Analysis Of Pollen Loads Research Articles

Quantifying forage specialisation in polyphagic insects: the polylectic and rare solitary bee, Colletes floralis (Hymenoptera: Colletidae)

Abstract. 1. Many insect species vary in their degree of foraging specialisation, with many bee species considered polyphagic (polylectic). Wild, non‐managed bee species vary in their conservation status, and species‐specific biological traits such as foraging specialisation may play an important role in determining variance in population declines. Current agri‐environment schemes (AESs) prescribe the introduction of flower seed mixes for agricultural systems to aid the conservation of wild bees. However, the extent to which flower combinations adequately meet bee foraging requirements is poorly known.2. We quantitatively assessed pollen use and selectivity using two statistical approaches: Bailey’s Intervals and Compositional Analysis, in an examplar species, a purportedly polylectic and rare bee, Colletes floralis, across 7 sites through detailed analysis of bee scopal pollen loads and flower abundance.3. Both approaches provided good congruence, but Compositional Analysis was more robust to small sample sizes. We advocate its use for the quantitative determination of foraging behaviour and dietary preference.4. Although C. floralis is polylectic, it showed a clear dietary preference for plants within the family Apiaceae. Where Apiaceae was uncommon, the species exploited alternative resources. Other plant families, such as the Apiaceae, could be included, or have their proportion increased in AES seed mixes, to aid the management of C. floralis and potentially other wild solitary bees of conservation concern.

Acerola pollinators in the savanna of Central Brazil: temporal variations in oil-collecting bee richness and a mutualistic network

We present parameters to support the conservation and management of Acerola pollinators. We monitored pollinator visits to this fruit shrub in a Brazilian savanna and identified the pollinator’s other food resources. Twenty-three species of pollinators were sampled. Although there were temporal variations in visitor frequency, satisfactory levels of fruit set were obtained. This temporal variation promoted a compensatory effect on plant reproduction as the pollinator species were replaced during the course of flowering. The analysis of pollen loads showed grains of 16 plant species and four pollen types belonging to seven families that formed a network with a nested pattern. Such a network suggests that generalist plants must be available in the crop vicinity. The data presented suggest the natural viability of cultivating Acerola in the savannas of Central Brazil and the importance of natural lands for providing nesting resources and to enhance the bee diversity in agroecosystems.

Unexpected Polylecty in the Bee Genus Meganomia (Hymenoptera: Apoidea: Melittidae)

The melittid bees represent an early branch of bee phylogeny. They are therefore of special interest in understanding the early evolution and diversification of bees. Most species have been observed to be oligolectic (i.e., highly specialized in their choice of host-plant species). However, knowledge of host-plant associations is not equivalent across all melittid groups. Dasypodainae and the Melittinae are relatively well-known, while the African Meganomiinae are poorly studied. Preliminary field records seem to indicate that at least some meganomiine species are oligolectic. Here we present the first palynological analysis of pollen loads and pollen preference in Meganomiinae. Our results indicate that M. binghami is clearly a polylectic species. More data are needed to draw conclusions on the foraging behaviour of the other Meganomiinae. Our results show that, while oligolecty is widespread among melittid bees, there are polylectic lineages as well.

Sex-dependent variation in the floral preferences of the hawkmoth Manduca sexta

Studies of plant–pollinator interactions have often documented species differences in preferences for floral advertisements and rewards. However, the contribution of intraspecific variation in behaviours, especially between sexes, remains less understood. We explored resource preference and resource use by male and female Manduca sexta hawkmoths, relative to two important nectar resources in southern Arizona, U.S.A. Manduca sexta is the major pollinator of one of these species (Datura wrightii, Solanaceae). Because females must also seek out D. wrightii as an oviposition resource, females were predicted to feed upon it more than would males, which should be free to choose the best nectar resource. Using naive laboratory-reared moths in flight arena experiments, we found that both sexes preferred Datura wrightii over Agave palmeri (Agavaceae). Exposure to only one species and an odourless paper control, however, revealed sex-specific differences in foraging behaviour, with females feeding longer from A. palmeri and males feeding longer from D. wrightii, leading us to reject our hypothesis. Differences in feeding preferences directly translated into differences in energy intake. Females gained significantly more energy than did males by feeding from A. palmeri. We also examined whether behavioural preferences of moths in the laboratory translated into foraging behaviour in the field. Pollen load analysis of moths caught in 2004 showed that females carried significantly more A. palmeri pollen than did males, whereas males carried more D. wrightii pollen than did females. Whereas most studies examine pollination associations at the species level, our results highlight the potential importance of between-sex variation in floral visits.

