Pollination Ecology and Effect of Nectar Removal in Macleania bullata (Ericaceae)1

The floral syndrome of Macleania bullataYeo (Ericaceae) reflects its adaptation to hummingbird pollination. Its flowers, however, are subject to high levels of nectar robbing. I examined the floral visitor assemblage of M. bullata in a tropical montane wet forest in southwestern Colombia, focusing on the behavior of the visitors. I also tested for the presence of nocturnal pollination and the effects of nectar removal on new nectar production. The principal floral visitors were the nectar robbing hummingbirds Ocreatus underwoodii (19.1% of visits) and Chlorostilbon mellisugus (18.9%). Only two species of long–billed hummingbirds visited the flowers of M. bullata as “legitimate” pollinators: Coeligena torquata (14.7% of visits) and Doryfera ludoviciae (14.3%). The remaining visits constituted nectar robbing by bees, butterflies, and other species of hummingbirds. Nocturnal pollination took place, although fruit set levels were 2.4 times higher when only diurnal pollination was allowed as opposed to exclusively nocturnal pollination. Nectar robbers removed floral nectar without pollinating the flower. Treatments of experimental nectar removal were carried out to examine if flowers synthesize more nectar after nectar removal. Nectar removal increased the total volume of nectar produced by each flower without affecting sugar concentration. Thus, nectar robbing can impose a high cost to the plants by forcing them to replace lost nectar.     

Floral traits variation, legitimate pollination, and nectar robbing in Polygala vayredae (Polygalaceae)

The variation of floral morphology and its effect on the flower visitors of Polygala vayredae Costa (Polygalaceae), a narrow endemic species from the Oriental pre-Pyrenees, were examined. First, to account for the main floral reward (i.e., nectar), the relationship between the dimensions of the nectar gland and nectar production was investigated. Second, floral traits variation was assessed within and between the three most representative populations of the species. Finally, the role of several floral traits in the female fitness was evaluated. Furthermore, as nectar robbing was highly frequent, preferences of robbers for specific floral traits and their impact on legitimate pollinations were also evaluated. The flowers of this species are characterized by significant variations in floral characteristics and nectar rewards. A significant and positive correlation between the nectar gland dimensions and nectar production per flower was observed, with the gland dimensions being a good measure to infer the rewards offered by the flowers of P. vayredae. In general, corolla traits were significant and positively correlated with each other. Nectar was revealed to be an important trait in flower–visitor interactions, with legitimate pollinations being primarily influenced by this floral reward. Negative correlations between robbing frequency and legitimate pollinations were observed in two of the studied populations, and positive correlations between flower size and robbing frequency were observed in one population. An indirect negative selection over phenotypic floral traits mediated by nectar robbers is proposed.     

Patterns and implications of floral nectar secretion, chemical composition, removal effects and standing crop in Mandevilla pentlandiana (Apocynaceae)

Flower morphology, nectar features (chemical composition, production pattern, removal effects, and standing crop) and floral visitors are analysed in an Argentine population of Mandevilla pentlandiana. Nectar variability was examined during the lifetime of a single flower, over the course of the flowering season, and at different times of the day. Nectar is sucrose dominant. There were some variations in the proportions of sugar throughout both the flower lifespan and the flowering season. Flowers produced most nectar during bud-stage. Nectar secretion ceased near the end of the first day after flower opening. Nectar quantity varied as a function of flower age due to a combination of nectar secretion, cessation, and resorption periods. Overall sugar production was increased by nectar removal. Standing crop data showed that each open flower and inflorescence offers c. 2 and 11 mg of sugar respectively at any time of the flowering season. There was higher nectar availability at the beginning of the flowering season compared with the rest of the period. Flowers were visited by bumblebees, honeybees and hummingbirds. The greater the number of open flowers and the nectar variance, the more the mean reward quantity per flower available in the inflorescence. The sources of nectar variability in M. pentlandiana seem to be linked with both the female function (nectar resorption, nectar cessation) and the male one (early and comparatively large nectar availability, variation in nectar production as the flower ages, nectar secretion stimulation by nectar removals).     

