Presence Of Nectaries Research Articles

Structure of floral nectaries and comparison of reproductive and vestigial organs in the staminate and pistillate flowers of dioeciousSilene latifolia(Caryophyllaceae)

Silene latifolia Poiret of Eurasia has established in North America, prompting this structural study of its mature unisexual buds and flowers. Floral nectaries, anther and stigma changes, and vestigial reproductive structures were studied using light and scanning electron microscopy. In staminate flowers, anthers dehisced before anthesis and >90% of their pollen was liberated within 36 h. Accumulated in the tubular calyx, nectar descended an anthophore from the stomatal-bearing nectary at the stamen bases. Nectary tissue surrounded the pistillode, a central filamentous organ lacking ovules but tipped by hairs resembling stigmatic papillae. In pistillate flowers, nectar flowed into an inflated calyx. The annular nectary had 10 regularly spaced, stomatal-lined craters and was continuous with the adaxial surfaces of the infertile antisepalous and epipetalous staminodes. Key elements of entomophilous pollination leading to successful sexual reproduction of this invasive species include secondary nectar presentation from disparate floral nectaries that, for pistillate flowers, also incorporate the staminodes; rapid pollen release from anthers; and elongation of papillae by tip growth that enhances each stigma’s receptive surface. Context is also provided for future studies of floral nectary development in this model dioecious species.

Unidirectional transitions in nectar gain and loss suggest food deception is a stable evolutionary strategy in Epidendrum (Orchidaceae): insights from anatomical and molecular evidence

BackgroundNectar gain and loss are important flower transitions observed in angiosperms, and are particularly common in orchids. To understand such transitions, the availability of detailed anatomical data and species-level phylogenies are crucial. We investigated the evolution of food deception in Epidendrum, one of the largest orchid genera, using genus phylogeny to map transitions between nectar gain and loss among different clades. Associations between anatomical and histochemical changes and nectar gain and loss were examined using fresh material available from 27 species. The evolution of nectar presence/absence in Epidendrum species was investigated in a phylogenetic framework of 47 species, using one nuclear and five plastid DNA regions available from GenBank and sequenced in this study.ResultsThe presence or absence of nectar was strongly associated with changes in the inner epidermal tissues of nectaries. Nectar-secreting species have unornamented epidermal tissue, in contrast to the unicellular trichomes found on the epidermis of food deceptive species. Bayesian tests confirmed that transitions occurred preferentially from nectar presence to nectar absence across the Epidendrum phylogeny. In addition, independent nectar loss events were found across the phylogeny, suggesting a lack of constraint for these transitions.ConclusionsOrnamented nectaries may play an important role in the deceptive pollination strategy by secreting volatile organic compounds and providing tactile stimuli to pollinators. The recurrent and apparently irreversible pattern of nectar loss in Epidendrum suggests that food deception may constitute an alternative evolutionarily stable strategy, as observed in other orchid groups.

Anatomical analyses of floral and extrafloral secreting structures indicate the presence of nectaries and colleters in Stanhopea grandiflora Lindl.

Anatomical studies involving secreting structures in Stanhopeinae have described lipid-producing structures, the osmophores, these structures have been linked to pollinator attraction. Stanhopea, which belongs to the subtribe Stanhopeinae, has Neotropical distribution and is exclusively pollinated by male Euglossini bees, which are attracted to the aromatic compounds exuded by osmophores—a secreting structure that produces volatile lipids. However, due to the structural diversity found in this genus and the lack of data on which foragers visit these flowers, our aim is to elucidate floral anatomical aspects of the Stanhopeinae group, focusing on the secreting structures of Stanhopea grandiflora Lindl., an orchid that occurs in the Amazon region. Analyses were performed under bright-field microscopy and scanning electron microscopy. Osmophores, nectaries, idioblasts and glandular trichomes were the secreting structures observed in Stanhopea grandiflora. The osmophores are responsible for attracting and offering rewards the male Euglossini bees, which are their exclusive pollinators, while the nectaries offering nectar to the foragers Dolichoderus and Azteca ants which in turn offer protection against herbivores. Nectariferous stomata and glandular trichomes role similar to those of colleters are described in the first record of the subtribe Stanhopeinae.

Community-wide integration of floral colour and scent in a Mediterranean scrubland.