Does Specialized Pollination Impede Plant Invasions?

Generalized pollination systems and autonomous self‐fertilization are traits that have been linked with plant invasiveness. However, whether specialized pollination requirements pose a significant barrier to plant invasions is not yet clear. Likewise, the contribution of pollinators to the fecundity of facultatively self‐pollinating invasive plant species is poorly understood. We addressed these issues using the self‐compatible and autonomously self‐pollinating Lilium formosanum, which also has large, showy flowers that are adapted for pollination by hawk moths. We investigated the pollination of this lily—which is indigenous to Taiwan—in KwaZulu‐Natal, South Africa, where it is invasive. The long‐tongued hawk moth Agrius convolvuli was identified as the primary pollinator on the basis of field observations, pollen load analysis, presence of lepidopteran scales on stigmas, and higher seed production in emasculated flowers exposed at night than in those exposed during the day. Remarkably, this moth is native to much of the Old World, including Taiwan and South Africa. Autonomous self‐pollination resulted in seed production, but at a reduced level relative to the seed production of open‐ and hand‐pollinated flowers, which was significant in one out of two populations examined. Thus, pollinators potentially contribute to invasion by increasing seed production and genetic variability through cross‐pollination, although contributions of pollinators to seed set versus that of autonomous self‐pollination may vary between populations. We conclude that specialized pollination requirements do not present a barrier to invasions when plants are specialized to pollinators or pollinator functional groups with very wide distributions.

Pollination of the red-hot poker Kniphofia laxiflora (Asphodelaceae) by sunbirds

Most of the species in the large African genus Kniphofia have floral traits that conform to the bird pollination syndrome, however there has been very little empirical work to confirm that birds are effective pollinators of Kniphofia species. From selective exclusion experiments, behavioural observations and pollen load analyses, we identified Amethyst Sunbirds ( Chalcomitra amethystina) and Malachite Sunbirds ( Nectarinia famosa) as the primary pollinators in two populations of Kniphofia laxiflora, with bees playing a smaller role. Bird visitors obtain moderate volumes (∼ 9 µl) of relatively concentrated (∼ 15%) hexose-rich nectar in the flowers. This species is shown to be genetically self-incompatible, and thus reliant on pollinator visits for seed set. Although mountain pride butterflies ( Aeropetes tulbaghia) have been identified as important pollinators of this species at two other populations, they did not occur at the two populations we studied.

Floral Resources and Nesting Requirements of the Ground-Nesting Social Bee,Lasioglossum malachurum(Hymenoptera: Halictidae), in a Mediterranean Semiagricultural Landscape

In order to adopt correct conservation strike plans to maintain bee pollination activity it is necessary to know the species' resource utilisation and requirements. We investigated the floral resources and the nesting requirements of the eusocial beeLasioglossum malachurumKirby at various sites in a Mediterranean landscape. Analysis of bees' pollen loads showed that Compositae was the more exploited family, although interpopulations differences appeared in the pollen types used. From 5 to 7 pollen types were used by bees, but only as few as 1–1.9 per load. Variations of the pollen spectrum through the annual nesting cycle were conspicuous. At all sites, bees nested in horizontal ground areas with high soil hardness, low acidity, and rare superficial stones. On the other side, the exploited soil was variable in soil granulometry (although always high in % of silt or sand) and it was moderately variable in content of organic matter and highly variable in vegetation cover. Creation of ground patches with these characteristics in proximity of both cultivated and natural flowering fields may successfully promote colonization of new areas by this bee.

