Fly Pollination Research Articles

Rocksitter Flies (Lauxaniidae: Cestrotus) are Key‐Pollinators of Ceropegia pulchellior—A Threatened and Localised South African Endemic With Foetid‐Scented Flowers

ABSTRACTShort‐tongued saprophilous flies are a diverse but under‐appreciated group of pollinators, which are particularly important for flowers in the subtribe Stapeliinae (Apocynaceae‐Asclepiadoideae‐Ceropegieae). This clade of plants is characterised by repeated shifts between tubular kettle‐trap and open non‐trap flowers and chemical mimicry (of decomposing substrates or dying insects) to attract specific fly pollinators. The biology of most Stapeliinae, particularly those with non‐trap flowers, remains poorly studied, hampering our understanding of the mechanisms driving diversification in this plant group. We examined the pollination biology and floral traits of Ceropegia pulchellior, a South African endemic with non‐trap flowers confined to Natal Group Sandstone on the Durban escarpment. Observations showed that flowers are visited exclusively by flies which forage on small amounts of nectar in the corona cavities. Flowers were pollinated primarily by lauxaniid flies in the genus Cestrotus, although several muscid fly species also contribute. Pollinator exclusion experiments confirmed that the plants depend on these flies for reproduction. Reproductive success was low (fruit set never exceeding 8% of flowers). Pollen transfer efficiency was relatively high but variable across the flowering period. GC–MS analysis of floral scent revealed that the foetid odour is dominated by aliphatic acids and p‐cresol with small amounts of indole, supporting the assumption that C. pulchellior mimics decaying substrates to selectively attract detritus‐feeding (saprophagous) flies as pollinators. Analysis of spectral reflectance of flowers indicates that flower colours, when viewed by the fly pollinators, are not chromatically distinct from the habitat background, suggesting that flowers rely on olfactory rather than visual signals to attract pollinators. This study contributes to the growing awareness of the complexity of pollination systems in the Stapeliinae, in terms of the wide diversity of fly taxa involved, the intricate pollen transfer mechanisms, and the unusual floral scent chemistry associated with mimicry of oviposition substrates and food sources.

The sweet path of Hansel and Gretel: pollination system of Masdevallia hortensis (Orchidaceae: Pleurothallidinae) in a cloud montane forest of the Cordillera Occidental, in Colombia

Pollination by deception is assumed as the general rule among pleurothallid orchids. However, considering the exceptional diversity of this group (44 genera and over 5100 species) and the relatively limited number of available studies (pollination ecology has been assessed in only 17 genera), generalized trends about their pollination systems might disregard a wide variety of specific life-history traits and inconspicuous honest signals/rewards for pollinators. The few known associations of pleurothallid orchids with a large assortment of fly taxa further support the assumption of generalized pollination by deception. We investigated the natural pollination system of Masdevallia hortensis, a strictly endemic species of cloud forests in the Western Andes of Colombia. This species exhibited a sophisticated and unique pollination mechanism, producing sugary secretions in the lateral sepals along purple dotted patches, fed upon by different visiting species of fruit flies (Drosophilidae). The sucrose concentration in these secretions varied throughout the day and significantly decreased after pollinaria removal. Visiting fruit flies appeared to be guided towards a chamber between the mobile lip and the column, by dotted lines in the lateral sepals. During visitations, individuals of the most abundant species in our observations (Drosophila sp. 1) were singly entrapped in the chamber until eventually freeing themselves with the pollinaria attached to their bodies. We also demonstrated that M. hortensis is strictly self-incompatible, which makes fly pollination an essential process for the maintenance of natural populations of the species. The flowers of M. hortensis offer rewards for visiting insects, an aspect that should be thoroughly evaluated before making generalizations. In this way, we urge integrative ecological studies to understand the reproductive evolutionary patterns in this group of orchids.

Divergence and convergence of gut microbiomes of wild insect pollinators.

