Effectiveness of buzz pollination in Pedicularis chamissonis: significance of multiple visits by bumblebees

Pollination success of plants is highly susceptible to the frequency of visits and foraging behavior of pollinators. Pollination of the nectarless flowers of Pedicularis species depends on bumblebee workers collecting pollen by vibrating the anthers (buzz pollination). However, little is known about the efficiency of the pollination system. Foraging behavior, pollen removal from anthers and pollen deposition on stigmas of P. chamissonis were studied to assess the effectiveness of buzz pollination in an alpine snowbed population of northern Japan. Although bumblebees tended to visit most of the flowers open at a given time within inflorescences during a single visit, pollen removal rate at the first visit was about 20%, and buzzing period decreased with increasing number of previous visits, resulting in a decreasing proportion of pollen removed per visit as the number of visits increased. These trends enable plants to provide pollen for more pollinators. The number of pollen grains deposited on stigmas was not saturated during the first visit and increased with additional visits. Irrespective of weak self-compatibility, evidence of interference between self and outcross pollen was lacking for seed production. Therefore, buzz pollination in P. chamissonis acts as a mechanism that improves the chance of cross-pollination upon multiple visits if pollinator visitation is frequent.     

Solitary invasive orchid bee outperforms co-occurring native bees to promote fruit set of an invasive Solanum

Our understanding of the effects of introduced invasive pollinators on plants has been exclusively drawn from studies on introduced social bees. One might expect, however, that the impacts of introduced solitary bees, with much lower population densities and fewer foragers, would be small. Yet little is known about the potential effects of naturalized solitary bees on the environment. We took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this solitary bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum require specialized buzz pollination. Through timed floral visitor watches and two pollination treatments (control and pollen supplementation) at three forest edge and three open area sites, we found that the fruit set of S. torvum was pollen limited at the open sites where the native bees dominate, but was not pollen limited at the forest sites where the invasive orchid bees dominate. The orchid bee’s pollination efficiency was nearly double that of the native halictid bees, and was also slightly higher than that of the native carpenter bee. Experiments using small and large mesh cages (to deny or allow E. viridissima access, respectively) at one forest site indicated that when the orchid bee was excluded, the flowers set one-quarter as many fruit as when the bee was allowed access. The orchid bee was the most important pollinator of the weed at the forest sites, which could pose additional challenges to the management of this weed in the fragmented, endangered tropical hardwood forests in the region. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed. Invasive solitary bees, particularly species that are specialized pollinators, appear to have more importance than has previously been recognized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fossil flowers and pollen ofLauraceae from the Upper Cretaceous of New Jersey

A fossil trimerous flower from the Turonian (ca. 90 MYBP, Upper Cretaceous) of New Jersey is described as a new genus in the familyLauraceae. The fossil flower is charcoalified and preserved in exceptional detail. This fossil specimen is particularly remarkable in that several pollen grains have been preserved; pollen grains ofLauraceae generally have very thin exine and are rarely preserved in the fossil record. Although the specimen is incomplete and lacks anthers, there are sufficient structural details preserved to permit an assignment to theLauraceae, as well as comparisons with the tribePerseeae. This new genus provides an important addition to our knowledge of systematic and structural diversity in CretaceousLauraceae.     

The association betweenCarpophilus beetles and cactus flowers

There is a close association between bowl-shaped cactus flowers and the nitidulid beetlesCarpophilus pallipennis (Say) andC. floralis Er. in North America. The nature of this association has not been clear. It now appears that the cactus flowers are brood sites of theCarpophilus beetles. The benefits in the association are one-sided, inasmuch as the beetles provide little or no pollination service for the flowers.Pollination of North American Cacti, VI.     

Behavioral responses by bumble bees to variation in pollen availability

Summary Pollen-collecting bumble bees (Bombus spp.) detect differences between individual flowers in pollen availability and alter their behavior to capitalize on rewarding flowers. Specific responses by bees to increased pollen availability included: longer visits to flowers; visits to more flowers within an inflorescence, including an increased frequency of revisits; an increased likelihood of grooming while the bee flow between flowers within the inflorescence; and more protracted inter-flower flights, probably because of longer grooming bouts. The particular suite of responses that a bee adopted depended on the pollen-dispensing mechanism of the plant species involved. Bees buzzed previously-unvisited Dode-catheon flowers longer than empty flowers. In contrast, pollen availability did not significantly affect the duration of visits to Lupinus flowers, which control the amount of pollen that can be removed during a single visit. Simulation results indicate that the observed movement patterns of bumble bees on Lupinus inflorescences would return the most pollen per unit of expended energy. The increased foraging efficiency resulting from facultative responses by bees to variation in pollen availability, especially changes in the frequency and intensity of grooming, could correspondingly decrease pollen dispersal between plants.     