Pollinators, “mustard oil” volatiles, and fruit production in flowers of the dioecious tree Drypetes natalensis (Putranjivaceae)

The Putranjivaceae is an enigmatic family, notable for being the only lineage outside the Capparales to possess the glucosinolate biochemical pathway, which forms the basis of an induced chemical defense system against herbivores (the "mustard oil bomb"). We investigated the pollination biology and floral scent chemistry of Drypetes natalensis (Putranjivaceae), a dioecious subcanopy tree with flowers borne on the stem (cauliflory). Flowering male trees were more abundant than female ones and produced about 10-fold more flowers. Flowers of both sexes produce copious amounts of nectar on disc-like nectaries accessible to short-tongued insects. The main flower visitors observed were cetoniid beetles, bees, and vespid wasps. Pollen load analysis indicated that these insects exhibit a high degree of fidelity to D. natalensis flowers. Insects effectively transfer pollen from male to female plants resulting in about 31% of female flowers developing fruits with viable seeds. Cetoniid beetles showed significant orientation toward the scent of D. natalensis flowers in a Y-maze olfactometer. The scents of male and female flowers are similar in chemical composition and dominated by fatty acid derivatives and isothiocyanates from the glucosinolate pathway. The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers.

Receptiveness of Foraging Wild Bees to Exotic Landscape Elements

Wild pollinators provide important services in both wild and human-dominated ecosystems, yet this group may be threatened by widespread anthropogenic landscape change. We explored the responses of wild bees to exotic floral species and novel habitat in a fragmented, suburban landscape using pollen grain identification. Pollen loads from bee specimens collected in 13 suburban grassland fragments in Denver, Colorado were sampled and compared with a pollen reference collection. Averaged across two seasonal sampling rounds, 45% of the bee-borne pollen grains were identified to the species level. Wild bees in this system were very receptive to using alien plants for pollen foraging; at least 45% of pollen sampled from bee specimens consisted of non-native pollen grains. During peak flowering in early summer, bees obtained at least 32% of their pollen resources from within-fragment sources and at least 7.5% from surrounding suburban residential yards. In midsummer, within-fragment sources represented 58% of pollen sampled while yards dropped to 1.5%. These bees appear to be more accepting of exotic floral species than of exotic habitat types (yards). The advantages and disadvantages of pollen load analysis for movement studies are discussed.

Analysis of pollen load based on color, physicochemical composition and botanical source

Pollen load samples from 10 hives of Apis mellifera (L.) were analyzed based on their physicochemical composition and botanical source, considering color as a parameter for quality control. In seven samples it was possible to establish the occurrence of more than 80% of a single pollen type, characterizing them as unifloral but with protein content variation. One of the samples was exclusively composed of saprophytic fungi (Cladosporium sp.). Comparing the mean results of the fungi loads with those of the nutritional components of pollen load, the former presented higher protein, mineral matter and dry matter and lower organic matter, ethereal extract and total carbohydrate values. The monochromatic samples met the physicochemical specifications regulating pollen load quality. The results showed that homogeneous coloration of the pollen load was not found to be a good indication of unifloral pollen, confirming the importance of physicochemical analysis and melissopalynological analysis for characterization of the quality of commercial pollen load.

Plant–pollinator networks: adding the pollinator’s perspective

Pollination network studies are based on pollinator surveys conducted on focal plants. This plant-centred approach provides insufficient information on flower visitation habits of rare pollinator species, which are the majority in pollinator communities. As a result, pollination networks contain very high proportions of pollinator species linked to a single plant species (extreme specialists), a pattern that contrasts with the widely accepted view that plant-pollinator interactions are mostly generalized. In this study of a Mediterranean scrubland community in NE Spain we supplement data from an intensive field survey with the analysis of pollen loads carried by pollinators. We observed 4265 contacts corresponding to 19 plant and 122 pollinator species. The addition of pollen data unveiled a very significant number of interactions, resulting in important network structural changes. Connectance increased 1.43-fold, mean plant connectivity went from 18.5 to 26.4, and mean pollinator connectivity from 2.9 to 4.1. Extreme specialist pollinator species decreased 0.6-fold, suggesting that ecological specialization is often overestimated in plant-pollinator networks. We expected a greater connectivity increase in rare species, and consequently a decrease in the level of asymmetric specialization. However, new links preferentially attached to already highly connected nodes and, as a result, both nestedness and centralization increased. The addition of pollen data revealed the existence of four clearly defined modules that were not apparent when only field survey data were used. Three of these modules had a strong phenological component. In comparison to other pollination webs, our network had a high proportion of connector links and species. That is, although significant, the four modules were far from isolated.

