Floral biology ofTrapa natans var.japonica

The floral behavior and insect visitors ofTrapa natans L. var.japonica Nakai are described. Individual flowers bloom for one day and are visited primarily by Coleoptera and Hemiptera. Exclusion experiments indicate flowers are self- and cross-compatible as well as apomictic. Insect visitors assist in self-pollination as they more within the flower.     

Flowers and Beetles in the South American Tropics

Examples of beetle pollination in the South American tropics are given. The case histories refer to representatives of the families Cyclanthaceae, Annonaceae, and Araceae. In most cases the cantharophilous syndrome does not seem to be the result of coevolution but of a one-sided adaptation of flowers to the behavior, necessities, and sense-capacities of beetle species. It is emphasized that cantharophily may not necessarily be an indication of ancientness of a flower/insect relationship. Besides primitive angiosperms, there are derived and modern groups which, in their pollination, are specialized for beetles. Carludovica palmata (Cyclanthaceae) is pollinated by small curculionids which are attracted by odors in the early morning hours. Annona coriacea (Annonaceae) and Philodendron selloum (Araceae) are pollinated by large dynastid scarab beetles in the evening hours. In all three species thermogenesis occurs. Although belonging to widely separate systematic groups, Annona flowers and Philodendron inflorescences have a similar pollination biology, which indicates that their adaptations to beetles are the result of convergent evolutionary developments.     

Flower-visiting insect communities on two closely related Rhododendron species flowering in different seasons

To determine the effects of flowering season on the community structure and dynamics of flower visitors, I examined annual and hourly variation in flower-visiting insects on two Rhododendron species in a deciduous secondary forest in central Japan. Rhododendron reticulatum flowers from late March to mid-April, whereas R. macrosepalum flowers from late April to late May. Bagged and hand-pollination experiments indicated that outcrossing by flower visitors was important for the pollination of both R. reticulatum and R. macrosepalum. Pollinator and pollen limitation were detected in both Rhododendron species, although the extent of both differed between the two species. The flowers of both Rhododendron species were visited by insects of diverse taxa, including Hymenoptera, Diptera and Lepidoptera. The composition of flower visitors differed between R. reticulatum and R. macrosepalum, although a few species visited both of them. The beefly Bombylius major (Diptera: Bombyliidae) most frequently visited R. reticulatum, whereas the bumblebee Bombus ardens ardens (Hymenoptera: Apidae) most frequently visited R. macrosepalum. Hourly changes in the number of flower visitors also differed between R. reticulatum and R. macrosepalum; insects visited R. reticulatum flowers less frequently in the morning than in the afternoon, whereas insect visitations to R. macrosepalum flowers did not differ between morning and afternoon. Differences in both insect community structure and hourly changes of visitations between the two Rhododendron species occurred annually and may be related to the life history of the abundant visitor species as well as flowering phenology.     

Temporal and microclimatic partitioning of the floral resources of Justicia aurea amongst a concourse of pollen vectors and nectar robbers

Summary The flowers of Justicia aurea, morphologically characteristic of ornithophily, attracted a diverse array of foragers where they occurred as a dense stand in the tropical forests at La Selva, Costa Rica, and so provided an arena for this study of competition and coexistence. Two hummingbird species (Phaethornis superciliosus and Campylopterus hemileucurus) visited the flowers legally early in the morning, and defended the nectar resource; a third smaller bird (P. longuemareus) foraged for nectar throughout the day but collected it illegally by piercing the corollas. In addition, nectar was harvested illegally by four species of stingless bee (Trigona) and by ants, creating a further drain on the limited floral resources.Consideration of the diurnal patterns of foraging activities in combination with a spatial axis (defined here in terms of microclimate and insolation) nevertheless showed a good separation of flower visits for the different nectarivores. Hummingbirds visited flowers in zones where the reward was highest, while insects foraged to minimise their energetic costs; each of these factors could in turn be related to microclimatic considerations. A comprehensive scheme of resource utilisation could therefore be extracted from the field observations and interpreted in these terms. The limited area of niche overlap thus revealed corresponded closely with the situations where direct interference competition was observed, between hummingbird species or between bees and aggressive ants.     

