Bee Visitation Research Articles

Wild bumble bee colony abundance, scaled by field size, predicts pollination services

AbstractAlthough bee visitation rate to flowers is often used to assess both pollination services and bee abundance, the abundance of social species needs to be assessed by quantifying the number colonies instead of the number of foraging individuals. Because accurately quantifying the number of wild bee colonies can be difficult, the relationship of visitation rates provided by foragers and the abundance of colonies contributing those foragers from the surrounding landscape is poorly documented for social species. Here, we use genetic methods and statistical inference to estimate the abundance of wild colonies of Bombus impatiens in the surrounding landscape providing foragers to 30 commercial pumpkin (Cucurbita pepo) fields over 4 yr across a 13,000‐km2 area in Pennsylvania, USA. We show that the abundance of wild colonies in the surrounding landscape providing foragers per field (colony abundance per field) ranges from 291 to 829 colonies per field. Furthermore, colony abundance per field has been stable across years, counties, and field size, resulting in a dilution of foragers from the available colonies across larger fields. Wild colony abundance, when scaled by field size, by expressing colony abundance on a per hectare basis, is predictive of visitation rate. Thus, we document the relationship of wild colony abundance per hectare to visitation rate at a level that provides sufficient pollination to a highly pollinator‐dependent crop. As expected, genetic differentiation among sampled populations is essentially non‐existent across different fields or regions, suggesting a panmictic population. Although many Bombus species are in decline, we document abundant and genetically resilient wild populations of B. impatiens associated with a mass‐flowering crop under current agricultural practices and provide baseline information needed to monitor these wild populations at a time when they face similar stressors implicated in the decline of congenerics.

A sophisticated case of division of labour in the trimorphic stamens of the Cassia fistula (Leguminosae) flower.

Buzz-pollinated pollen flowers have pollen as the primary resource for pollinators and must deal with a conflict between the exploitation of pollen grains by bees and pollination success. It has been hypothesized that heterostemony allows division of labour between stamens as a solution to the pollen dilemma. To test the division of labour hypothesis, we chose Cassia fistula, which has a trimorphic androecium and analysed androecium development, pollen grain release mechanisms and visitor behaviour. We explored the reflectance of floral organs and carried out an exclusion experiment to test the attractiveness of each stamen morph to the bee species. Finally, we explored the structural, ultrastructural and functional variation between the pollen grains, including pollen viability across stamen morphs. The differences among the three stamen morphs, which is developed from two whorls of the stamen, are the first evidence of the division of labour in our study system. Large Bombus and Xylocopa bees actively and exclusively exploited the pollen grains from the central poricidal anthers generating pollen deposition on their bodies. The reflectance pattern of floral organs indicated a targeting of these large bees to the central anthers, corroborated by the anther manipulative experiment where only the exclusion of the anthers positioned in the flower centre, especially the intermediate stamens, reduced bee visits. Both results revealed a division of labour, in which the intermediate stamen morph was responsible for both floral attractiveness and pollen resources. Only the largest stamen morph produced germinable pollen grains, highlighting their role as pollinating stamens. The smallest stamen morph has a less clear function, likely representing an economy in pollen production for feeding function. Our findings suggest that the evolution of the trimorphic androecium is associated with division of labour in large pollen flowers and can represent a strong strategy for circumventing the pollen dilemma, optimizing the feeding function by reducing pollen grain investment from central anthers.

Quid Pro Quo? A Review on Bee Utilization of Pollinator-Independent Crops

Abstract Previous exploration has found that bee visitation tends to benefit yields of many pollinator-independent crops. However, the reverse of this relationship—if pollinator-independent crops benefit bees—has not been extensively studied or explicitly reviewed. Therefore, we initiated a review of the literature using Web of Science and EBSCOhost to determine whether: 1) bees collect pollen from pollinator-independent crops, and 2) pollinator-independent crops provided adequate nutrition for bees. These factors help establish if pollinator-independent crops could benefit bees. We found 45 peer-review articles that included bee pollen trap data on 13 pollinator-independent crops (self-pollinating and wind-pollinated plants), with Zea mays, Brassica napus, and Glycine max pollen most often found in pollen traps. Pollinator-independent crops averaged 12% of total pollen loads, but due to high variability, the median was only 1.6%. Pollen from pollinator-independent crops increased in landscapes with more agricultural cover, but our data was heavily skewed towards honey bees (Apis mellifera). We found the average crude protein for B. napus and G. max was high enough to support honey bee requirements (>20%), along with providing essential amino acids; however, average crude protein and essential amino acids may be lacking in Z. mays. Although some pollinator-independent crops are found in pollen traps and provide adequate resources for bees, they may fail to provide temporally stable resources and chemical-free space. For improved health and reproduction, bees need access to semi-natural landscapes within diverse cropping systems to increase diet mixing. This will help amplify the mutualistic relationship between bees and pollinator-independent crops.