Adaptive radiation of the putrid perianth: Ferraria (Iridaceae: Irideae) and its unusual pollinators

Field studies of 13 of the estimated 17 species of the southern African geophytic genus Ferraria (Iridaceae: Iridoideae) identified four distinct pollination systems. Ferraria flowers are radially symmetric and cupped with a large, mostly pale or dull-colored perianth. Perigonal nectaries secrete hexose dominant (fructose and glucose) nectar. Most species are pollinated by Diptera of four families, apparently attracted by strong floral odors, mostly putrid or fermenting, but sometimes apparently sweet, and a large perianth mottled and edged with dark color. Concentrated sugary secretions are produced on the tepal claws that form a shallow floral cup. In contrast, flowers of F. ferrariola have a deep, narrow floral cup, a pale blue or yellow perianth, and a spicy scent and are pollinated by bees in the family Apidae, rewarded by nectar of moderate sugar concentration. Ferraria divaricata and F. variabilis have dull-colored, darkly speckled or streaked perianths and produce ample, highly dilute nectar pooled at the base of the floral cup and are pollinated by eumenid and masarine wasps (Vespidae). Lastly, F. uncinata has flowers with a narrow floral cup and dull violet tepals with brown margins. They are visited only by meloid and melyrid beetles. All pollen transfers from the anther of a Ferraria flower to an insect’s body are passive, regardless of pollinator. Pollen load analyses suggests that all pollinators show a high degree of faithfulness to Ferraria flowers.

Subamostragem de pólen apícola para análise melissopalinológica

Este trabalho teve por objetivo avaliar os vários critérios de subamostragens empregados na análise melissopalinológica de cargas de pólen coletadas por abelhas Apis mellifera (L.) africanizadas. O experimento considerou quatro diferentes pesos de subamostras (0,5; 1,0; 2,0 e 5,0 g) retiradas de lotes de cargas de pólen heteroflorais de 60 g, 100 g e 200 g. A riqueza de tipos polínicos foi maior em subamostras de maior peso (p = 0,006), no entanto, tipos polínicos adicionais ocorreram com baixa representatividade. O peso da subamostra não influenciou na mudança da classe de frequência dos principais tipos polínicos (p = 0,263). Houve um maior número de trocas de posições na classificação dos principais tipos polínicos com a redução do tamanho do grão de pólen (p = 0,001). Os resultados indicaram o uso de subamostragens de 5 g para estudos de avaliação da riqueza de tipos polínicos em amostras heteroflorais, entretanto, subamostragem de 0,5 g não limitou a avaliação dos principais tipos polínicos.

Analysis of pollen loads in a wild bee community (Hymenoptera: Apidae) – a method for elucidating habitat use and foraging distances

Resource utilisation and foraging ranges of Apidae (excluding Apis and Bombus) were studied in sandy grasslands of the temperate zone by pollen analysis combined with direct observation of bees. Planttaxa composition of 558 pollen loads collected from 56 bee species was determined. We recorded flower-visits using plot-based observations and resource utilisation using pollen analysis. For the most important entomophilous plant species flower-visitation and pollen-analytical data correspond (e.g. Berteroa incana, Centaurea stoebe, Potentilla argentea). Whenever pollen of plant species that are limited in their occurrence could be detected, we were able to use pollen analysis to determine foraging distances, but not maximum foraging distances. Using tree pollen, minimum flight ranges up to 1250 m were documented even for bees with 7 mm body size. Thus pollen analysis not only provides valuable information about foraging on different spatial scales, but also enables foraging ranges to be calculated without experimental manipulation.