Pollinator foraging behavior and pollen collection on the floral morphs of tristylous Pontederia cordata L.

Summary The foraging behavior of the pollinators of tristylous Pontederia cordata was studied to determine if differences in floral morphology would lead to preferential visitation of the floral morphs. Although nectar production is not different in the three floral morphs, differences in the production and size of pollen grains produced by the three anther levels results in the morphs offering variable amounts of resources to pollen-collecting insects. Bumblebees (Bombus spp.) and the solitary bee Melissodes apicata used P. cordata primarily as a nectar source and therefore did not seem to exhibit any morph preference. In contrast, honeybees visited flowers mainly for pollen and preferred to forage on long-level anthers of the short-and mid-styled morphs. An analysis of the composition of corbicular pollen loads indicated that, relative to the frequency of production in the population: 1) honeybees collected an excess of pollen from long-level anthers; 2) bumblebees collected the three types of pollen without any apparent preference; and 3) M. apicata preferentially collected pollen from the short-level anthers — presumably because their proboscides are modified by the presence of tiny hairs. The results suggest that P. cordata in Ontario is serviced by a diverse, unspecialized pollinator fauna which is not co-adapted to the tristylous floral polymorphism.     

Mobility of Impatiens capensis flowers: effect on pollen deposition and hummingbird foraging

Flexible pedicels are characteristic of birdpollinated plants, yet have received little attention in studies of hummingbird-flower interactions. A major implication of flexible pedicels is that flowers may move during pollination. We examined whether such motion affected interactions between ruby-throated hummingbirds (Archilochus colubris) and jewelweed (Impatiens capensis) by increasing pollen deposition and by altering the effectiveness of nectar removal. For I. capensis, flower mobility enhanced pollen deposition: birds had significantly longer contact with anthers and more pollen deposited on their bills and crowns when foraging at mobile flowers than at flowers that had been experimentally immobilized. In contrast, flower mobility imposed a cost on hummingbirds by significantly increasing their handling times and reducing their extraction rates relative to their interactions with immobile flowers. Field observations indicated that the motion observed during hummingbird visits did not occur when bees (Bombus spp., Apis mellifera) visited I. capensis flowers, which suggests that the mobility of I. capensis flowers is an adaptation for hummingbird pollination.     

Combined effects of inflorescence architecture, display size, plant density and empty flowers on bumble bee behaviour: experimental study with artificial inflorescences

Pollen dispersal by pollinators is governed by the extent to which diverse effects on pollinator behaviour act independently or augment or moderate each other. Using artificial inflorescences, we assessed the behavioural responses of bumble bees to inflorescence architecture (raceme, panicle, and umbel), inflorescence size (7 or 13 flowers), inter-inflorescence distance and the proportion of empty flowers per inflorescence. The advantage of large inflorescences in terms of attractiveness was larger for racemes and umbels than for panicles, whereas the effect of inter-inflorescence distance on the number of successive probes was smaller for racemes than for panicles and umbels. The number of flowers probed per visit increased almost proportionally with display size when fewer flowers were empty, whereas the number increased less when many flowers were empty. Our results suggest that display size and the spatial arrangement of flowers and nectar within inflorescences can contribute to efficient pollination by affecting pollinator behaviour interactively.     

