Specialized pollination by spider-hunting wasps in the African orchid Disa sankeyi

Disa sankeyi Rolfe was found to be pollinated almost exclusively by Hemipepsis wasps (Pompilidae) at sites across its range in the Drakensberg mountains of South Africa. Wasps of both sexes appear to locate the cryptic yellow-green flowers primarily by using scent cues, as they show a classic zigzag flight pattern when approaching inflorescences. The sweet-spicy fragrance emitted by the flowers is strong enough to be discernable by a human from several metres away and consists of a blend of at least 65 volatile compounds, with (E)- cinnamic aldehyde and eugenol as the major constituents. On settling, wasps lick the exposed droplet of nectar that is secreted from the mouth of the reduced floral spur on each flower. Pollinaria become attached to the front feet of the wasps as they grasp flowers adjacent to those on which they are feeding. Pollen transfer to stigmas similarly takes place on flowers adjacent to those that are used as a nectar source. Almost 100% of flowers in the study populations were found to have been pollinated. Specialized pollination by pompilid wasps appears to be a rare phenomenon that has been reported only in southern African plant species. It appears to be associated with cryptic green-yellow flowers and highly accessible nectar. Behavioural assays are required to determine whether the basis of the specialization in this pollination system lies in a particular chemical composition of the floral fragrance.     

Observations of hawkmoth pollination in the South African orchid Disa cooperi

Johnson, S. D. 1995. Observations of hawkmoth pollination in the South African orchid Disa cooperi . - Nord. J. Bot. 15: 121–125. Copenhagen. ISSN 0107–055X.
Disa cooperi is a robust grassland orchid with long-spud white flowers which are strongly scented in the evening. Observations at a site in Natal province, South Africa showed that hawkmoths are frequent visitors to the orchid at dusk. The hawkmoth Basiothia schenki was an effective pollinator of D. cooperi; this hawk-moth has a medium length proboscis (x = 4.3 cm) which can be fully inserted into the nectar-containing spur of the orchid. Pollinaria are attached ventrally to the basal portion of the proboscis where it joins the head. Another hawkmoth, Agrius convolvuli , commonly foraged on nectar from D. cooperi , but did not carry pollinaria, probably because its proboscis is too long (x = 10 cm) to allow contact between the thick basal portion of the proboscis and the orchid column. Lips in Disa are typically linear and do not produce scent, thus the autapomorphic spathulate and scent-producing lip of D. cooperi indicates that hawkmoth pollination is derived in this species, probably from a long-proboscid fly pollinated ancestor.     

Scaling of nectar foraging in orchid bees

Morphology influences the rate at which foraging bees visit nectar flowers, the quantity of nectar they must consume to fuel their activities, and, consequently, the profitability of flower species. Because feeding time is a major determinant of visitation rate, I used a biomechanical model to examine how energy intake rate (E) varies with sucrose concentration, body mass (M), and proboscis length in orchid bees (Apidae: Euglossini). Under geometric scaling, the optimal sugar concentration (Smax) should be largely independent of body size, and E proportional to M1.0. In a comparative study of 30 orchid bee species ranging from 50 to 800 mg, Smax fell between 35% and 40% w/w, but E proportional to M0.54, significantly less than model predictions. Proboscis length and radius scale geometrically with body mass, but proboscis length exhibits substantial size-independent variation, particularly in small bees. One cost of a long proboscis is a reduction in both E and Smax in accordance with the scaling model. This finding highlights a difference between the lapping mechanism used by bumblebees and the suction mechanism used by orchid bees. A field study confirms that orchid bees harvest nectars with between 34% and 42% sucrose, independent of body size.     

Pollination biology of fruit-bearing hedgerow plants and the role of flower-visiting insects in fruit-set

Background and Aims

In the UK, the flowers of fruit-bearing hedgerow plants provide a succession of pollen and nectar for flower-visiting insects for much of the year. The fruits of hedgerow plants are a source of winter food for frugivorous birds on farmland. It is unclear whether recent declines in pollinator populations are likely to threaten fruit-set and hence food supply for birds. The present study investigates the pollination biology of five common hedgerow plants: blackthorn (Prunus spinosa), hawthorn (Crataegus monogyna), dog rose (Rosa canina), bramble (Rubus fruticosus) and ivy (Hedera helix).