Angiosperm flowers have evolved a dazzling palette of colours and a rich bouquet of scents, principally serving to attract pollinators. Despite recent progress in the ecology of pollination, the sensory floral traits that are important for communication with pollinators (for example, colour and scent) have not been assessed in an unbiased, integrative sense within a community context. Nonetheless, floral sensory stimuli are known key factors that mediate flower visitation, thus affecting community dynamics. Here we show that flowers of the phrygana, a natural Mediterranean scrubland, display integrated patterns of scent composition and colour (as perceived by pollinators). Surprisingly, the data reveal predictive relationships between patterns of volatile composition and flower reflectance spectra. The presence of nectar is related to visual cues and the qualitative composition of floral aromas. Our results reveal a coordinated phenotypic integration consistent with the sensory abilities and perceptual biases of bees, suggesting potential facilitative effects for pollination and highlighting the fundamental importance of bees in Mediterranean-type ecosystems. We offer our unbiased approach as a starting point for more extensive, global investigations of the diversity of floral sensory phenotypes and its role in the community ecology of plant-pollinator interactions.

Pollination ecology and seed production of some species of the genus Pedicularis L. in the highlands of Altai

The paper presents data on the pollination ecology and seed production of three Pedicularis L. species in the high mountains of Altai. It was determined that the investigated species are highly specialised entomophiles. Specialisation to entomophily is expressed in a number of adaptations: the presence of nectar in flowers of Pedicularis, pollen and secondary attractants (visual and tactile) that attract insects, as well as specific morphological structures which facilitate the process of pollen hitting a certain area of the body of the insect. Hercogamy and protogyny and gradual explication of the flowers in the inflorescence and their long lifespan in wide ranges of temperature and humidity are also adaptations to cross-pollination. The investigated species have high fertility and viability of the pollen grains. Seed production ranges from 57.1 to 261.3 seeds per stem. The seeds have organic rest. Promoting agents of seeds germination of the investigated species are cold stratification in conjunction with the gibberellic acid treatment. The biology of louseworts is peculiar because they combine autotrophic feeding with parasitism on other higher plants. The lack of strict species specificity in the choice of host plants was discovered. The complex of host plants includes 27 species.

Bees also like a sticky mess.

Foraging Ecology Flowers produce all kinds of cues that attract bees and alert them to the presence of nectar, indicating that bees are highly attuned to flower signals. But contrary to expectations, bees do not solely rely on flower signals to look for nectar. Meiners et al. found that bees' ability to find resources is likely much more flexible than we have realized. After observing large numbers of bees visiting nonflowering chamise shrubs, they discovered that 42 bee species were collecting honeydew produced by scale insects found on the shrubs. Bees also swiftly located sugar daubed on shrub limbs. As for how they locate an unadvertised resource such as honeydew, the authors suggest that they may be using social cues from other foraging bees. Am. Nat. 10.1086/692437 (2017).

Laboratory Evaluations of the Foraging Success ofTamarixia radiata(Hymenoptera: Eulophidae) on Flowers and Extrafloral Nectaries: Potential use of Nectar Plants for Conservation Biological Control of Asian Citrus Psyllid (Hemiptera: Liviidae)