REPRODUCTIVE BIOLOGY OF WEEDY AND CULTIVATED MIRABILIS (NYCTAGINACEAE)

The reproductive biology of Mirabilis nyctaginea (Michx.) MacM. contributes to the plant's success as a weed and invader of disturbed habitats whereas that of M. Jalapa L. reflects its success as a cultivar. Plants of M. nyctaginea flowering in early summer produce chasmogamous flowers whereas plants flowering in late summer produce cleistogamous flowers. Plants of both species are self-compatible and flower behavior contributes to self-pollination. The flowers open late in the afternoon and close late the following morning. In M. nyctaginea flowers are effectively pollinated by bees both in the afternoon and morning, and during the night moths are effective pollinators. Mirabilis Jalapa is self-pollinating. Anther closure during rain showers, a result of water droplets falling into open anthers, minimizes pollen loss and is highly adaptive. The reproductive biology of M. nyctaginea and M. Jalapa is contrasted with that of the obligate outcrossing species M. multiflora (Torr.) Gray and M. froebelii (Behr) Greene.     

Persistence of flower visitors and pollination services of a generalist tree in modified forests

Flower‐visiting insects provide essential pollination services to many plant species. It is thus of critical importance to understand the effects of anthropogenic landscape modification on these animals. Particularly at the landscape scale, we still lack information on how flower visitors are affected by different intensities of human disturbance. In this study, we chose six representative types of forest modification across a heterogeneous South African landscape. At 36 study sites we observed insect visitation to Celtis africana flowers in two consecutive years. This generalist tree species has small unspecialized flowers which we found to be pollinated by a diverse array of insects as well as by wind. Visitation rates to flowers of C. africana differed significantly among the six forest types and between two study years. Visitation rates were enhanced in modified forests, facilitated by a high abundance of feral honeybees (Apis mellifera). Fruit set in C. africana showed significant positive associations with insect visitation and with the diversity of flower visitors, but was only weakly predicted by forest type. Our findings imply that even though forest modification can strongly alter flower visitors, pollination services for trees with unspecialized flowers may persist at a landscape scale. We advise conservation managers to maintain modified forest fragments in addition to natural forests as these may contribute to sustain pollination services in human‐modified landscapes.     

Assemblage of flower visitors to Dillenia suffruticosa and possible negative effects of disturbances in Sarawak,Malaysia

Dillenia suffruticosa (Dilleniaceae), a common pioneer shrub in Southeast Asia, is broadly distributed along roadsides. This species flowers throughout the year and is thought to be a keystone species for maintaining populations of flower visitors. To examine the flower visitors of this species, we conducted field surveys and described the behaviors of each flower visitor species within four different research sites: Primary Forests 1 and 2, Secondary Forest, and Mixed Vegetation. We caught 1087 individuals belonging to 51 species from 11 insect families and one species of arachnid. Most flower visitors belonged to Hymenoptera (98.6% of individuals); Trigona spp. and Xylocopa spp. (Apidae) accounted for 64.0% and 20.0%, respectively, of all caught individuals. According to observations of behavior by each species, effective pollinators may include Xylocopa spp. and Amegilla spp. (Apidae). We compared the research results among four research sites and found that the effective pollinators were not different among sites. However, the number of species and the abundances of flower visitors decreased in disturbed areas, especially in Secondary Forest. This research suggests the effects of human disturbances on the diversity and abundance of flower visitors.     

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.     

Is floral morphology a good predictor of floral visitors to Antirrhineae (snapdragons and relatives)?

