Bird-pollination of three Durio species (Bombacaceae) in a tropical rainforest in Sarawak, Malaysia

Pollination ecology of three Durio species, D. grandiflorus, D. oblongus, and D. kutejensis (Bombacaceae), was studied in a lowland dipterocarp forest in Sarawak, Malaysia, during a peak flowering period when at least 305 species of plants bloomed in 1996. Durio has been reported to be pollinated by bats in Peninsular Malaysia. However, my observations of flower visitors and pollination experiments indicated that two species, D. grandiflorus and D. oblongus, were pollinated by spiderhunters (Nectariniidae) and that the other species, D. kutejensis, was pollinated by giant honey bees and bats as well as birds. Hand-pollination experiments showed that all three species were obligate outbreeders. A resource limitation in fruit production was suggested. The former two species were visited only by spiderhunters, and the bagged flowers that were opened for animal visitors only at night bore no fruit, while those that were opened only during the day bore fruits, at comparable fruiting ratios to open pollination. Durio kutejensis was observed to be visited by giant honey bees, birds, and bats at different times of day, and three series of bagged experiments that exposed the flowers to animal visitors at different times of day bore fruits at a comparable ratio to open-pollination.     

Floral biology and pollination in Cucumis melo L., a tropical andromonoecious cucurbit

We studied floral biology and the role of flower visitors in fruit set of muskmelon (Cucumis melo L.). Muskmelon produced Staminate (hereafter ‘S’) and Hermaphrodite (hereafter ‘H’) flowers with a ratio of 18:1. Flowers opened around 40 days after planting and flowering continued for another 40 days. Longevity of both types of flowers was one day. Anthesis in S flowers was earlier (0545–0700 h) than that of H flowers (0700–0830 h). Anther dehiscence occurred 10–15 min after anthesis in both the flowers. The number of pollen grains in H flowers was significantly lower (2715 ± 143) than S flowers (4968 ± 398). Pollen viability and stigma receptivity was maximum between 1600 and 1800 h. The pollen tube of pollen grains from H flowers grew very slowly and never reached the ovary. There were two peaks in nectar production in a day (1000–1200 h and 1400–1800 h). Sixteen species of insects belonging to Hymenoptera (81.25%), Diptera (12.50%) and Lepidoptera (6.5%) visited muskmelon flowers. Major visitors were honeybees, Apis cerana F. and A. florea F. and both were efficient pollinators. Diversity and abundance of flower visitors positively correlated with floral abundance. In pollination exclusion experiments, no fruit set was observed in bagged, self-pollinated and the flowers artificially crossed only with other H pollen. But, those flowers hand pollinated with pollen from S flowers and ones that were allowed for open pollination set maximum fruits. The crop needs a minimum of 8–10 bee visits per flower to achieve the same level of pollination efficiency provided with natural/unrestrained visits.     

Pollination ecology of Yucca elata

The pollination biology of a population of 250 Yucca elata (Liliaceae) plants was studied in southern New Mexico. Yucca elata and the prodoxid yucca moth Tegeticula yuccasella have a mutualistic association that is essential for the successful sexual reproduction of both species. However, a wide range of other invertebrate species visit flowers during the day and at night. Our aim was to quantify the role of yucca moths and other invertebrate visitors in pollination and fruit set, using manipulative field experiments. Inflorescences were bagged during the day or night (N=12 inflorescences) to restrict flower visitors to either nocturnal or diurnal groups. Yucca moths were active exclusively nocturnally during the flowering period and thus did not visit inflorescences that were unbagged during the day. None of the 4022 flowers exposed only to diurnal visitors set fruit, whereas 4.6% of the 4974 flowers exposed only to nocturnal visitors (including yucca moths) produced mature fruit. The proportion of flowers producing fruit in the latter treatment was not significantly different from unbagged control inflorescences. In a series of experimental manipulations we also determined that: (1) flowers opened at dusk and were open for two days on average, but were only receptive to pollen on the first night of opening; (2) pollen must be pushed down the stigmatic tube to affect pollination; and (3) most plants require out-cross pollination to produce fruit. The combination of these results strongly suggests that yucca moths are the only species affecting pollination in Y. elata, and that if another species was to affect pollination, it would be a rare event.     