Flower orientation enhances pollen transfer in bilaterally symmetrical flowers

Zygomorphic flowers are usually more complex than actinomorphic flowers and are more likely to be visited by specialized pollinators. Complex zygomorphic flowers tend to be oriented horizontally. It is hypothesized that a horizontal flower orientation ensures effective pollen transfer by facilitating pollinator recognition (the recognition-facilitation hypothesis) and/or pollinator landing (the landing-control hypothesis). To examine these two hypotheses, we altered the angle of Commelina communis flowers and examined the efficiency of pollen transfer, as well as the behavior of their visitors. We exposed unmanipulated (horizontal-), upward-, and downward-facing flowers to syrphid flies (mostly Episyrphus balteatus), which are natural visitors to C. communis. The frequency of pollinator approaches and landings, as well as the amount of pollen deposited by E. balteatus, decreased for the downward-facing flowers, supporting both hypotheses. The upward-facing flowers received the same numbers of approaches and landings as the unmanipulated flowers, but experienced more illegitimate landings. In addition, the visitors failed to touch the stigmas or anthers on the upward-facing flowers, leading to reduced pollen export and receipt, and supporting the landing-control hypothesis. Collectively, our data suggested that the horizontal orientation of zygomorphic flowers enhances pollen transfer by both facilitating pollinator recognition and controlling pollinator landing position. These findings suggest that zygomorphic flowers which deviate from a horizontal orientation may have lower fitness because of decreased pollen transfer.     

Didymocarpus geitleri,a remarkable new species ofGesneriaceae with deceptive pollen flowers

Didymocarpus geitleri spec. nov. is described from Sungai Pandan, Kuantan distr., Pahang, Peninsular Malaysia. Distinctive features include: leaden-grey leaves with long, erect hairs on the upper side and whitish, campanulate flowers with a long exserted, bright yellow style. The colouring of the latter is caused by densely arranged glands. Together with two yellow blotches in front of the filament insertion, the style apparently acts as an anther (pollen) dummy.The paper and the species is dedicated to my greatly respected teacher of Systematic Botany, Prof. DrLothar Geitler, on the occasion of his 90th birthday.     

Use of Honey Bees and Bumble Bees to Disseminate Trichoderma harzianum 1295-22 to Strawberries for Botrytis Control

The effectiveness of using honey bees and bumble bees to vector a commercial formulation of Trichoderma harzianum 1295-22 for the control of Botrytis cinerea on strawberries was evaluated from 1994 to 1997 in 2 strawberry fields at the New York State Agricultural Experiment Station in Geneva, New York and in 10 grower fields in eight counties of New York. Commercial bumble bee colonies were used to deliver the biocontrol agent in 1994 and 1995 and five-frame nuclear honey bee hives were used in 1995–1997. Each honey bee exiting the hive carried about 1 × 10⁵ colony-forming units of T. harzianum, with the majority found on the bees' legs (58%). Flowers collected from the bee-delivered treatment generally had half the density of T. harzianum as those from the sprayed treatment. However, during the 4 years of this study, T. harzianum delivered by bumble bees or honey bees provided better Botrytis control than that applied as a spray. In addition, the bee-delivered T. harzianum provided the same or a better level of control of Botrytis as commercial fungicides applied at bloom. Strawberries collected from the bee-visited treatments averaged 22% more seeds and weighed between 26 and 40% more than berries in nonvisited treatments. The number of seeds per berry and berry weight were reduced by 7–12% in plots treated with fungicides and visited by bees, indicating that the use of some commercial fungicides at bloom may impact pollination and yield. Bee delivery of T. harzianum 1295-22 is a viable option for strawberry growers interested in controlling Botrytis with minimal fungicide use.     

野慈姑(Sagittaria trifolia)人工授粉的有效性:授粉工具与花粉保存

人工授粉作为一项关键性技术在生态研究与农业生产领域广泛应用,但是授粉过程中的工具有效性以及花粉保存尚未受到研究者的关注。以植物野慈姑为试验材料,研究了人工授粉方式和花粉保存条件对繁殖的影响。两年的结果表明,相较于直接接触式授粉,借助毛刷工具授粉显著降低了野慈姑的座果概率和种子数。花粉经过半小时野外高温保存后,其授粉的座果概率显著高于对照组,但单果种子数和种子大小保持稳定。综上,在野慈姑的人工授粉中应避免使用毛刷等工具,离体花粉可置于野外环境适当保存。在相关应用中,研究人员应当警惕工具授粉造成的负面影响,注意比较工具与其他授粉方式的等效性,保证实验的科学性。     

On some pollen types withinArum (Araceae)

In a second paper onArum pollen seven further taxa are investigated. Most of them have spinose pollen, only inA. korolkowii the pollen is scabrose. The possible relation between pollen sculpturing and the actual pollination mode is discussed.     

