Pollination of the lady's slipper Cypripedium henryi Rolfe (Orchidaceae)

The pollination ecology of Cypripedium henryi Rolfe, a slipper orchid endemic to west China, was investigated, and its floral shape, size, colour, and scent were analysed. Examination of the breeding system suggests that the flowers are self-compatible, but need pollen vectors for successful reproduction. The flower is rewardless; over 15 insects belonging to Araneida, Hymenoptera, Diptera, Lepidoptera, and Coleoptera were recorded as flower visitors, but most only alighted or rested on the flower. In the total 32 h of observations over 2 years, female Lasioglossum bees were found to be the most frequent visitors and the only pollinators. They showed a high visitation frequency and, surprisingly, re-visited the same flowers frequently. Cypripedium henryi probably attracts pollinators visiting the flowers through general food deception (odour components, colour, false nectar guides), as well as special structures (slippery labellum, slippery staminode). Although three Lasioglossum species visited the flowers, only L. sauterum Fan et Ebmer was found with pollen. Lasioglossum flavohirtum Ebmer was large and climbed out from the entrance. Morphologically, L. sichuanense Fan et Ebmer could be considered as a potential pollinator, but the collected specimens were found to have no pollen of C. henryi on their bodies. It was speculated that the particular floral scent of C. henryi discouraged the entrance of L. sichuanense bees. Lasioglossum sauterum was matched morphologically to the flower, but not all of the visitations resulted in effective pollinations, as some flowers of C. henryi were frequently re-visited and the pollen mass had been taken away by bees on previous visitations. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 491–499.     

Pollination Biology of Anisomeles indica and A. malabarica (Lamiaceae)

Abstract The flowers of Anisomeles indica and A. malabarica are zygomorphic, bilabiate, gulletshaped and nectariferous, and are visited by insects as well as birds for nectar and/or pollen. The bees Xylocopa latipes, X. Pubescens, Amegilla sp., Apis florea and Megachile sp., and the sunbirds of the genus Nectarinia are the principal pollinators of A. indica , while the former three and the last and the wasp Rhynchium metallicum are for A. malabarica. Pollination by Xylocopa and Nectarinia is nototribic and that by Apis, Megachile, Amegilla is noto- and/or sternotribic. The small bodied Trigona, Pseudapis and Ceratina collected pollen sternotribically. It is concluded that adaptation of both species to insect and bird pollination and to a flexible breeding system involving both selfing and crossing, safeguards their survival under changing environments.     

草豆蔻传粉生物学的研究

比较研究了花柱卷曲性植物草豆蔻 Alpinia hainanensis两种表型(上举型和下垂型)的传粉生物学特性。结果表明:草豆蔻的花柱卷曲运动节律与其他已报道的山姜属Alpinia植物基本一致,而下垂型花的花柱卷曲运动明显滞后于上举型花约2 h。草豆蔻的花柱卷曲运动中存在一些不同步的现象,甚至在同一花序上的两朵花的花柱运动节律亦会表现出不一致的现象,但上举型花的花药开裂时间却严格同步,都发生在同类型个体的柱头全部位于花药上方之后进行。草豆蔻上举型花的花蜜分泌量、单花花粉量、花粉/胚珠比率(P/O)均明显比下垂型花多,而两种表型的胚珠数、花蜜糖含量、氨基酸含量无显著差异。在草豆蔻的单花期内不同时间段进行人工授粉,上举型花在其柱头位于花药下方时进行人工授粉,其结实率明显比柱头位于花药上方时人工授粉的处理高,下垂型花则没有显著差异。在自然居群中,草豆蔻的主要传粉者是无垫蜂Ameglla sp.和两种木蜂Xylocopa sp.,但存在传粉者不足而影响结实率的现象。完全套袋、去雄和去雌(去柱头)处理的均不结实,表明草豆蔻中不存在无融合生殖、主动自花授粉和滞后自交的生殖保障现象。而人工自交和异交均具有较高的结实率,表明草豆蔻为自交亲和植物。草豆蔻的繁育系统是具花柱卷曲性运动的异花授粉的交配系统。     

Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees

Background and Aims

Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees.

Methods

For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.

Key Results

Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.

Conclusions

Species-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.     