Floral biology and pollinators of Trichocereus pasacana (Cactaceae) in Parque Nacional Los Cardones, Argentina]

Many columnar cacti are bat pollinated. It has been suggested that this kind of pollination would be more important in tropical than in temperate regions where flowers are open only one night. Thrichocereus pasacana produces big and resistant white flowers. We analyzed flower characteristics, floral cycle, stigmatic receptivity, nectar production, pollen presence and floral visitors in a T. pasacana population at National Park Los Cardones (Salta, Argentina) in November 1997. Flower features were constant between individuals of the population. Flowers start opening at evening and anthesis time is from 18 to 40 hs. The estigma was receptive throughout the floral cycle. Anther dehiscence occurs with flower opening. Nectar production was highest between 18 to 24 hs. Although T. pasacana are open during the night, floral visitors are diurnal. The most frequent was Xylocopa sp. In the study area, nectarivorous bats were not detected. The morphological features of T. pasacana flowers were similar but bigger compared to other columnar cacti. Anthesis time was also longer while nectar production was lower. T. pasacana pollination at National Park Los Cardones is done by bees.     

Are Nectar Sugar Composition and Corolla Tube Length Related to the Diversity of Insects that Visit Asteraceae Flowers?

Abstract: In this work, we analysed interspecific variation in nectar sugar composition, corolla tube length, and the diversity of floral visitors of 35 Asteraceae species. The potential correlations between these variables could arise either as a result of selection to improve pollinator attractiveness or simply as a consequence of phylogenetic constraints. Samples of nectar and flowers, and data on floral visitors, were obtained from living plants in natural populations from Argentina. Asteraceae species showed a large variability in corolla tube length. Nectar of most species presented a larger proportion of hexoses than sucrose. All species were visited by numerous insects belonging to 2 different orders. Results showed that floral traits are not significantly correlated with the diversity of floral visitors. These characters seem to be linked to the phylogeny of the species. Early branching species (species phylogenetically close to the root of the Asteraceae tree) tend to have longer corollas, higher sucrose proportions and lesser diversity of floral visitors than late branching species. Considering that longer corolla tubes and higher nectar sucrose percentages may indicate some specialization in the pollination system, we suggest that there is an evolutionary tendency toward generalist pollination systems within the family.     

Beyond the pollination syndrome: nectar ecology and the role of diurnal and nocturnal pollinators in the reproductive success of Inga sessilis (Fabaceae)

Inga species present brush‐type flower morphology allowing them to be visited by distinct groups of pollinators. Nectar features in relation to the main pollinators have seldom been studied in this genus. To test the hypothesis of floral adaptation to both diurnal and nocturnal pollinators, we studied the pollination ecology of Inga sessilis, with emphasis on the nectar secretion patterns, effects of sequential removals on nectar production, sugar composition and the role of diurnal and nocturnal pollinators in its reproductive success. Inga sessilis is self‐incompatible and pollinated by hummingbirds, hawkmoths and bats. Fruit set under natural conditions is very low despite the fact that most stigmas receive polyads with sufficient pollen to fertilise all ovules in a flower. Nectar secretion starts in the bud stage and flowers continually secreting nectar for a period of 8 h. Flowers actively reabsorbed the nectar a few hours before senescence. Sugar production increased after nectar removal, especially when flowers were drained during the night. Nectar sugar composition changed over flower life span, from sucrose‐dominant (just after flower opening, when hummingbirds were the main visitors) to hexose‐rich (throughout the night, when bats and hawkmoths were the main visitors). Diurnal pollinators contributed less than nocturnal ones to fruit production, but the former were more constant and reliable visitors through time. Our results indicate I. sessilis has floral adaptations, beyond the morphology, that encompass both diurnal and nocturnal pollinator requirements, suggesting a complementary and mixed pollination system.     

