Floral Visitors Research Articles

Foraging behavior and pollination efficiency of generalist floral visitors of Leucas aspera (Willd.) link (Lamiaceae)

Pollination services from insects are important for the reproductive success of flowering plants. Measuring the effectiveness of floral visitors provide relative contributions of different insect taxa to pollination services. Here, we tested the efficiency of pollinators visiting flowers of Leucas aspera based on single-visit pollen deposition and visitation frequency. We monitored the visitation behaviors of different insects during the peak flowering seasons. We observed a total of 23 insect taxa representing three orders and eight families, among them 18 floral visitors deposited a significant proportion of pollen grains on the stigma. The flower handling time was significantly higher for most butterfly species relative to bees and flies. The number of flowers and inflorescences visited during each foraging bout varied significantly among pollinators. The proportion of conspecific and heterospecific pollen deposited on the stigma varied significantly among floral visitors. L. aspera was not pollen-limited, and the presence of fruit and seed sets in the pollinator exclusion treatments indicated a self-compatible breeding system. Overall, the findings suggested that the different flower visitors of L. aspera provide complementary pollination services and highlight the importance of having diverse communities of pollinators to ensure successful pollination and reproductive success.

Temperature and soil moisture manipulation yields evidence of drought-induced pollen limitation in bee-pollinated squash.

Climate change alters environmental conditions in ways that directly and indirectly affect plants. Flowering plants, for example, modify reproductive allocation in response to heat and drought stress, and such changes can in turn affect pollinator visitation and, ultimately, plant reproduction. Although the individual effects of warming and drought on plant reproductive allocation are well known, these factors may interact to influence reproduction. Here, we conducted a fully crossed temperature by irrigation manipulation in squash (Cucurbita pepo) to test how temperature and soil moisture variation affect pollinator-mediated reproduction. To tease apart the direct and indirect effects of temperature and soil moisture, we compared hand-pollinated plants to bee-pollinated plants and restricted bee foraging (i.e., pollen transfer) to one experimental group per day. Temperature and soil-moisture limitation acted independently of one another: warming decreased flower size and increased pollen production, whereas the effects of soil-moisture limitation were uniformly inhibitory. While treatments did not change squash bee (Xenoglossa spp.) behavior, floral visitation by the honey bee (Apis mellifera) increased with temperature in male flowers and decreased with soil moisture in female flowers. Pollen deposition by bees was independent of plant soil moisture, yet reducing soil moisture increased pollen limitation. This result stemmed at least in part from the effects of soil-moisture limitation on pollen viability; seed set declined with increasing deposition of fluorescent pigment (a proxy for pollen) from plants experiencing decreased soil moisture. These findings suggest that the transfer of lower-quality pollen from plants experiencing soil-moisture limitation led to drought-induced pollen limitation. Similar effects may occur in a wide variety of flowering plant species as climate warming and drought increasingly impact animal-pollinated systems.

Zygomorphic flowers last longer: the evolution of floral symmetry and floral longevity.

Floral longevity, the length of time a flower remains open and functional, is a phylogenetically conserved trait that balances floral costs against the rate at which flowers are pollinated. Floral symmetry has long been considered a key trait in floral evolution. Although zygomorphic (bilaterally symmetric) flowers typically receive fewer floral visitors than actinomorphic (radially symmetric) flowers, it is yet to be determined whether this could be associated with longer floral longevity. Using newly collected field data combined with data from the literature on 1452 species in 168 families, we assess whether floral longevity covaries with floral symmetry in a phylogenetic framework. We find that zygomorphic flowers last on average 1.1 days longer than actinomorphic flowers, a 26.5% increase in longevity, with considerable variation across both groups. Our results provide a basis to discuss the ecological and evolutionary costs of zygomorphy for plants. Despite these costs, zygomorphy has evolved numerous times throughout angiosperm history, and we discuss which rewards may outweigh the costs of slower pollination in zygomorphic flowers.

The Key Role of Amino Acids in Pollen Quality and Honey Bee Physiology-A Review.