Onion (Allium cepa L.) hybrid seed production: Sugar content variation during the flowering period

AbstractHoneybees (Apis mellifera L.) are the most used pollinators for onion (Allium cepa L.) seed production. Two types of onion varieties are mainly grown worldwide: hybrids and open pollination (OP) cultivars. Although hybrids offer advantages to bulb growers, seed yields of hybrids are lower than OP cultivars. Since honeybees play a major role in onion pollination, understanding the contribution of the floral rewards to bee visitation is crucial to improve seed yield. The goal of this study is to establish the best moment for the introduction of honeybee hives into onion fields to increase seed yields. To reach this goal, the correlation between sugar compounds in nectar throughout the flowering period and honeybee foraging activity was determined. The sugar profile and bee visits were highly correlated, and fructose concentration was strongly linked to bee frequency of foraging on the onion umbels. The highest number of bee visits was recorded at 70% of flowering. Based on these results, beehives should be introduced once 40–50% of flowering is reached.

Wild bees and natural enemies prefer similar flower species and respond to similar plant traits

Designing wildflower habitats to support beneficial insects providing pollination and pest control services is important for supporting sustainable crop production. It is often desirable to support both groups of insects, making the selection of resource plants for insect conservation programs more challenging. Moreover, the process of selecting resource plants is complicated by the array of possible options in each region, and the need to provide resources over the entire growing season. Identifying traits shared by resource plants that are attractive to both bees and natural enemies can reduce the need to evaluate new plants in each region, by providing a guide for the types of plants expected to be rewarding to these insects. Using insect visitation data collected from replicated common garden plantings of native wildflower and shrub species from the Great Lakes region of the United States, we found a high degree of correlation between the abundance of bees and natural enemies visiting native plant species. These results were used to identify a set of 15 plant species that can provide resources for these insects throughout the summer. Across all tested species, pollen quantity per flower and the week of bloom were positively correlated with some, but not all, taxonomic groupings of beneficial insects. In contrast, floral area was consistently positively associated with visitation of both natural enemies and wild bees. This trait is easy to document and can allow for efficient local testing of potential resource plants, providing a faster path to implementing insect conservation in working landscapes.

Non-pollinating floral visitors of the Cucurbita genus plants and their relationship with the presence of pollinating bees

Flower-visiting insects may be pollinators or, conversely, unrelated to the reproductive process of plants. Interactions between pollinating and non-pollinating flower visitors can negatively influence pollen transfer. Little is known about the effects of bee visits on pollination of squash (Cucurbita spp.) flowers and their interactions with the presence of other floral visitors. The study was conducted at the Facultad de Ciencias Agrarias (Universidad Nacional de Rosario) in the south of Santa Fe (Argentina) and evaluated the effect of the presence of non-pollinating floral visitors on bee foraging in the flowers of two cultivated squash species. Flower sex and squash species C. maxima and C. moschata were included as variables. A total of 937 visitors were recorded in 403 flowers. Bees of the tribes Eucerini and Apini were the most abundant pollinators with an average of 2.3 individuals per flower during 10 minutes of observation. Diptera, flower sex and squash species did not influence the number of bee visits, whereas the prolonged stay of coleoptera and formicids negatively affected the presence of bees on both squash species. The presence of coleoptera reduced bee visits by 38%, while in the presence of ants, bees did not visit the flowers. The theft of nectar and pollen by non-pollinating floral visitors could have a negative effect on the reproductive success of squash.

Effect of Indigenous Bee Attractants on Qualitative and Quantitative Parameters of Egyptian Clover, Trifolium alexandrinum L.

