Flower visitation patterns of the coexisting honey bees Apis cerana japonica and Apis mellifera (Hymenoptera: Apidae)

We compared flower visitation patterns of two coexisting honey bees, Apis mellifera Linnaeus and Apis cerana japonica Radoszkowski, on 20 plant species, including three exotics, under natural conditions in Nara, Japan, from April to August 2012. We also measured flower color based on bee color vision (15 flower species), nectar volume (nine species) and nectar concentration (eight species). Flowers colored white, pink, red, purple and cream were classified as bee‐blue‐green, and yellow was classified as bee‐green. Apis cerana visited 14 plant species and A. mellifera visited 11. Although the two Apis species are similar in morphology, they visited different plants: in particular, A. cerana visited native plant species more often than did A. mellifera. Both A. mellifera and A. cerana visited not only nectariferous flowers but also those with no nectar. We also found different visitation patterns between A. cerana and A. mellifera: Apis cerana more often visited flowers with smaller color angle (bee‐blue‐green), lower chroma and higher brightness, and flowers secreting nectars of higher concentration and smaller volume than did A. mellifera.     

Intra‐floral resource partitioning between endemic and invasive flower visitors: consequences for pollinator effectiveness

1. Sympatric flower visitor species often partition nectar and pollen and thus affect each other's foraging pattern. Consequently, their pollination service may also be influenced by the presence of other flower visiting species. Ants are solely interested in nectar and frequent flower visitors of some plant species but usually provide no pollination service. Obligate flower visitors such as bees depend on both nectar and pollen and are often more effective pollinators. 2. In Hawaii, we studied the complex interactions between flowers of the endemic tree Metrosideros polymorpha (Myrtaceae) and both, endemic and introduced flower‐visiting insects. The former main‐pollinators of M. polymorpha were birds, which, however, became rare. We evaluated the pollinator effectiveness of endemic and invasive bees and whether it is affected by the type of resource collected and the presence of ants on flowers. 3. Ants were dominant nectar‐consumers that mostly depleted the nectar of visited inflorescences. Accordingly, the visitation frequency, duration, and consequently the pollinator effectiveness of nectar‐foraging honeybees (Apis mellifera) strongly decreased on ant‐visited flowers, whereas pollen‐collecting bees remained largely unaffected by ants. Overall, endemic bees (Hylaeus spp.) were ineffective pollinators. 4. The average net effect of ants on pollination of M. polymorpha was neutral, corresponding to a similar fruit set of ant‐visited and ant‐free inflorescences. 5. Our results suggest that invasive social hymenopterans that often have negative impacts on the Hawaiian flora and fauna may occasionally provide neutral (ants) or even beneficial net effects (honeybees), especially in the absence of native birds.     

锦鸡儿(Caragana sinica(Buchoz) Rehd)传粉生物学研究

对唐家河国家自然保护区内锦鸡儿(Caragana sinica(Buchoz)Rehd)的花期、访问者、有效传粉者种类及行为、花蜜分泌节律和繁育系统等进行定点观察和实验处理。结果表明:锦鸡儿单花花期约5d,种群花期约20d。拥有以吸蜜为主的条蜂属(Anthophora)、熊蜂属(Bombus)和太阳鸟属(Aethopyga)3种传粉者功能群。综合访花频率和花粉落置数,茜条蜂(Pyganthophora rubricus Dours)和蓝喉太阳鸟(Aethopyga gouldiae)为主要有效传粉者,熊蜂(Bombus)为次要有效传粉者;蚂蚁(formicidae)和西方蜜蜂(Apis mellifera Linnaeus)为主要盗蜜者。套袋处理结果表明,花蜜分泌日变化中,最大花蜜量发生在16:00左右;花蜜随单花花期变化中,花蜜体积最大发生于单花第5天;分泌均呈递增趋势。花蜜分泌节律与访花频率呈正相关。繁育系统检测显示,花粉胚珠比为3779±320.92,柱头最适可授期在开花第2—3天;结合不同授粉处理表明:锦鸡儿自交不亲和,需要传粉者,为蜂媒兼鸟媒植物。     

Why do nectar-foraging bees and wasps work upwards on inflorescences?