Pollination services provided by wild insect pollinators are critical to natural ecosystems and crops around the world. There is an increasing appreciation that the gut microbiota of these insects influences their health and consequently their services. However, pollinator gut microbiota studies have focused on well-described social bees, but rarely include other, more phylogenetically divergent insect pollinators. To expand our understanding, we explored the insect pollinator microbiomes across three insect orders through two DNA sequencing approaches. First, in an exploratory 16S amplicon sequencing analysis of taxonomic community assemblages, we found lineage-specific divergences of dominant microbial genera and microbiota community composition across divergent insect pollinator genera. However, we found no evidence for a strong broad-scale phylogenetic signal, which we see for community relatedness at finer scales. Subsequently, we utilized metagenomic shotgun sequencing to obtain metagenome-assembled genomes and assess the functionality of the microbiota from pollinating flies and social wasps. We uncover a novel gut microbe from pollinating flies in the family Orbaceae that is closely related to Gilliamella spp. from social bees but with divergent functions. We propose this novel species be named Candidatus Gilliamella eristali. Further metagenomes of dominant fly and wasp microbiome members suggest that they are largely not host-insect adapted and instead may be environmentally derived. Overall, this study suggests selective processes involving ecology or physiology, or neutral processes determining microbe colonization may predominate in the turnover of lineages in insect pollinators broadly, while evolution with hosts may occur only under certain circumstances and on smaller phylogenetic scales. IMPORTANCE Wild insect pollinators provide many key ecosystem services, and the microbes associated with these insect pollinators may influence their health. Therefore, understanding the diversity in microbiota structure and function, along with the potential mechanisms shaping the microbiota across diverse insect pollinators, is critical. Our study expands beyond existing knowledge of well-studied social bees, like honey bees, including members from other bee, wasp, butterfly, and fly pollinators. We infer ecological and evolutionary factors that may influence microbiome structure across diverse insect pollinator hosts and the functions that microbiota members may play. We highlight significant differentiation of microbiomes among diverse pollinators. Closer analysis suggests that dominant members may show varying levels of host association and functions, even in a comparison of closely related microbes found in bees and flies. This work suggests varied importance of ecological, physiological, and non-evolutionary filters in determining structure and function across largely divergent wild insect pollinator microbiomes.

Crop-pollinating Diptera have diverse diets and habitat needs in both larval and adult stages.

Insects are important pollinators of global food crops and wild plants. The adult and larval diet and habitat needs are well known for many bee taxa, but poorly understood for other pollinating taxa. Non-bee pollinators often feed on different substrates in their larval and adult life stages, and this diet and habitat diversity has important implications for their conservation and management. We reviewed the global literature on crop pollinating Diptera (the true flies) to identify both larval and adult fly diet and habitat needs. We then assembled the published larval and adult diets and habitat needs of beneficial fly pollinators found globally into a freely accessible database. Of the 405 fly species known to visit global food crops, we found relevant published evidence regarding larval and adult diet and habitat information for 254 species, which inhabited all eight global biogeographic regions. We found the larvae of these species lived in 35 different natural habitats and belong to 10 different feeding guilds. Additionally, differences between adult Diptera sexes also impacted diet needs; females from 14 species across five families fed on protein sources other than pollen to start the reproductive process of oogenesis (egg development) while males of the same species fed exclusively on pollen and nectar. While all adult species fed at least partially on floral nectar and/or pollen, only five species were recorded feeding on pollen and no fly larvae fed on nectar. Of the 242 species of larvae with established diet information, 33% were predators (n = 79) and 30% were detritivores (n = 73). Detritivores were the most generalist taxa and utilized 17 different habitats and 12 different feeding substrates. Of all fly taxa, only 2% belonged to the same feeding guild in both active life stages. Our results show that many floral management schemes may be insufficient to support pollinating Diptera. Pollinator conservation strategies in agroecosystems should consider other non-floral resources, such as wet organic materials and dung, as habitats for beneficial fly larvae.