Comparative Studies on Pollination Biology of Mosla hangchouensis and M.chinensis (Labiatae)

Mosla hangchouensis Matsuda and M. chinensis Maxim. are sibling species. The former is endemic to the coastal areas of Zhejiang Province, and the latter occupies southern China. Their morphological differences were associated with their different breeding systems indicated by pollen-ovule ratio (P/O). M. hangchouensis was predominantly outcrossing with P/O ranging from 756 to 6163 due to the variation among populations. Floral characters also showed that M. hangchouensis is an outcrosser: corolla tube 5～10 mm long, 3~5 mm wide, bright red: style 6～15 mm long; stigma 1.5～2.0 mm horizontally away from anthers. On the contrary, M. chinensis was predominantly a selfer with a low P/O ratio (P/O= 110). Its floral parameters contrasted sharply with M. hangchouensis: corolla tube 3.0 mm long, 1.0 ～ 1.5 mm wide, pale colored; style 2.5 mm long. stigma close to or touching anthers. The pollinators of M. hangchouensis most frequently seen are: Bombus trifascitus Smith., Scolia spp., Apis cerana Fabricius, Hylaeus sp. and Lasioglossum spp. These pollinators began to visit flowers at about 8:00 am, when flower buds were ready to open. When insects entered corolla tube for honey and (or) pollen, the stigmata touched the insects body hairs to which pollen grains adhered, and pollen grains were transferred to the stigmata. Meanwhile the hairs collected pollen from anthers under the upper lips of corolla as the insects thrusted their bodies forward. Bumble bees and honey bees were considered more efficient pollinators because they were hair-rich and their body size fitted corolla tube fairly well. Due to the'short flight distance of pollinators between two visits (average flight distances of honey bees and solitary bees were 0.52 m and 0.32 m respectively), pollen dispersal was probably restricted. Pollen vectors were important for the reproductive success of M. hangchouensis because 84.3 % of its seed-set depended on the pollinators' visitation. Although insects did pay visits to M. chinensis occasionally, such visitation was insignificant in seed-set due to cleistogamy. Discussions are made on the evolutionary significance of breeding system divergence between M. hangchouensis and M. chinensis, and the contribution of studies on pollination biology to conservation biology. Further studies are suggested for more thorough understanding of pollination biology of M. hangchouensis.     

Role of floral repellents in the regulation of flower visits of extrafloral nectary-visiting ants in an Indian crop plant

Abstract.  1. Field investigation of the association between sponge gourd, Luffa cylindrica plants and its ant visitors revealed that five of the six most frequent species: Camponotus compressus, C. paria, Pheidole sp., Pachycondyla tesserinoda and Tetramorium sp. mainly visited the extrafloral (EF) nectaries present on the leaves, bracts, bracteoles and calyx of the plant. Tapinoma melanocephalum was the only ant species observed at the floral as well as the EF nectaries.
2. A bioassay of ant behaviour revealed aversion to young and mature unisexual flowers of sponge gourd in the five predominantly EF nectary-visiting ant species, while floral preference was demonstrated in T. melanocephalum. A significant difference was not found in the number of insect pollinators visiting T. melanocephalum occupied and un-occupied flowers, suggesting the absence of deterrent effect of this tiny ant species on the pollinators.
3. Further behavioural assays showed preference for 2- and 4-day-old leaves and also 2-day-old buds, while the 4-day-old buds induced avoidance in all the species. Androecium and gynoecium had significantly higher repellent effects in comparison to the petals. Thus floral repellents, probably help to reduce nectar theft and prevent loss of pollen function.
4. This aversion was not demonstrated in the case of old flowers. A significantly greater number of insect pollinators visited young and mature flowers compared with old flowers, suggesting that selective exclusion of medium- and large-sized EF nectary-visiting ant species from the flowers, as a result of aversion to floral repellents, serves to avoid the threat of attack to insect pollinators of sponge gourd.     

