High Pollen Loads Research Articles

Pollen load, pollen species diversity and conspecific pollen carried by pollinators across 24-hour cycles

Plant-pollinator interactions are key for the reproduction of wild plants and for food security. However, the role nocturnal pollinators play in wild plant communities is not yet clear. Specifically, it has rarely been studied whether nocturnal pollinators are comparable to diurnal ones in the pollination services they deliver in plant communities. We tested whether nocturnal pollinators have the potential to provide high pollination services to the plants they visit by carrying high conspecific pollen loads. We studied pollen loads carried by nocturnal and diurnal pollinators captured over 24-hour cycles in co-flowering plant communities in Swiss ruderal meadows. Pollen load was less diverse at night, and the proportion of conspecific pollen carried by nocturnal pollinators was higher than that of diurnal ones. Because the majority of plant species visited at night were also visited during the day, floral resource availability could drive the observed patterns in pollen load and amount of conspecific pollen. Nevertheless, nocturnal pollinators do not only carry pollen but can remove and potentially deposit conspecific pollen to the plants they visit. Therefore, pollinators active at night might be an important pollination vector for more plant species than previously thought and should not be neglected in pollination studies.

Effects of short- and long-term experimental warming on plant–pollinator interactions and floral rewards in the Low Arctic

Plant phenological and growth responses to experimental warming are widely documented, but less is known about warming effects on plant–pollinator interactions. We investigated the effects of short- and long-term passive warming on flowering phenology, insect visitation, fruit production, and floral rewards in the Low Arctic in northern Alaska. To better understand the role of insect visitors in plant reproductive success, we quantified pollen loads on floral visitors and tested for pollen limitation in four species. Long-term warming advanced flowering onset in evergreen shrubs and forbs. Warming, in general, increased the duration of flowering for forbs, evergreen shrubs, and deciduous shrubs. Considering all growth forms together, long-term warming increased floral density. This pattern was primarily driven by deciduous and evergreen shrubs. Dipterans accounted for more visits than Hymenopterans, although Hymenopterans had higher pollen loads. Insect exclusion and warming decreased fruit set in the forb, Bistorta officinalis Delarbre. Nectar volume in the deciduous shrub, Vaccinium uliginosum, was higher in the warmed plots than the control, but nectar quality did not differ. Advanced flowering onset, longer flowering duration, and increased flower density and nectar volume may have important implications for the pollinator community, warranting further research on long-term warming effects on tundra ecosystems.

The diurnal and seasonal variability of ice-nucleating particles at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland

Abstract. Cloud radiative properties, cloud lifetime, and precipitation initiation are strongly influenced by the cloud phase. Between ∼ 235 and 273 K, ice-nucleating particles (INPs) are responsible for the initial phase transition from the liquid to the ice phase in cloud hydrometeors. This study analyzes immersion-mode INP concentrations measured at 243 K at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.) between February 2020 and January 2021, thereby presenting the longest continuous, high-resolution (20 min) data set of online INP measurements to date. The high time resolution and continuity allow us to study the seasonal and the diurnal variability of INPs. After exclusion of special events, like Saharan dust events (SDEs), we found a seasonal cycle of INPs, highest in April (median in spring 3.1 INP std L−1) followed by summer (median: 1.6 INP std L−1) and lowest in fall and winter (median: 0.5 and 0.7 INP std L−1, respectively). Pollen or subpollen particles were deemed unlikely to be responsible for elevated INP concentrations in spring and summer, as periods with high pollen loads from nearby measurement stations do not coincide with the periods of high INP concentrations. Furthermore, for days when the site was purely in the free troposphere (FT), no diurnal cycle in INP concentrations was observed, while days with boundary layer intrusions (BLIs) showed a diurnal cycle. The seasonal and diurnal variability of INPs during periods excluding SDEs is within a factor of 7 and 3.3, respectively, significantly lower than the overall variability observed in INP concentration including SDEs of more than 3 orders of magnitude, when peak values result from SDEs. The median INP concentration over the analyzed 12 months was 1.2 INP std L−1 for FT periods excluding SDEs and 1.4 INP std L−1 for both FT and BLI, and including SDEs, reflecting that despite SDEs showing strong but comparatively brief INP signals, they have a minor impact on the observed annual median INP concentration.