Tamarixia radiata (Waterson) (Hymenoptera: Eulophidae) is a specialist parasitoid of late-instar nymphs of Asian citrus psyllid, Diaphorina citri (Kuwayama) (Hemiptera: Liviidae), a vector of the causal agent of huanglongbing disease of citrus (Sapindales: Rutaceae). Tamarixia radiata is mass reared; however, parasitism levels following inundative releases have remained relatively low. One possible explanation for the low parasitism levels is the lack of sugar resources available for adult wasps in targeted release landscapes, such as abandoned commercial citrus groves and residential areas. Establishing nectar plants can be an effective means of increasing nutritional resources in targeted sites for biocontrol agents. Some eulophids forage effectively only on fully exposed nectaries, i.e., those unobstructed by other floral parts. Therefore, care must be taken to select plants that possess nectary architecture compatible with parasitoid morphology and foraging ability. A series of laboratory studies were undertaken as a first step to determine the potential for T. radiata to obtain sugar from natural sources in target landscapes. Following contact with a sugar spot on filter paper, the wasps engaged in stereotypical zigzagging movements, demonstrating that contact with sugar induced arrestment and induction of localized searching behavior. Tamarixia radiata fed on sugars found in nectar (sucrose, glucose, fructose) and honeydew (melizitose, raffinose), indicating that it should feed well on both nectar and honeydew resources. At the highest concentration tested (1 M), it preferred sucrose and melizitose, whereas at the lowest concentration tested (0.1 M), it preferred sucrose and glucose. There was no preference among sugars when tested at the 0.5 M concentration. Choice tests with wasps previously exposed to scented sucrose solution showed that the wasps were stimulated and attracted by nectar odor and could learn to associate a particular odor with the presence of nectar. Observations conducted with starved wasps on freshly cut sprigs of nectar plants showed that foraging success was highest on extrafloral nectaries and flowers with exposed nectaries. The wasps readily located the extrafloral nectaries on snap bean and cowpea, and fed on them for the majority of the observation periods. Likewise, they quickly located the fully exposed nectaries in the inflorescences of euphorbiaceous plants, such as Euphorbia heterophylla L. (Malpighiales: Euphorbiaceae). Foraging success declined in flowers with nectaries that were only partially exposed; the wasps' movements were deterred by floral parts or trichomes that obstructed the nectary. The wasps were unable to obtain nectar from composites and other plants with hidden nectaries. Overall, the results of these laboratory evaluations showed that T. radiata responds to sugars and chemical cues associated with nectaries and is capable of foraging on extrafloral nectaries and flowers with exposed nectaries.

When it pays to cheat: Examining how generalized food deception increases male and female fitness in a terrestrial orchid.

BackgroundExperimental manipulations of floral nectar in food deceptive species can reveal insights into the evolutionary consequences of the deceptive strategy. When coupled to pollen tracking, the effects of the deceptive pollination syndrome on both male and female reproductive success may be quantified. Attraction of pollinators in deceit-pollinated species often relies on producing a conspicuous floral display which may increase visibility to pollinators, but in-turn may increase within plant selfing.MethodologyTo understand the role of deception in Orchidaceae reproduction we studied Cypripedium candidum. All species of the Cypripedium genus employ a generalized food deceptive pollination strategy and have been suggested as a model system for the study of pollinator deception. We conducted a nectar addition experiment that randomly assigned the four plants closest to a transect point to receive one of four histochemical dyes. Two individuals selected for nectar addition in each of altogether 25 blocks received 2μl of 25% sucrose solution in the labellum of each flower, while two others received no artificial nectar. Number of fruits produced, fruit mass and fruit abortion were scored at the end of the four-month experiment.ResultsNectar addition increased (p<0.0001) self-pollination and pollen discounting by nearly 3x, while plants not receiving nectar had greater (p<0.0001) numbers of non-self pollinia deposited and lower rates of pollen discounting. There was a non-significant (p = 0.0645) trend for deceptive plants to set more fruit, while presence of nectar did not affect pollen export.ConclusionsThis study demonstrates the adaptive advantages of food deception by showing a concurrent reduction in particular male and female functions when a food reward is restored to a deceptive flower. We found generalized food deception to not only decrease inbreeding depression in the system, but concurrently have no effect on pollinator attraction and fruit set when compared with rewarding flowers.

Plant secondary metabolites in nectar: impacts on pollinators and ecological functions

SummaryThe ecological function of secondary metabolites in plant defence against herbivores is well established, but their role in plant–pollinator interactions is less obvious. Nectar is the major reward for pollinators, so the occurrence of defence chemicals in the nectar of many species is unexpected. However, increasing evidence supports a variety of potential benefits for both plant and pollinator from these compounds.Beneficial effects may include: (i) mediating specialization in plant–pollinator interactions, (ii) protecting nectar from robbery or larceny and (iii) microbial activity including preservation of nutrients in nectar from degradation and reduction in disease levels in pollinators.Secondary metabolites in nectar can be toxic or repellent to flower visitors, but equally they can go undetected or even make nectar more apparent or attractive. These biological effects are concentration dependent, so must be considered at a range of ecologically relevant doses. For example, caffeine occurs in nectar and improves honeybee memory for odours associated with food rewards, which enhances pollen transfer at naturally occurring concentrations but is repellent to honeybees at higher concentrations.This review synthesizes evidence from recent literature that supports selection for secondary metabolites in floral nectar as an adaptation that drives the co‐evolution between plants and their pollinators. However, their presence in nectar could still simply be a consequence of their defensive role elsewhere in the plant (pleiotropy). We highlight the need for more studies demonstrating measurable benefits to the plant, the importance of exposure levels and effects on target species beyond the current emphasis on alkaloids and bees.ALay Summaryis available for this article.