When studying honey bee nutrition, it is important to pay attention not only to the quantity but also to the quality of pollen for floral visitors. The recommended way to determine the value of pollen is to determine both the protein concentration and the amino acid composition in the insect's hemolymph. In addition, the composition of pollen also includes lipids, sterols and biogenic elements such as carbon, nitrogen, etc. Very high protein concentration is observed in aloe pollen, averaging 51%. Plants with a high protein content, at the level of 27% in Europe, are rapeseed and phacelia. In turn, a plant that is poor in protein (at the level of 11%) is buckwheat. The aforementioned plants are sown over very large areas. Vast acreages in Central and Eastern Europe are occupied by pollen- and nectar-providing invasive plants, such as goldenrod. Therefore, bees are forced to use one food source-a mono diet-which results in their malnutrition. In the absence of natural pollen, beekeepers use other foods for bees; including soy protein, powdered milk, egg yolks, fish meal, etc. However, the colony is the strongest when bees are fed with pollen, as opposed to artificial protein diets. More research is needed on the relationship between bee pollen composition and nutrition, as measured by protein concentration and amino acid composition in apian hemolymph, colony strength, honey yield and good overwintering.

Differential impacts of land‐use change on multiple components of common milkweed (Asclepias syriaca) pollination success

AbstractLand‐use change is one the greatest threats to biodiversity and is projected to increase in magnitude in the coming years, stressing the importance of better understanding how land‐use change may affect vital ecosystem services, such as pollination. Past studies on the impact of land‐use change have largely focused on only one aspect of the pollination process (e.g., pollinator composition, pollinator visitation, and pollen transfer), potentially misrepresenting the full complexity of land‐use effects on pollination services. Evaluating the impacts across multiple components of the pollination process can also help pinpoint the underlying mechanisms driving land‐use change effects. This study evaluates how land‐use change affects multiple aspects of the pollination process in common milkweed populations, including pollinator community composition, pollinator visitation rate, pollen removal, and pollen deposition. Overall, land‐use change altered floral visitor composition, with small bees having a larger presence in developed areas. Insect visitation rate and pollen removal were also higher in more developed areas, perhaps suggesting a positive impact of land‐use change. However, pollen deposition did not differ between developed and undeveloped sites. Our findings highlight the complexity evaluating land‐use change effects on pollination, as these likely depend on the specific aspect of pollination evaluated and on the of the intensity of disturbance. Our study stresses the importance of evaluating multiple components of the pollination process in order to fully understand overall effects and mechanisms underlying land‐use change effects on this vital ecosystem service.

Extreme heat exposure of host plants indirectly reduces solitary bee fecundity and survival.

Extreme heat poses a major threat to plants and pollinators, yet the indirect consequences of heat stress are not well understood, particularly for native solitary bees. To determine how brief exposure of extreme heat to flowering plants affects bee behaviour, fecundity, development and survival we conducted a no-choice field cage experiment in which Osmia lignaria were provided blueberry (Vaccinium corymbosum), phacelia (Phacelia tanacetifolia) and white clover (Trifolium repens) that had been previously exposed to either extreme heat (37.5°C) or normal temperatures (25°C) for 4 h during early bloom. Despite a similar number of open flowers and floral visitation frequency between the two treatments, female bees provided with heat-stressed plants laid approximately 70% fewer eggs than females provided with non-stressed plants. Their progeny received similar quantities of pollen provisions between the two treatments, yet larvae consuming pollen from heat-stressed plants had significantly lower survival as larvae and adults. We also observed trends for delayed emergence and reduced adult longevity when larvae consumed heat-stressed pollen. This study is the first to document how short, field-realistic bursts of extreme heat exposure to flowering host plants can indirectly affect bee pollinators and their offspring, with important implications for crop pollination and native bee populations.

By the Way, Does the Presence of Ants in Flowers Interfere with Floral Visitation, or Not? A community Ecology Study

By the Way, Does the Presence of Ants in Flowers Interfere with Floral Visitation, or Not? A community Ecology Study

Onion (Allium cepa L.) Attracts Scoliid Wasps by Means of Generalist Floral Volatiles.