Provisioning Australian Seed Carrot Agroecosystems with Non-Floral Habitat Provides Oviposition Sites for Crop-Pollinating Diptera

The addition of floral resources is a common intervention to support the adult life stages of key crop pollinators. Fly (Diptera) crop pollinators, however, typically do not require floral resources in their immature life stages and are likely not supported by this management intervention. Here, we deployed portable pools filled with habitat (decaying plant materials, soil, water) in seed carrot agroecosystems with the intention of providing reproduction sites for beneficial syrphid (tribe Eristalini) fly pollinators. Within 12 to 21 days after the pools were deployed, we found that the habitat pools supported the oviposition and larval development of two species of eristaline syrphid flies, Eristalis tenax (Linnaeus, 1758) and Eristalinus punctulatus (Macquart, 1847). Each habitat pool contained an average (±S.E.) of 547 ± 117 eristaline fly eggs and 50 ± 17 eristaline fly larvae. Additionally, we found significantly more eggs were laid on decaying plant stems and carrot roots compared to other locations within the pool habitat (e.g., on decaying carrot umbels, leaves, etc.). These results suggest that deploying habitat pools in agroecosystems can be a successful management intervention that rapidly facilitates fly pollinator reproduction. This method can be used to support future studies to determine if the addition of habitat resources on intensively cultivated farms increases flower visitation and crop pollination success by flies.

Pollination systems and nectar rewards in four Andean species of Salvia (Lamiaceae)

Adaptation to the most effective pollinator is often conceived as the primary explanation of widespread convergence in flower phenotypes. However, specialization does not exclude the presence of other floral visitors, which may contribute to plant reproduction. Here we combined observations about pollinators’ visitation rates and effectiveness with nectar secretion dynamics and sugar composition in four Andean Salvia species from Bolivia. The study revealed a wider diversity than expected both in pollination systems and in nectar strategies. While Salvia haenkei Benth. and Salvia stachydifolia Benth. were almost exclusively pollinated by either hummingbirds or bees, respectively, mixed pollination was found in Salvia orbignaei Benth., a species previously described as hummingbird-pollinated. Salvia personata Epling. was exclusively pollinated by syrphid flies. Differences in nectar volume and sugar concentration were found between insect-pollinated species and mixed- or hummingbird-pollinated species. However, the four Salvia species displayed different strategies regarding nectar sugar composition, with sucrose-rich nectar in Salvia orbignaei, glucose-rich nectar in Salvia haenkei and Salvia stachydifolia, and glucose-rich nectar lacking fructose in Salvia personata, suggesting an adaptation to syrphid fly pollination. Our results provide a clearer picture of floral trait evolution in Salvia and highlight the contribution of some pollinators different from those expected according to the floral syndromes.

Impact of Bee and Fly Pollination on Physical and Biochemical Properties of Strawberry Fruit

Improvement in physical and biochemical properties of fruits through cross-pollination is a highly variable phenomenon. It mainly depends on the species of the pollinator and the nature of the crop being pollinated. It is therefore imperative to quantify the relative pollination effectiveness of an insect species for a certain crop species. In the present study, pollination effectiveness of two native bees (i.e., Apis dorsata and A. florea) and two syrphid flies (i.e., Eristalinus aeneus and Eupeodes corollae) were evaluated in terms of physical properties of strawberry fruits at Multan, Pakistan. The physical parameters of resultant fruits included length, pole, equator, fruit set ratio, number of days to reach market maturity, and shelf life. The biochemical properties of fruits resulted from open-pollinated plants (free insect visits) and caged plants (no insect visits) were also compared. The biochemical parameters included TSS (total soluble solids), TA (titratable acidity), vitamin C, and pH. Apis dorsata was the most abundant pollinator, followed by E. aeneus and E. corollae. Based on single-visit effectiveness, A. dorsata proved to be the most effective pollinator, in terms of physical properties, of strawberry fruit. Eristalinus aeneus outcrossed A. florea in terms of fruit set (%). The open-pollinated plants showed better physical and biochemical properties (26% higher TSS, 34% higher TA, but 25% lower pH value) in terms of fruits than the caged plants. Conservation of A. dorsata and E. aeneus can enhance physical and biochemical properties of strawberry fruits in the region.