新疆荒漠植物耳叶补血草的爆发式开花式样与传粉模式

荒漠环境中干热、大风、浮尘、温度骤变等突发性天气状况,对植物的有性生殖具不利影响.耳叶补血草(Limonium otolepis)是新疆盐生荒漠的主要建群种,对其适应荒漠恶劣环境的生殖策略仍缺乏研究.为了探讨荒漠植物适应环境的开花式样和传粉模式,作者通过野外定点观测和室内电镜扫描等方法对耳叶补血草的开花进程、花部特征、传粉媒介、结实特性等进行了研究.耳叶补血草的花期在6月上旬至7月中旬,花期较长且具明显不同步的单株开花状态.在一天中,单花表现出极为集中的开花、散粉过程:一般早上8:00开始开放,9:00达开放高峰期,11:00以后基本不再有单花开放;开放后的单花持续6-8 h后闭合.每单花平均有花粉752粒,花粉表面有网状纹饰,有花蜜.传粉者主要为蜜蜂科和食蚜蝇科昆虫,访花高峰期在9:00-14:00.人工授粉实验表明耳叶补血草以异交为主,自动自花授粉率低.自然状态下结实率为36％,在花序中基部第一位上单花的结实率(45.7％)明显高于第二位上单花(3.3％).耳叶补血草爆发式开花、在短时间内快速完成传粉过程,可能是躲避荒漠环境突发性天气条件的一种策略;而居群分散的开花时间及较长的花期在应对不稳定生境,分摊生殖风险方面具重要意义.     

Pollination ecology ofOxalis violacea (Oxalidaceae) following a controlled grass fire

Vernal grass fires may encourage profuse flowering in clonal, colonies ofOxalis violacea. Long-styled colonies appear to be more floriferous than short-styled colonies and set a greater number of capsules. Individual flowers of both morphs live one or two days, change position on their respective pedicels and advertise nectar concealed at the base of the floral throat. AlthoughDiptera, Hymenoptera, andLepidoptera forage for nectar, bees (Andrenidae,Anthophoridae, Halictidae, andMegachilidae) probably make the only effective pollen transfers between the two morphs. Both male and female bees may transport pollen of both morphs and short-tongued bees (e.g.,Augochlorella spp.,Dialictus spp.) may be more common but as effective as pollinators as long-tongued bees (e.g.,Calliopsis andreniformis andHoplitis spp.). The conversion rate of flowers into capsules is only 13–17%. The spreading style in the short-styled morph is interpreted as an adaptation restricting insect-mediated, self-pollination but encouraging bee-stigma contact during nectar foraging.     

RELATIVE POLLINATOR EFFECTIVENESS AND EVOLUTION OF FLORAL TRAITS IN SPATHIPHYLLUM FRIEDRICHSTHALII (ARACEAE)

We studied the relative effectiveness of different pollinators of Spathiphyllum friedrichsthalii Schott for 15 months on Barro Colorado Island, Panama. Pollen-foraging stingless bees (Apidae: Trigona) made 87% of floral visits. Experiments showed that these bees pollinate flowers, and correlations of fruit- and seed-set with visitation frequencies and floral contact times suggested that they were responsible for the majority of seeds produced. Fifteen species of fragrance-foraging, male euglossine bees (Apidae: Euglossini) collectively accounted for a small portion of seed-set in fewer than 27% of the inflorescences. Neocorynura (Halictidae) were pollen thieves and were unimportant as pollinators. We propose that euglossine and stingless bees differentially influence outcrossing rates and the evolution of floral traits of S. friedrichsthalii. Foraging behavior of male euglossines should allow for more long-distance pollen flow whereas stingless bees are likely to promote near-neighbor and geitonogamous pollinations. We discuss why the prolonged male phase of anthesis in this protogynous species may be maintained through pollination by stingless bees rather than male euglossines. Furthermore, although the floral fragrance is attractive to many species of male euglossines, it attracts few individuals. This condition may represent an intermediate step in the evolution of predominant pollination by male euglossines.     

Flower color change accelerated by bee pollination in Tibouchina (Melastomataceae)

Floral color changes are common among Melastomataceae and have been interpreted as a warning mechanism for bees to avoid old flowers, albeit increasing long-distance flower display. Here the reproductive systems of Tibouchina pulchra and T. sellowiana were investigated by controlled pollinations. Their pollinators were identified, and experiments on floral color and fragrance changes were conduced to verify if those changes affect the floral visitation. Both Tibouchina species are self compatible. The flowers lasted three days or more, and the floral color changed from white in the 1st day to pink in the following days. Pollen deposition on stigma induced floral color change. The effectiveness of the pollination is dependent on bees’ size; only large bees were regarded as effective pollinators. In experimental tests, the bees in T. pulchra preferred the natural white flowers while the visitors of T. sellowiana were attracted by both natural and mimetic 1st-day flowers (2nd-day flowers with experimentally attached 1st-day flower petals). During the experiments on floral fragrance, the bees visited both natural and mimetic 1st-day flowers (2nd-day flowers with 1st-day flower scents). In both experiments, the bees avoided natural 2nd-day flowers, but seldom visited modified 2nd-day flowers. The attractiveness of T. pulchra and T. sellowiana flowers cannot be attributed exclusively to the color or the fragrance separately, both factors seemingly act together.     