Methods

The requirement for insect pollination was investigated initially by excluding insects from flowers by using mesh bags and comparing immature and mature fruit-set with those of open-pollinated flowers. Those plants that showed a requirement for insect pollination were then tested to compare fruit-set under two additional pollination service scenarios: (1) reduced pollination, with insects excluded from flowers bagged for part of the flowering period, and (2) supplemental pollination, with flowers hand cross-pollinated to test for pollen limitation.

Key Results

The proportions of flowers setting fruit in blackthorn, hawthorn and ivy were significantly reduced when insects were excluded from flowers by using mesh bags, whereas fruit-set in bramble and dog rose were unaffected. Restricting the exposure of flowers to pollinators had no significant effect on fruit-set. However, blackthorn and hawthorn were found to be pollen-limited, suggesting that the pollination service was inadequate in the study area.

Conclusions

Ensuring strong populations of insect pollinators may be essential to guarantee a winter fruit supply for birds in UK hedgerows.Key words: Blackthorn, bramble, Crataegus monogyna, frugivorous birds, hawthorn, Hedera helix, hedgerows, ivy, insect pollination, Prunus spinosa, Rubus fruticosus, Rosa canina     

Ancestral deceit and labile evolution of nectar production in the African orchid genus Disa

An outstanding feature of the orchid family is that approximately 30–40% of the species have non-rewarding flowers and deploy various modes of deception to attract pollinators, whereas the remaining species engage in pollination mutualisms based on provision of floral rewards. Here, we explore the direction, frequency and reversibility of transitions between deceptive and rewarding pollination systems in the radiation of the large African genus Disa, and test whether these transitions had consequences for diversification. By optimizing nectar production data for 111 species on a well-resolved phylogeny, we confirmed that floral deception was the ancestral condition and that nectar production evolved at least nine times and was lost at least once. Transitions to nectar production first occurred ca 17 million years ago but did not significantly affect either speciation or extinction rates. Nectar evolved independently of a spur, which was lost and gained multiple times. These results show that nectar production can be a highly labile trait and highlight the need for further studies of the genetic architecture of nectar production and the selective factors underlying transitions between deception and mutualism.     

Recipe for disruption: multiple recent arrivals of megachilid bees in Pacific archipelagos

When examining how the ecosystems of remote islands have developed, it is important to know the timing of when various elements arrived and whether they then diversified. Our understanding of the histories behind the biodiverse south west Pacific (SWP) archipelagos is limited, and further impeded by the complex geological histories of this region. Previous studies of the SWP short-tongued halictine bee fauna suggest their presence is much younger than the geological ages of these archipelagos, which is surprising given their critical role as pollinators in other terrestrial ecosystems. The long-tongued megachilid bees represent a considerable proportion of the known bee species for the region, yet little is known of their origin. Here we use genetic diversity within mitochondrial DNA to infer the likely ages and origins of megachilid species from Vanuatu, Fiji, and Samoa. Our results indicate a very recent origin for megachilids in the SWP, with many species exhibiting small intraspecific genetic distances. Three species share almost identical haplotypes with specimens from Southeast Asia, suggesting multiple human-aided introductions. Combined with data from recent studies on other bee groups present in the region, our results have broad implications for how the Pacific island biota developed and how we should approach its management.     