Onion flowers require pollinator-mediated cross-pollination. However, the cues that pollinators use to locate the flowers are not well understood. The floral scent, along with floral visual cues, might acts as important signal to pollinators in order to locate the floral resources. We used electrophysiological methods combined with behavioural assays to determine which compounds in a floral scent are more attractive and thus biologically important to foraging scollid wasps. The majority of the molecules identified as floral fragrances in onions are common compounds that are already known from other angiosperms, and onion floral scents were predominately composed of aromatic components. The antennae of scoliid wasps responded to a large number of compounds, among them o-cymene, cis-β-ocimene, benzaldehyde and allo-ocimene were behaviourally active. In contrast to other wasp flowers investigated nectar analysis demonstrated the dominance of hexose sugars over sucrose. Our findings provide fresh insights into the floral volatile chemistry of a key vegetable crop grown around the world. We demonstrate here that onion is using generalist floral volatiles to attract floral visitors. This insight could be utilised to make onion blooms more attractive to minor pollinators as well as major pollinators in order to maximise seed set.

The mechanical fit of the flowers of Crotalaria paniculata Willd. for the pollination success of large-bodied bees

The present study investigates the morphology of floral parts adapted towards the mode of pollination by bees in a lesser-known shrub, Crotalaria paniculata Willd of the family Fabaceae. The morphology and orientation of flowers, colour, shape, size and number of each floral part were recorded. The floral odour was assessed qualitatively at various stages of flowers manually and the quantity of nectar produced per flower was also measured. The flowering individuals were regularly monitored to observe the floral visitors and their foraging activity on a series of aged flowers. The performance of each floral visitors like visitation frequency, handling time, relative abundance, activity rate, visitation rate index and visitor activity index was calculated. The flowers of C. paniculata are typical papilionaceous and keel-blossom types that function as floral advertisement and nectar and pollen grains are served as floral rewards. The standard petal serves an advertisement whereas the wing-keel complex acts as a landing platform for floral visitors. The large-bodied bees tend to break the wing-keel complex which facilitates cross-pollination. Xylocopa latipes (Apidae) was observed as the most effective pollinator due to their higher frequency of visits, activity rate, visitation rate index and visitor activity index. Due to the pressure applied by large-bodied bees like Xylocopa latipes by landing on the wing-keel complex, the reproductive parts become exposed and the stigma brushes the pollen load in the body of the visitors and effect cross-pollination. The study concludes that large-bodied bees are effective floral visitors of C. paniculata which effect cross-pollination.

Flower visitor networks: Reduced reproductive success driven by antagonists in a hummingbird‐pollinated species

AbstractFlower–animal interactions encompass a continuum of mutualistic to antagonistic behaviors. Although the importance of pollinators in interaction networks has been widely reported, the role of floral antagonists remains overlooked. In Collaea cipoensis, an endemic shrub from southeastern Brazil, we modeled an individual‐based network assessing the flower visitors' functional behavior and tested if plant centrality increases fitness. Centrality indicates how well‐connected a given plant is with the rest of the conspecifics through shared flower visitors. Specifically, we tested if flower visitor interactions are amplified by many‐flowered individuals, and whether the relationship between centrality and plant fitness encompasses the effects of mutualists or antagonists. Subsequently, we quantified each visiting species' effectiveness. Antagonistic interactions were the most frequent in the network (97% of visits), primarily conducted by the nectar‐robbing bee Trigona spinipes (66%), which was also the most central species and detrimental antagonist. The hummingbirds Colibri serrirostris and Eupatomena macroura were the most efficient pollinators, with a high contribution to the quantity—floral visitation—and the quality—viable seeds—components, respectively. Many‐flowered plants showed greater centrality, which boosted the plant's cohesion in the network and increased flower visitation. Accordingly, many‐flowered plants were better connected, mainly due to antagonistic visitors. Thus, centrality increases were not positively translated into more reproductive success. Our results reinforce the dynamic scenarios of flower–animal interactions, with consequences to plant reproductive ecology. We highlight the importance of incorporating distinct types of interactions to unveil the complexity of interacting systems, that when not explored, hide potential evolutionary consequences for plant reproductive success.Abstract in Portuguese is available with online material.