Summary Wasps (Dolichovespula and Vespula spp.) worked predominantly upwards when foraging for nectar on inflorescences of the protogynous Scrophularia aquatica, in which the standing crop of nectar sugar per flower showed no clear pattern of vertical distribution up an inflorescence. Bumblebees taking nectar (Bombus hortorum visiting legally, and certain individuals of B. terrestris which positioned themselves head-upwards while taking nectar through holes bitten in the corolla) worked predominantly upwards on the racemose inflorescences of Linaria vulgaris, although the standing crop of nectar sugar per open flower increased up the raceme. Individuals of B. terrestris which robbed Linaria flowers in a head-down position worked predominantly downwards on inflorescences. The upward or downward directionality of intra-inflorescence movements by foraging insects may depend in part on the position these adopt during their flower visits.     

Foraging and pollination behaviour of Xylocopa calens Lepeletier (Hymenoptera: Apidae) on Phaseolus coccineus L. (Fabaceae) flowers at Yaounde (Cameroon)

To evaluate impact of carpenter bee, Xylocopa calens, on pod and seed set of Phaseolus coccineus, its foraging and pollinating activities were studied in Yaounde, for two seasons (May–July 2008 and April–June 2009). Observations were made on 40 inflorescences per treatment. The treatments included unlimited floral access by all visitors, bagged flowers to deny all visits, and limited visits by X. calens only. In addition, all flower visitors were recorded. The carpenter bee's seasonal rhythm of activity, its foraging behavior on flowers, its pollination efficiency, the fructification rate and the number of seeds per pod were recorded. Individuals from 16 species of insects were recorded visiting flowers of P. coccineus in the 2 years. Xylocopa calens was the most frequent, followed by Chalicodoma cincta cincta and Apis mellifera. Apart from bees, wasps were also recorded as likely predators. Xylocopa calens mainly foraged for nectar resources. The mean foraging speed was 9.62 flowers/min. Flowers visited by X. calens had higher fruiting rate compared with others, while those bagged had the lowest. In addition, seed formation was higher in X. calens‐visited flowers compared with all others. The results show that this crop experiences pollination deficit even under normal circumstances, considering that flowers visited by X. calens had higher yields compared with those under unlimited access by all visitors. The fruiting rate, the number of seeds/pod and the percentage of normal seeds of unprotected inflorescences were significantly higher than those of inflorescences protected from insects. X. calens foraging resulted in a significant increment of the fruiting rate by 25.80%, as well as the number of seeds/pod by 14.97% and the percentage of normal seeds by 27.75% in 2008 and 18.39% in 2009. Conservation of X. calens nests close to P. coccineus fields could be recommended to improve pod and seed production in the region.     

Floral biology and pollination in Cucumis melo L., a tropical andromonoecious cucurbit

We studied floral biology and the role of flower visitors in fruit set of muskmelon (Cucumis melo L.). Muskmelon produced Staminate (hereafter ‘S’) and Hermaphrodite (hereafter ‘H’) flowers with a ratio of 18:1. Flowers opened around 40 days after planting and flowering continued for another 40 days. Longevity of both types of flowers was one day. Anthesis in S flowers was earlier (0545–0700 h) than that of H flowers (0700–0830 h). Anther dehiscence occurred 10–15 min after anthesis in both the flowers. The number of pollen grains in H flowers was significantly lower (2715 ± 143) than S flowers (4968 ± 398). Pollen viability and stigma receptivity was maximum between 1600 and 1800 h. The pollen tube of pollen grains from H flowers grew very slowly and never reached the ovary. There were two peaks in nectar production in a day (1000–1200 h and 1400–1800 h). Sixteen species of insects belonging to Hymenoptera (81.25%), Diptera (12.50%) and Lepidoptera (6.5%) visited muskmelon flowers. Major visitors were honeybees, Apis cerana F. and A. florea F. and both were efficient pollinators. Diversity and abundance of flower visitors positively correlated with floral abundance. In pollination exclusion experiments, no fruit set was observed in bagged, self-pollinated and the flowers artificially crossed only with other H pollen. But, those flowers hand pollinated with pollen from S flowers and ones that were allowed for open pollination set maximum fruits. The crop needs a minimum of 8–10 bee visits per flower to achieve the same level of pollination efficiency provided with natural/unrestrained visits.     