Background: Egyptian clover (Trifolium alexandrinum L.) is one of the most important annual, winter, multi-cut fodder legumes grown in northern India. Many a times, poor activity of pollinators cited for lower seed production in berseem. Therefore, an appropriate local food-based bee attractants need to be identified and their effectiveness in enhancing berseem seed yield needs to be assessed. Methods: The experiment was conducted to evaluate the significance of bee visit on yield parameters of berseem. In addition, the effect of attractant (jaggery and sugar at 10%) in enticing honey bees towards the berseem flower was evaluated at ICAR- IGFRI, Jhansi during 2017 and 2018. Result: Both the attractants (jaggery and sugar at 10%) are equally effective in drawing the Apis dorsata towards berseem and higher bee visits (8.75 and 8.54/m2/5 min) were recorded one hour after application. Maximum seed setting percentage was recorded in plots sprayed with jaggery (83.53) followed by sugar solution (82.58), which is significantly superior over farmers practice i.e. crop left for open pollination (74.86). Maximum seed yield was obtained from plots sprayed with jaggery solution (8.15 q/ ha). The bee visit had significant positive effect on seed yield (0.685*) and 1000 seed weight (0.671*).

Diversity and Abundance of Bee Flower Visitors of Beans in Borabu Sub-County, Western Kenya

Globally bees form the main animal pollinators of most crops. Most agricultural crops rely on pollinators, particularly bees for pollination services. Smallholder farmers in Africa commonly use maize/bean intercropping in order to achieve the optimum yields hence providing them with significant food security and economic impacts. Declining of bee colonies due to anthropogenic factors has led to declines in food production in the world. Yet little is known about crop pollination in African countries. In Kenya pollination studies are still scanty, lack harmonisation and only a few crops have been studied. It is against this background that the study was chosen. One administrative sub location was purposively selected. Three plots were selected at equal 1km distance along atransect laid in that sub location. Sampling of 3 plots each of 100m x 100 m was established along transects. Bee sampling was done for 3 months using a sweep net and a bowl trap to collect bees. Diversity was computed using Shannon’s diversity index while abundance was recorded using abundance curves. A total of 992 bee visitors from 2 families and 9 species were collected from the three study farms. High diversity and abundance of bees was recorded. Therefore, farmers, extension workers and other stakeholders should be sensitized and trained on the importance of bee pollination and its contribution to their welfare and on utilization of cost-effective strategies for bee conservation. Key words: Diversity, Abundance, Pollination, Apis, Nyansiongo

Floral resource selection by wild bees and honey bees in the Midwest United States: implications for designing pollinator habitat

Many seed mix recommendations for creating pollinator habitat are in part based on anecdotal evidence or field observations of bees visiting forbs (i.e. use). However, there is limited information on what forbs are preferred by bees, particularly in working landscapes where bee forage may be limited. We examined floral resource selection by wild bees and honey bees on grasslands in the Midwest using a 5‐year dataset containing over 8,000 plant‐bee interactions. We observed wild bees visiting 83 forb species, but only 14 species were significantly selected (i.e. bees visited a plant more than expected based on availability). Approximately 70% of all wild bee visitations were on native flowers, whereas only 20% of all honey bee visitations were on natives. Honey bees visited 70 forb species, but only four forbs were significantly selected. The selection ratio for each forb species was not correlated with proportion of use by wild bees or honey bees, suggesting that bee visitation data alone do not elucidate patterns of forb selection or avoidance. We then compared our resource selection results to forbs recommended by U.S. Department of Agriculture (USDA) for regional pollinator habitat plantings. Many forbs that were selected by bees in our study were also recommended by USDA; however, some USDA‐recommended forbs were selected against by bees. A greater understanding of which floral resources are selected by bees can assist land managers in assessing conservation seed mixes and ultimately provide diverse, season‐long pollinator forage in working landscapes.