Nectar ecology of Datura ferox (Solanaceae): an invasive weed with nocturnal flowers in agro-ecosystems from central Argentina

Plant–pollinator interactions provide highly important ecological functions, and are influenced by floral nectar characteristics. The night blooming Datura ferox is an excellent model to test general hypotheses on the relationship between nectar traits (e.g., nectar secretion patterns, nectar chemical composition), pollinators and reproductive success for invasive, weedy species in highly modified ecosystems as crop fields. We hypothesized an adjustment between nectar composition and secretion dynamics through flower anthesis and the activity and requirements of nocturnal pollinators. Nectar chemical analyses showed low quantities of amino acids and lipids, phenolics, and alkaloids were not detected. D. ferox showed sucrose-dominant nectar with comparable amount of hexoses. Sugar proportions did not vary between populations or during flowering season. Most nectar is secreted before flower opening. Nectar resorption was detected at the end of anthesis. Experimentally drained flowers of both populations increased nectar production up to 50 % in the total amount of sugar per flower compared to control flowers. Nectar standing crop was relatively constant during the flowering season, but differences were detected between populations. Nectar traits of D. ferox would be favoring cross-pollination and maintaining seed production of this weed, since recently open flowers display a higher amount of nectar and they can renew nectar after a pollinator visit or reabsorb it at the end of anthesis. This nectar source may be important for native pollinators considering that human-induced forest fragmentation is related with the impoverishment of native flora from agro-ecosystems.     

Reproductive biology, variability of nectar features and pollination of Combretum fruticosum (Combretaceae) in Argentina

Flower morphology, nectary structure, nectar features (chemical composition, secretion pattern, standing crop, removal effects) and flower visitors are analysed in an Argentinian population of Combretum fruticosum. The variability of these data was examined throughout the flower lifetime. Nectar is hexose dominant. Its chemical composition and concentration are constant for all flowering stageS. Nectar volume varies as a function of flower age due to a combination of nectar secretion, cessation and resorption periods. The overall sugar production is decreased by nectar removal. The plant is self-incompatible and xenogamouS. Only 16.2% of the flowers set seedS. Inflorescences with green flowers were exclusively visited by two hummingbird and three perching bird species which transfer the pollen. A clear link was observed among nectar production pattern, standing crop of nectar, and visitors' behaviour.     

Nectar robbers deter legitimate pollinators by mutilating flowers

Nectar robbing – harvesting nectar illegitimately – can have a variety of outcomes for plant sexual reproduction and for the pollinator community. Nectar robbers can damage flowers while robbing nectar, which could affect the behavior of subsequent flower visitors and, consequently, plant reproduction. However, only nectar manipulation by nectar robbers has so far received attention. We found a short-tongued bee, Hoplonomia sp. (Halictidae), mutilating the conspicuous lower petal of the zygomorphic flowers of Leucas aspera (Lamiaceae) while robbing nectar. We hypothesized that the mutilation of the conspicuous lower petal deters legitimate pollinators on L. aspera flowers, which, in turn, might affect plant reproduction. We first assessed the proportion of naturally-robbed flowers in plant populations for three years to confirm that it was not a purely local phenomenon due to a few individual bees. We then studied diversity, community and visitation characteristics of pollinators, nectar dynamics and fruit set in unrobbed and robbed open flowers in naturally-robbed populations. The proportion of robbed flowers varied significantly across sites and years. Robbing did not affect nectar dynamics in flowers, but it did alter flower morphology, so much so that it reduced pollinator visitation and altered the pollinator community on robbed flowers. However, the maternal function of plant reproduction was not affected by nectar robbing. This study for the first time shows that a nectar robber can have an ecologically significant impact on floral morphology.     

Floral nectaries, nectar production dynamics and chemical composition in six ipomoea species (convolvulaceae) in relation to pollinators