Effects of heterospecific pollen on stigma behavior in Campsis radicans: Causes and consequences.

Pollinator sharing of co-flowering plants may result in interspecific pollen receipt with a fitness cost. However, the underlying factors that determine the effects of heterospecific pollen (HP) are not fully understood. Moreover, the cost of stigma closure induced by HP may be more severe for plants with special touch-sensitive stigmas than for plants with non-touch-sensitive stigmas. Very few studies have assessed HP effects on stigma behavior. We conducted hand-pollination experiments with 10 HP donors to estimate HP effects on stigma behavior and stigmatic pollen germination in Campsis radicans (Bignoniaceae) at low and high pollen loads. We assessed the role of phylogenetic distance between donor and recipient, pollen size, and pollen aperture number in mediating HP effects. Additionally, we observed pollen tube growth to determine the conspecific pollen-tube-growth advantage. Stigma behavior differed significantly with HP of different species. Pollen load increased, while pollen size decreased, the percentage of permanent closure and stigmatic germination of HP. Stigmatic HP germination increased with increasing aperture number. However, HP effects did not depend on phylogenetic distance. In addition, conspecific pollen had a pollen-tube-growth advantage over HP. Our results provide a good basis for understanding the stigma-pollen recognition process of plant taxa with touch-sensitive stigmas. We concluded that certain flowering traits drive the HP effects on the post-pollination period. To better understand the impact of pollinator sharing and interspecific pollen transfer on plant evolution, we highlight the importance of evaluating more factors that determine HP effects at the community level.

Local Insect Availability Partly Explains Geographical Differences in Floral Visitor Assemblages of Arum maculatum L. (Araceae).

Geographical variation in abundance and composition of pollinator assemblages may result in variable selection pressures among plant populations and drive plant diversification. However, there is limited knowledge on whether differences in local visitor and pollinator assemblages are the result of site-specific strategies of plants to interact with their pollinators and/or merely reflect the pollinator availability at a given locality. To address this question, we compared locally available insect communities obtained by light-trapping with assemblages of floral visitors in populations of Arum maculatum (Araceae) from north vs. south of the Alps. We further investigated whether and how the abundance of different visitors affects plants’ female reproductive success and examined the pollen loads of abundant visitors. Local insect availability explained inter-regional differences in total visitor abundance, but only partly the composition of visitor assemblages. Northern populations predominantly attracted females of Psychoda phalaenoides (Psychodidae, Diptera), reflecting the high availability of this moth fly in this region. More generalized visitor assemblages, including other psychodid and non-psychodid groups, were observed in the south, where the availability of P. phalaenoides/Psychodidae was limited. Fruit set was higher in the north than in the south but correlated positively in both regions with the abundance of total visitors and psychodids; in the north, however, this relationship disappeared when visitor abundances were too high. High pollen loads were recorded on both psychodids and other Diptera. We demonstrate for the first time that the quantitative assessment of floral visitor assemblages in relation to locally available insect communities is helpful to understand patterns of geographical variation in plant–pollinator interactions. This combined approach revealed that geographical differences in floral visitors of A. maculatum are only partly shaped by the local insect availability. Potential other factors that may contribute to the geographical pattern of visitor assemblages include the region-specific attractiveness of this plant species to flower visitors and the population-specific behavior of pollinators.