Contribution of small insects to pollination of common buckwheat, a distylous crop

Crop pollination by animals is an essential ecosystem service. Among animal-pollinated crops, distylous plants strongly depend on animal pollination. In distylous pollination systems, pollinator species are usually limited, although flowers of some distylous plants are visited by diverse animals. We studied the pollination biology of common buckwheat ( Fagopyrum esculentum ), a distylous crop mainly pollinated by honeybees and visited by many insect species, to evaluate the effects of non-honeybee species on pollination services. We focused on insects smaller than honeybees to determine their contribution to pollination. We applied pollination treatments with bags of coarse mesh to exclude flower visits by honeybees and larger insects and compared the seed set of bagged plants with that of untreated plants for pin and thrum flower morphs. We found a great reduction of seed set only in bagged pin flowers. We also confirmed that small insects, including ants, bees, wasps and flies, carried pin-morph pollen. These small insects transfer pollen from the short anthers of pin flowers to the short styles of thrum flowers, leading to sufficient seed set in thrum flowers. Consequently, small, non-honeybee insects have the potential to maintain at least half of the yield of this honeybee-dependent distylous crop.     

Thrips Cross-Pollination of Popowia pisocarpa (Annonaceae) in a Lowland Dipterocarp Forest in Sarawak1

This paper reports thrips (Thysanoptera) cross-pollination in the primitive angiosperm, Popowia pisocarpa (Annonaceae), in lowland rain forest of Sarawak, Malaysia. Flowers of P. pisocarpa have a tiny pollination chamber (3–4 mm in depth) with the entrance almost closed by the disk-shaped stigmatic heads, allowing only small insects to enter. Experiments showed that thrips were effective pollinators and flowers ofP. pisocarpa were self-incompatible. Seed set was limited by pollen. Clumped adult trees had higher seed-set than more distant individuals (>5 m from nearest flowering neighbor), indicating limited inter-tree movement by thrips.     

Nocturnal Versus Diurnal Pollination Success in Isertia laevis (Rubiaceae): A Sphingophilous Plant Visited by Hummingbirds

Abstract: Isertia laevis (Rubiaceae) possesses flowers with traits typical for the pollination syndrome of sphingophily. Diurnal flower observation showed that nine different hummingbirds (Trochilidae) and one flower piercer (Coerebidae) were frequent visitors. Their activity on the flowers peaked in the morning hours. Very low nectar volumes were found in the morning (8.00 h) in unbagged flowers. Nectar volumes, however, reached their peaks (27 μl) at night (2.00 h) in bagged, as well as in unbagged flowers. At night few individuals of sphingids were observed. Pollination experiments showed that flowers presented to nocturnal pollinators from 18.00 h to 6.00 h had low fruit set (14 %) but high seed set (59 %). Flowers accessible from 6.00 h to 18.00 h for diurnal flower visitors showed high fruit set of 63 % but low seed set of 14 %. This suggests that pollination of individual flowers is less effective during daytime. Regarding relative reproductive success, i.e., efficiency of pollination defined as fruit set x seed set, both diurnal and nocturnal pollinators, however, are equally successful. We conclude that frequently occurring, but not very effective pollinators contribute substantially to seed production, when the expected pollinators are scarce.     

Pollination biology of a night‐flowering Galápagos endemic,Ipomoea habeliana (Convolvulaceae)

Ipomoea habeliana is an endemic, night‐flowering member of the Galápagos flora. Pollination experiments, flower‐visitor observations, nectar sampling, pollen transfer, and pollen to ovule ratio and pollen size studies were included in this project. The large, white flowers of this species set fruit via open pollination (55%), autonomous autogamy (51%), facilitated autogamy (91%), cross‐pollination (80%), diurnal open pollination (60%) and nocturnal open pollination (60%). Fruit set is pollen‐limited. Ants, beetles, crickets and hawk moths regularly visit the flowers. Ants are the most frequent visitors, but hawk moths are the only effective pollinators. Nectar is available throughout the night, but is most abundant early in the evening when hawk moth visits are most frequent. Experiments with fluorescent dust demonstrate intra‐ and inter‐plant pollen movement by hawk moths. Although this species is adapted for hawk moth pollination, it readily sets fruit via autonomous autogamy when no visits are made. Thus, it is concluded that it is facultatively xenogamous. Additional support for this conclusion is provided by the pollen to ovule ratio of 1407 and by the fact that the plants grow in a region that has few or no faithful pollinators. Conservation efforts for I. habeliana should include hand pollinations, which could significantly increase seed set. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 11–20.     