Choice of flowers by foraging honey bees (Apis mellifera): possible morphological cues

Abstract.

• 1 Honey bees foraging for nectar on lavender (Lavandula stoechas) chose inflorescences with more of their flowers open. The number of open flowers predicted whether an inflorescence was visited by bees, inspected but rejected, or ignored. Inflorescences chosen arbitrarily by observers had numbers of open flowers intermediate between those of visited and ignored inflorescences.
• 2 Differences in morphological characters between types of inflorescence correlated with nectar volume and sugar weight per flower so that visited inflorescences had a disproportionately greater volume of nectar and weight of sugar per flower and greater variance in nectar volume.
• 3 Although there were significant associations between nectar content and the morphological characters of inflorescences, discriminant function analysis revealed discrimination on the basis of morphology rather than nectar content.
• 4 Visited inflorescences tended to have smaller than average flowers but bees tended to probe the largest flowers on visited inflorescences.
• 5 Choice of flowers within inflorescences is explicable in terms of the relationship between flower size and nectar content.

     

栽培细叶百合的传粉生态

对栽培的细叶百合进行传粉生态学的初步观察结果显示：细叶百合2:30～3:00开始开花,5:30～7:00完全开放;单花开放时间3～4 d,群体花期为12 d。花蜜分泌在开花当日,分泌高峰在9:00～11:00,花蜜分泌与昆虫访花谐调一致。花蜜成分主要为葡萄糖、阿拉伯糖和β－D吡喃果糖,花朵挥发物的成分是软脂酸、软脂酸甲酯、肉豆蔻酸、月桂酸、3－叔戊基戊酮、十三烷和1－甲基,2异丙烯基环丁基乙醇。访花昆虫主要是蝶类、蜂类和蝇类;传粉昆虫为绿豹蛱蝶、大红蛱蝶、绢粉蝶及单齿切叶蜂、小齿淡脉隧蜂,其中小齿淡脉隧蜂的传粉活动最为活跃。晴天时小齿淡脉隧蜂访花频率的日变化与光照的日变化呈极显著的正相关,与温度的日变化呈显著的正相关,与湿度的日变化呈显著的负相关;阴天时与空气温度相关极显著,与空气湿度相关显著。细叶百合以异花虫媒传粉为主,部分自交可育。     

The exploitation of floral nectar in Eucalyptus incrassata by honeyeaters and honeybees

Summary During October and November, 1977, a study of nectar production and nectarivore foraging in Eucalyptus incrassata was conducted at Wyperfeld National Park in south-eastern Australia in order to evaluate the extent to which introduced honeybees (Apis mellifera) compete with native honeyeaters for floral nectar. Data on nectar production, nectar availability, ambient air temperature and the numbers of visiting honeyeaters and honeybees were collected. Most of the daily nectar production in E. incrassata occurs early in the morning when temperatures are too low for insects to forage. In addition, insects, particularly honeybees, are unable to exploit nectar in the youngest flowers because the stamens are clustered tightly around the style. As a result of these temporal and structural characteristics of the flowers, honeyeaters are able to harvest most of the nectar. Honeybees potentially have access to 35–47% of the average daily production of floral nectar in E. incrassata and actually harvest considerably less. These data show that E. incrassata flowers are adapted to restrict insect foragers despite their superficially unspecialized appearance. Eight forest and woodland eucalypts do not have a flower stage which excludes insects and the significance of this difference is discussed.     