Attraction of males of the cupreous polished chafer Protaetia pryeri pryeri (Coleoptera: Scarabaeidae) for pollination by an epiphytic orchid Luisia teres (Asparagales: Orchidaceae)

Males of the cupreous polished chafer Protaetia pryeri pryeri (Janson) (Coleoptera: Scarabaeidae: Cetoniinae) were observed to fly toward, hover around, and land on flowers of an epiphytic orchid Luisia teres (Thunberg) Blume (Orchidaceae). Female chafers were never attracted. When on a flower, a male chafer held the lip with his legs, and then inserted his head deep into the base of the flower column, where pollinia stuck onto his frons. Subsequently some P. p. pryeri males showed pseudocopulation on the lips: downward elongation of the abdomen and extrusion of the copulatory organ. When the chafer carrying pollinia visited another flower, the pollinia were found deposited on the flower stigma. Thus this chafer was considered to be an effective pollinator for this orchid. Males were also attracted to orchid flowers covered with loose cloth that eliminated their visibility, and to a solvent extract of the flower treated on a cotton ball. Therefore, we concluded that the chafer can use olfactory cues released from the orchid flower. Chemical analysis of the nectar secreted from the flower showed that sugar content was about 2–5 %. The pseudocopulation behavior by the pollinator and the presence of nectar on the flower are intriguing and may indicate an evolutionary transitional step between rewarding and rewardless species in deceptive pollination.

Floral resource limitation severely reduces butterfly survival, condition and flight activity in simplified agricultural landscapes

Agricultural intensification has a strong negative impact on farmland biodiversity (including flower-visiting insects), but understanding the mechanisms involved in this requires experimental work. We document the impact of nectar limitation on the performance of a flower-visiting insect, the meadow brown butterfly Maniola jurtina. We conducted two types of experiments: a field experiment in agricultural landscapes with grasslands of different management intensity and an experiment in outdoor flight cages in which the nectar supply was simulated. For the field experiment, we introduced an array of nectar resources in intensively managed, nectar-poor meadows and in extensively managed, flower-rich grasslands and counted flower visitors. Despite higher butterfly abundance in the extensive meadows, our introduced nectar sources were more frequently visited in intensive meadows, indicating the lack of floral resources. The 48-h confinement under nectar-poor conditions in the flight cages had a strong negative effect on body condition, flight activity and lifetime survival compared to butterflies under nectar-rich conditions. Female lifespan was reduced by 22% and male lifespan even by 43%. Agricultural landscapes that provide limited amounts of floral nectar, and no high-quality, preferred nectar sources relative to the needs of the flower-visiting species, may create ecological sinks. Regards an insect's performance, the simple presence of nectar is not necessarily functionally adequate. The effectiveness of agri-environmental schemes for flower-visiting insects (e.g. flower strips) could be improved based on ecological and evolutionary insights on the effects of specific nectar quantities and qualities.

Foraging responses of bumble bees to rewardless floral patches: importance of within-plant variance in nectar presentation.

Spatiotemporal variation in nectar distribution is a key factor affecting pollinator movements between flowers and plants within a population. Pollinators having systematic searching ability can flexibly respond to the reward condition of floral patches, and they tend to revisit rewarding patches. However, foraging behaviour may be influenced by the nectar distribution within populations. To evaluate the effects of unrewarding experiences and plant distribution, we compared bumble bee foraging behaviours between naturally rewarding and artificially rewardless (by nectary removal) patches in two aconite populations with different plant densities. Visitation frequency to the patches, number of successive flower visits within inflorescences, and successive inflorescence visits within patches were recorded. Nectar production and standing crop were also measured. Bumble bees increased the movements between neighbouring inflorescences instead of leaving the patches when they faced rewardless flowers. A large variance in nectar production existed among flowers within plants. This might explain the observed bumble bee behaviour, because they could be rewarded by moving to the adjacent inflorescences even after a rewardless experience. Our results imply that a highly variable nectar reward in a population might mask the disadvantage of completely rewardless individuals.