• The association between plants and flower visitors has been historically proposed as a main factor driving the evolutionary change of both flower and pollinator phenotypes. The considerable diversity in floral morphology within the tribe Antirrhineae has been traditionally related to pollinator types. We used empirical data on the flower visitors from 59 Antirrhineae taxa from the literature and our own field surveys, which provide an opportunity to test whether flower phenotypes are reliable predictors of visitors and pollinator niches.
• The degree of adjustment between eight key floral traits and actual visitors was explored by testing the predictive value of inferred pollinator syndromes (i.e. suites of floral traits that characterise groups of plant species related to pollination). Actual visitors and inferred pollinator niches (categorisation of visitors’ association using a modularity algorithm) were also explored using Linear Discriminant Analysis (LDA).
• The bee pollinator niche is correctly classified for flowers with dull corolla colour, without nectar guides, as the most important predictor. Both predictive value and statistical classification prove useful in classifying Antirrhineae taxa and the bee pollinator niche, mostly as a consequence of the high proportion of genera and taxa with occluded corollas primarily visited by bees. Our predictive approach rendered a high Positive Predictive Value (PPV) of floral traits in the diagnosis of visitors/pollinator niches. In particular, a high PPV was found for bees as both visitors and forming pollinator niches. In addition, LDA showed that four pollinator niches are well defined based on floral traits.
• The large number of species visited by bees irrespective of pollinator syndromes leads us to hypothesise their generalist pollinator role, despite the phenotypically specialised flowers of Antirrhineae.

     

Does Invasion of Exotic Plants Promote Invasion of Exotic Flower Visitors? A Case Study from the Temperate Forests of the Southern Andes

Habitat disturbance, particularly of human origin, promotes the invasion of exotic plants, which in turn might foster the invasion of alien-interacting animals. Here we assess whether the invasion of exotic plants – mostly mediated by habitat disturbance – facilitates the invasion of exotic flower visitors in temperate forests of the southern Andes, Argentina. We recorded visit frequencies and the identity of visitors to the flowers of 15 native and 15 exotic plant species occurring in different highly disturbed and less disturbed habitats. We identified three alien flower visitors, the hymenopterans Apis mellifera, Bombus ruderatus, and Vespula germanica. We found significantly more visitation by exotic insects in disturbed habitats. This pattern was explained, at least in part, by the association between alien flower visitors and flowers of exotic plants, which occurred more frequently in disturbed habitats. However, this general pattern masked different responses between the two main alien flower visitors. Apis mellifera exploited almost exclusively the flowers of a subset of herbaceous exotic plants that thrive under disturbance, whereas B. ruderatus visited equally flowers of both exotic and native plants in both disturbed and undisturbed habitats. We did not find any strong evidence that flowers of exotic plants were more generalist than those of native plants, or that exotic flower visitors were more generalist than their native counterparts. Our results suggest that alien plant species could facilitate the invasion of at least some exotic flower visitors to disturbed habitats. Because flowering plants as well as flower visitors benefit from this mutualism, this association may enhance, through a positive feedback, successful establishment of both exotic partners.     

On flower visitors and true pollinators: The case of protandrous Heracleum sphondylium L. (Apiaceae)

Hogweed (Heracleum sphondylium L.), a common European umbellifer, is very variable in terms of flower and inflorescence morphology. Its flowers are visited by numerous insects, yet little is known about the importance of the particular insect taxa. I observed umbels of two colour morphs (subspecies) of Heracleum sphondylium growing in NE Poland, which were visited by more than 108 insect species during two study seasons. Analysis of the insects' importance suggests that the most efficient pollinators are the medium-sized flies Eriozona syrphoides, and Lucilia spp. (Diptera). Bumblebees Bombus terrestris (Hymenoptera), beetles of genus Stenurella spp. and Dasytes spp. (Coleoptera) and flies Eristalis spp., Meliscaeva cinctella, Phaonia angelicae and Thricops nigrifrons also contribute to pollination of the studied plants, but their efficiency shows considerable seasonal variation. Although the dense umbels of the white flowered H. sphondylium subsp. sphondylium are generally more attractive for insect visitors than the loose yellowish inflorescences of H. sphondylium subsp. sibiricum, these taxa do not seem to attract different sets of the pollinators. For both subspecies, flowers in the staminate phase were visited significantly more often than those in the pistillate phase. Some flower visitors visited the staminate phase only, which suggests they may be parasites rather than pollinators.     