The earliest large carpenter bee (Xylocopa) and its adhering pollen (Araliaceae, Theaceae)

AbstractThe association of pollinators with their host plants is a critical element of ecosystem functioning and one that is usually determined indirectly in the fossil record from specific morphological traits of flowers or putative pollinating animals. The exceptionally fine preservation at Messel, Germany, offers an excellent source of data on pollen from fossil flowers as well as preserved adhering to insects as direct evidence of their association with specific floral lineages. Here, we report on pollen recovered from the body and legs of a large carpenter bee (Apidae: Xylocopinae: Xylocopini) from the Eocene of Messel. The fossil is the earliest occurrence of the tribe Xylocopini and represents an extinct subgenus and species, described as Xylocopa (Apocolyx) primigenia subgen. et sp. nov. Two eudicot pollen types were recovered from the bee, one of the family Theaceae (Asterids: Ericales) and another of Araliaceae (Euasterids: Apiales). The pollen grains are compared with various extinct and extant pollen types, and data on floral visitors to modern theaceous and araliaceous flowers are explored in relation to understanding the association of the fossil carpenter with these floral types in the paratropical Eocene biota of Messel.

Recent evolutionary divergence in a plant ring-species is not accompanied by floral phenology or pollinator shifts

Background and aims – The study of factors and processes involved in evolutionary divergence can inform how biodiversity is generated and maintained. We evaluate shifts in phenology or in pollination systems as potential barriers to gene exchange and thus promoters of divergence at the population-species boundary in the plant ring-species Euphorbia tithymaloides in the Caribbean. Material and methods – Combining collections-based and field-based observations and measurements, we evaluate evidence supporting that shifts in tempo of reproductive activity (floral phenology) or pollinator guilds (using visitation as a proxy) could be acting as mechanisms promoting divergence in E. tithymaloides. We focus on the geographic region where evolutionary divergence in this species has been documented: Greater and Lesser Antilles. Phenology data were derived from herbaria and online databases, for a total of 376 records across the Greater and Lesser Antilles. We quantified and characterized reward (nectar n = 13 sites) and gathered visitation data using direct observation (n = 12 sites) for a total of over 133 hours of observation/site. Key results – The peak of floral activity of E. tithymaloides is in winter, when days are short (~late October–late May). Under natural conditions, plants in the Antilles produce up to 22.4 µL of nectar, with mean sugar concentrations of ~ 46.5 ºBrix that amount to up to 10.3 mg of total sugars, with no significant differences observed between plants of the Lesser and Greater Antilles. Hummingbirds are the main floral visitors of E. tithymaloides in both areas: Greater Antilles: 61%, Lesser Antilles: 85%, and network analyses support a floral visitor community turnover across islands/countries. Conclusion – Evolutionary divergence in Caribbean E. tithymaloides along the Greater and Lesser Antilles is not accompanied by shifts in floral phenology or pollinator systems. Other factors, like pollinator turnover or pollinator-plant trait matching, might be at play. We outline hypotheses to this effect.

Pollination by birds, non-flying mammals, and European honeybees in a heathland shrub, Banksia catoglypta (Proteaceae)