Visitation rate of pollinators and nectar robbers to the flowers and inflorescences of Tabebuia aurea (Bignoniaceae): effects of floral display size and habitat fragmentation

Large floral displays favour pollinator attraction and the import and export of pollen. However, large floral displays also have negative effects, such as increased geitonogamy, pollen discounting and nectar/pollen robber attraction. The size of the floral display can be measured at different scales (e.g. the flower, inflorescence or entire plant) and variations in one of these scales may affect the behaviour of flower visitors in different ways. Moreover, the fragmentation of natural forests may affect flower visitation rates and flower visitor behaviour. In the present study, video recordings of the inflorescences of a tree species (Tabebuia aurea) from the tropical savannah of central Brazil were used to examine the effect of floral display size at the inflorescence and tree scales on the visitation rate of pollinators and nectar robbers to the inflorescence, the number of flowers approached per visit, the number of visits per flower of potential pollinators and nectar robbers, and the interaction of these variables with the degree of landscape disturbance. Nectar production was quantified with respect to flower age. Although large bees are responsible for most of the pollination, a great diversity of flower insects visit the inflorescences of T. aurea. Other bee and hummingbird species are highly active nectar robbers. Increases in inflorescence size increase the visitation rate of pollinators to inflorescences, whereas increases in the number of inflorescences on the tree decrease visitation rates to inflorescences and flowers. This effect has been strongly correlated with urban environments in which trees with the largest floral displays are observed. Pollinating bees (and nectar robbers) visit few flowers per inflorescence and concentrate visits to a fraction of available flowers, generating an overdispersed distribution of the number of visits per inflorescence and per flower. This behaviour reflects preferential visits to young flowers (including flower buds) with a greater nectar supply.     

中华蜜蜂在滇山茶上的访花行为研究

对中华蜜蜂在滇山茶上的访花行为的研究表明,中华蜜蜂全天在滇山茶上的访花过程呈现出单峰型的节律,高峰在13:00～14:00.在31朵观察的样花上,中华蜜蜂全天共到访613次,访花627次,对花的连续访问率为2.23％,每朵花平均被访20.23次,每次到访花停留时间均值为10.23 s,全天在样花上总的累计停留时间为6 270 s,单花累计访问时间达到202.26 s.蜜蜂全天访花累计时间占全部访花昆虫总访花的累计停留时间的比例达到97.80％.在滇山茶访花昆虫中,中华蜜蜂具有明显的优势度,是绝对的优势种.对滇山茶花蜜的研究表明,其单花1天的花蜜分泌量平均为69.5 μL(n=100);花蜜含糖量(124.95～200.64) mg/mL.花蜜成分以多糖为主,占66％以上,此外还含有单糖,占1.9％～33％,其他未知名的组分占16％～22％,部分花蜜中含有山梨醇,占11％.对滇山茶花的挥发物分析结果表明,总的挥发物有59种,萜烯类、酯类和醇类是滇山茶花的主要挥发物成分,分别占46.468％、27.035％和21.609％.     

Flower choice by honey bees (Apis mellifera L.): sex-phase of flowers and preferences among nectar and pollen foragers

Bees foraging for nectar should choose different inflorescences from those foraging for both pollen and nectar, if inflorescences consist of differing proportions of male and female flowers, particularly if the sex phases of the flowers differ in nectar content as well as the occurrence of pollen. This study tested this prediction using worker honey bees (Apis mellifera L.) foraging on inflorescences of Lavandula stoechas. Female flowers contained about twice the volume of nectar of male flowers. As one would predict, bees foraging for nectar only chose inflorescences with disproportionately more female flowers: time spent on the inflorescence was correlated with the number of female flowers, but not with the number of male flowers. Inflorescence size was inversely correlated with the number of female flowers, and could be used as a morphological cue by these bees. Also as predicted, workers foraging for both pollen and nectar chose inflorescences with relatively greater numbers of both male and female flowers: time spent on these inflorescences was correlated with the number of male flowers, but not with the number of females flowers. A morphological cue inversely associated with such inflorescences is the size of the bract display. Choice of flowers within inflorescences was also influenced predictably, but preferences appeared to be based upon corolla size rather than directly on sex phase.     

Pollination ecology of Penstemon roseus (Plantaginaceae), an endemic perennial shifted toward hummingbird specialization?