A preliminary study on pollination biology of Omphalogramma souliei Franch. (Primulaceae), a species endemic to China

The pollination biology of Omphalogramma souliei Franch., a species endemic to southwestern China, was investigated. Floral phenology, flower visitors, pollen/ovule ratio, attractants and rewards to the visitors were observed, measured, and recorded. Bagging experiments to exclude pollinators were carried out in the wild for two years. Our results revealed five important aspects of the reproductive biology of Omphalogramma souliei. 1) The pollen-ovule ratio was 1748±233. The breeding system was self-compatible, with facultative xenogamy. 2) The pollination syndrome is entomophily, and this species could not be pollinated by wind if the pollinators were unavailable. 3) Six insect species were observed visiting the flowers of Omphalogramma souliei in the wild, of them, three species of hymenoptera, Lasioglossum sp., Heriades parvula Cockerell and Micrapis florae Fabricius, are the principal floral visitors and effective pollinators. 4) The visual attractants to the visitors are floral color and shape, the large yellow anthers, and the rewards for visitors are pollen and nectar. 5) Cleistogamy may also occur, since the anthers of some flowers dehisced before opening of the corolla. The results of floral biology and pollination characters suggest that xenogamy predominated and autogamy played an assistant role in the evolution of reproduction and breeding system of O. souliei.     

Three pollination guilds and variation in floral characteristics of Bornean gingers (Zingiberaceae and Costaceae)

The pollinators of 29 ginger species representing 11 genera in relation to certain floral morphological characteristics in a mixed-dipterocarp forest in Borneo were investigated. Among the 29 species studied, eight were pollinated by spiderhunters (Nectariniidae), 11 by medium-sized Amegilla bees (Anthophoridae), and ten by small halictid bees. These pollination guilds found in gingers in Sarawak are comparable to the pollination guilds of neotropical Zingiberales, i.e., hummingbird-, and euglossine-bee-pollinated guilds. Canonical discriminant analysis revealed that there were significant correlations between floral morphology and pollination guilds and suggests the importance of plant–pollinator interactions in the evolution of floral morphology. Most species in the three guilds were separated on the plot by the first and second canonical variables. Spiderhunter-pollinated flowers had longer floral tubes, while Amegilla-pollinated flowers had wider lips than the others, which function as a platform for the pollinators. Pistils and stamens of halictid-pollinated flowers were smaller than the others. The fact that gingers with diverse morphologies in a forest with high species diversity were grouped into only three pollination guilds and that the pollinators themselves showed low species diversity suggests that many species of rare understory plants have evolved without segregating pollinators in each pollination guild.     

Pollination in a cryptically dioecious plant Decaspermum parviflorum (Lam.) A. J. Scott (Myrtaceae) by pollen-collecting bees in Sulawesi, Indonesia

Decaspermum parviflorum is a common shrub or treelet in clearings in eastern Sulawesi, Indonesia. It is widely distributed in SE Asia. It produces numerous white flowers and small blue-black fruits. Individual shrubs were of two types in 1:1 ratio, one bearing staminate flowers, the other bearing flowers with both stamens and carpels. The 'hermaphrodite' flowers were shown to have sterile pollen so the species is functionally dioecious. The flowers and floral sprays of the two sexes differed in several measurements: the male flowers had more anthers and were larger and more numerous, making the corporate visual image of male sprays more than twice as large as that for sprays of female flowers. Flowers, individuals of which last only one day, opened only every second day, when all bushes flower synchronously. When the anthers burst in the morning, pollen and sterile pollen was collected vigorously by a variety of bees, mostly Apis dorsata and Nomia spp. Most of the pollen was collected within 1 h of anthesis. Anthesis in males takes place about 20 min earlier than in females; insect visitation follows this pattern. The minute quantity of nectar was collected by only few insects and mostly after the pollen had gone, if at all. Fruits were eaten by birds. The species displays many features typical of dioecious tropical plants with the unusual feature of pollen being the main food reward for pollinators. It was pollinated effectively in Sulawesi.     