In vitro pollination of angiosperm ovules with gymnosperm pollen grains

Summary Pollen grains of the gymnosperm species Ephedra distachya and Pinus wallichiana germinated abundantly on the in vitro cultured placentae of the angiosperm species Nicotiana tabacum, Melandrium album and Allium moly. Some P. wallichiana pollen tubes entered the micropyles of M. album. Embryological observations of cross-pollinated M. album ovules 2 or 3 d after cross-pollination revealed the presence of pollen tube remnants within the embryo sacs. Karyological disturbances in the two- and three-celled proembryos and endosperm nuclei indicated their probable hybrid origin. In some crosses, gynogenetic haploid proembryos were also noticed.     

Pollination biology ofTernstroemia laevigata andT. dentata (Theaceae)

The flowers of two species ofTernstroemia from Central Amazonia were observed to be pollinated by female bees performing vibrational foraging. The anthers of these flowers are longitudinally dehiscent. They are completely included in a petal tube, which opens by a small pore at the apex. Pollen is expelled out of this pore when the bees vibrate the flower while curling over the apex of the petal tube. The much elongated connectives probably transmit the vibrations from the petals to the anthers. The possible occurrence of this mode of pollination in other species ofTernstroemia is briefly discussed.     

Exploding pollen in Montrichardia arborescens (Araceae)

Pollen grains of Montrichardia are inaperturate with psilate ornamentation. The pollen wall is formed by a thin ectexine and an extraordinarily thick intine. In living as well as in dead pollen grains contact with water leads to a rapid swelling of the intine followed by an explosive opening of the exine. Within a few seconds a thick tube is formed, which is not the pollen tube. The pollen protoplast is situated at the tip of the tube. These intine tubes are interpreted as pollen connecting tools to keep pollen grains together and adhere them to the cuticle of the hairless pollinators.     

Protogynous flowers inMonimiaceae

Among theMonimiaceae only five relatively primitive genera belonging toHortonioideae andAtherospermoideae have regularly bisexual flowers. Three species of two genera (Hortonia, Daphnandra), one of each subfamily, were studied for the occurrence of dichogamy. In all of them protogyny occurs.Monimiaceae are, thus, a further example for the preponderant protogyny inMagnoliidae.     

The expression of a potato (Solanum tuberosum) S-RNase gene in Nicotiana tabacum pollen

Self-incompatibility in the Solanaceae is controlled by a single multiallelic genetic locus, the S locus. The stylar gene products of the S locus are abundant glycoproteins with ribonuclease activity, secreted in the transmitting tract tissue of the pistil. To investigate the structural and functional integrity and possible phenotypic effects of expression of the S-gene product in the male gametophyte, N. tabacum plants were transformed with a construct containing the genomic S ₂ -RNase coding sequence from S. tuberosum under the control of the promoter of the pollen-specific LAT52 gene from tomato. The expression pattern of the S ₂ RNase in the male gametophyte at both the protein and RNA level was found to be identical to that already reported for expression of the -glucuronidase (GUS) gene directed by the LAT52 promoter in transgenic tomato and tobacco. The S ₂ -RNase gene fusion led to a tissue-specific and developmentally regulated accumulation of the S ₂ polypeptide in pollen of transgenic tobacco plants. The transgenic protein product was of the same size and charge as the potato stylar product, had ribonuclease activity, and was glycosylated. The transgenic plants, however, did not show any morphological variations in their flower organs, and their fertility was not influenced by the accumulation of the S ₂ -RNase protein in pollen.     

Seed set inCichorium intybus L. by pollination of flowers developedin vitro

Formation of viable seeds ofCichorium intybus L. was achieved in anin vitro system. Flower formation, pollination, fertilization, embryogenesis and seed development occurredin vitro on chicory root explants on culture medium lacking plant growth regulators. After flower induction under a 24-h daylength treatment, the explants were transferred to a 16-h daylength at 40 E m^-2s^-1 irradiance for pollination and further seed development. Negative results were obtained when root explants were maintained continuously under a 24-h daylength during the whole culture period. Lower seed set was obtained when the cultures were at low irradiance. The need of a dark period and adequate level of irradiance are suggested as important factors to obtain viable seeds. The developedin vitro system can be used as a model to study the factors controlling the reproductive processes, and for the study of self-incompatibility in chicory.