THRIPS-MEDIATED SELF-POLLINATION OF TWO FACULTATIVELY XENOGAMOUS WETLAND SPECIES

Thrips and/or aphids played an important role in the self-pollination of two facultatively xenogamous herbs that inhabit wetlands in northwestern Iowa. In both Ranunculus sceleratus and Potentilla rivalis the fruit set and/or successful pollination of plants that were sprayed with malathion to kill thrips and aphids and caged to exclude typical flower visitors was substantially and significantly lower than that of open-pollinated and caged plants. We observed pollenbearing thrips and aphids on the flowers. The high fruit sets of emasculated flowers of R. sceleratus showed that insects moved pollen between flowers, and our observations of bees collecting pollen and moving between plants suggest that cross-pollination can occur in both species.     

Pollination efficiencies of flower-visiting insects as determined by direct genetic analysis of pollen origin

The amount and genetic composition of pollen grains that are transported to flowers influence the reproduction and fitness of plants. Despite the importance of insect-pollination systems, an understanding of those systems is still lacking due to the absence of a genetic analysis of pollen grains that are transported to flowers. We evaluated the pollination efficiencies of bumblebees (Apidae, Bombus spp.), flower beetles (Scarabaeidae, subfamily Cetoniinae, Protaetia and Eucetonia sp.), and small beetles (Lagriidae, Arthromacra sp.) that visited the flowers of Magnolia obovata (Magnoliaceae) using quantitative (flower visitation frequency, amount of adherent pollen per insect) and qualitative (origin and genetic diversity of adherent pollen per insect) criteria. Most of the pollen adhering to bumblebees and small beetles was self-pollen. This result suggests that visitation by these insects may cause geitonogamous pollen flow and negatively affect the reproduction of M. obovata, causing inbreeding depression. In contrast, flower beetles transported large amounts of genetically diverse outcross pollen. Our results suggest that certain beetle species contribute quantitatively and qualitatively to the pollination of M. obovata. Direct genetic analysis of pollen grains will advance our understanding of plant mating systems and may shed light on the mutualism and coevolution of plants and flower visitors.     

Sex Expression and the Evolutionary Advantages of Male Flowers in an Andromonoecious Species, Sagittaria guyanensis subsp. lappula (Alismataceae)

Sex expression in Sagittaria guyanensis H.B.K. subsp. lappula (D. Don) Bojin is typically andromonoecious while the other species in the same genus are basically monoecious. The evolutionary advantages of male flowers and hermaphrodite flowers in S. guyanensis subsp. lappula were assessed by measuring sex allocation and pollen movements in two wild populations of the species. Two cultivated populations served as controls. The percentage of male flowers was very low in the two wild populations in Dongxiang, Jiangxi Province and Wuyishan, Fujian Province, viz., 2.48% and 0.96% respectively. In the two cultivated populations, male flower percentage significantly increased when the soil was of higher nutrient content. This indicates that the allocation to male versus female reproduction might change in response to environmental factors. Pollen production per male flower was 4.1 times higher than that of a hermaphrodite flower. The floral shape and size of male and hermaphrodite flowers were similar. No difference was observed between these dimorphological flowers in pollen germination rate in vitro and in the speed of pollen tube growth in vivo. Anthesis was only 4-5 h. Male flowers usually opened 0.5 h earlier than hermaphrodite flowers. An unexpected finding was that no pollen from the male flowers was found on the stigmas of the hermaphrodite flowers, in spite of the occasional visits by insects to both types of flowers in both wild and control populations. A consistent pattern of fruit development was found to exist in open pollinated flowers as well as in flowers that had been bagged. The sex ratios did not have significant influence on fruit set. Approximately 25% of the pistils in a gynoecium failed to develop into fruits because no pollen was deposited on them, indicating that the fruit set of this andromonoecious plant is mainly affected by pollen limitation rather than resource limitation. Reproduction in S. guyanensis subsp. lappula in the habitats was dependent on self-pollination in hermaphrodite flowers. The male flowers in this species might be a potential source of additional pollination and may facilitate cross-pollination. The fact that the flowers of monoecious species in Sagittaria pollinated by a wide diversity of insect visitors may contribute enormously to the diversification of sex expression in this genus.     