Phylogeny and floral trait evolution in Jaborosa (Solanaceae)

AbstractThe genus Jaborosa (Solanaceae), which comprises 22 species endemic to southern South America, encompasses remarkable flower variation. To test if this interspecific variation is related to transitions in pollination mode and to major concomitant geological changes, phylogenetic relationships within the genus were reconstructed. To determine when such major transitions in flower traits occurred, divergence times were estimated and the evolution of relevant floral traits was studied. Sequences of four plastid spacer regions (trnH‐pbsA, trnDGUC‐trnTGGU, rpl32‐trnLUAG, ndhF‐rpl32) and one nuclear region (granule‐bound starch synthase) were used to resolve relationships among 18 Jaborosa species, using species of the “Atropina clade” as outgroup. Phylogenetic reconstruction strongly supports the monophyly of Jaborosa, with species resolved in two major clades: (1) a “Lowland clade” (L) comprised of three noticeably sphingophylous species distributed below 1000 m and north of 36° S latitude, and (2) an “Andean clade” (A) composed of the remaining species, which strongly differ in floral morphology and mainly occur at high altitudes (more than 3000 m in the Puna desert) or high latitudes (up to 53° S latitude in the Patagonia steppe of Tierra del Fuego). Species in the Andean clade have flowers that range from black, rotate, deceptive, saprophilous fly‐pollinated flowers to green, tubular, nectar‐producing flowers with a mixed pollination system. Estimation of divergence times suggests a split of Jaborosa from its sister genus Atropa L. at ca. 16.7 Ma. The split between the L and A clades possibly occurred ca. 10 Ma, with recent species diversification co‐occurring with the uplift of the Andes during the Pleistocene (ca. 1–3 Ma). Reconstruction of ancestral states of pollination mode, altitudinal distribution, and floral traits (corolla colour, flower morphology, presence of nectar) suggests that pollination by moths probably evolved once within the L clade, whereas brood‐site deceptive pollination probably evolved once within the A clade. These contrasting pollination modes are associated with changes in corolla colour, flower morphology and loss of a functional nectary.

Visual signalling of nectar-offering flowers and specific morphological traits favour robust bee pollinators in the mass-flowering treeHandroanthus impetiginosus(Bignoniaceae)

Mass flowering is a widespread blooming strategy among Neotropical trees that has been frequently suggested to increase geitonogamous pollination. We investigated the pollination ecology of the mass-flowering tree Handroanthus impetiginosus, addressing its breeding system, the role in pollination of different visitors, the impact of nectar robbers on fruit set and the function of colour changes in nectar guides. This xenogamous species is mainly pollinated by Centris and Euglossa bees (Apidae) seeking nectar, which are known to fly long distances. The flowers favour these bees by having: (1) a closed entrance in newly opened flowers which provides access only to strong bees capable of deforming the flower tube; and (2) a nectar chamber that is accessible only to long-tongued bees. Only first-day flowers with yellow nectar guides produce nectar. Pollinators prefer these flowers over second- and third-day flowers with orange and red nectar guides, respectively. Nectar robbers damage two-thirds of the flowers and this robbing activity decreases fruit set by half. We attribute the low fruit set of H. impetiginosus to the intense nectar robbing and hypothesize that visual signalling of nectar presence in newly opened (receptive) flowers reduces geitonogamy by minimizing bee visits to unrewarding (non-receptive) flowers. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176, 396–407.

Pollination ecology of the Gray Nicker Caesalpinia crista (Caesalpiniaceae) a mangrove associate at Coringa Mangrove Forest, Andhra Pradesh, India