AN EXPERIMENTAL STUDY OF THE FLORAL ECOLOGY OF DODECATHEON MEADIA

An established colony of Dodecatheon meadia on glacial drift in southeastern Wisconsin was observed for its insect pollination interrelationships. Twelve randomly distributed plants from which insects were excluded failed to produce seed, while plants exposed to insect visits set abundant seed. Female solitary bees of 2 species, viz., Augochloropsis metallica fulgida (Smith) and Lasioglossum forbesii (Robertson), and queens and workers of 7 species of Bombus were observed collecting pollen from the pendant anther cone by rapid wing vibration, while hanging inverted from the cone tip. This behavior—cinematographically recorded—was found fundamentally identical to that of females of the same species of solitary bees and of queens and workers of 5 species of Bombus on Solanum dulcamara, and of females of Lasioglossum forbesii (Robertson) and workers of 2 species of Bombus on Lycopersicum esculentum Mill. No other insects were found to pollinate these morphologically similar flowers in this manner, and crepuscular pollinators were not observed. Experimental modifications of form, function, and position of Dodecatheon flowers were offered to the pollinators, and behavioral changes of the insects were noted. Constituents of insect pollen loads were examined, and relationships of the pollinators to the flora of the region were noted. The detailed ecological study of insect pollen vector behavior as an aid in discovering biosystematic relationships of plant populations is suggested.     

The pollination ecology of buzz-pollinated Rhexia virginica (Melastomataceae)

We examined the function of floral traits associated with buzz pollination through studies of Rhexia virginica (Melastomataceae) in the Muskoka region of Ontario, Canada. Controlled pollinations demonstrated that the species is self-compatible, but dependent on insects for pollen transfer. Bumble bees made 82 and 90% of observed insect visits to R. virginica in 1996 and 1997, respectively, and effectively buzzed flowers. Buzz pollination did not appear to be highly "specialized" since various species of bumble bee were capable of pollination, and pollen transfer efficiency appeared to be relatively low. Experimental manipulations provided little support for the hypothesis that the yellow color of melastome anthers mimics abundant pollen, thereby deceiving pollinators to visit regardless of whether most pollen has been removed. Fruit set averaged 52.6% among populations, owing largely to infrequent pollinator visits and pollen limitation. Flowers of R. virginica were infertile after a single day of anthesis, but petals were subsequently maintained for 1-2 d and stamens underwent a color change from bright yellow to red. Second-day flowers may function to increase floral display size and hence fertility, without a concomitant increase in pollen discounting. Studies of bumble bee foraging behavior and correlates of seed set provided indirect support for this hypothesis.     

Floral specialization for different pollinators and divergent use of the same pollinator among co‐occurring Impatiens species (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.     

Pollinator responses to variation in floral display and flower size in dioecious Sagittaria latifolia (Alismataceae)

In animal-pollinated plants with unisexual flowers, sexual dimorphism in floral traits may be the consequence of pollinator-mediated selection. Experimental investigations of the effects of variation in flower size and floral display on pollinator visitation can provide insights into the evolution of floral dimorphism in dioecious plants. Here, we investigated pollinator responses to experimental arrays of dioecious Sagittaria latifolia in which we manipulated floral display and flower size. We also examined whether there were changes in pollinator visitation with increasing dimorphism in flower size. In S. latifolia, males have larger flowers and smaller floral displays than females. Visitation by pollinators, mainly flies and bees, was more frequent for male than for female inflorescences and increased with increasing flower size, regardless of sex. The number of insect visits per flower decreased with increasing floral display in males but remained constant in females. Greater sexual dimorphism in flower size increased visits to male inflorescences but had no influence on the number of visits to female inflorescences. These results suggest that larger flower sizes would be advantageous to both females and males, and no evidence was found that females suffer from increased flower-size dimorphism. Small daily floral displays may benefit males by allowing extended flowering periods and greater opportunities for effective pollen dispersal.     