片断化生境中濒危植物黄梅秤锤树的开花生物学、繁育系统与生殖成功的因素

 研究处于片断化生境中濒危植物的繁育系统、传粉过程及生殖成功状况, 可为评估物种的受胁迫程度及制订相应的保护和管理策略提 供重要依据。通过野外观察和人工授粉实验等方法,对片断化生境中濒危植物黄梅秤锤树(Sinojackia huangmeiensis)的开花生物学和繁育系统 进行了初步研究, 并探讨了影响其生殖成功的因素。黄梅秤锤树的总状花序上通常有两性花2～6朵, 单花花期约5～7 d, 单花花药不同步开裂 使整朵花花粉活力持续时间延长。虽然花开放过程中柱头始终高于花药, 在单花水平上可在一定程度上避免同花自交的发生, 但由于花粉活力 和柱头可授期之间有一定的重叠期, 在自然情况下, 由于外界媒介动物和风媒的作用, 不可避免地会产生同株同花和同株异花传粉。实验结果 表明, 该种不存在无融合生殖现象, 繁育类型以异交为主, 部分自交亲和且需要传粉者。主要的传粉昆虫为黑带食蚜蝇(Epistrophe balteata) 、中华蜜蜂 (Apis cerana) 和中华回条蜂(Habropoda sinensis)。黄梅秤锤树自然状态下的结实率较低(10.33%), 平均每果种子数较少(0.387 个), 这主要与传粉昆虫少、花粉传递效率低, 以及柱头上自花及同株异花花粉的落置和自交亲和性低有关。但是单株较大的开花量保证了一定 的果实和种子产量, 使居群能自然更新。部分自交亲和性可能为该物种适应生境片断化提供了一定的生殖保障及进化潜力。对该残存居群的保 护, 应着眼于加强对传粉昆虫赖以生存的自然生态系统的恢复。     

冠果草的性表达状态及其进化含义

通常认为雄花两性花同株是植物性表达两性花进化到雌雄异株的过渡类型之一。慈姑属仅冠果草（Ｓａｇｉｔｔａｒｉａ ｇｕｙａｎｅｎｓｉｓ Ｈ．Ｂ．Ｋ．ｓｕｂｓｐ．ｌａｐｐｕｌａ（Ｄ．Ｄｏｎ）Ｂｏｊｉｎ）的性表达为典型的雄花两性花同株,其他种为雌雄同株。对冠果草野外和实验居群的性配置进行了定量观察。东乡和武夷山居群雄花的比例分别为２．４８％０．９６％。实验表明,栽培条件影响冠果草的性表达：在营养较好的条件下     

Pollination ecology of Acacia gerrardii Benth. (Fabaceae: Mimosoideae) under extremely hot-dry conditions

Talh trees (Acacia gerrardii Benth.) are acacias that are native to the arid and semiarid Africa and west Asia. We investigated the flowering biology, pod set and flower visitors of Talh and discussed the role of these visitors in pollen transfer. The Talh trees blossomed laterally on the nodes of one-year-old twigs. Each node produced 21 flower buds seasonally. Each flower bud opened to a flower head (FH) of 60 florets. The bagged FHs podded significantly (p ⩽ 0.05) less than did the unbagged FHs. The FHs were visited by 31 insect species (25 genera, 16 families and 5 orders). The major taxa were honeybees, megachilids, butterflies, ants, beetles and thrips. Each of honeybees, megachilids and beetles showed a significant (p ⩽ 0.05) hourly pattern, while each of butterflies, ants and thrips had no hourly pattern (p > 0.05). Furthermore, some birds and mammals touched the Talh FHs. Talh trees evolved a mass flowering behavior to face pre- and post-flowering obstacles. Megachilids seemed to play the major effort of zoophily because of their relatively high numbers of individuals and species and their effective movement behavior on the FH surface. Nevertheless, honeybees and other insects and vertebrate taxa also contributed to the pollen transfer. These results greatly contribute to our understanding of the pollination ecology of acacias, especially Arabian acacias.     