Abstract Vertebrate pollination has evolved in many plant lineages, with pollination by birds the most prevalent strategy. However, in Banksia (Proteaceae) many species are visited by a combination of nectarivorous birds, non-flying mammals (NFMs), and insects, though the relative importance of these pollen vectors for reproduction remains poorly understood. Here, we investigate the contribution to fruit set of birds, NFMs, and insects in Banksia catoglypta—a heathland shrub from south-west Australia. This species flowers in winter and produces large, golden-yellow inflorescences that are typically presented near the ground and consist of rigid, strongly scented flowers with a long stigma-nectary distance—suggesting pollination by vertebrates. The primary floral visitors were white-cheeked honeyeaters (Phylidonyris niger), honey possums (Tarsipes rostratus), house mice (Mus musculus), and introduced European honeybees (Apis mellifera), all of which carried B. catoglypta pollen. Banksia catoglypta was found to be obligately outcrossing with no evidence of pollen limitation. Selective exclusion of flying pollinators revealed that inflorescences pollinated solely by NFMs produced 50% fewer fruit than open-pollinated controls. Therefore, while mammals are pollinators of B. catoglypta, they may contribute comparatively little to fruit set in some Banksia species displaying floral traits considered adaptations to NFM pollination. Exclusion of vertebrate pollinators had no effect on fruit set, demonstrating that European honeybees can be effective pollinators of some primarily vertebrate-pollinated plants.

Pollination Syndrome, Florivory, and Breeding System of Satyrium nepalense var. ciliatum (Orchidaceae) in Central Yunnan, China.

Research on Satyrium nepalense var. ciliatum (Lindl.) Hook. f. has primarily focused on populations in Northwestern Yunnan, with limited studies on pollination syndromes and insect behavior. In addition, it is geographically limited in its breeding system studies. Here, pollination syndromes, florivory, and breeding systems of S. nepalense var. ciliatum from Liangwang Mountain (Central Yunnan, China) were investigated through field work, microscope, scanning electron microscope (SEM), and parafin section. It was revealed that the pollination syndrome was possessing out-crossing, such as bright color, a developed rostellum, nectar glands in the spur, and food hairs at the lip base. The color and nectar attracted flower visitors, and florivory was observed. Some flower visitors pollinated their companion species. Ants were identified as floral visitors for the first time in Satyrium, although substantial pollination was not observed. Ants might be potential pollinators. S. nepalense var. ciliatum possessed a mixed breeding system, including selfing, out-crossing, and apomixis, with apomixis being predominant in nature. It is suggested that the pollination syndrome, florivory, and pollination competition would contribute to its mixed breeding systems, particularly leading to the occurrence of apomixis.

Insect floral visitors of thermo-Mediterranean shrubland maquis (Ajaccio, Corsica, France).

The Mediterranean Region represents a biodiversity hotspot with a high rate of endemism. In its western part, Corsica Island is notable in terms of biodiversity due to its large surface and its large range of habitats from seaside to alpine biotopes. Amongst diverse groups, insects, notably the main orders of pollinators composed of Coleoptera, Hymenoptera, Diptera and Lepidoptera, represent a good part of the insular richness. Our sampling effort focused on the insects from these four orders visiting flowers in a characteristic thermo-Mediterranean vegetation. Our database is an insight into the Corsican floral visitor biodiversity from three sites separated by a few kilometres in the region of Ajaccio during 13 months over two successive years. In total, 4012 specimens were sampled and 252 species or morpho-species identified from 133 genera and 47 families. Beetles were by far the most abundant order representing about 54% of the sampled specimens. The most diverse order was the Hymenoptera representing 39% of the species. Our continuous survey showed that these orders are temporally dynamic both between years and between seasons in terms of abundance and diversity.

Fire Severity Effects on Floral Visitor Community and Fruit Production of Wax Currant1

Fire Severity Effects on Floral Visitor Community and Fruit Production of Wax Currant1

First evidence of late-acting self-incompatibility in the Aristolochiaceae.