BACKGROUND AND AIMS: Floral nectaries and nectar features were compared between six Argentinian Ipomoea species with differences in their pollinator guilds: I. alba, I. rubriflora, I. cairica, I. hieronymi var. hieronymi, I. indica, and I. purpurea. METHODS: Pollinators were recorded in natural populations. The morpho-anatomical study was carried out through scanning electron and light microscopy. Nectar sugars were identified via gas chromatography. Nectar production and the effect of its removal on total nectar sugar amount were determined by using sets of bagged flowers. KEY RESULTS: Hymenopterans were visitors of most species, while hummingbirds visited I. rubriflora and sphingids I. alba. All the species had a vascularized discoidal nectary surrounding the ovary base with numerous open stomata with a species-specific distribution. All nectar samples contained amino acids and sugars. Most species had sucrose-dominant nectars. Flowers lasted a few hours. Mean nectar sugar concentration throughout the lifetime of the flower ranged from 34.28 to 39.42 %, except for I. cairica (49.25 %) and I. rubriflora (25.18 %). Ipomoea alba had the highest nectar volume secreted per flower (50.12 microL), while in the other taxa it ranged from 2.42 to 12.00 microL. Nectar secretion began as soon as the flowers opened and lasted for a few hours (in I. purpurea, I. rubriflora) or it was continuous during the lifetime of the flower (in the remaining species). There was an increase of total sugar production after removals in I. cairica, I. indica and I. purpurea, whereas in I. alba and I. rubriflora removals had no effect, and in I. hieronymi there was a decrease in total sugar production. CONCLUSIONS: The chemical composition, production dynamics and removal effects of nectar could not be related to the pollinator guild of these species. Flower length was correlated with nectary size and total volume of nectar secreted, suggesting that structural constraints may play a major role in the determination of nectar traits of these species.     

盗蜜行为在植物繁殖生态学中的意义

在动植物的相互关系中,盗蜜行为被认为是一种不同于普通传粉者的非正常访花行为。动物之所以要采取这种特殊的觅食策略,有假说认为是由访花者的口器和植物的花部形态不匹配造成的,也有认为是盗蜜行为提高了觅食效率从而使盗蜜者受益。在盗蜜现象中,盗蜜者和宿主植物之间的关系是复杂的。盗蜜对宿主植物的影响尤其是对其繁殖适合度的影响归纳起来有正面、负面以及中性3类。与此同时,盗蜜者的种类, 性别及其掠食行为差异不仅与生境因素密切相关,而且会对宿主植物的繁殖成功产生直接或间接的影响。另外,盗蜜者的存在无疑对其它正常传粉者的访花行为也产生一定的影响,从而间接地影响宿主植物的繁殖成功, 而植物在花部形态上也出现了对盗蜜现象的适应性进化。作者认为, 盗蜜是短嘴蜂对长管型花最有效的一种掠食策略, 它不仅增加了盗蜜者对资源的利用能力, 而且由于盗蜜对宿主植物繁殖成功的不同的影响使其具有调节盗蜜者和宿主之间种群动态的作用, 两者的彼此适应是一种协同进化的结果。     

Nectar sugar composition and volumes of 47 species of Gentianales from a southern Ecuadorian montane forest

BACKGROUND AND AIMS: This study investigates 47 taxonomically related species (Gentianales), all native to a tropical montane forest in southern Ecuador, in terms of nectar chemistry and nectar volumes in relation to pollination biology. METHODS: Nectar volumes of covered (24-h production) and uncovered (standing crop) flowers were measured in the natural habitat. Sucrose, fructose and glucose were quantified in the nectar using high performance liquid chromatography. Flower visitors were observed. KEY RESULTS: Nectar sugar concentration did not differ significantly among the pollination syndromes. Regarding sugar composition, the only significant differences were found in chiropterophilous and myiophilous flowers, which had a significantly lower sugar ratio than sphingophilous flowers. A separation of chiropterophilous and myiophilous flowers from the other pollination syndromes is further substantiated by non-linear multidimensional scaling using the chord-normalized expected species shared index of dissimilarity based on nectar sugar compositions. The matrix test revealed no correlation of observed floral visitors to nectar concentrations; however, a weak significant correlation was found between floral visitors and nectar sugar compositions. The nectar volumes of covered and uncovered flowers are related to, and differ significantly among, pollination syndromes. Matrix tests revealed correlation between floral visitors and nectar volume of covered flowers and, to a lesser extent, of uncovered flowers. CONCLUSIONS: Sucrose is the predominant floral nectar sugar in the order Gentianales, suggesting that nectar sugar composition is a conservative characteristic. However, some degree of an adaptive convergence of floral nectar compositions to principal pollinator type within the constraints set by phylogenetic history is likely. The driving force to visitation appears to be the volume of nectar the visitor can expect to consume.     