Low legitimate pollen flow in distylic Turnera hermannioides (Passifloraceae) and its consequences on fruit and seed set

Turnera hermannioides is a ruderal distylic subshrub, native to NE-Brazil. In the Catimbau National Park, situated within the semi-arid Caatinga region, we studied the pollination ecology of this species, emphasizing (1) effective pollinators; (2) characteristics of short- and long-styled flowers; (3) intra- and intermorph pollen flow; and (4) fruit and seed set. Short and long-styled morphs differ in pollen size and ornamentation, stigmatic surface, style and stamen length and nectar production. The flowers are obligate intermorphic outcrossers and depend on animals for pollination. The flowers of T. hermannioides attracted insect visitors of 25 species, among them butterflies, beetles, but mainly bees. Polylectic bees, such as Apis mellifera, stingless bees, and solitary Callonychium brasiliense were the most frequent visitors and the principal pollinators. The frequency of visits, however, was very low (on average 1.9 visits/flower/day), resulting in a low and unbalanced legitimate pollen flow, i.e. a much lower number of pollen grains from short-styled flowers reaching stigmas of long-styles than vice versa, which in turn compromised fruit and seed set. Surprisingly, Protomeliturga catimbaui and P. turnerae, both oligolectic on flowers of the Turneraceae-clade of the Passifloraceae s.l., were very rare flower visitors and did not contribute significantly to the pollination of Turnera hermannioides. We discuss how the low visitation rate and the inefficiency of pollinators (i.e. inefficiency in promoting legitimate pollination) compromise pollen flow and, consequently, fruit and seed set in this species.     

Autogamy of an endangered species: Loropetalum subcordatum (Hamamelidaceae)

The reproductive biology of Loropetalum subcordatum was studied. The floral phenology, pollen histochemistry, pollen-ovule ratio (P/O), pollen viability and floral visitors were investigated and determined. Assisted pollination experiments were carried out to examine the breeding system of L. subcordatum. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) were employed to check the pollen germination and the growth of pollen tubes. Results were obtained as follows: (1) The flowering period of L. subcordatum was from September to the next February with a peak at September-October; the longevity of a single flower was 4-6 days. (2) L. subcordatum was protogynous, and pollen grains could be found on self-stigmata when the anthers opened 12-24 h after petals unrolling. (3)The pollen viability (MTT test) maintained for ca. 26 hours; the pollen was starchless; the P/O was 8420±720.86 (n=10); no nectar secretion was observed. (4) Thrips (Thrips sp.) were the only floral visitors observed but which seldom moved among inflorescences, thus played limited role in pollination. (5) Fruit sets of untreated bagged (5.30±1.83%) and hand assisted cross pollinated flowers (6.67±1.91%) were not significantly different from that of open flowers (4.79±1.45%). (6) SEM and FM observations proved that pollen germinated on self-stigmata and pollen tubes growed in self-styles. The results indicated that L. subcordatum was facultatively autogamous and without apomixes. The possibility of outcrossing and the protogyny might indicate that the species was originally a crosser. Flowers pollinated in September-October usually start ovule growth in next summer, and set mature fruits in next October (after the next flowering peak), suggesting the occurrence of retard embryo development. The possibility that autogamy in Hamamelidaceae could have been developed from fly pollination was also discussed.     

Relative importance of diurnal and nocturnal pollinators for reproduction in the early spring flowering shrub Stachyurus praecox (Stachyuraceae)

Generalized pollination systems may be favored in early spring flowering plants, as during this period pollinator activity is unpredictable. Many previous studies have concentrated on the importance of diurnal visitors in pollination, and consequently, information on the contribution of nocturnal visitors to pollination in early spring is limited. This study was conducted to evaluate the relative importance of diurnal and nocturnal pollinators in the early spring flowering dioecious shrub Stachyurus praecox (Stachyuraceae), in two temperate forests in central Japan. Visitors to the female and male flowers were observed during day and night, and their relative contributions to seed set were compared. The pollinator observations revealed that the diurnal and nocturnal insects visited both male and female flowers, and that the main flower visitors were diurnal small bees and flies as well as nocturnal settling moths. The diurnal and nocturnal flower visitors also acted as pollinators, as the pollen grains of S. praecox were attached to the insects collected from the female flowers. Pollination experiments demonstrated that the contributions of diurnal pollinators to the seed set were higher than those of the nocturnal pollinators. The results of this study indicate that S. praecox has a generalized pollination system, comprising both diurnal insects and nocturnal settling moths. Although the roles of diurnal insects are more important in the pollination of S. praecox, nocturnal settling moths may have a complementary role in early spring.     