Pollination biology and breeding systems in the terrestrial orchid Bletilla striata

The levels of fruit set in different habitats (three inland populations vs. three coastal populations) and the breeding system in the terrestrial orchid Bletilla striata were examined in two groups of populations in Haenam-gun, Jollanam-do Province in southern Korea. In total inland populations (mean fruit set=13.3%) showed about eight-fold higher fruit set per plant than the coastal populations (1.6%), probably due to mild climatic conditions in the inland populations during the flowering period. Honey bee workers Apis mellifera were observed in the inland populations, but no visitors were found in the coastal populations. However, a great increase in fruit set was achieved by hand-pollination: the percentage of fruit set through artificial self-pollination and geitonogamous pollination were close to 90%, indicating that B. striata is self-compatible. Agamospermy and spontaneous autogamy (automatic self-pollination) were not detected in this study. These indicate that pollinia vectors are essential for achieving fruit set in natural populations of B. striata. Except in one inland population examined in 2001, there was no significant correlation between the patch size per population and the average percentage of fruit set, which might reflect deception-pollination of B. striata and/or paucity of pollinators. Overall levels of fruit sets within and among patches in each population were homogeneous during a two-year period.     

Pollination biology of the Chilean endemic orchid Chloraea lamellata

Chloraea lamellata Lindl. is one of the 50 taxa of terrestrial orchids occurring in Chile. In this paper we report the breeding system, phenology and pollinator activity in a population of the species located in the Province of Valdivia, X Región, Chile (39°28 S). Chl. lamellata flowers from November to January, forming a lax spike with ca. 13 flowers. The floral life-span is 14 ± 4 days. The species is self-compatible. There was no statistical difference between the amount of seed produced after hand cross-pollination and hand self-pollination treatments. Neither direct autogamy nor agamospermy are involved in seed setting, thus pollinating agents are essential for the species' reproduction. Also, it has a high number of pollen grains (881733) and ovules (599833) per flower. The P/O ratio calculated is low (1.46). Probable pollinators belong to the orders Hymenoptera (Corynura chloris and Ruizantheda proxima) and Diptera (Sarcophagidae); these insects had a low visitation rate (0.00002 visits/spike/minute). The rate of pollination observed was low (28.6% flowers with pollinia deposited versus 71.3% flowers with pollinia removed). The reproductive features of Chl. lamellata suggest that the survival capability and long-term persistence of the species will be seriously threatened if the plant–pollinator interaction is disrupted.     

Population genetics of orchid bees in a fragmented tropical landscape

The prospects for persistence of bees living in fragmented landscapes is a topic of considerable interest due to bees’ importance as pollinators of agricultural crops and wild plants, coupled with the ubiquity of native habitat loss and evidence that bees may be declining worldwide. Population persistence in fragmented areas depends on dispersal potential and maintenance of gene flow among fragments of habitat. Here we used population genetic techniques to characterize, for two equally abundant orchid bee species that differ in their physiology and ecology, levels of genetic differentiation among fragments of tropical forest in southeastern Costa Rica in a ~200 km² landscape. We measured population differentiation with ϕ_PT (an analogue to the traditional summary statistic Fst), as well as two measures that may more accurately reflect the level of differentiation when highly variable loci are used: G’st and D_est. We also calculated pairwise genetic distances among individuals and conducted Mantel tests to test the correlation of genetic and geographic distance, for each species. We found strong differences in genetic structure between the species. Contrary to our expectations, each measure of genetic structure revealed that the larger-bodied species, Eulaema bombiformis, had higher levels of differentiation than the smaller species, Euglossa championi. Furthermore, for Eulaema bombiformis there was a significant positive correlation of genetic and geographic distance while for Euglossa championi there was no significant positive correlation. Our results demonstrate that bee species can have strikingly different levels of gene flow in fragmented habitats, and that body size may not always act as a useful proxy for dispersal, even in closely related taxa.     

