy examinations done on 27 birds were hampered by freezing artifact and autolysis, but results indicated death was caused by the consequences of acute hypoglycemia. A presumptive diagnosis of xylitol toxicity was made based on the history, clinical signs, and absence of other obvious causes of death. This is potentially the first record of xylitol toxicity in wild birds.

Is Protein Content in the Diet of Wahlberg's Epauletted Fruit Bats,Epomophorus wahlbergi, Important?

Wahlberg's epauletted fruit bat, Epomophorus wahlbergi, feeds on a range of fruit, nectar, pollen and flowers. Frugivores may have difficulties in maintaining their protein requirements since fruit are generally high in sugar content but low in protein content. Some studies have found that fruit bats obtain most of their food protein when feeding on a variety of fruits. We investigated if E. wahlbergi prefers additional protein to sugar-only nectar solutions. They were offered equicaloric 15% glucose solutions with varying protein concentrations (2.58, 5.68, 7.23 g soy protein/kg H2O) and a solution with no protein. This was repeated using 15% sucrose instead of glucose solutions. Epomophorus wahlbergi's volumetric intake of the respective glucose and sucrose solutions varied among individual bats, with total volumetric intake being highest for solutions with no protein. This suggests they have low protein dietary requirements, which may be a response to the low-protein fruit available in the wild. Alternatively they may supplement their diet by actively preying on insects, but this needs to be investigated.

Is protein content in the diet of Wahlberg’s epauletted fruit bats, Epomophorus wahlbergi, important?

Wahlberg’s epauletted fruit bat, Epomophorus wahlbergi, feeds on a range of fruit, nectar, pollen and flowers. Frugivores may have difficulties in maintaining their protein requirements since fruit are generally high in sugar content but low in protein content. Some studies have found that fruit bats obtain most of their food protein when feeding on a variety of fruits. We investigated if E. wahlbergi prefers additional protein to sugar-only nectar solutions. They were offered equicaloric 15% glucose solutions with varying protein concentrations (2.58, 5.68, 7.23 g soy protein/kg H2O) and a solution with no protein. This was repeated using 15% sucrose instead of glucose solutions. Epomophorus wahlbergi’s volumetric intake of the respective glucose and sucrose solutions varied among individual bats, with total volumetric intake being highest for solutions with no protein. This suggests they have low protein dietary requirements, which may be a response to the low-protein fruit available in the wild. Alternatively they may supplement their diet by actively preying on insects, but this needs to be investigated.

The systematic significance of floral morphology, nectaries, and nectar concentration in epiphytic cacti of tribes Hylocereeae and Rhipsalideae (Cactaceae)

A long-standing interest in cactus taxonomy has existed since the Linnaean generation, but an appreciation of the reproductive biology of cacti started early in the 1900s. Numerous studies indicate that plant reproductive traits provide valuable systematic information. Despite the extensive reproductive versatility and specializations in breeding systems coupled with the striking floral shapes, the reproductive biology of the Cactaceae has been investigated in approximately 10% of its species. Hence, the systematic value of architectural design and organization of internal floral parts has remained virtually unexplored in the family. This study represents the most extensive survey of flower and nectary morphology in the Cactaceae focusing on tribes Hylocereeae and Rhipsalideae (subfamily Cactoideae). Our objectives were (1) to conduct comparative morphological analyses of flowers and floral nectaries and (2) to compare nectar solute concentration in these two tribes consisting of holo- and semi-epiphytic species. Flower morphology, nectary types, and sugar concentration of nectar have strong taxonomic implications at the tribal, generic and specific levels. Foremost, three types of nectaries were found, namely chamber nectary (with the open and diffuse subtypes), furrow nectary (including the holder nectary subtype), and annular nectary. All Hylocereeae species possess chamber nectaries, in which the nectarial tissue has both trichomes and stomata. The Rhipsalideae are distinguished by two kinds of floral nectaries: furrow and annular, both nectary types with stomata only. The annular nectary type characterizes the genus Rhipsalis. Nectar concentration is another significant taxonomic indicator separating the Hylocereeae and Rhipsalideae and establishing trends linked to nectar sugar concentration and amount of nectar production in relation to flower size. There is an inverse relationship between flower size and amount of nectar production in the smaller Rhipsalideae flowers, in which nectar concentration is more than two-fold higher despite the smaller volume of nectar produced when compared to the large Hylocereeae flowers. Variability of nectary morphology and nectar concentration was also evaluated as potential synapomorphic characters in recent phylogenies of these tribes. In conclusion, our data provide strong evidence of the systematic value of floral nectaries and nectar sugar concentration in the Cactaceae, particularly at different taxonomic levels in the Hylocereeae and Rhipsalideae.