Caesalpinia crista L., commanly known as Gray Nicker, is an oligohaline mangrove associate confined to landward marginal areas of the Coringa Mangrove Forest, Andhra Pradesh, India. The flowering occurs during the wet season from June to November. The flowers are hermaphroditic, self-compatible and exhibit a mixed breeding system. The floral characteristics that constitute melittophilous pollination syndrome include diurnal anthesis, slight fragrance, zygomorphy, yellow petals, with a flag petal displaying a conspicuous nectar guide, and the presence of nectar with a high sugar concentration. Extra-floral nectar along the rachis is an additional attractant and is easily perceivable by bees. The plant is pollinated almost exclusively by bees, especially carpenter bees. The floral characteristics such as free petals, fully exposed stamens with dry and powdery pollen grains and hairy stigma facilitate anemophily which is effective due to high winds during the rainy season. The prolific growth and near synchronous flowering at population level contribute to pollen availability in huge quantities and enable anemophily as an effective mode of pollination. The functionality of melittophily and anemophily together constitutes ambophily. Hand-pollination experiments indicated that the plant is principally out-crossing. The natural fruit set does not exceed 10%; this lowest percentage could be partly due to flower-feeding by the beetle, Mylabris phalerata. The fruits are indehiscent, 1-seeded, which are buoyant and are not dispersed far away from the parental sites. The viable seeds produce new plants in the vicinity of parental plants during the rainy season. This plant builds up its population as small patches or in pure stands and hence is important in building landward mangrove cover.

Reproductive biology of Vasconcellea quercifolia A. St.-Hil. (Caricaceae), a moth-pollinated ‘highland papaya’

Vasconcellea species, often referred to as highland papayas, are wild relatives of common papaya (Carica papaya) widely distributed in tropical America, with a preference for cooler climates. The genus deserves special attention as its species show potential as raw materials in the tropical fruit industry, papain source or as genetic resources in breeding programs of C. papaya. However, studies related to breeding system and pollination biology of genus are still unexplored. We characterize the reproductive biology of dioecious Vasconcellea quercifolia, one of the southernmost Caricaceae. According to floral shape and presence of nectar, we expected that this species had a specializated pollination system, with moths as the primary pollinators. To test this, we studied floral biology, floral visitors, pollinators, and breeding system of this species. Controlled pollination experiments show that V. quercifolia is a xenogamous species that depends on its pollinators to set fruits (18 and 79 % fruit and seed set under open-pollination, respectively). Anemophily and apomixis occur very seldom. The treatments of exclusion of floral visitors and pollen load analysis showed that the main pollinators are moths belonging to Arctiidae, Noctuidae, and Pyralidae. The only reward for pollinators is the nectar produced by male flowers. Female flowers are pollinated by deceit because they do not produce floral rewards.

HE GENERA BELOTIA Rich. AND TRICHOSPERMUM Bl. (Tiliaceae)

The genus Belotia was founded in 1845 by A. Richard (in R. de la liagra, Hist. Cuba, Bot. 1: 207), based on a single species: B. grewiifolia; liichard added Grewia mexicana DC. (1824) as a synonym.Sprague (in Kew Bull. 1921: 270-278) wrote a monograph on the knus. He characterized Belotia as follows: Presence of nectaries at the Itase of the petals and their absence on the androgynophore; the blue or Inlet, rarely white petals, the bilocular ovary with pluriovulate loculi; the a– culicidal capsule, strongly compressed transversally to the septum and a–ediscoid ciliate seeds. He than adds: In all these respects Belotia resem-Ihles the Old-World genus Trichospermum, which differs in having a pair of I nectaries at the base of the lamina, and a pseudo- umbellate inflorescence.The differences are consequently very small and since I found that le laminal nectaries occur only occasionally in one species of Tricho-tpermmn (javanicuvi), it becomes debatable, whether the inflorescence character is of such importance as to keep both genera apart.Burret (in Notizbl. bot. Garten Berlin 9: 603. 1927) keys out Belotia against Trichospermum in the following way: Trichospermum with 25-50 ovules,irregularly placed, as against Belotia with 12-16 ovules per locule in two regular rows; inflorescences in the former axillary and bi-or pluri-chasial,in Belotia axillary and terminal panicles.Furthermore he adds: fruit with 2, rarely 3 cells Trichospermum is to the 2-3 celled fruit in Belotia; this- of course -is a differential character of little or no value. Burret does not mention at all the laminal nectaries; according to him (p. 855) the number of ovules and their placentation should be the main differential character.I had at my disposal far more material of Trichospermum than Burret and could examine numerous young fruit,where the number of ovules and their placentation may be easily observed.

Does Oeceoclades maculata (Orchidaceae) reabsorb nectar?