Pollinator and floral odor specificity among four synchronopatric species of Ceropegia (Apocynaceae) suggests ethological isolation that prevents reproductive interference

Possession of flowers that trap fly pollinators is a conservative trait within the genus Ceropegia, in which pollination systems can be generalized or highly specialized. However, little is known about the role of plant–pollinator interactions in the maintenance of species boundaries. This study examined the degree of plant–pollinator specialization and identified the parameters responsible for specificity among four co-occurring Ceropegia species with overlapping flowering times. All investigated plant species were functionally specialized on pollination by Chloropidae and/or Milichiidae flies and each Ceropegia species was, in turn, ecologically highly specialized on only two pollinating fly morphospecies, though one plant species appeared more generalist. Species-specific fly attraction was due to the differences between plant species in floral scents, floral morphology, colour patterns, and presence of other functional structures, e.g., vibratile trichomes, which were shown to contribute to pollinator attraction in one study species. The combination of these olfactory and visual cues differentially influenced pollinator preferences and thus hindered heterospecific visitation. Furthermore, a pollinator exchange experiment also highlighted that species integrity is maintained through efficient ethological isolation (pollinator attraction). The mechanical isolation mediated by the fit between floral morphology and size and/or shape of fly pollinators appears less pronounced here, but whether or not the morphological match between male (pollinium) and female (guide rails) reproductive organs can impede hybridization remains to be investigated.

Comparative reproductive ecology of two sister Asarum species (Aristolochiaceae) in relation to the evolution of elongated floral appendage.

Genus Asarum (Aristolochiaceae) shows diverse floral morphology and is hypothesized to have diversified as a result of pollinator-mediated selection. Yet most aspects of their reproductive ecology, including pollinators, remain unclear. This study focuses on A. costatum and A. minamitanianum in Japan, a sister species pair having remarkable differences in calyx lobe length (10-20 mm and 70-180 mm, respectively). The objectives of this study are to elucidate multiple aspects of reproductive ecology of these two species and obtain evolutionary insights into floral organ elongation. We adopted combined approaches, including field observations, molecular analyses and cultivation experiments, such as pollinator observation for 3 years, fine-scale spatial genetic analysis of 769 individuals, paternity analysis based on 566 seeds over 4 years, and control pollination experiments. Both Asarum species had strong spatial genetic structures, indicating limited seed dispersal. Pollinator observation revealed that flies and ground-dwelling insects visited flowers of both species, but that the pollinator fauna differed between the species. The visitation rate of flies was extremely low but was more than twice as high in the species with an elongated floral appendage. Paternity analysis revealed A. minamitanianum was predominantly outcrossing, while A. costatum showed a wide range of selfing rates among fruits. These two Asarum species are likely adapted to fly pollination in the shady forest understorey, where available pollinator fauna is limited. In addition, although its function remains unclear, the elongated calyx lobe of A. minamitanianum could have evolved for effective pollen dispersal by attracting fly visitors.

Antennae of psychodid and sphaerocerid flies respond to a high variety of floral scent compounds of deceptive Arum maculatum L.

Insect-pollinated plants often release complex mixtures of floral scents to attract their pollinators. Yet scent compounds eliciting physiological or behavioural responses in pollinators have only been identified in few plant species. The sapromyiophilous aroid Arum maculatum releases a highly diverse dung-like scent with overall more than 300 different compounds recorded so far to attract its psychodid and other fly pollinators. The volatiles’ role in pollinator attraction is mostly unknown. To identify potential behaviourally active compounds, we recorded electroantennographic responses of four Psychodidae and one Sphaeroceridae species to (1) inflorescence scents of A. maculatum and (2) the scents released by cow dung, likely imitated by the plant species. Here we show that these flies are sensitive to 78 floral volatiles of various chemical classes, 18 of which were also found in cow dung. Our study, which for the first time determined physiologically active compounds in the antennae of Psychoda spp. and Sphaeroceridae, identified various volatiles not known to be biologically active in any floral visitors so far. The obtained results help deciphering the chemical basis that enables A. maculatum and other plants, pollinated by psychodids and sphaerocerids, to attract and deceive their pollinators.