Why do ants shift their foraging from extrafloral nectar to aphid honeydew?

AbstractWhen aphids parasitize plants with extrafloral nectaries (EFNs) and aphid colony size is small, ants frequently use EFNs but hardly tend aphids. However, as the aphid colony size increases, ants stop using EFNs and strengthen their associations with aphids. Although the shift in ant behavior is important for determining the dynamics of the ant–plant–aphid interaction, it is not known why this shift occurs. Here, we test two hypotheses to explain the mechanism responsible for this behavioral shift: (1) Extrafloral nectar secretion changes in response to aphid herbivory, or (2) plants do not change extrafloral nectar secretion, but the total reward to ants from aphids will exceed that from EFNs above a certain aphid colony size. To judge which mechanism is plausible, we investigated secretion patterns of extrafloral nectar produced by plants with and without aphids, compared the amount of sugar supplied by EFNs and aphids, and examined whether extrafloral nectar or honeydew was more attractive to ants. Our results show that there was no inducible extrafloral secretion in response to aphid herbivory, but the sugar concentration in extrafloral nectar was higher than in honeydew, and more ant workers were attracted to an artificial extrafloral nectar solution than to an artificial aphid honeydew solution. These results indicate that extrafloral nectar is a more attractive reward than aphid honeydew per unit volume. However, even an aphid colony containing only two individuals can supply a greater reward to ants than EFNs. This suggests that the ant behavioral shift may be explained by the second hypothesis.

The effects of aluminum and nickel in nectar on the foraging behavior of bumblebees

Metals in soil are known to negatively affect the health of many groups of organisms, but it is unclear whether they can affect plant-pollinator interactions, and whether pollinators that visit plants growing on contaminated soils are at risk of ingesting potentially toxic resources. We address whether the presence of metals in nectar alters foraging behavior by bumblebees by manipulating nectar with one of two common soil contaminants (Al or Ni) in flowers of Impatiens capensis (Balsaminaceae). While the presence of Al in nectar did not influence foraging patterns by bumblebees, flowers containing Ni nectar solutions were visited for shorter time periods relative to controls, and discouraged bees from visiting nearby Ni-contaminated flowers. However, because bumblebees still visited these flowers, they likely ingested a potentially toxic resource. Our findings suggest that soil metals could cascade to negatively affect pollinators in metal contaminated environments.

Floral nectary structure, nectar production, and carbohydrate composition in theLiliumAsiatic hybrid ‘Trésor’

Floral nectary structure, nectar production, and carbohydrate composition were compared from petals (“inner tepals”) and sepals (“outer tepals”) of Lilium Asiatic hybrid ‘Trésor’ (Liliaceae). The six nectaries each occupied a narrow furrow bordered by two convergent ridges extending adaxially from the petal and sepal base. Each sepal nectary furrow was shorter and more concealed. In both nectary types, many vascular bundles comprising xylem and phloem supplied 5.5–8 layers of nectariferous parenchyma cells below the epidermis, which lacked stomata. Transmission electron microscopy of sepal nectaries demonstrated that parts of the outer epidermal wall adhered to an intact but uplifted cuticle in nectar-secreting flowers. Both apoplastic and symplastic routes were continuous from the vascular bundles to the nectary epidermis. Starch breakdown from amyloplasts throughout the nectary likely augmented nectar production. Nectar solute concentration from another Asiatic hybrid, ‘Orange Pixie’, was also significantly higher in petals. In ‘Trésor’, significantly more nectar was available from sepals, possibly reflecting reduced evaporation from multiple nectar droplets within the covered nectary furrow. However, for both hybrids, the same quantity of nectar sugar was produced by petals and sepals. Nectar composition from petals and sepals also was alike, in ‘Orange Pixie’ averaging 67/19/14 (= sucrose/fructose/glucose) and 59/25/17, respectively, and in ‘Trésor’ averaging 68/23/10 and 62/27/12, respectively.