Limited Fruit Production in Hancornia speciosa (Apocynaceae) and Pollination by Nocturnal and Diurnal Insects1

Frequency and efficiency of pollinator visits strongly influence the reproductive success of self‐incompatible plants. We investigated the breeding and pollination systems of Hancornia speciosa, a small tree that produces fleshy berries used in the Brazilian fruit industry. Observation and experiments were carried out in Northeastern Brazil. Thirty‐three species of the visitor were recorded. Hawkmoths (Sphingidae), bees (Euglossini and Centridini), and butterflies (Nymphalidae and Hesperiidae) with long mouth parts were effective pollinators of H. speciosa. Access to nectar, the only reward for flower visitors, is determined by corolla tube length. Nylon threads of various diameters and dried mouth parts from a number of flower visitors were used in experiments to simulate flower visits. The number of pollen grains removed during such simulated visits showed no significant difference. Although xenogamic, H. speciosa presented a low pollen/ovule ratio (77). This might be related to the high efficiency of its pollination mechanism. Flowers of H. speciosa had 76 ovules on average. Seed set varied from 1 to 25, indicating that individual flowers received different amounts of outcross‐pollen. Fruit production of hand cross‐pollinated flowers increased by 90 percent when compared to natural pollination, suggesting pollinator limitation of H. speciosa.     

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。     

Reproductive biology of Pachira aquatica Aubl. (Malvaceae: Bombacoideae): a tropical tree pollinated by bats,sphingid moths and honey bees

We investigated the reproductive biology, including the floral biology, pollination biology, breeding system and reproductive success, of Pachira aquatica, a native and dominant tropical tree of fresh water wetlands, throughout the coastal plain of the Gulf of Mexico. The flowers present nocturnal anthesis, copious nectar production and sugar concentration (range 18–23%) suitable for nocturnal visitors such as bats and sphingid moths. The main nocturnal visitors were bats and sphingid moths while bees were the main diurnal visitors. There were no differences in legitimate visitation rates among bats, moths and honey bees. Bats and honey bees fed mainly on pollen while moths fed on nectar, suggesting resource partitioning. Eight species of bats carried pollen but Leptonycteris yerbabuenae is probably the most effective pollinator due to its higher pollen loads. The sphingid moths Manduca rustica, Cocytius duponchel and Eumorpha satellitia were recorded visiting flowers. Hand pollination experiments indicated a predominant outcrossing breeding system. Open pollination experiments resulted in a null fruit set, indicating pollen limitation; however, mean reproductive success, according to a seasonal census, was 17 ± 3%; these contrasting results could be explained by the seasonal availability of pollinators. We conclude that P. aquatica is an outcrossing species with a pollination system originally specialized for bats and sphingid moths, which could be driven to a multimodal pollination system due to the introduction of honey bees to tropical America.     

Pollinator limitaton in a deceptive orchid, Pogonia japonica, on a floating peat mat

Deceptive orchid species that offer no floral rewards to pollinators often experience pollinator limitation because they. The breeding system and fruit set were investigated in order to examine pollinator limitation for a population of a deceptive orchid, Pogonia japonica , on a floating peat mat in Mizorogaike Pond, western Japan. Fruit sets for outcross-pollinated, self-pollinated and pollinator-excluded flowers were 75%, 80%, and 0%, respectively. Thus, this species was self-compatible but neither autogamous nor apogamous. The fruit set for open-pollinated flowers was 22.9% and 17.4% in 1994 and 1995, suggesting that pollinator limitation did occur in the field. Larger flowers were more likely to develop into fruit than smaller ones in open pollination (36% vs 8%). Thus, flower size seems to affect fruiting of this species. No effective visits by major pollinators such as bees, which could carry pollinia, were observed during 16.5 h of observation during daytime. Instead, thrips were often found moving on gynostemium or pollinia and circumstantial evidence that suggests thrips may partly transfer pollen in pieces out of a granular pollinium of P. japonica was obtained. Pogonia japonica should come to use thrips as a pollinator to supplement low fruit set under limited flower visitation by major pollinators.