Characterization of Salix nigra floral insect community and activity of three native Andrena bees

Salix nigra (black willow) is a widespread tree that hosts many species of polylectic hymenopterans and oligolectic bees of the genus Andrena. The early flowering of S. nigra makes it an important nutritive resource for arthropods emerging from hibernation. However, since S. nigra is dioecious, not all insect visits will lead to successful pollination. Using both visual observation and pan‐trapping, we characterized the community of arthropods that visited S. nigra flowers and assessed differences among male and female trees as well as the chemical and visual drivers that influenced community composition across 3 years. We found that male trees consistently supported higher diversity of insects than female trees and only three insect species, all Andrena spp., consistently visited both sexes. Additionally, Andrena nigrae, which was the only insect that occurred more on female than male flowers, correlated strongly to volatile cues. This suggests that cross‐pollinators cue into specific aspects of floral scent, but diversity of floral visitors is driven strongly by visual cues of yellow male pollen. Through time, the floral activity of two Andrena species remained stable, but A. nigrae visited less in 2017 when flowers bloomed earlier than other years. When native bee emergence does not synchronize with bloom, activity appears to be diminished which could threaten species that subsist on a single host. Despite the community diversity of S. nigra flowers, its productivity depends on a small fraction of species that are not threatened by competition, but rather rapidly changing conditions that lead to host‐insect asynchrony.     

Pollination of Schisandra henryi (Schisandraceae) by female, pollen-eating Megommata species (Cecidomyiidae, Diptera) in south-central China

BACKGROUND AND AIMS: The mutualistic interaction between insects and flowers is considered to be a major factor in the early evolution of flowering plants. The Schisandraceae were, until now, the only family in the ANITA group lacking information on pollination biology in natural ecosystems. Thus, the objective of this research was to document the pollination biology and breeding system of Schisandra henryi. METHODS: Field observations were conducted in three populations of S. henryi and the floral phenology, floral characters and insect activities were recorded. Floral fragrances were sampled in the field and analysed using TCT-GC-MS. Floral thermogenesis was measured with a TR-71U Thermo Recorder. Pollen loads and location of pollen grains on insect bodies (including the gut) were checked with a scanning electron microscope and under a light microscope. KEY RESULTS: Schisandra henryi is strictly dioecious. Male flowers are similar to female flowers in colour, shape, and size, but more abundant than female flowers. The distance between tepals and the androecium or gynoecium is narrow. Neither male nor female flowers are fragrant or thermogenic. Schisandra henryi is pollinated only by adult female Megommata sp. (Cecidomyiidae, Diptera) that eat the pollen grains as extra nutrition for ovary maturation and ovipositing. Both male and female flowers attract the pollinators using similar visual cues and thus the female flowers use deceit as they offer no food. CONCLUSIONS: Schisandra henryi exhibits a specialized pollination system, which differs from the generalized pollination system documented in other ANITA members. Pollen is the sole food resource for Megommata sp. and the female flowers of S. henryi attract pollinators by deceit. This is the first report of predacious gall midges utilizing pollen grains as a food source. The lack of floral thermogenesis and floral odours further enforces the visual cues by reducing attractants for other potential pollinators.     

A generalised mimicry system involving angiosperm flower colour, pollen and bumblebees’ innate colour preferences

Flower colour is a major advertisement signal of zoophilous plants for pollinators. Bees, the main pollinators, exhibit innate colour preferences, which have often been attributed to only one single floral colour, though most flowers display a pattern of two or several colours. The existing studies of floral colour patterns are mostly qualitative studies. Using a model of bee colour vision we quantitatively investigate two questions: whether or not component colours of floral colour patterns may mimic pollen signals, and whether or not bumblebees exhibit innate preferences for distinct parameters of naturally existing floral colour patterns. We analysed the spectral reflectances of 162 plant species with multicoloured flowers and inflorescences, distiniguishing between inner and outer colours of floral colour patterns irrespective of the particular structures so coloured.We found that:– The inner colour of radially symmetrical flowers and inflorescences and of zygomorphic flowers appears less diverse to bees than the peripheral colour.– The inner colour of most radial flowers and inflorescences as well as the inner colour of a large number of non-related zygomorphic flowers appears to bees to be very similar to that of pollen.– Bumblebees (Bombus terrestris) exhibit innate preferences for two-coloured over single-coloured dummy flowers in a spontaneous choice test.– Bumblebees exhibit innate preferences for dummy flowers with a large over those with a small centre area.– Bumblebees exhibit innate preferences for dummy flowers with a centre colour similar to that of pollen over those with another centre colour.Our findings support the hypotheses that the inner component of floral colour patterns could be interpreted as a generalised and little recognised form of mimicry of the colour of visually displayed pollen, that bumblebees exhibit innate preferences regarding colour and size parameters of floral colour patterns, and that these correspond to visually displayed pollen. These findings together suggest a prominent role of floral colour patterns in advertisement to and guidance of naive flower visitors.