High post-season Alnus pollen loads successfully identified as long-range transport of an alpine species

Abstract Alnus pollen is one of the Northern Hemisphere's major aeroallergens. In Central Europe, the genus is represented by three species (Alnus glutinosa, Alnus incana, and Alnus viridis). The most common one, A. glutinosa (L.) Gaertn., is widespread in lowland riparian forests, swamps, and forest edges. However, to date is still unknown if all of them - in terms of pollen exposure - are clinically relevant for sensitized individuals. To investigate the associated pollen exposure, particularly also because of long-range transport of airborne pollen, we used backward air mass trajectories and tested this method for the year 2015, based on daily Alnus pollen concentrations at 26 sites in Bavaria, Germany. A. glutinosa's main pollen season extends from February to March, but a six-day, post-season episode was additionally identified in June. For this episode and all sites, 72-h backward trajectories were calculated at 3-h intervals using high spatial and temporal resolution ERA5 reanalysis data and the HYSPLIT (hybrid single-particle Lagrangian integrated trajectory) model. This backward trajectory method identified air masses from the alpine region in Switzerland and Austria, where relevant areas of A. viridis (Chaix) DC as potential pollen sources exist. These may explain the post-season episode in June, as additionally confirmed by its unique spatial distribution, by a considerably later flowering period, and by repeated long-range transport events as observed in a 23-year pollen time series.

Modeling hay fever risk factors caused by pollen from Ambrosia spp. using pollen load mapping in Ukraine

The paper provides a simulation of the occurrence of <em>Ambrosia</em> pollen in Ukraine both in terms of a determination of the regions with high pollen concentrations and the time when the high pollen load occurs. Simulation was performed using the SILAM system and the following pollen mapping using the Grid Analysis and Display System. Simulation results were compared with the aerobiological data available from six monitoring stations in Ukraine. A decrease in the concentrations of <em>Ambrosia</em> pollen, the duration of the <em>Ambrosia</em> season, and patient exposure to the <em>Ambrosia</em> pollen were apparent from SE to NW of Ukraine. A close correlation between the modeled and actually registered pollen concentration values and ragweed pollen release periods was observed in all the cities for which the <em>Ambrosia</em> pollen monitoring data had been collected. Further investigations are required to provide accurate forecasts for other types of airborne allergens.

Environmental grass pollen levels in utero and at birth and cord blood IgE: Analysis of three birth cohorts

BackgroundEarly life factors are associated with allergic respiratory diseases, but the role of high grass pollen concentrations during pregnancy and shortly after birth is not known. ObjectiveTo assess outdoor levels of grass pollen during the intrauterine period and at birth during peak pollen season on cord blood IgE in birth cohorts. MethodsThree birth cohorts were included: MACS (n = 429), Australia; COPSAC2000 (n = 200), Denmark; and LISA (n = 1968), Germany. Cord blood IgE was categorized (<0.5 kU/L, 0.5–1 kU/L, >1 kU/L) and dichotomized (high IgE ≥ 0.5 kU/L). Birth during the grass pollen season months and cumulative exposure to outdoor grass pollen counts during pregnancy with cord blood IgE were analysed using multinomial regression and analysed in meta-analysis using binomial regression adjusted for potential confounders. ResultsBirth during the grass pollen season had higher pooled odds of cord blood IgE >0.5 kU/L 1.37 (95% CI 1.06, 1.77) in a meta-analysis with little heterogeneity between the three cohorts. Cumulative exposure to outdoor grass pollen counts during the entire pregnancy was associated with slightly lower pooled odds but significant (OR = 0.98, 95% CI: 0.96 to 0.99). ConclusionsBirth during grass pollen seasons were associated with increased risk of high cord blood IgE in cities from both hemispheres, but high pollen loads in the environment during the entire pregnancy appeared protective. As IgE responses develop during the first months of life, our study findings provide new insights into the mechanisms of grass pollen exposure at birth and shortly after on possible allergic respiratory diseases.

Frequent Insect Visitors Are Not Always Pollen Carriers in Hybrid Carrot Pollination.