Impacts of beekeeping on wild bee diversity and pollination networks in the Aegean Archipelago

Maintaining the diversity of wild bees is a priority for preserving ecosystem function and promoting stability and productivity of agroecosystems. However, wild bee communities face many threats and beekeeping could be one of them, because honey bees may have a strong potential to outcompete wild pollinators when placed at high densities. Yet, we still know little about how beekeeping intensity affects wild bee diversity and their pollinator interactions. Here, we explore how honey bee density relates to wild bee diversity and the structure of their pollination networks in 41 sites on 13 Cycladic Islands (Greece) with similar landscapes but differing in beekeeping intensity. Our large‐scale study shows that increasing honey bee visitation rate had a negative effect on wild bee species richness and abundance, although the latter effect was relatively weak compared to the effect of other landscape variables. Competition for flowering resources (as indicated by a resource sharing index) increased with the abundance of honey bees, but the effect was more moderate for wild bees in family Apidae than for bees in other families, suggesting a stronger niche segregation in Apidae in response to honey bees. Honey bees also influenced the structure of wild bee pollination networks indirectly, through changes in wild bee richness. Low richness of wild bees in sites with high honey bee abundance resulted in wild bee networks with fewer links and lower linkage density. Our results warn against beekeeping intensification in these islands and similar hotspots of bee diversity, and shed light on how benefits to pollination services of introducing honey bees may be counterbalanced by detriments to wild bees and their ecosystem services.

Blueberry Yields Increase With Bee Visitation Rates, but Bee Visitation Rates are not Consistently Predicted by Colony Stocking Densities.

Pollinator-dependent crops rely on the activity of managed and wild pollinators. While farm management and surrounding landscape can influence wild pollinator contributions, managed pollinator contributions may be primarily driven by their stocking densities, though this is not well studied across crops. We selected 20 southern highbush blueberry farms along two independent gradients of honey bee Apis mellifera L. (Hymenoptera: Apidae) stocking density (~1-11 hives/acre) and bumble bee Bombus impatiens Cresson (Hymenoptera: Apidae) stocking density (0 - 3 colonies/acre) ensuring that stocking densities were not correlated with farm or landscape attributes. Across farms, we observed managed and wild bee visitation rates, and measured yield estimates. Farms with greater bumble bee stocking densities had higher bumble bee visitation rates and yield estimates, but farms with higher honey bee stocking densities only received higher honey bee visitation rates at the end of bloom and did not have higher yield estimates. The main wild pollinator, the southeastern blueberry bee Habropoda laboriosa (Fabricius) (Hymenoptera: Apidae), showed higher visitation rates on organic farms and in late bloom. In general, higher visitation rates by honey bees, bumble bees, and H. laboriosa were correlated with higher yields. Our results suggest that yields are limited by bee visitation rates, and that within the stocking density ranges studied, increasing managed bumble bees, but not honey bees, increases their visitation rates. While H. laboriosa had the greatest effect on yield estimates, its activity appears to be limited by both a phenological mismatch with crop bloom and farm management.

Low bee visitation rates explain pollinator shifts to vertebrates in tropical mountains

Evolutionary shifts from bee to vertebrate pollination are common in tropical mountains. Reduction in bee pollination efficiency under adverse montane weather conditions was proposed to drive these shifts. Although pollinator shifts are central to the evolution and diversification of angiosperms, we lack experimental evidence of the ecological processes underlying such shifts. Here, we combine phylogenetic and distributional data for 138 species of the Neotropical plant tribe Merianieae (Melastomataceae) with pollinator observations of 11 and field pollination experiments of six species to test whether the mountain environment may indeed drive such shifts. We demonstrate that shifts from bee to vertebrate pollination coincided with occurrence at high elevations. We show that vertebrates were highly efficient pollinators even under the harsh environmental conditions of tropical mountains, whereas bee pollination efficiency was lowered significantly through reductions in flower visitation rates. Furthermore, we show that pollinator shifts in Merianieae coincided with the final phases of the Andean uplift and were contingent on adaptive floral trait changes to alternative rewards and mechanisms facilitating pollen dispersal. Our results provide evidence that abiotic environmental conditions (i.e. mountain climate) may indeed reduce the efficiency of a plant clade's ancestral pollinator group and correlate with shifts to more efficient new pollinators.