Summary Pink-flowered tubular Penstemon roseus (Plantaginaceae), which has shifted partially to hummingbird pollination, blooms on high-elevation slopes in the mountains in Tlaxcala, Mexico. We studied the interactions between pollinator visitation rates to flowers, pollen removal and deposition, flower size, and nectar removal frequency on seed production in P. roseus. We combine observational and experimental studies in two contrasting natural populations. Our manual pollinations revealed that P. roseus is fully self-compatible. Autonomous self- and manual self-pollinated flowers matured as many seeds as when outcrossed, but outcrossing seems to become better than selfing as the flowering season progressed. Early in the season flowers that were bagged and hand-selfed, hand-outcrossed, or autonomously selfed, or unbagged and naturally pollinated had equal seed set in all four treatments. But later in the season, outcross pollen gave approximately twice as much seed set as the two self-treatments. Low levels of pollen receipt and pollen removal were consistent with the long time elapsed for a given plant to be visited by hummingbirds, which suggests pollen shortage in both sites. Despite differences in pollinator visitation rates to flowers, probability of flower visitation, removal and deposition of pollen, and nectar production rates between populations, we found that total nectar production had no effect on seed production at either site. The daily nectar secretion rate of 0.3–0.65 mg sugar per flower per 1–3 days was low relative to other hummingbird-adapted Penstemon species (typical range: 1.5–5 mg sugar per flower), and it might be intermediate between hummingbird- and bee-adapted Penstemon flowers. Our results support the hypothesis about a shift toward hummingbird pollination, and provide an example of a ‘despecialized’ Penstemon species, which attracts high-energy pollinators (hummingbirds) and profits from outcrossing, but retains bee-syndrome floral traits and low sugar production rates.     

Pollination ecology of Yucca elata

The pollination biology of a population of 250 Yucca elata (Liliaceae) plants was studied in southern New Mexico. Yucca elata and the prodoxid yucca moth Tegeticula yuccasella have a mutualistic association that is essential for the successful sexual reproduction of both species. However, a wide range of other invertebrate species visit flowers during the day and at night. Our aim was to quantify the role of yucca moths and other invertebrate visitors in pollination and fruit set, using manipulative field experiments. Inflorescences were bagged during the day or night (N=12 inflorescences) to restrict flower visitors to either nocturnal or diurnal groups. Yucca moths were active exclusively nocturnally during the flowering period and thus did not visit inflorescences that were unbagged during the day. None of the 4022 flowers exposed only to diurnal visitors set fruit, whereas 4.6% of the 4974 flowers exposed only to nocturnal visitors (including yucca moths) produced mature fruit. The proportion of flowers producing fruit in the latter treatment was not significantly different from unbagged control inflorescences. In a series of experimental manipulations we also determined that: (1) flowers opened at dusk and were open for two days on average, but were only receptive to pollen on the first night of opening; (2) pollen must be pushed down the stigmatic tube to affect pollination; and (3) most plants require out-cross pollination to produce fruit. The combination of these results strongly suggests that yucca moths are the only species affecting pollination in Y. elata, and that if another species was to affect pollination, it would be a rare event.     

Bumblebee visits to Impatiens spp.: pattern and efficiency

Summary Three Japanese species of Impatiens, which secrete nectar continuously in long spurs, were visited by Bombus diversus workers consecutively throughout the day. B. diversus workers showed characteristic patterns of behavior in flower use, flower choice, and patch departure. (1) Bumblebees stayed longer on a flower which had been unvisited for a while than on a flower which had been visited recently. (2) Bumblebees preferred visiting flowers which had been unvisited for a while to visiting those which had been visited recently, and to visiting those which had been unvisited for a long period. (3) Bumblebees had a higher probability of leaving a patch after they had stayed on a flower for a short period than after they had stayed for a longer period. The bumblebees appeared to perceive both remotely and proximately chemical cues deposited by other foraging individuals, which indicated nectar rewards in a flower, and thus obtained a higher nectar intake than the mean amount of nectar left in a flower.     