Remarkable floral colour variation in the functionally specialized fly-pollinated iris,Moraea lurida

AbstractSapromyophilous flowers are visited by flies seeking carrion or faeces, and flowers of this guild are typically large, purple or red-brown, often speckled and produce a pungent scent. Flowers of the South African iris Moraea lurida conform to this syndrome, but show considerable variation in colour and pattern. We were intrigued by the floral variation within a single population and investigated floral visitors and the effect of body size on pollen loads and whether different colour forms attracted different pollinator assemblages. We found a diverse array of insect visitors, but Diptera comprised the overwhelming majority, with Calliphoridae considered to be the most important for pollination on the basis of their visitation frequency and pollen loads. Effective pollination appeared to be dependent on large-bodied flies that, unlike smaller flies, fit the entire crawl space between the anthers and petals and thus acted like a key in a lock. Choice experiments revealed that the most important fly pollinators showed no colour preferences, and fly vision modelling showed that flies may not be able to discriminate among the different colour forms. This may lead to relaxed selection on colour. Floral scent was dominated by an unusual mix of aliphatic acids and alcohols, characteristic of mammalian skin products and gut microbiome, probably exploiting the perceptual bias of flies to compounds that typify the mammalian microbiome and fermenting carbohydrates.

Fly pollination drives convergence of flower coloration.

Plant-pollinator interactions provide a natural experiment in signal evolution. Flowers are known to have evolved colour signals that maximise their ease of detection by the visual systems of important pollinators such as bees. Whilst most angiosperms are bee pollinated, our understanding on how the second largest group of pollinating insects, flies, may influence flower colour evolution is limited to the use of categorical models of colour discrimination that do not reflect the small colour differences commonly observed between and within flower species. Here we show by comparing flower signals that occur in different environments including total absence of bees, a mixture of bee and fly pollination within one plant family (Orchidaceae) from a single community, and typical flowers from a broad taxonomic sampling of the same geographic region, that perceptually different colours, empirically measured, do evolve in response to different types of insect pollinators. We show evidence of both convergence among fly-pollinated floral colours but also of divergence and displacement of colour signals in the absence of bee pollinators. Our findings give an insight into how both ecological and agricultural systems may be affected by changes in pollinator distributions around the world.

Cypripedium lichiangense (Orchidaceae) mimics a humus-rich oviposition site to attract its female pollinator, Ferdinandea cuprea (Syrphidae).

Most species in the genus Cypripedium (Cypripedioideae) produce trap flowers, making it a model lineage to study deceptive pollination. Floral attractants in most species studied appear to target bee species of different sizes. However, more recent publications report fly pollination in some subalpine species, suggesting novel suites of adaptive floral traits. Cypripedium lichiangense (section Trigonopedia) is an endangered subalpine species endemic to the Hengduan Mountains, China. We observed and analysed its floral traits, pollinators and breeding systems over 2 years insitu and in the lab. Cypripedium lichiangense was visited by females of Ferdinandea cuprea (Syrphidae). The pollinia were carried dorsally on the fly thoraces. The eggs of this fly were frequently found in the saccate labellum and on other floral organs, suggesting brood-site mimesis. The orchid is self-compatible, but cross-pollination produces more viable embryos. We propose a new mode of floral mimesis, humus-rich oviposition site mimicry, for C. lichiangense. Compared with the mimesis of aphid colonies attracting syrphid pollinators (subfamily Syrphinae), whose larvae are entomophagic, as reported in some Paphiopedilum species (Cypripedioideae), pollination by deceit in C. lichiangense represents a distinct and separate mode of exploitation of another saprophagic (or phytophagic) larvae syrphid lineage in the subfamily Eristalinae and appears to indicate diversity of pollination strategies in SectionTrigonopedia of Cypripedium. However, this new brood-site mimesis seems to be less attractive to pollinators. As a possible adaptation to the weak attracted pollination strategy, this plant species has a long flowering period and extended lifespan of individual flowers to ensure reproductive success.