Juggling with volatiles: exposure of perfumes by displaying male orchid bees

Male orchid bees (Euglossini) pollinate 10% of the neotropical orchid flora while collecting floral scents, which they store and accumulate in hind tibial pouches. The purpose of these fragrances is unclear, as is the context, timing and mechanism of their possible exposure. Here we show for the first time that males expose and relocate their fragrances during courtship display. We present high-speed video analyses revealing an intricate and repetitive leg movement performed by displaying male Euglossa cognata. The behavior involves several morphological structures of hitherto unknown function and suggests transfer of substances from the hind tibia to a contralateral mid-tibial tuft of hairs. Body-side-specific fluorescent dye application and consecutive detection of signals on males after display confirmed this transfer. Deposited on the mid-tibial tufts, the fragrances are ideally placed in order to become ventilated by jugal combs on the wing bases, as previously suggested by Bembé (in Apidologie 35:288–291, 2004). Being clearly distinct from motor patterns involved in fragrance collection, the described movement is continuously performed by displaying males, suggesting an equally continuous exposure of volatiles. Although the findings strengthen, the view that the volatiles serve as attractants in the context of mating behavior, the signal addressee, conspecific males or females, has yet to be found.Electronic Supplementary Material Supplementary material is available for this article at     

Reproductive biology of Trichocentrum pumilum: an orchid pollinated by oil-collecting bees

The reproductive biology, reward production and pollination mechanism of Trichocentrum pumilum were studied in a gallery forest in the interior of the State of São Paulo, southeast Brazil. The floral visitors and pollination mechanism were recorded, and experimental pollinations were carried out in order to determine the breeding system of this species. Trichocentrum pumilum blooms in spring. Each paniculate inflorescence bears an average of 85 flowers that present a central yellow callus and finger‐like trichomes on the lateral lobes of the lip. A lipoidal substance is produced and stored among these trichomes. In the studied population, T. pumilum is exclusively visited and pollinated by two bee species (Tetrapedia diversipes and Lophopedia nigrispinis). Pollinaria are deposited on mouthparts of bees during collection of the lipoidal substance from the lateral lobes of the labellum. Trichocentrum pumilum is self‐incompatible and pollinator‐limited. Natural fruit set was low (9%, compared to 45% in experimentally cross‐pollinated flowers). Potentially viable seed exceed 97% in fruits obtained through cross‐pollination and in natural conditions (open pollination).     

Enfleurage, lipid recycling and the origin of perfume collection in orchid bees

Enfleurage, the extraction of elusive floral scents with the help of a lipophilic carrier (grease), is widely used in the perfume industry. Male neotropical orchid bees (Euglossini), which accumulate exogenous fragrances as pheromone analogues, use a similar technique. To collect fragrances, the bees apply large amounts of straight-chain lipids to odoriferous surfaces from their cephalic labial glands, which dissolve the volatiles, and the mixture is then transferred to voluminous hind-leg pockets. Here, we show that males do in fact operate a lipid conveyor belt to accumulate and concentrate their perfume. From the hind-leg pockets of caged male Euglossa viridissima, deuterated derivatives of carrier lipids were consecutively sequestered, shuttled back to the labial glands and reused on consecutive bouts of fragrance collection. Such lipid cycling is instrumental in creating complex perfume bouquets. Furthermore, we found that labial glands of male orchid bees are strikingly similar to those of scent-marking male bumblebees in terms of size, form and structure. This, and a prominent overlap in secretory products, led us to propose that perfume collection evolved from scent-marking in ancestral corbiculate bees.     

Pollination success in monochromic yellow populations of the rewardless orchid Dactylorhiza sambucina

Dactylorhiza sambucina is a European terrestrial orchid that lacks a pollinator reward. Throughout most of its range, populations contain yellow- and purple-flowering individuals, but in western Germany, monomorphic yellow populations predominate. As elsewhere, bumblebee queens are the most important pollinators in these populations, and mean fruit set over two years was 19%, well within the range reported from dimorphic populations. Multivariate analyses of plant and population traits, including plant height, leaf number, flower number and density on the spikes, flowering population density, and nearest neighbor distance, showed that only individual plant height and population density had a unique positive effect on pollen export; female function was unrelated to height or population density. The positive effects of dense spacing of flowering conspecifics and tall size appear due to greater visual attractiveness. Good visual exposure may also explain that flowers higher up on the spikes, in spite of opening late in the season, had higher male reproductive success than early flowers.     