Effects of nectar-robbing on plant reproduction and evolution

The relationship between plant and pollinator is considered as the mutualism because plant benefits from the pollinator's transport of male gametes and pollinator benefits from plant's reward.Nectar robbers are frequently described as cheaters in the plant-pollinator mutualism,because it is assumed that they obtain a reward (nectar) without providing a service (pollination).Nectar robbers are birds,insects,or other flower visitors that remove nectar from flowers through a hole pierced or bitten in the corolla.Nectar robbing represents a complex relationship between animals and plants.Whether plants benefit from the relationship is always a controversial issue in earlier studies.This paper is a review of the recent literatures on nectar robbing and attempts to acquire an expanded understanding of the ecological and evolutionary roles that robbers play.Understanding the effects of nectar robbers on the plants that they visited and other flower visitors is especially important when one considers the high rates of robbing that a plant population may experience and the high percentage of all flower visitors that nectar robbers make to some species.There are two standpoints in explaining why animals forage on flowers and steal nectar in an illegitimate behavior.One is that animals can only get food in illegitimate way because of the mismatch of the morphologies of animals'mouthparts and floral structure.The other point of view argues that nectar robbing is a relatively more efficient,thus more energy-saving way for animals to get nectar from flowers.This is probably associated with the difficulty of changing attitudes that have been held for a long time.In the case of positive effect,the bodies of nectar robbers frequently touch the sex organs of plants during their visiting to the flowers and causing pollination.The neutral effect,nectar robbers' behavior may destruct the corollas of flowers,but they neither touch the sex organs nor destroy the ovules.Their behavior does not affect the fruit sets or seed sets of the hosting plant.Besides the direct impacts on plants,nectar robbers may also have an indirect effect on the behavior of the legitimate pollinators.Under some circumstances,the change in pollinator behavior could result in improved reproductive fitness of plants through increased pollen flow and out-crossing.     

The relative strength of different floral visitors driving floral evolution within a <Emphasis Type="Italic">Primula secundiflora</Emphasis> population

Floral visitor assemblages within plant populations are usually composed of different visitors, and the relative abundance of these visitors also varies. Therefore, identifying the relative strength of these floral visitors driving floral evolution within the population is an important step in predicting the evolutionary trajectory of floral traits. Using supplemental hand pollination and nectar-robbing exclusion treatments, we experimentally identified the relative strengths of legitimate pollinators (that visit flowers through the corolla tube entrance) and nectar robbers (that visit flowers by biting a hole in the corolla tube or using an existing hole) driving floral evolution within the Primula secundiflora population. We also estimated legitimate pollinator- and nectar robber-mediated selection separately for pin and thrum flowers. Both legitimate pollinators and nectar robbers mediated selection on pollination efficiency traits in P. secundiflora population. Legitimate pollinators mediated selection for wider corolla tubes, whereas nectar robbers mediated selection for longer corolla tubes. In addition, nectar robber-mediated selection on corolla tube length marginally varied between the pin and thrum flowers. Nectar robber mediated selection for longer corolla tube length in the pin flowers not in the thrum flowers. These results indicate that legitimate pollinators and nectar robbers within a population can drive differential evolutionary trajectories of floral traits.     

Nectar Dynamics and Sugar Composition in Flowers of Silene and Saponaria Species (Caryophyllaceae)