Insect crop visitations do not necessarily translate to carriage or transfer of pollen. To evaluate the potential of the various insects visiting hybrid carrot flowers to facilitate pollen transfer, this study examines insect visitation rates to hybrid carrot seed crops in relation to weather, time of day and season, pollen carrying capacity, inter-row movement, and visitation frequency to male-fertile and male-sterile umbels. The highest pollen loads were carried by nectar scarabs, honey bees, and the hover fly Eristalis tenax (Linnaeus). Honey bees and muscoid flies were observed to forage mostly within the male fertile carrot row while nectar scarabs and E. tenax foraged across rows, carrying equal pollen loads regardless of their distance from the pollen source. All observed insect taxa were more frequently seen visiting male-fertile than male-sterile umbels. In contrast to other visiting insects, honey bees were abundant and frequent visitors and were observed carrying high pollen loads. Consequently, we suggest both optimizing honey bee management and improving the attraction of carrot lines to honey bees to improve pollination rates for hybrid carrot seed crops.

Sterile stamens do not enhance seed set in females of the cryptically dioeciousThalictrum macrostylum(Ranunculaceae)

In cryptically dioecious species, at least one morph is functionally unisexual despite hermaphroditic morphology. In such species, sterile reproductive structures may indirectly increase fitness of the cryptic morph. This study manipulates pollination mode to investigate two hypotheses regarding the influence of sterile stamens on female fitness in the cryptically dioecious Thalictrum macrostylum. Pollination mode and the presence of pollen limitation in natural populations were also investigated. In two natural populations, pollen receipt on pistils was quantified in open-pollinated and pollinator-exclusion flowers with varying numbers of stamens. Seed set was quantified in additional open-pollinated flowers, a subset of which received supplemental pollen to test for pollen limitation. Females were not significantly insect pollinated at either site. Number of sterile stamens per flower was positively related to pollen receipt in open-pollinated flowers at one site, but had no influence on seed set at either site. In one population, seed set was significantly pollen limited, and high variance in seed set among pollen-addition flowers in both populations indicates that high pollen loads do not always increase seed set. In the wind-pollinated and cryptically dioecious Thalictrum macrostylum, sterile stamens in females do not appear to increase female fitness. Other explanations for the persistence of stamens and sterile pollen in females of T. macrostylum should be sought.

Reproductive biology of Sorghum halepense (L.) Pers. (Poaceae; Panicoideae; Andropogoneae) in relation to invasibility

Sorghum halepense (L.) Pers. is the most aggressive grass weed of the world resulting from an efficient system of its reproduction and propagation through a combination of vegetative and sexual means. However, reproductive biology of the species is not understood in sufficient details and had serious gaps of information on its pollen and pollination system, breeding behaviour, fruit and dispersal biology. The species was found to be chasmogamous with an andromonoecious sexual system of well-developed bisexual and male spikelets in pairs and terminal triads. Precocious extrusion of receptive stigmas preceding anther dehiscence, abundant pollen of high fertility and longevity and a high pollen-ovule ratio strongly indicate xenogamy in the species. Laser Confocal Microscopy revealed rapid germination of pollen and growth of pollen tubes down the pistil to the ovule which caused high fruit set and facilitated the amphimictic cycle. The present study is presumably the first report on the role of several insect pollinators mainly from the order Diptera (Isomyia paurogonita Fang & Fan.) and Hymenoptera (Hylaeus sp., Sphecodes ephippius Linnaeus , Megachile sp.). The visitation time of insect pollinators closely synchronized with peak anthesis resulting in high pollen loads. Breeding experiments revealed significantly higher fruit set in open pollinated in comparison to bagged synflorescences. The diaspore enclosed a well-developed caryopsis surrounded by accessory bracts along with persistent pedicels and a rachis segment preparing them for dispersal through autochory and endozoochory. Thus, cosmopolitan and invasive nature of S. halepense could be attributed to a combination of xenogamous breeding system, high seed production and efficient fruit dispersal through resistant diaspores. This study on the reproductive system of S. halepense shall provide a framework for developing management strategies both for the control of this invasive grass species as also for its propagation as a fodder crop in vacant rangelands.