Movement-assisted dichogamy in Atamisquea emarginata (Capparaceae)

 Various aspects of the reproductive biology of Atamisquea emarginata Miers ex Hook. et Arn. were studied in a population from Tucumán, northern Argentina. Flowering took place in late (austral) spring to early summer. The creamy white, entomophilous flowers were protandrous and lasted 3.5–4.5 days. A pleasant odor along with nectar and pollen attracted 36 mostly diurnal insect species of which 41.7% were Hymenoptera, 38.9% Lepidoptera and 19.4% Diptera. However, 75% from all recorded species were infrequent, and domestic bees made ca. 94% of all visits. One halictid bee, one sphecid wasp, one myzinid wasp, four small- to medium-sized butterflies and a hawkmoth completed the set of relatively frequent insect visitors. Pollen and stigma were presented in the same place within the flower, but interference was prevented by a movement-assisted, complete dichogamy mechanism in which the bending ability of the gynophore played a fundamental role. This form of dichogamy was previously unknown in the Capparaceae. In comparison with the known species of the closely allied genus Capparis L., A. emarginata has diurnal, smaller, longer-lasting flowers, that offer much smaller nectar amounts, and that attract a rather generalized array of non-hovering visitors, while Capparis behaves as a more crepuscular-biased sphingophile or ornithophile or chiropterophile. Low levels of seed set under bagging indicates dependence on insect visits and are partly congruent with an earlier report of self-incompatibility in A. emarginata. Pollen tubes arrived to ovules in 90.6% of the inspected flowers. Fruit set of open-pollinated flowers was 43.6%–53.7%. Ninety-five percent of all ovules were regularly aborted in each fruiting ovary; thus, each fruit contained 1.2 developed seeds. Full-sized individuals were expected to produce ca. 10,700 potential offspring per year. Received August 19, 2002; accepted October 8, 2002 Published online: February 7, 2003     

Decorative sterile flowers in nine Japanese species of Viburnum (Adoxaceae) and their influence on pollinator visits

Framed inflorescences are unique arrangements in which a cluster of small fertile flowers is surrounded by several larger, decorative sterile flowers. Viburnum (Adoxaceae) species vary in their inflorescence arrangements; some species exhibit framed inflorescences, whereas others do not. We hypothesize that the decorative flowers increase the pollinator-attracting functions of the inflorescences; as proved by previous studies, they additionally function as landing-sites for pollinators. To test our hypotheses, field manipulation experiments were carried out for nine Viburnum species, three with inherently framed inflorescences and six without them: sterile flowers were removed and mounted on species with and without framed inflorescences, respectively. Results show that inflorescences with decorative flowers had higher visit rates than inflorescences without them, and that insect flower visitors did not show landing preference for either flower type. These results suggest that decorative flowers appeared only in a subset of Viburnum species to increase their pollination chances by, mainly, enhancing the attractiveness of the inflorescence. It is likely that species without framed inflorescences use other attraction-enhancing mechanisms, such as a high flowering synchrony within a single cluster of fertile flowers, a trait found in most studied species without decorative flowers.     