Synergism between local‐ and landscape‐level pesticides reduces wild bee floral visitation in pollinator‐dependent crops

Abstract The hazard pesticides pose to pollinators are well‐understood from laboratory studies. However, the field‐level response of pollinators to pesticide use in agroecosystems is not well‐established, nor is it clear if synergisms between pesticides affect pollinator visitation to crops. Here, we evaluated if fungicide and insecticide use posed a hazard to wild and honeybees at 87 cucurbit—pumpkin, cucumber, watermelon—farms in the Midwestern United States. We also evaluated if synergisms between local‐ (i.e. focal cucurbit field) and landscape‐level (i.e. surrounding crops) pesticide use influence wild and honeybee visitation to crop flowers. We found that bees were exposed to pesticides above regulatory levels of concern and that synergisms between a few local insecticides and landscape‐level fungicides reduced wild bee visitation to cucurbit flowers. Honey and bumblebee visitation to crops was not strongly influenced by synergisms between pesticides used at the local and landscape level. Synthesis and applications. We found pesticides posed hazards to honey and wild bee species. However, pesticides were less likely to affect short‐term visitation rates of honeybees compared with wild bee species. Thus, there is a need for changes in pesticide use at large spatial scales to reduce reliance on honeybees and maximize wild bee visitation to pollinator‐dependent crops. We suggest that a multifaceted approach, involving collaborations between farmers, consumers and policymakers, will be fruitful to promote changes in pesticide use and wild bee pollinators.

Landscape complexity benefits bumble bee visitation in faba bean (Vicia faba minor L.) but crop productivity is not pollinator-dependent

Faba bean (Vicia faba minor L.) is partially dependent on insects for pollination, but the degree of pollinator-dependency and whether crop productivity is limited by insufficient insect pollination remain unknown. We monitored insect pollinators and their foraging behaviors (i. e., legitimate flower visitation, nectar robbing and extra-floral nectary visitation) in a total of 20 faba bean fields of a single cultivar (Tiffany) 2018–2019. Focal fields were situated along a gradient of landscape complexity. In each field, a pollination experiment was established, where plants were either bagged to exclude pollination by insects or remained open for pollinator visits. In addition, all flowers on half of the bagged and open-pollinated plants were pollinated by hand to measure the degree of pollen limitation. We found that bumble bee abundance was higher, and legitimate flower visitor abundance tended to be higher, in complex landscapes with more semi-natural habitat, indicating that the faba bean pollination potential is higher in complex landscapes. The pollination experiment showed that the number of beans per pod was lower in bagged plants compared with other treatments in one of the years, but the lower number of beans per pod was compensated for by a higher individual bean weight, such that there was no pollinator-dependency or effect of hand pollination on total bean mass per plant. We conclude that to be able to characterize the value of insect pollination services in faba bean we need an improved understanding of how pollinator-dependency varies across modern cultivars, and how environmental conditions can increase or, as in our case, cancel this pollinator-dependency.

Connective appendages in Huberia bradeana (Melastomataceae) affect pollen release during buzz pollination.

Floral structures, such as stamen appendages, play crucial roles in pollinator attraction, pollen release dynamics and, ultimately, the reproductive success of plants. The pollen‐rewarding, bee buzz‐pollinated flowers of Melastomataceae often bear conspicuous staminal appendages. Surprisingly, their functional role in the pollination process remains largely unclear. We use Huberia bradeana Bochorny & R. Goldenb. (Melastomataceae) with conspicuously elongated, twisted stamen appendages to investigate their functional role in the pollination process.We studied the effect of stamen appendages on pollinator behaviour and reproductive success by comparing manipulated flowers (appendages removed) with unmanipulated flowers. To assess bee pollinator behaviour, we measured three properties of buzzes (vibrations) produced by bees on Huberia flowers: frequency, duration and number of buzzes per flower visit. We measured male and female reproductive success by monitoring pollen release and deposition after single bee visits. Finally, we used artificial vibrations and laser vibrometry to assess how flower vibrational properties change with the removal of stamen appendages.Our results show that the absence of staminal appendages does not modify bee buzzing behaviour. Pollen release was higher in unmanipulated flowers, but stigmatic pollen loads differ only marginally between the two treatments. We also detected lower vibration amplitudes in intact flowers as compared to manipulated flowers in artificial vibration experiments.The presence of connective appendages are crucial in transmitting vibrations and assuring optimal pollen release. Therefore, we propose that the high diversity of colours, shapes and sizes of connective appendages in buzz‐pollinated flowers may have evolved by selection through male fitness.