Reproductive biology of Alpinia blepharocalyx (Zingiberaceae): another example of flexistyly

The floral biology and breeding system of Alpinia blepharocalyx were studied in Yunnan province, southwest China. Our results indicate that populations of A. blepharocalyx have two floral morphs, which differ in flowering behaviour: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther at afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon; the flowering period of both floral morphs is 12 hours; the stylar movements in the two floral morphs are synchronous, and they have similar traits to those found in other Alpinia species previously reported. Also, on average, cataflexistylous flowers are larger than anaflexistylous flowers, especially the labellum and corolla tube length; moreover, the P/O ratio of the two floral morphs is significantly different: the cataflexistylous morph has more pollen grains and fewer ovules than the anaflexistylous morph; the evolutionary significance of this comparison is discussed. Cataflexistylous flowers were observed to produce a lower concentration of nectar than that of anaflexistylous flowers before 11:00 a.m., but they then have higher nectar concentration; cataflexistylous flowers always have more nectar than anaflexistylous flowers. Flowers of A. blepharocalyx were visited by fewer insects at a lower frequency, including honey bees (Apis cerana cerana) and two species of carpenter bees (Xylocopa spp.). No significant differences were found in the fruit set among the hand-pollination treatments regardless of selfing (geitonogamy and autogamy) or crossing (intermorph and intramorph); but all hand-pollination treatments exhibited much higher fruit set than the controls; meanwhile, no fruit set occurred in the unpollinated bagged plants. Pollen tube growth was examined using fluorescence microscopy following self, intramorph, and intermorph hand pollinations at different times of the day; the pollen tubes of both floral morphs have the same growth rate and the capability to reach the ovary. Both the results of pollen tube growth and fruit sets under different pollination conditions show that A. blepharocalyx is self-compatible and dependent upon insects for pollination. The distinctive flexistyly mechanism of A. blepharocalyx is likely a floral mechanism that promotes effective intermorph pollen transfer.     

基于山地蜂蜜花粉组成的中华蜜蜂传粉多样性研究

中华蜜蜂为多种植物传粉,具有重要的生态服务价值。为进一步了解中华蜜蜂选择蜜粉源植物的多样性与特征,采用聚合酶链式反应(PCR)、DNA条形码、高通量测序等技术,研究了源自陕西宝鸡、贵州望谟和广西凤山蜂巢蜜中的花粉来源。通过对样品花粉rbcL基因片段扩增及测序、分析,发现各样本间可操作分类单元(OTU)水平上蜜粉源植物Alpha多样性指数无显著差异,同一地点样品不同重复间存在较高的相关性,而不同地区样本相关性较低。三地共鉴定出27目46科71属82种蜜粉源植物,其中宝鸡市、望谟县、凤山县样本中分别鉴定出57种、30种和40种,各地蜜粉源植物的物种组成存在较大差异。这些蜜粉源植物中,菊目植物种类最多,其次为毛茛目,分别有12种和7种。其中草本植物和木本植物(含乔木、灌木和木质藤本等)分别有44种和38种。研究对蜜粉源植物花序特点进行了分析,但并未发现相关性状对中华蜜蜂选择具有的影响。从属的区系成分分析,总体上温带分布区类型的植物属多于热带分布区类型的属,所占比例分别为46.5%和36.6%,但在凤山县样本中出现热带分布区类型多于温带分布区类型的情况。在不同样品中,红足蒿(Artemisia rubripes)、向日葵(Helianthus annuus)、芜青(Brassica rapa)、粗糠柴(Mallotus philippensis)、枇杷(Eriobotrya japonica)等分别占有一定优势,其与中华蜜蜂的关系值得进一步研究。根据蜜粉源植物的系统进化关系,中华蜜蜂访问的蜜粉源植物处于不同进化地位的分支,其中在菊类分支和蔷薇类分支比较集中。研究揭示了中华蜜蜂传粉植物组成特点,为进一步认知中华蜜蜂传粉服务功能的重要性提供依据。     

Pollination ecology of Christmas Bells (Blandfordia nobilis): Patterns of standing crop of nectar