Pollination biology of Erica aristata: First confirmation of long-proboscid fly-pollination in the Ericaceae

Long-proboscid fly (LPF) pollination has been recorded in multiple plant lineages in South Africa. However in the large and morphologically diverse genus Erica, evidence for LPF pollination is limited to predictions based upon floral syndromes as well as anecdotal observation and limited citizen science records. Here we use breeding system experiments, pollinator exclusion, remote camera traps, spectral analysis and field observation in the Klein River Mountains, Western Cape Province, South Africa, to demonstrate this mode of pollination in the range-restricted taxon Erica aristata. This species has long narrow corolla tubes with narrow opening and contrasting white and crimson pink petals. Flowers were visited and pollinated exclusively by one long-proboscid fly species, Prosoeca rubicunda (Nemestrinidae) over four years at this study site. Breeding experiments showed that E. aristata is not self-compatible and pollinator exclusion experiments indicate that pollinator visits were required for seed-set. Low nectar volume and moderately high nectar sugar concentration were consistent with other long-proboscid fly-pollinated plant species in the Cape. This study represents the first confirmed instance of long-proboscid fly-pollination in the genus Erica.

Floral Scent Evolution in the Genus Jaborosa (Solanaceae): Influence of Ecological and Environmental Factors.

Floral scent is a key communication channel between plants and pollinators. However, the contributions of environment and phylogeny to floral scent composition remain poorly understood. In this study, we characterized interspecific variation of floral scent composition in the genus Jaborosa Juss. (Solanaceae) and, using an ecological niche modelling approach (ENM), we assessed the environmental variables that exerted the strongest influence on floral scent variation, taking into account pollination mode and phylogenetic relationships. Our results indicate that two major evolutionary themes have emerged: (i) a ‘warm Lowland Subtropical nectar-rewarding clade’ with large white hawkmoth pollinated flowers that emit fragrances dominated by oxygenated aromatic or sesquiterpenoid volatiles, and (ii) a ‘cool-temperate brood-deceptive clade’ of largely fly-pollinated species found at high altitudes (Andes) or latitudes (Patagonian Steppe) that emit foul odors including cresol, indole and sulfuric volatiles. The joint consideration of floral scent profiles, pollination mode, and geoclimatic context helped us to disentangle the factors that shaped floral scent evolution across “pollinator climates” (geographic differences in pollinator abundance or preference). Our findings suggest that the ability of plants in the genus Jaborosa to colonize newly formed habitats during Andean orogeny was associated with striking transitions in flower scent composition that trigger specific odor-driven behaviors in nocturnal hawkmoths and saprophilous fly pollinators.

Specialization for Tachinid Fly Pollination in the Phenologically Divergent Varieties of the Orchid Neotinea ustulata

Despite increased focus on elucidating the various reproductive strategies employed by orchids, we still have only a rather limited understanding of deceptive pollination systems that are not bee- or wasp-mediated. In Europe, the orchidNeotinea ustulatahas been known to consist of two phenologically divergent varieties, neither of which provide rewards to its pollinators. However, detailed studies of their reproductive biology have been lacking. Our study aimed to characterize and understand the floral traits (i.e., morphology, color, and scent chemistry) and reproductive biology ofN. ustulata. We found that the two varieties differ in all their floral traits; furthermore, whileNeotinea ustulatavar.ustulataappears to be pollinated by both bees (e.g.,Anthophora,Bombus) and flies (e.g.,Dilophus, Tachina), var.aestivalisis pollinated almost entirely by flies (i.e.,Nowickia, Tachina). Tachinids were also found to be much more effective than bees in removing pollinaria, and we show experimentally that they use the characteristic dark inflorescence top as a cue for approaching inflorescences. Our results thus suggest that while bothN. ustulatavarieties rely on tachinids for pollination, they differ in their degree of specialization. Further studies are, however, needed to fully understand the reproductive strategy ofN. ustulatavarieties.

Dual mechanisms of autonomous selfing in Roscoea nepalensis (Zingiberaceae).