Key factors influencing forager distribution across macadamia orchards differ among species of managed bees

To achieve maximised and sustainable crop productivity, it is critical that we develop crop-specific strategies for managing pollination. Honey bees (Apis mellifera) and stingless bees (Tetragonula carbonaria) are considered effective pollinators of macadamia (Macadamia integrifolia). The introduction of managed honey bee or stingless bee hives into orchards is likely to boost the numbers of these insects visiting flowers; however, there is a lack of published information and consensus regarding their management for pollination. Here, we identify factors that affect the distribution of both honey bees and stingless bees across cultivated macadamia, and establish whether increased flower visitation leads to higher nut set. A gradient of bee visitation rates was created by placing colonies on the ends of a four-hectare block, and mixed-effect models were applied to assess forager abundance and nut set with respect to distance from hive, time of day, cultivar, and floral display size. Distance from colony had a strong effect on stingless bee numbers, with >96% of individuals recorded within 100 metres of colonies, whereas the distribution of honey bees was more closely related to daily floral display: trees with greater numbers of flowers attracted more honey bees. Simplified surveys conducted in a further 17 macadamia blocks confirm that these are broadly occurring distribution patterns. Bee abundance alone did not significantly predict nut production; however, an indirect effect of bee visits to flowers is inferred, as nut production increased with size of floral display. To encourage a more even distribution of bees and uniform pollination, we recommend placement of stingless bee hives to maximise their distribution through a block (e.g. at 100-m intervals) and management practices that promote even distributions of flowers across trees.

Studies on the influence of natural resource utilization by humans on foraging behavior of honey bees at rural ecosystems.

Human utilization of natural resources acts as a main driver in altering the ecosystem service and functions. Apart from indirect influence, these human activities also tempt for the behavioral shift in insects especially in honey bees. The foraging behavior of honey bees from the natural floral resources to the man-made food sources eventually degrade the ecosystem's services and cause declining of the honey bee population. Understanding this foraging behavior of bees could help in opting for viable conservation measures for honey bees. In order to understand the influence of human utilization of natural resources on the foraging behavior of bees and its negative impacts on the bee population, the study was carried out in the sites where humans collect palm sap. Palm sap collectors used different containers (mud pots and pet bottles) to collect the palm sap from Borassus flabellifer. The number of containers per tree, volume of palm sap per container/tree, bee visiting frequency, and bee mortality per container/tree were measured at different ecosystems. Palm saps were collected freshly and volatile compounds of samples were identified using FT-IR and GC-MS analysis. The identified volatile compounds were used to study the interaction between volatile compounds and odorant-binding proteins (OBPs) of honey bees for understanding the foraging behavior of bees using in silico approach. Our results clearly showed that bee visitation frequency was directly correlated (0.94) with bee mortality in palm sap in different study sites. The average number of bee mortality was recorded as 491.2 ± 23.48 bees per container/tree/day. GC-MS analyses revealed the presence of 35 volatile compounds in collected palm sap from different study sites. Furthermore, molecular docking studies were performed for all 35 palm volatile compounds OBPs of honey bees to analyze their binding affinities. Docking studies showed that 1-methylbutylmandelate and 6-(hydroxymethyl)-1,4,4-trimethylbicyclo [3.1.0] hexan-2-ol have high binding affinity with OBP residues of bees. These volatile compounds might act as an attractant for bee populations for their foraging behavior. Based on this study, we conclude that human utilization of palm sap has created new ecological niches which highly alters the foraging behavior of bees and results in declining bee populations.

Higher bee abundance, but not pest abundance, in landscapes with more agriculture on a late-flowering legume crop in tropical smallholder farms.