Abstract: Nectar production in Saponaria officincilis and in five species of Silene (S. ciba, S. dioica, S. noctiflora, S. nutans, S. vulgaris ) was examined during two consecutive years (May to July 1993, and May to June 1994) in the Botanical Garden of the University of Giessen. Nectar volume and sugar concentration were studied in relation to time of day, flower sex, flower age, and flowering stage. Nectar amount in all species studied (except S. dioica ) increased in the afternoon or in the evening until midnight (or until the early morning in S. nutans ). After midnight and until midday, nectar volume in non-visited flowers (except S. dioica ) decreased. Nectar volume in non-visited S. dioica flowers increased constantly with flower age, indicating a stable nectar secretion rate, possibly favouring both day- and night-active flower visitors. Even at the time of highest nectar secretion, all species studied presented several nectarless flowers. Sucrose dominance in the nectar of the nocturnal species S. nutans and Saponaria officinalis fits well with the general syndrome of flowers pollinated by hawkmoths. The syndrome also applies to the nocturnal but regularly selfing, S. noctiflora . The more generalis-tic species S. dioica and S. vulgaris , which are regularly visited by bumblebees as well as nocturnal moths, secreted hexose-domi-nant nectar. Unexpectedly, Silene alba , the only nocturnal species that strictly excluded day-active flower visitors by closing flowers during the day, also secreted hexose-dominant nectar. In some cases, nectar volumes and nectar concentration differed significantly between hermaphroditic, male, and female flowers. Female flowers of S. alba, S. dioica , and S. nutans contained significantly less concentrated nectar than male or hermaphroditic ( S. nutans ) ones. In S. noctifiora and S. vulgaris the difference was not statistically significant but nectar concentration did show the same tendency.     

Micromorphological and histochemical attributes of flowers and floral reward in <Emphasis Type="Italic">Linaria vulgaris</Emphasis> (Plantaginaceae)

The self-incompatible flowers of Linaria vulgaris have developed a range of mechanisms for attraction of insect visitors/pollinators and deterrence of ineffective pollinators and herbivores. These adaptive traits include the flower size and symmetry, the presence of a spur as a “secondary nectar presenter,” olfactory (secondary metabolites) and sensual (scent, flower color, nectar guide—contrasting palate) signals, and floral rewards, i.e. pollen and nectar. Histochemical tests revealed that the floral glandular trichomes produced essential oils and flavonoids, and pollen grains contained flavonoids, terpenoids, and steroids, which play a role of olfactory attractants/repellents. The nectary gland is disc-shaped and located at the base of the ovary. Nectar is secreted through numerous modified stomata. Nectar secretion began in the bud stage and lasted to the end of anthesis. The amount of produced nectar depended on the flower age and ranged from 0.21 to 3.95 mg/flower (mean?=?1.51 mg). The concentration of sugars in the nectar reached up to 57.0%. Both the nectar amount and sugar concentration demonstrated a significant year and population effect. Pollen production was variable between the years of the study. On average, a single flower of L. vulgaris produced 0.31 mg of pollen. The spectrum of insect visitors in the flowers of L. vulgaris differed significantly between populations. In the urban site, Bombus terrestris and Apis mellifera were the most common visitors, while a considerable number of visits of wasps and syrphid flies were noted in the rural site.     

Nectar Production of Calliandra longipedicellata (Fabaceae: Mimosoideae), an Endemic Mexican Shrub with Multiple Potential Pollinators

The nectar resource environment across which nectarivores forage may be patchy and variable. To understand the sources and consequences of such a variation, nectar production was investigated in Calliandra longipedicellata . Nectar was measured once a month throughout a 3-mo winter season in two successive years at three sites. We also conducted diurnal and nocturnal field observations to describe visitation rates of floral visitors, and a pollinator exclusion experiment to evaluate diurnal and nocturnal pollination at the three sites. In all populations, nectar secretion was primarily nocturnal, although flowers produced some nectar during the day. Sugar production per flower varied significantly at both the seasonal and population levels, although nectar production rates and a well-defined afternoon to morning production pattern were consistent across months, populations, and years. Average nectar production rates were high compared to other Calliandra species, and to most hummingbird- or hawkmoth-pollinated plants in the region. Flowers were regularly visited by hawkmoths, bats, hummingbirds and various diurnal insects, and all populations had similar rates of visitation. Nocturnal insects had the highest overall visitation rates (three times as high as those by diurnal insects). Fruit production varied among pollination treatments and populations, and significant differences were found in fruit production when flowers exposed to both diurnal and nocturnal visitation were compared to flowers exposed only to diurnal visitation. Our results and the bright-red staminal filaments of C. longipedicellata indicate lack of specialization for particular pollinators.     