FLORAL BIOLOGY OF BABIANA (IRIDACEAE: CROCOIDEAE): ADAPTIVE FLORAL RADIATION AND POLLINATION1

Field observations, floral dissections, floral nectar, and pollen load analyses of captured insects of 53 species of Babiana Ker Gawl. show that flowers of this geophytic genus of some 90 species of Iridaceae subfamily Crocoideae, predominantly of the southern African winter-rainfall zone, are cross pollinated by a wide range of animals. These include passerine birds and insects of four different orders, Hymenoptera (mainly Apidae), Diptera (mainly Nemestrinidae), Coleoptera (Scarabaeidae), and Lepidoptera (mainly Noctuidae). Apid pollination involves two discrete systems—passive pollination by anthophorines and native Apis mellifera foraging for nectar and active pollen gathering by A. mellifera and other Apoidea foraging for pollen. From what is known about relationships within Babiana and Crocoideae, it seems likely that passive pollination by anthophorines and honeybees, with nectar secreted in zygomorphic, bilabiate flowers as a reward, is the ancestral condition; it is also the most common, demonstrated for 18 and inferred for 35 more species from all three taxonomic sections of the genus. Active pollination by honeybees and female Apoidea foraging for pollen was demonstrated in one species and is inferred for four more, all of which have radially symmetric flowers and prominent anthers. Pollination by long-proboscid nemestrinids, mostly species of Prosoeca, is recorded for 13 species and inferred for five more, while moth pollination is recorded for one species and inferred for another two. Pollination exclusively by hopliine scarab beetles, known for six species, is associated with development of radial symmetry of the flower. Passerine bird pollination, associated with the classic syndrome of a wide floral tube, red floral pigmentation, and rigid, well-exserted stamens, occurs in two species, and is inferred for one more. Species with a bimodal system in which bees and beetles both visit and accomplish pollen transfer is known for three species. Comparing pollination systems with what is known about species relationships in Babiana, we infer that long-proboscid fly pollination evolved at least four times and moth pollination three times. Active pollination by pollen-collecting bees and hopliine beetle pollination also probably evolved three times each and bird pollination twice. Pollination systems are labile, and we postulate that there has been a minimum of 14 shifts in pollination system, approximately one shift for every six species. Lastly, Babiana species show the same correlation of morphology and floral presentation with particular sets of pollinators, described for several other genera of Iridaceae, e.g., Gladiolus L., Hesperantha Ker Gawl., and Lapeirousia Pourr., as well as Geraniaceae and Orchidaceae. This increases our confidence in predicting pollinators on the basis of floral presentation in other species and genera in which pollinators have not been established.

Nectar and Pollen Sources for Honeybee (Apis cerana cerana Fabr.) in Qinglan Mangrove Area, Hainan Island, China

In the present study, nectar and pollen sources for honeybee (Apis cerana cerana Fabr.) were studied in Qinglan mangrove area, Hainan Island, China, based on microscopic analysis of honey and pollen load (corbicular and gut contents) from honeybees collected in October and November 2004. Qualitative and quantitative melittopalynological analysis of the natural honey sample showed that the honey is of unifloral type with Mimosa pudica L. (Mimosaceae) as the predominant (89.14%) source of nectar and pollen for A. cerana cerana in October. Members of Araceae are an important minor (3%-15%) pollen type, whereas those of Arecaceae are a minor ( 1 000 000). Pollen analysis from the corbicular and gut contents of A. cerana cerana revealed the highest representation (95.60%) of members of Sonneratia spp. (Sonneratiaceae), followed by Bruguiera spp. (Rhizophoraceae), Euphorbiaceae, Poaceae, Fabaceae, Arecaceae, Araceae, Anacardiaceae, and Rubiaceae. Of these plants, those belonging to Sonneratia plants are the most important nectar and pollen sources for A. cerana cerana and are frequently foraged and pollinated by these bees in November. (Managing editor: Ya-Qin Han)

Assessing the value of annual and perennial forage mixtures for bumblebees by direct observation and pollen analysis

The value of introduced seed mixtures in providing forage for bumblebees on farmland was assessed by direct observation of individuals and analysis of pollen loads. Two mixtures of perennial grasses and wildflowers were compared with an annual mix of mostly seed-bearing crops over three years. Foraging bees showed contrasting patterns of visitation depending on species. Longer-tongued Bombus species preferred the perennial mixtures in which Trifolium pratense was dominant, whilst shorter-tongued Bombus and honeybees, Apis mellifera, visited mainly Borago officinalis in the annual mix. These patterns were supported by analysis of pollen loads from B. pascuorum and B. terrestris, both species showing a high degree of flower constancy to sown species. The relative specialisation of different bee species towards certain plant families, and the flowering phenology of seed mix components, must be considered in the design of agri-environment measures to conserve these and other pollinators.