Gynoecium structure and extra-gynoecial pollen-tube growth in an apocarpous species, Sagittaria trifolia (Alismataceae)

Apocarpy is regarded as an original feature obtained during the evolution of angiosperms. Compared with syncarpous plants, apocarpous plants have some adaptive disadvantages in apocarpous plants, for example, the number of offspring is lower under conditions of uneven pollen-tube distribution. However, in some apocarpous species, extra-gynoecial pollen-tube growth (EGPG) may remedy this disadvantage. We conducted micro-observations and field studies of Sagittaria trifolia, to investigate the gynoecium structure and the pathway of pollen-tube growth in the entire gynoecium. In a single-carpel pollination experiment, we found that the extra-gynoecial pollen tubes from a carpel of S. trifolia were able to fertilize approximately 13 carpels. Simulated EGPG in the entire gynoecium of S. trifolia revealed that its effect on the seed set could be divided into two stages: stage of low/high-level stigmas pollination, in which the cutoff point was about 0.1. The seed set would be markedly improved during the low-level stigmas pollination stage by EGPG when the maximum distance of extra-gynoecial pollen tubes could span three carpels, as in the present experiment. Our simulation also showed that the high pollen load could enhance the effect of EGPG on the seed set, and if the number of germinating pollen is triple the carpel number in the gynoecium, a 100% seed set rate would be obtained when approximately 50% of the stigmas are pollinated.

Conspecific Pollen on Insects Visiting Female Flowers on the Oak Parasite Phoradendron coryae (Viscaceae)

Phoradendron coryae (Viscaceae) is a dioecious, parasitic plant on oak trees and shrubs in Quercus (Fagaceae), and it occurs from Arizona to Texas and into northern Mexico. The species produces minute spherical flowers during summer. Dioecious flowering requires pollinating insects to carry pollen from male to female plants. I investigated the pollination of P. coryae parasitizing Quercus turbinella shrubs at 3 sites at different elevations in the Cerbat Mountains of northwestern Arizona during August–September 2015. I examined pollen from male flowers, aspirated insects landing on female flowers, and counted conspecific pollen grains carried by insects. The tricolpate pollen of P. coryae was semiangular to subangular in polar view and circular to depressed oval in equatorial view. Female flowers were visited by 2 species of Coleoptera in 2 families, 6 species of Diptera in 6 genera and 3 families, and 1 species of Hymenoptera. Insects on flowers were extremely small (most <3 mm in length), and nearly all (99%) of the pollen carried by insects was from P. coryae. Conspecific pollen was found on 67% of the insects identified. Pollen loads were low, with only 25% of the insects carrying ≥5 grains. The beetle Attalus futilis (Melyridae) was the most frequently aspirated species, comprising 71% of the insects collected and occurring at all 3 sites. Most A. futilis (64%) carried P. coryae pollen. The second most frequently collected insects were 2 species of Hippelates and Liohippelates flies (Chloropidae). The Liohippelates carried the most P. coryae pollen. Other insects with pollen included 2 additional species of Chloropidae, 2 species of flies in Tachinidae and Tephritidae, a species of beetle in Chrysomelidae, and a species of parasitic wasp in Figitidae. Phoradendron coryae appeared to be pollinated mostly by A. futilis beetles due to their apparent abundance and by Liohippelates flies due to their relatively high pollen loads.

English

Local allergic rhinitis (LAR) is a phenotype of allergic rhinitis characterized by the presence of a localized immune response in the nasal mucosa of patients with negative skin prick test (SPT) results and undetectable serum specific IgE (sIgE). It unknown whether LAR is limited to areas with low or moderate aeroallergen exposure. To explore the presence of LAR and the clinical and immunological characteristics of this entity in geographic areas with high grass pollen loads. A cross-sectional observational study was carried out in 2 hospitals in central Spain (Madrid and Ciudad Real). Sixty-one patients with seasonal rhinitis and negative SPT results and undetectable serum sIgE were evaluated using a clinical questionnaire, determination of serum total IgE, and a nasal allergen provocation test (NAPT) with Phleum species. The response to NAPT was monitored using assessment of nasal symptoms, acoustic rhinometry, and determination of sIgE, tryptase, and eosinophil cationic protein in the nasal cavity. Seasonal LAR was detected in 37 patients (61%) using the techniques described above. Eleven percent of patients with LAR were adolescents or children, and 14% reported onset of rhinitis in childhood. Most patients reported persistent-moderate seasonal nasal symptoms, and 41% reported worsening of the disease during the last 2 years. Conjunctivitis was the most common comorbidity, affecting 95% of cases. LAR to grass pollen is relevant in patients with seasonal symptoms indicative of allergic rhinitis but with a negative skin test result who live in areas with high allergenic pollen loads. This entity should be included the differential diagnosis of rhinitis.