Most Aristolochiaceae species studied so far are from temperate regions, bearing self-compatible protogynous trap flowers. Although self-incompatibility has been suggested for tropical species, the causes of self-sterility in this family remain unknown. To fill this gap, we studied the pollination of the tropical Aristolochia esperanzae, including the physical and physiological anti-selfing mechanisms. Floral visitors trapped inside flowers were collected to determine the pollinators. Protogyny was characterized by observing the temporal expression of sexual phases and stigmatic receptivity tests. The breeding system was investigated using hand-pollination treatments. Pollen tube growth was observed using epifluorescence to identify the self-incompatibility mechanism. Flies were the most frequent visitors found inside A. esperanzae trap flowers, with individuals from the family Ulidiidae being potential pollinators since they carried pollen. The characteristic flower odour and presence of larvae indicate that A. esperanzae deceives flies through oviposition-site mimicry. Although this species showed incomplete protogyny, stigmatic receptivity decreased during the male phase, avoiding self-pollination. Fruits developed only after cross- and open pollination, indicating that the population is non-autonomous, non-apomictic, and self-sterile. This occurred through a delay in the growth of geitonogamous pollen tubes to the ovary and lower ovule penetration, indicating a late-acting self-incompatibility mechanism. Our findings expand the number of families in which late-acting self-incompatibility has been reported, demonstrating that it is more widespread than previously thought, especially when considering less-studied tropical species among the basal angiosperms.

Effects of Thidiazuron and Pollinator visits on Fruit Set and Quality of 'Maxigala' Apple Trees

The objective of this study was to assess the effects of thidiazuron (TDZ) application and pollinator visits on fruit set and quality in apple trees of the cultivar Maxigala. The experiment was conducted at the Temperate Fruit Farming Experimental Station of the Brazilian Agricultural Research Corporation (EMBRAPA Grape and Wine), in Vacaria, RS, Brazil. The evaluated treatments were: TDZ application; floral visitors combined with TDZ application; floral visitors; and control (no floral visitors with no TDZ application). The highest mean final fruit set was found for the treatment with only TDZ application, followed by that with floral visitors and TDZ application.

Contradistinctive floral attributes, pollination guilds and their consequence on the outcrossing rate in two elevational morphs of Rhododendron arboreum Sm.

Infraspecific floral trait variations may appear in response to elevational differences in alpine plant species. There is enormous information on the selection of such morphs mediated by biotic and/or abiotic variables. Whether such differences contribute to differences in reproductive strategy and mating outcomes is rarely investigated. We investigated these aspects in two distinct elevational floral morphs (Red and Pink) of Rhododendron arboreum Sm. in Western Himalaya. The red morphs occupy the lower elevations while pink morphs the higher elevations. The two morphs differ in floral traits like phenology, dimension, display, quality of floral rewards, and pollinators that happen to influence interaction with available pollinator pool at each elevation. The pink morph exhibits entomophily, while the red ones show ornithophily. Although experimental pollinations established that both the morphs are self-compatible, selfing results in significantly lower fruit-set than either cross- or open-pollinations. The outcrossing rate in the red morph, as determined by using simple sequence repeat (SSR) markers, was higher (tm=0.82) than that in the pink morph (tm=0.76), with a tendency of the latter to be shifting towards mixed-mating strategy. However, the extent of biparental inbreeding was comparable among the two morphs. It is inferred that the differences in the mating outcomes among the morphs in the tree species are linked to those emerging from floral traits and the pollination by different functional groups of floral visitors.

Nectar robbing effects on pollinators of a key nectar source plant (Tecoma fulva, Bignoniaceae) in a dry tropical Andean valley

AbstractZoophilous flowering plants have features to attract their pollinators, which may also be used by exploiters like nectar robbers. Nectar robbers access nectar by probing flower corollas (primary robbing) or use existing holes (secondary robbing). Nectar robbing can negatively impact a plant's fitness directly by damaging the reproductive structures of the flower or indirectly by modifying the visitation patterns of pollinators. We tested the hypothesis that the robbed flowers are less visited by legitimate pollinators by comparing floral visitors and visitation frequency in primary‐, secondary‐, and un‐robbed flowers of Tecoma fulva spp. Altoandina, a native shrub species that is an important nectar source for nectarivores in the dry valleys of the Bolivian Andes (Bignoniaceae). The Giant Hummingbird, Patagona gigas (Trochilidae), was the main visitor of T. fulva and visited more frequently un‐robbed flowers, followed by secondary robbed and primary robbed flowers. The variation in visitation frequency may result in less pollen transport to robbed flowers, which may have negative consequences for the biological fitness, probably manifested in decreased seed production.Abstract in Spanish is available with online material.