Melissopalynology in Brazil: a review of pollen analysis of honeys, propolis and pollen loads of bees

This paper reviews current knowledge on the occurrence of several types of pollen grains in the sediments of honey samples, propolis and bee loads of Apiinae and Meliponinae in Brazil. After a short historical introduction about research activities in Melissopalynology using Brazilian samples, bee products were analyzed in respect to the greater Brazilian regions (South, Southeast, Northeast and North), emphasizing monofloral honeys and the green propolis. Numerous bibliographic references and a short glossary of the technical terms used is presented.

Energy density patterns of nectar resources permit coexistence within a guild of Neotropical flower‐visiting bats

AbstractNeotropical rainforests support guilds of nectar feeding bats (Phyllostomidae: Glossophaginae) with up to six coexisting species. To analyse guild structure and mechanisms of coexistence in a Costa Rican tropical lowland rainforest, the resource use and morphology of bats were compared to the energetic characteristics of preferred nectar resources and their spatio‐temporal distribution. The relative abundance of nectar‐feeding bats was determined from mistnet captures over 26 months. Food items were identified by analysis of pollen loads and faecal samples. Phenology, flower density and nectar sugar content of resource plants permitted quantitative estimations of resource availability expressed as energy density (kJ ha−1 day−1) throughout the annual cycle. Four glossophagine bat species co‐occurred at La Selva: two permanent residents (Glossophaga commissarisi, Hylonycteris underwoodi) and two seasonal species (Lichonycteris obscura, Lonchophylla robusta) that were found in small numbers during a period of high nectar availability. The two resident species differed in their abundance and in their temporal feeding strategies. After the main flowering peak, the common G. commissarisi shifted to a more frugivorous diet, while the rarer H. underwoodi fed on the few remaining bat‐flowers. Resource plant species differed in their energy density by up to two orders of magnitude. Hylonycteris underwoodi visited more often plant species with a low energy yield than G. commissarisi. Because of its smaller body size and a wing morphology that promotes fast flight, H. underwoodi appears to be better adapted to low and scattered nectar resource levels. The two seasonal species differed greatly in body mass, which suggests different strategies for high‐quality resource tracking. Large body mass in Lonchophylla robusta provides an energy buffer that permits daily commuting flights between a permanent roost and profitable foraging areas, while the small Lichonycteris obscura seems to track resources nomadically. It is proposed that energy density may be a major niche dimension that restricts access of species to certain habitats and that may profoundly influence the structure of nectar‐feeding bat guilds.

Pollination by fungus gnats (Diptera: Mycetophilidae) and self-recognition sites in Tolmiea menziesii (Saxifragaceae)

Observations of insects visiting strongly protandrous flowers of Tolmiea menziesii (Saxifragaceae) show that Gnoriste megarrhina (Mycetophilidae), a large fungus gnat with a body ca. 7 mm long and a proboscis ca. 6.5 mm long, is the primary pollinator. Pollen is transferred to ventral portions of the gnat’s thorax while it probes for an unusually dilute nectar (8.3% to 12% sucrose equivalents) produced at the base of the floral tube. Grains are transferred to the two receptive stigmas on each pistil when it forages for nectar on a female phase flower. Pollen load analyses indicate that Tolmiea menziesii may be the only nectar source visited by the gnat while it is in bloom. While hoverflies (Syrphus spp.) and bumblebees ( Bombus spp.) also visit T. menziesii flowers, they do not forage for nectar and usually behave as pollen robbers visiting only male phase flowers after earlier visits by G. megarrhina. When the modes of floral presentation of T. menziesii are compared to other species pollinated primarily by micro-dipterans, and mycetophilids in particular, there appears to be a floral convergence in some spring-flowering, perennial herbs of moist, evergreen woodlands and forests. Analyses of open (gnat-pollinated) vs. hand-pollinated pistils show that manual cross-pollinations are slightly more successful than open pollinations. Fluorescence microscopy confirms two sites of self-recognition and rejection within the pistil: following controlled self-pollination experiments almost half of the pollen tubes produced either stop growing once they reach the top of the ovary and/or grow horizontally. The remaining tubes produced by self-pollination penetrate ovules but seed is never set. This double mode of self-recognition and rejection is similar to the one described for Heuchera micrantha var. diversifolia (Saxifragaceae) but may also confirm an earlier report of post-zygotic rejection made for Tolmiea.