Small but attractive: female‐biased nectar production and floral visitors in a dimorphic shrub

• In sexually dimorphic species, hermaphrodite flowers in gynodioecious species or male flowers in dioecious species are often larger and produce more nectar than their conspecific female flowers. As a consequence, hermaphrodite or male flowers frequently receive more pollinator visits.
• Sex ratio, flower size, floral display, nectar production and floral visits were evaluated in two natural populations of Fuchsia thymifolia, a morphologically gynodioecious but functionally subdioecious insect‐pollinated shrub.
• Sex ratio did not differ from the expected 1:1 in the two studied populations. As expected, hermaphrodite flowers were larger than female flowers, but in contrast to the general pattern, hermaphrodite flowers did not produce nectar or produced much less than female flowers. Flower visitors were flies (68%) and bumblebees (24%), both of which showed a preference for female flowers. No sex difference was detected in either flower longevity or floral display across the flowering season.
• Higher nectar production by females may attract more pollinators, and may be a strategy to enhance female reproductive success in this species. Finally, floral dimorphism and insect preferences did not seem to hamper the maintenance of sub‐dioecy or prevent the evolution of dioecy in F. thymifolia.

     

Survey of insect visitation of ornamental flowers in Southover Grange garden,Lewes, UK

Ornamental flowers commonly grown in urban gardens and parks can be of value to flower‐visiting insects. However, there is huge variation in the number of insects attracted among plant varieties. In this study, we quantified the insect attractiveness of 79 varieties in full bloom being grown in a public urban garden that is popular due to its beautiful flowers and other attractions. The results showed very clearly that most varieties (77%, n = 61) were either poorly attractive or completely unattractive to insect flower visitors. Several varieties (19%, n = 15) were moderately attractive, but very few (4%, n = 3) were highly attractive. Closer examination of Dahlia varieties showed that “open” flowered forms were approximately 20 times more attractive than “closed” flowered forms. These results strongly suggest that there is a great potential for making urban parks and gardens considerably more bee‐ and insect‐friendly by selecting appropriate varieties.     

Reproductive biology ofFrangula alnus (Rhamnaceae) in southern Spain

Various aspects of the reproductive biology of the perennial hermaphroditeFrangula alnus Mill. were studied in two populations located in the province of Cádiz, southern Spain. Flowering extends from the second week of May to early July. The small, whitegreenish, entomophilous flowers are incompletely protandrous and last 8–10 days, but pollen transfer takes place only on days 1–3. A very weak, pleasant odour along with nectar and pollen attract over 45 insect species, of which 21 are probable pollinators. These are mainlyDiptera but also includeHymenoptera and the unusual (as flower visitors)Mecoptera. Reproduction is exclusively sexual and strictly xenogamous, with pollen transfer depending solely on insect vectors. Although flower morphology and individual flower phenology do not fully prevent self-pollination, and geitonogamy can easily take place, the level of autogamy was negligible. Therefore, some self-incompatibility mechanism is operative in this species. Only 2.8% of open-pollinated flowers set fruit. At the flower level, fruit initiation was apparently limited by availability of cross-pollen, which in turn seemed influenced by the structure of the population. The seed/ovule ratio in ripe fruits was ca. 50%. Predispersal (maternal) reproductive success (percent ovules becoming filled seeds) was 1.42%. For mature individuals this corresponded to ca. 430 to 1560 potential offspring per year.     

Garden Flowers: Insect Visits and the Floral Reward of Horticulturally-modified Variants

Garden flowers can be valuable to wildlife if they produce nectar,pollen and/or seeds. To provide information needed by gardenersto select wildlife-friendly plants, we investigated nectar productionand insect visits toTropaeolum majus, Consolidasp.,Antirrhinummajus, Violaxwittrockiana, Tagetes patulaandAlcea rosea, ineach case comparing a near-original flower type with a cultivarthat had spurless, doubled, peloric or enlarged flowers. Allspecies showed high secretion rates and standing crops of nectar.In most cases the horticultural modifications affected the numbersor species composition of the assemblage of insect visitors,and they generally reduced the value of the floral reward toinsects, often affecting accessibility. Effects on seed yieldwere not investigated directly here, but are likely to furtherreduce the wildlife value of modified variants.Copyright 1999Annals of Botany Company. Garden plants, horticultural modification, nectar, pollen, coevolution, insects, pollinators,Bombus, Apis mellifera,foraging.     