The genus Roscoea, a Himalayan endemic and only alpine member of the predominately tropical family Zingiberaceae, is well-known for possessing elaborate floral traits commonly associated with biotic pollination, and particularly with long-tongued fly pollination. These traits include showy, easily detectable flowers with wide labellum serving as a landing platform for floral visitors, absence of discernible fragrance, presence of nectar as a reward, elongated reproductive organs situated away from the nectar source, and long corolla tube that is compatible with the tongue length of long-tongued insects (Goldblatt and Manning 2000, Cowley 2007).

Preliminary observations on the flower visitors ofNasa colanii(Loasaceae), a poorly known species endemic to northern Peru

Nasa is the most diverse genus among the family Loasaceae and it is mainly distributed in Peru. Most species of this genus are microendemics, with distributions restricted to very specific locations; such is the case of Nasa colanii Dostert & Weigend. This species — previously only known from the type collected in 1978 from the Amazonas region of Peru — lacks information about its biology and ecology. To improve our understanding of the reproductive biology and pollination ecology of N. colanii, we observed flower development and insect floral visits in a cloud forest in the Amazonas region. The flowers of N. colanii are nectariferous and protandrous. The typical stamen movement to the flower center of the subfamily Loasoideae appears to be autonomous. Only well-developed (elongated) pistils showed positive stigmatic receptivity to 3% hydrogen peroxide. Syrphid flies (Baccha sp.) and small beetles (Baridinae spp. and Alticini sp.) were the only observed flower visitors. The syrphid flies visited the flower and foraged for pollen, whereas the small beetles were found already in the flowers and seemingly used it as a shelter. Results suggest that N. colanii might be adapted to fly pollination.

Corolla stickiness prevents nectar robbing in Erica.

Floral stickiness is a rare trait with unknown function, but it is common in the mega-diverse Cape genus Erica (Ericaceae). This study investigated the role of stickiness measured as adhesive strength in Erica as protection against nectar robbing and its correlation with floral traits. We compared the incidence of nectar robbing in flowers of the same species with or without experimentally added stickiness, and amongst communities of co-occurring species with flowers differing in stickiness. Additionally, we tested the relationship between stickiness and pollination syndrome, corolla shape, corolla length and sepal-corolla ratio across the whole genus. Stickiness was correlated with lower floral damage rates within and between species, indicating it functions as an anti-nectar robbing trait. Across the genus Erica, stickiness is most strongly correlated with bird and long-proboscid fly pollination, presumably because of their larger nectar rewards. Stickiness was also correlated with floral traits that are often associated with high risk of being damaged by nectar robbers: narrow-mouthed corollas, long corollas and shorter sepals. These results show that corolla stickiness defends Erica flowers against nectar robbing and thereby potentially improves fitness.

Diversification in both the floral morphology and chemistry in two daciniphilous orchid ecotypes in Borneo

Morphological and floral chemical components are both important cues used by plants to attract pollinators. Two local ecotypes named ‘Nabawan’ and ‘Apin-Apin’ produced by the tropical orchid, Bulbophyllum ecornutum subspecies verrucatum, exhibit different morphology and scents to attract males of certain Bactrocera and Zeugodacus fruit fly species in the tribe Dacini as potential pollinators. Flowers of the Nabawan-ecotype possess a narrow-shaped lip (= labellum) structure and emit a characteristic fragrance of raspberry ketone along with smaller amounts of rhododendrol, whereas those of Apin-Apin-ecotype possess a broad-shaped lip and emit zingerone and zingerol as major components. Nevertheless, the structure of stiff hamulus appears similar and acts as a ‘crowbar’ during pollinarium removal by a fruit fly, indicating the basic mechanics of the movable see-saw lip structure to trap a fly is essentially the same. The changes in both morphology and chemistry, despite no significant difference in chloroplast DNA sequences, shown by the two ecotypes, might have occurred as part of a coevolutionary process involving both the Dacini fruit fly pollinators and the Bulbophyllum orchids in their natural habitats.