Standing crop of nectar (both volume and sugar concentrations) was measured from flowers in a population of Blandfordia nobilis. Nectar in this honeyeater-pollinated species was extremely viscous during one flowering season and averaged approximately 95% sugar, while it averaged only 25% sugar two seasons later. Nectar volume was significantly and negatively correlated with sugar concentration on nine often sampling dates. There was no significant relationship between either nectar volume or sugar concentration and a number of measures of plant size (inflorescence height, numbers of open flowers, buds, spent flowers and total flowers). Similarly, no consistent relationship was found between measures of flower size and reward level. There were significant positive correlations between the reward (both volume and sugar concentration) offered by blossoms on the same plant. The nectar volume of flowers from nearest neighbouring inflorescences were significantly and positively correlated with one another on three of six occasions while the sugar concentrations of those blossoms were significantly correlated on just two of six sampling dates. There was no significant difference in reward (both volume and sugar concentration) between open flowers and those bagged to exclude pollinators. There was significant heterogeneity in the nectar volumes offered by plants to pollinators during a single flowering season.     

Nectar secretion dynamic links pollinator behavior to consequences for plant reproductive success in the ornithophilous mistletoe Psittacanthus robustus

The mistletoe Psittacanthus robustus was studied as a model to link flower phenology and nectar secretion strategy to pollinator behaviour and the reproductive consequences for the plant. The bright‐coloured flowers presented diurnal anthesis, opened asynchronously throughout the rainy season and produced copious dilute nectar as the main reward for pollinators. Most nectar was secreted just after flower opening, with little sugar replenishment after experimental removals. During the second day of anthesis in bagged flowers, the flowers quickly reabsorbed the offered nectar. Low values of nectar standing crop recorded in open flowers can be linked with high visitation rates by bird pollinators. Eight hummingbirds and two passerines were observed as potential pollinators. The most frequent flower visitors were the hummingbirds Eupetomena macroura and Colibri serrirostris, which actively defended flowering mistletoes. The spatial separation between anthers, stigma and nectar chamber promotes pollen deposition on flapping wings of hovering hummingbirds that usually probe many flowers per visit. Seed set did not differ between hand‐, self‐ and cross‐pollinated flowers, but these treatments set significantly more seeds than flowers naturally exposed to flower visitors. We suggest that the limitation observed in the reproductive success of this plant is not related to pollinator scarcity, but probably to the extreme frequency of visitation by territorial hummingbirds. We conclude that the costs and benefits of plant reproduction depend on the interaction strength between flowers and pollinators, and the assessment of nectar secretion dynamics, pollinator behaviour and plant breeding system allows clarification of the complexity of such associations.     

Nectar dynamics and reproductive success in Saponaria officinalis (Caryophyllaceae) in southern Germany

Nectar production and flower visitors of the night-flowering Saponaria officinalis L. (Caryophyllaceae) were studied in relation to the reproductive success. Nectar production was worthwhile for nocturnal flower visitors. Nectar standing crop was about 267 μg sugar per flower, and comparison of nectar offering of covered and freely exposed flowers revealed that main nectar secretion time is mainly during the night up to the morning hours. In both covered and freely exposed flowers nectar volumes decreased over the day. In covered flowers, nectar volume, sugar concentration, and sugar amount per flower increased up to the third day; in older flowers sugar secretion ceased. In 1996 Autographa gamma (Noctuidae) was the exclusive nocturnal flower visitor, but pollen transfer experiments proved that A. gamma (Noctuidae) is a very ineffective pollinator of S. officinalis. In 1999 up to 50% of the observed visitors were Sphingidae, which resulted in a significantly higher seed set. Fruit set was constantly high independent of pollinator availability. In the nectar manipulation experiments seed set was highest in non-emasculated flowers filled with unnaturally high concentrated sucrose solutions. Differences to seed set on stalks treated with a sucrose solution mimicking naturally concentrated nectar were significant. Lowest fruit and seed set were found on inflorescences with emasculated flowers filled with a sucrose solution mimicking naturally concentrated nectar.