The influence of the nature of soil and plant and pollution on the 238U, 232Th, 222Rn and 220Rn concentrations in various natural honey samples using nuclear track detectors: Impact on the adult consumers

238U and 232Th concentrations as well as 222Rn and 220Rn α-activities per unit volume were measured in various natural honey samples collected from different regions in Morocco using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). These radionuclides were also measured in soils, plant flowers and nectar solutions corresponding to the honey samples studied. In addition, these radionuclides were measured in different imported honey samples. The measured 238U, 232Th, 222Rn and 220Rn concentrations ranged from (1.5±0.1) mBq kg−1 to (10.6±0.6) mBq kg−1, (1.1±0.1) mBq kg−1 to (4.2±0.2) mBq kg−1, (1.5±0.1) Bq kg−1 to (10.6±0.6) Bq kg−1 and (1.1±0.1) Bq kg−1 to (4.2±0.2) Bq kg−1 for the honey samples studied, respectively. Annual 238U, 232Th and 222Rn intakes by Moroccan adults from the consumption of honey were assessed. The influence of the nature of soil and plant on the 238U and 232Th contents of the studied honey samples was investigated. These measurements were completed by an investigation of the 238U and 232Th transfer between soils and plant flowers and that between plant flowers and honey, and also by the investigation of the influence of pollution due to different material dusts on 238U, 232Th and 222Rn in the honey samples studied. Committed equivalent doses due to the annual intake of 238U, 232Th and 222Rn were evaluated in the organs of adult members of the Moroccan rural population from the ingestion of the honey samples. The maximum total committed effective dose due to 238U, 232Th and 222Rn from the ingestion of natural honey by the Moroccan rural population was found to be equal to 0.64 µ Sv y−1.

Field methods for sampling and storing nectar from flowers with low nectar volumes

Although several methods of sampling and storing floral nectar are available, little information exists on sampling and storing nectar from flowers with low nectar volumes. Methods for sampling and storing nectar from the flowers of species with low floral nectar volumes (<1 microL) were investigated using the flowers of Eucalyptus species. Sampling with microcapillary tubes, blotting up with filter paper, washing and rinsing were compared to determine masses of sugars recovered and differences in sugar ratios. Storage methods included room temperature, refrigeration and freezing treatments; the addition of antimicrobial agents benzyl alcohol or methanol to some of these treatments was also evaluated. Nectar samples were analysed using high-performance liquid chromatography and the masses of sucrose, glucose and fructose in each sample were determined. Masses of sugars varied significantly among sampling treatments, but the highest yielding methods, rinsing and washing, were not significantly different. A washing time of 1 min was as effective as one of 20 min. Storage trials showed that the sugar concentration measurements of nectar solutions changed rapidly, with the best results achieved for refrigeration with no additive (sucrose and fructose were stable for at least 2 weeks). Sugar ratios, however, remained relatively stable in most treatments and did not change significantly across 4 weeks for the methanol plus refrigerator and freezing treatments, and 2 weeks for the refrigeration treatment with no additive. Washing is recommended for nectar collection from flowers with low nectar volumes in the field (with the understanding that one wash underestimates the amounts of sugars present in a flower), as is immediate analysis of sugar mass. In view of the great variation in results depending on nectar collection and storage methods, caution should be exercised in their choice, and their accuracy should be evaluated. The use of pulsed amperometric detection, more specific than refractive index detection, may improve the accuracy of nectar sugar analysis.

222RN and 220RN concentrations measured in various natural honey samples by using nuclear track detectors and resulting radiation doses to the members of the rural populations in Morocco

Radon (222Rn) and thoron (220Rn) concentrations were measured in sixteen natural honey material samples collected from different regions in Morocco by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). The concentrations of these radionuclides were also measured in nectar solutions corresponding to the studied honey samples. The measured concentrations of 222Rn and 220Rn in honey samples ranged from (2.3 +/- 0.2) to (8.1 +/- 0.6) Bq.l(-1) and (1.8 +/- 0.1) to (3.9 +/- 0.3) Bq.l(-1), respectively. Committed equivalent doses due to annual intakes of 222Rn were evaluated in the human gastrointestinal tract compartments of adult members of the Moroccan populations from the ingestion of studied honey samples. The influence of the target tissue mass and activities due to 222Rn on the annual committed equivalent doses in the compartments of the human gastrointestinal tract was investigated.