Pollination and floral ecology of Arundina graminifolia (Orchidaceae) at the northern border of the species’ natural distribution

Arundina graminifolia is an early successional plant on Iriomote Island, the Ryukyus, Japan, where it is endangered. Populations flower for more than half a year, and many inflorescences bloom for one to several months. The nectarless gullet flowers, which open for up to six days, are self-compatible but cannot self-pollinate spontaneously; thus they rely on pollinating agents for capsule production. Field observations at two habitats identified at least six species of bees and wasps, primarily mate-seeking males of Megachile yaeyamaensis and Thyreus takaonis, as legitimate pollinators. Thus, this orchid is a pollinator generalist, probably owing to its long blooming period and simple flower morphology. Carpenter bees, which were previously reported to pollinate this orchid, frequently visited flowers but were too large to crawl into the labellum chamber and never pollinated the flowers. Extrafloral nectaries on inflorescences attracted approximately 40 insect taxa but were not involved with pollination. Fruit-set ratios at the population level varied spatiotemporally but were generally low (5.2–12.4 %), presumably owing to infrequent flower visits by mate-seeking pollinators and the lack of food rewards to pollinators.     

Floral ecology of Oreocharis pumila (Gesneriaceae): a novel case of sigmoid corolla

Attraction of pollinators and successful pollen transfer represent the primary targets of selection during flower evolution, leading to repeated evolutionary shifts between pollinators and consequently to the diversification of floral forms. However, most studies in floral evolution focus on the characteristics of flowers with straight corolla tube. Here, we report on an unusual form of sigmoid corolla combined with protandry and herkogamy in a Chinese species of Gesneriaceae, Oreocharis pumila (formerly Opithandra pumila). Contrary to species with sigmoid corollas studied previously, the base of the corolla tube of this species is inclined at an oblique angle downwards before the tube bends forward, and the stigma and anthers are included in the upper part of the corolla tube. The plants were found to be self‐compatible but incapable of autonomous selfing. Successful pollination was found to depend fully on the presence of insect pollinators (Nomia sp.) and pollen grains are the greatest reward for the visitors. Different from the other sigmoid flowers, the sigmoid corolla of O. pumila was not found to favor insect pollinators with long flexible proboscises. A mechanical fit between floral morphology and pollinator was found, in which only small insect visitors with specialized visiting behavior are legitimate pollinators. The protandry combined with herkogamy in the sigmoid corolla tube strongly ensures pollination efficiencies. Oreocharis pumila is the only species with sigmoid corolla in the genus Oreocharis. We hypothesize that such a corolla has arisen through selection due to inadequate pollination in early spring in the mountainous habitat that O. pumila occupies.     

EXPERIMENTAL ASSESSMENT OF REPRODUCTIVE INTERACTIONS BETWEEN SYMPATRIC ASTER AND ERIGERON (ASTERACEAE) IN INTERIOR ALASKA

Erigeron glabellus and Aster sibiricus have similar flowers, share pollinators, but bloom sequentially in interior Alaska. Both species depend on insect pollination for seed set: the Erigeron is self-incompatible, and the Aster is apparently self-compatible but allogamous. To test the hypothesis that sequential blooming is maintained by natural selection generated by reproductive interference, we manipulated the flowering time of Erigeron, forcing it to bloom simultaneously with Aster, and measured female fecundity in both species. We found no evidence of reduced female fecundity in either species caused by the presence of the sympatric “competitor” or by artificial pollination with the heterospecific pollen prior to conspecific pollination. Two-species mixtures of simultaneously blooming Aster and Erigeron experienced significant interspecific visitation, which may, under natural conditions, cause loss of pollen to alien stigmas and depressed male fecundity, at least in Erigeron. We found no evidence that sequential blooming in Erigeron and Aster is maintained by depressed female fecundity through pollinator sharing. If sequential blooming is maintained by natural selection, it seems more likely to be the result of selection generated by depressed male fitness through pollen loss to alien stigmas.