Conspecific Pollen Loads on Insects Visiting Female Flowers on ParasiticPhoradendron californicum(Viscaceae)

Desert mistletoe, Phoradendron californicum (Viscaceae), is a dioecious parasitic plant that grows on woody legumes in the Mojave and Sonoran Deserts, produces minute flowers during winter, and is dispersed by birds defecating fruits. Pollination of desert mistletoe has not been examined despite the species' reliance on insects for transporting pollen from male to female plants. I investigated the pollination of P. californicum parasitizing Acacia greggii (Fabaceae) shrubs at 3 sites at different elevations in the Mojave Desert of southern Nevada during February 2015. I examined pollen from male flowers, aspirated insects landing on female flowers, and counted pollen grains in insect pollen loads. Desert mistletoe's tricolpate pollen differed from a previous description by being oblate instead of subprolate in equatorial view. Female flowers were visited by 13 species of Diptera in 10 genera and 6 families and 3 species of Hymenoptera in 3 families. Almost all (98.5%) of the pollen carried by insects was from desert mistletoe. Five species of phytophagous fruit flies in Tephritidae were frequently found on flowers, comprising 53% of the insects collected, but carried low amounts of P. californicum pollen. Two species of blow flies in Calliphoridae, both larval decomposers of animals, were also relatively abundant on flowers and carried moderate to high pollen loads. Flies in Syrphidae, 2 predators and 1 plant-decomposer, carried varying amounts of conspecific pollen. Conspecific pollen loads also varied on a species of native bee in Halictidae and on naturalized honey bees in Apidae. Desert mistletoe appears to be pollinated mostly by tephritids, due to their abundance on female flowers, and by calliphorids. Blow flies would be more likely than fruit flies to carry pollen between male and female plants on different host shrubs due to their larger size and stronger flight. Parasitic, dioecious P. californicum plants appear to rely on a web of mutualism between fruit-eating birds and flower-fertilizing insects.

Conspecific Pollen Loads on Insects fromPrunus fasciculata(Rosaceae) Female Flowers in Southern Nevada

Desert almond, Prunus fasciculata (Rosaceae), is a Mojave Desert shrub that primarily produces male and female flowers on different plants. I investigated the plant's pollination by examining pollen loads on insects aspirated from female flowers on 3 dioecious shrubs, growing near male-flowering shrubs, at one locality in southern Nevada during March 2014. Pollen loads were analyzed on 9 species of Diptera in Bombyliidae, Syrphidae, Calliphoridae, and Tachinidae and 4 species of Hymenoptera in Andrenidae (all female Andrena). All but 4 of the 65 flies and 38 bees aspirated carried P. fasciculata pollen grains, recognized by their tricolpate shape in polar view and oblate shape in equatorial view. Two species of syrphid flies in Copestylum were frequently aspirated and carried high P. fasciculata pollen loads and moderate proportions of conspecific pollen. High conspecific pollen loads on the tachinid Chaetogaedia also indicated potential for pollinating P. fasciculata. Three of the 4 species of Andrena bees carried large amounts of P. fasciculata pollen. Conspecific pollen also comprised most of the pollen load on Andrena bees, suggesting high flower constancies to the plant. Pollinators of P. fasciculata would vary over the plant's range, and likely between years, because of the localized populations or narrow larval diets of many of the insects collected from flowers. The female desert almond shrubs examined in southern Nevada during 2014 appeared to be pollinated by a variety of native flies and bees, especially syrphid flies in Copestylum and andrenid bees in Andrena.

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

AbstractWe 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.