云南草蔻花蜜分泌格局与访花动物行为及其对果实和种子产量的影响

依靠动物传粉的植物, 其繁殖成功 (胚珠受精与花粉散布 ) 很大程度上取决于访花动物的种类和拜访行为, 而访花动物的种类和行为又受植物提供给传粉者的回报, 主要是花蜜分泌格局的影响。通过对姜科山姜属植物云南草蔻 (Alpiniablepharocalyx) 花蜜分泌量及糖分含量的测定, 拜访动物种类、传粉昆虫拜访频率及停留时间的调查, 主要盗蜜者花松鼠 (Tamiopsswinhoei) 的盗蜜行为观察, 植物的结实率以及结籽量的分析等, 探讨花蜜分泌与传粉昆虫的关系以及盗蜜对果实及种子生产的影响。研究表明 :云南草蔻的两种花型花蜜的分泌量在一天的单花开花过程中呈现相反的格局, 花柱上举型花下午的花蜜分泌量高于上午, 而花柱下垂型花则上午略高于下午 ;两种花型花蜜的糖分浓度都随着开花时间而下降 ;共有 17种访花动物拜访云南草蔻的花, 其中 8种具有传粉作用 ;传粉昆虫的停留时间随拜访频率的不断增加而缩短 ;被盗蜜植株与未被盗蜜植株的结实率差异不显著而结籽量差异显著。     

Oilseed rape (Brassica napus) as a resource for farmland insect pollinators: quantifying floral traits in conventional varieties and breeding systems

Oilseed rape (OSR; Brassica napus L.) is a major crop in temperate regions and provides an important source of nutrition to many of the yield‐enhancing insect flower visitors that consume floral nectar. The manipulation of mechanisms that control various crop plant traits for the benefit of pollinators has been suggested in the bid to increase food security, but little is known about inherent floral trait expression in contemporary OSR varieties or the breeding systems used in OSR breeding programmes. We studied a range of floral traits in glasshouse‐grown, certified conventional varieties of winter OSR to test for variation among and within breeding systems. We measured 24‐h nectar secretion rate, amount, concentration and ratio of nectar sugars per flower, and sizes and number of flowers produced per plant from 24 varieties of OSR representing open‐pollinated (OP), genic male sterility (GMS) hybrid and cytoplasmic male sterility (CMS) hybrid breeding systems. Sugar concentration was consistent among and within the breeding systems; however, GMS hybrids produced more nectar and more sugar per flower than CMS hybrid or OP varieties. With the exception of ratio of fructose/glucose in OP varieties, we found that nectar traits were consistent within all the breeding systems. When scaled, GMS hybrids produced 1.73 times more nectar resource per plant than OP varieties. Nectar production and amount of nectar sugar in OSR plants were independent of number and size of flowers. Our data show that floral traits of glasshouse‐grown OSR differed among breeding systems, suggesting that manipulation and enhancement of nectar rewards for insect flower visitors, including pollinators, could be included in future OSR breeding programmes.     

Nectar concentration and composition of 26 species from the temperate forest of South America

BACKGROUND AND AIMS: Floral nectar concentration and chemical composition of 26 plant species native to the temperate forest of southern South America are reported and the relationships with the flower type are evaluated. METHODS: Nectar concentration was measured with a hand refractometer and sugar composition was analysed by gas-liquid chromatography. Plant species were classified into flower type categories based not only on floral features but also on data from the literature and field observations on their pollinators. KEY RESULTS: Most data on nectar are new reports at the generic and/or specific level. Plant species in which more than one population was studied showed significant among-population variation in nectar sugar concentration and composition. Results showed a weak relationship between nectar traits and flower type. Many species had nectar containing 50 % or more sucrose (17 of 26 species), independent of the main pollinator. CONCLUSIONS: Considering that (a) nectar characteristics did not show a clear association with different flower types or with plant taxonomic membership, and (b) different populations of the same species showed large variability in sugar composition, the results suggest that other factors (e.g. historical and environmental) could be involved in determining the sugar composition of the highly endemic plant species from this region.