Beta diversity of orchid bees in a tropical biodiversity hotspot

A controversial issue in ecology and conservation is whether community composition is controlled by niche or dispersal assembly. We assessed the importance of climatic factors and geographic gradients on the distribution of orchid bees in a severely-fragmented and species-rich tropical forest region in Brazil. Orchid-bee males were attracted to 17 different scent baits and collected in 15 forest sites. In total we captured 11,081 bees from 40 species. Climatic variables explained twice as much of the observed variation in the bee species data set as did pure spatial variation. However, most of the climatic explained variation was spatially structured, indicating that the species and the climatic data have a similar spatial arrangement. In fact, part of the observed latitudinal changes in community composition appears to be explained by a concomitant gradient in precipitation seasonality. Similarly, reduced temperatures and a more seasonal precipitation may help to explain the relative distinctiveness of the fauna from some of the westernmost sites. The level of similarity among the sampled sites, although highly variable, decayed both as function of the climatic and geographic distances among these sites. The greatest pairwise dissimilarities in the composition of the orchid-bee fauna were observed among sites 200–300 km from each other, since in many case those sites were more dissimilar in terms of climate than those further apart. It is suggested that global warming and consequent altered climatic regimes will influence the distribution patterns of orchid bees in a region already threatened by deforestation and forest fragmentation.     

Disa introrsa sp. nov. (Orchidaceae) from the Western Cape of South Africa, with notes on the phylogeny of Disa sect. Disella

Disa introrsa Kurzweil, Liltved and Linder (Orchidaceae - Orchidoideae - Diseae) is described from the Ceres District of the Western Cape of South Africa, and is placed in sect. Disella Lindl. The species is so far known from only two collections. Flowering is strongly stimulated through the effects of fire which may account for the apparent rarity of D. introrsa. Possible phylogenetic relationships among the species of D. sect. Disella are outlined.     

Pollination biology of the endangered orchid Cypripedium japonicum in a fragmented forest of Japan

Pollination biology studies of the endangered orchid Cypripedium japonicum were conducted in its natural habitat using pollinator observation and hand‐pollination experiments. The observed fruit set was as follows: artificial outcross‐pollinated, 100%; artificial self‐pollinated, 100%; pollinator‐excluded, 0%; and emasculated flowers, 0%. These results show that this species, although self‐compatible, is neither autogamous nor agamospermous. The fruit set for open‐pollinated flowers was 14.9%, which suggests that the study population was subject to pollinator limitation. The nectarless flowers of C. japonicum were exclusively visited and pollinated by the queens of two bumblebee species (Bombus ardens and B. diversus diversus). It is probable that the nectarless flowers of C. japonicum attract pollinators through a generalized food deceptive system.     

Pollination by hummingbirds and bees in eight syntopic species and a putative hybrid of Ericaceae in Southeastern Brazil

We report on flowering phenology, floral morphology, pollinators, and nectar for eight species and a putative natural hybrid belonging to Agarista, Gaultheria and Gaylussacia that occur syntopically in a montane area. The campanulate to tubular flowers of eight out of nine Ericaceae taxa are primarily pollinated by either hummingbirds or bees. Flowering overlaps in all species but slight differences of floral shape, colour, and nectar characterize pollination by each pollinator group. Differences in floral traits are not large enough to exclude secondary pollinators. Thus, either the main pollinators of a species belonging to its syndrome, or secondary pollinators of a species belonging to different syndromes, may allow for inter-specific crosses.     

Pollination mechanism in southern Brazilian orchids which are exclusively or mainly pollinated by halictid bees

The pollination process is documented in three sympatric orchids found in Curitiba, Paraná State, southern Brazil. InCampylocentrum aromaticum (Epidendroideae: Angraeciinae) andPrescottia densiflora (Spiranthoideae: Prescotiinae) halictid bees act as main pollinators with minor contributions from other insects, such as Syrphid flies. Because of the pollinarium and column structure inCyclopogon diversifolius. (Spiranthoideae, Spiranthinae), halictid bees are the only insects capable of performing pollination. In the three studied species pollinarium removal and deposition are achieved by interaction between the column and bee's mouth parts. Morphological and ecological flower features in agreement with this pollination mode are discussed and pollination by halictid bees is suggested to occur in a number of South American orchids.