Triple interaction network among flowers, flower visitors and crab spiders in a grassland ecosystem

This study presents the first description of a tri-trophic interaction network with crab spiders as predators. Monthly observations of flowering entomophilous plant species were recorded between December 2009 and March 2010 and their flower visitors and predators (crab spiders) were caught, with or without prey. Moreover, flower visitors of different orders were caught to evaluate the amount of pollen transported. In order to analyze changes in the plant species and crab spiders, we evaluated the interaction networks in which we had removed different orders of prey (Hymenoptera, Diptera and Lepidoptera) from the original network. Our results indicate that crab spiders select their preys within the community. Furthermore, the Hymenoptera carried higher pollen loads and were the less frequent prey. When the Diptera preys were removed from the initial interaction network, network changes mainly affected the species richness of crab spiders. Decrease in density of Diptera could increase plant resources useful for flower visitors carrying great pollen loads and could promote pollination. Crab spider prey might be restricted to only the more vulnerable flower visitors (e.g. smaller dimensions, without sting or with delicate cuticula) which consume resources and are inefficient as pollen carriers. The selected predation could not negatively affect the fitness of plants.

Aeropalynological study in Rohtak city, Haryana, India: a 2-year survey

An aeropalynological survey was conducted at two different sites in Rohtak city, Haryana, at a height of 1.8 m, three times a day, for two consecutive years (July 2007–June 2009). A total of 31 pollen types were identified to the lowest taxonomical level whenever possible. The major contributor to the pollen load was Cannabis sativa (28.9 %) followed by Poaceae (20.65 %), Chenopodiaceae/Amaranthaceae (10.56 %), Parthenium hysterophorus (6.80 %), Morus alba (6.15 %), Artemisia sp. (4.03 %), Cyperus sp. (3.20 %) and Eucalyptus sp. (3.07 %). Two major pollen seasons were recognized, that is, July–October and March–April, although pollen was recorded in varying concentrations all along the year. Spatial variations were also observed, with higher pollen loads at the site surrounded by dense vegetation. The study will provide preliminary but useful data to local allergologists for effective diagnosis and treatment of respiratory allergic ailments.

Nectar replenishment and pollen receipt interact in their effects on seed production of Penstemon roseus

Resource supply and pollen delivery are often thought to equally limit seed production in animal-pollinated plants. At equilibrium, plants should show no response to experimental pollen supplementation because resources limit seed set above the current level of pollen attraction, while experimental reduction in pollen deposition below the equilibrium level would reduce seed set. The predicted equilibrium may be disrupted, however, if plants expend additional energy to replenish removed nectar. We investigated the combined effects of nectar removal and pollen delivery on female reproductive success of Penstemon roseus (Plantaginaceae), a hummingbird-pollinated plant that replenishes removed nectar. We first documented that the frequency of experimental nectar removal was correlated with total nectar secretion; and increased frequency of nectar removal resulted in increased female reproductive costs to the plant. Trade-offs between investing resources in nectar and investing resources in seeds were then investigated in two contrasting natural populations by removing nectar from flowers at increasing frequencies while simultaneously hand-pollinating flowers with increasing amounts of pollen. Seed set was lowest at low levels of pollen deposition, highest at medium-sized pollen loads, and intermediate when pollen loads were highest. At both sites, the frequency of nectar removal and pollen deposition had an interactive effect on seed production, in that intermediate levels of nectar removal result in the absolute highest seed set, but only at intermediate pollen loads. At high pollen loads, seed set was higher following little to no nectar removal, and at low pollen loads, all rates of nectar removal affected fecundity equally. Seed mass responded to nectar removal and pollination differently than did seed set. High levels of nectar removal and pollen delivery both lowered seed mass, with little interaction between main effects. Our findings are among the first to demonstrate that nectar replenishment costs and pollination intensity jointly affect seed production. This conflict between nectar replenishment costs and pollen-limiting factors results in trade-offs between pollinator attraction and seed provisioning. Thus, resource allocation towards nectar production should more often be considered in future studies of pollen limitation.