Nectar is the most common resource offered by orchid flowers. In some cases, flowers reabsorb nectar as part of a resource-recovery strategy. Nectar is present only in the morning in the widespread orchid Oececoclades maculata (Lindl.) Lindl. To determine whether this is due to reabsorption or evaporation of water, the volume of nectar and its concentration in previously bagged flowers were determined throughout the day at two hourly intervals. In addition, the entrance to the nectary of flowers of cultivated plants was obstructed with petroleum jelly in the morning, to prevent the evaporation of water and, in the afternoon, the presence of nectar was recorded. Furthermore, manually self-pollinated flowers, also with the entrance to the nectary obstructed, had their nectary checked 24 hours after pollination to determine whether post-pollination reabsorption occurred. In addition, the period when the pollinators of O. maculata foraged for nectar was determined in order to establish whether it was associated with the period when nectar was available. The volume and concentration of nectar in O. maculata flowers vary from 0.82 μl (25.10%) between 10–12 h and 0.36 μl (33.73%) between 16–18 h and this difference is caused by evaporation of water. Post-pollination reabsorption does not occur in this species. Pollinators forage most actively between 10–12 h. Thus, O. maculata does not reabsorb nectar, but evaporative water loss is a significant factor determining the variation in the volume and concentration of this reward and this is positively correlated with butterfly visitation.

Ineffectiveness of nectar scent in generating bumblebee visits to flowers of Impatiens textori

AbstractTo clarify if bumblebees can recognize nectar through its scent in Impatiens textori flowers, we examined the behavior of Bombus diversus on nectarless flowers in which the spurs had been artificially removed. Bumblebee visits to both natural flowers and spur‐cut flowers were captured using a long‐term video recording system. Visiting behavior and frequency were compared between the two flower types. Many bumblebees visited both types of flower, and their visit frequencies were not significantly different. However, the length of stay on each flower type did differ, with the bumblebees remaining on the spur‐cut flowers for a significantly shorter time than on the natural flowers. Our results suggest that bumblebees cannot detect the absence of nectar in I. textori flowers before probing them. Therefore, the nectar scent of I. textori does not serve to attract bumblebees although the presence of nectar will detain bumblebees on flowers for longer periods.

Nectar secretion on fern fronds associated with lower levels of herbivore damage: field experiments with a widespread epiphyte of Mexican cloud forest remnants

The oldest group of plants in which nectar secretions have been observed are the Polypodiopsida (ferns sensu lato). Nectaries have been reported in a dozen extant genera. The function of these nectaries has been investigated in several fern species, and in some circumstances has been demonstrated to have an antiherbivore role, attracting and maintaining biotic defence (ants and/or other predatory arthropods). This study documents foliar nectaries in Pleopeltis crassinervata, a widespread Central American epiphyte growing on a variety of trees in cloud forest areas of Veracruz, Mexico. This is a new record for this genus and species. As previous experimental work on epiphytic species of Polypodium has demonstrated a protective role of ants for developing fronds, we conducted similar experiments (using nylon nail polish to cover nectaries rather than excluding ants with bands of sticky resin as in earlier work). The fronds of Pl. crassinervata developed over 6 weeks, at which time damage was assessed. The experiment was simultaneously conducted on a sympatric species lacking nectaries, Polypodium furfuraceum. Herbivore placement experiments were conducted with large and small caterpillars on both of these ferns. Fronds with nectaries covered suffered greater damage from herbivores over the course of their development, compared with fronds that had uncovered nectaries functioning normally. The parallel experiment on Po. furfuraceum showed no difference between manipulated and control fronds. Six species of ants (Brachymyrmex minutus, Crematogaster formosa, Paratrechina longicornis, Solenopsis geminata, S. picea and Wasmannia auropunctata) were observed visiting nectaries of Pl. crassinervata; most were effective in removing herbivore larvae placed on the fronds. The long evolutionary history of ferns may explain why some previous studies of fern nectaries have shown little or no benefit to ferns from nectary visitors, as any coevolved herbivores are those resistant to ant defence. The results suggest that ants protect Pl. crassinervata fronds against herbivory. The presence of nectaries, and the relationship with ants, may contribute to this fern's widespread occurrence and persistence in the face of disturbance, though many other factors also play a role. Ant defence may be more likely to benefit a widespread species of disturbed habitats that encounters a wide range of non-adapted herbivores.