BackgroundLandscape composition is known to affect both beneficial insect and pest communities on crop fields. Landscape composition therefore can impact ecosystem (dis)services provided by insects to crops. Though landscape effects on ecosystem service providers have been studied in large-scale agriculture in temperate regions, there is a lack of representation of tropical smallholder agriculture within this field of study, especially in sub-Sahara Africa. Legume crops can provide important food security and soil improvement benefits to vulnerable agriculturalists. However, legumes are dependent on pollinating insects, particularly bees (Hymenoptera: Apiformes) for production and are vulnerable to pests. We selected 10 pigeon pea (Fabaceae: Cajunus cajan (L.)) fields in Malawi with varying proportions of semi-natural habitat and agricultural area within a 1 km radius to study: (1) how the proportion of semi-natural habitat and agricultural area affects the abundance and richness of bees and abundance of florivorous blister beetles (Coleoptera: Melloidae), (2) if the proportion of flowers damaged and fruit set difference between open and bagged flowers are correlated with the proportion of semi-natural habitat or agricultural area and (3) if pigeon pea fruit set difference between open and bagged flowers in these landscapes was constrained by pest damage or improved by bee visitation.MethodsWe performed three, ten-minute, 15 m, transects per field to assess blister beetle abundance and bee abundance and richness. Bees were captured and identified to (morpho)species. We assessed the proportion of flowers damaged by beetles during the flowering period. We performed a pollinator and pest exclusion experiment on 15 plants per field to assess whether fruit set was pollinator limited or constrained by pests.ResultsIn our study, bee abundance was higher in areas with proportionally more agricultural area surrounding the fields. This effect was mostly driven by an increase in honeybees. Bee richness and beetle abundances were not affected by landscape characteristics, nor was flower damage or fruit set difference between bagged and open flowers. We did not observe a positive effect of bee density or richness, nor a negative effect of florivory, on fruit set difference.DiscussionIn our study area, pigeon pea flowers relatively late—well into the dry season. This could explain why we observe higher densities of bees in areas dominated by agriculture rather than in areas with more semi-natural habitat where resources for bees during this time of the year are scarce. Therefore, late flowering legumes may be an important food resource for bees during a period of scarcity in the seasonal tropics. The differences in patterns between our study and those conducted in temperate regions highlight the need for landscape-scale studies in areas outside the temperate region.

Abejas silvestres visitantes florales de Salvia assurgens (Lamiaceae): aportes a la ecología de la polinización de una salvia mexicana endémica de flores blancas

Antecedentes y Objetivos: Según su arquitectura floral, Salvia assurgens (salvia con flores blancas) ha sido considerada como especie melitófila. Sin embargo, no existen datos empíricos que apoyen la asignación a dicho síndrome de polinización. Este trabajo tuvo como objetivo registrar los visitantes florales diurnos de S. assurgens para confirmar su condición melitófila y evaluar qué especies de abejas podrían ser potenciales polinizadores. Métodos: Durante el verano de 2018 y 2019 se colectaron los visitantes florales diurnos en una población de S. assurgens ubicada al noreste de Michoacán, México. Se realizó un análisis descriptivo de las cargas polínicas por especie y áreas corporales de cada visitante floral. Además, se registró el comportamiento de algunos de los visitantes florales sobre las flores. Resultados clave: Se registraron 17 especies de abejas de tres familias (Apidae, Halictidae y Megachilidae) como visitantes florales de S. assurgens. Noventa por ciento de los granos de polen en las cargas polínicas pertenecieron a S. assurgens. Cuatro especies de abejas nativas fueron los visitantes más frecuentes; estas concentraron 94.2% del polen de S. assurgens y presentaron diferencias en la distribución del polen según el área corporal. Dos de estas especies, Bombus pennsylvanicus sonorus y Megachile sp. 1, concentraron hasta 90% del polen de S. assurgens en su frente y dorso, lugares que hacen más probable la transferencia de polen al estigma de S. assurgens. Conclusiones: Este estudio proporciona una evidencia de la condición melitófila de S. assurgens. De hecho, la riqueza de abejas silvestres registrada en este trabajo fue similar o mayor a la reportada en estudios anteriores sobre visitantes florales de salvias neotropicales. Además, nuestros resultados destacan la utilidad de las cargas de polen para aumentar nuestro conocimiento sobre la ecología de la polinización en Salvia.

High honeybee abundances reduce wild bee abundances on flowers in the city of Munich

The increase in managed honeybees (Apis mellifera) in many European cities has unknown effects on the densities of wild bees through competition. To investigate this, we monitored honeybees and non-honeybees from 01 April to 31 July 2019 and 2020 at 29 species of plants representing diverse taxonomic and floral-functional types in a large urban garden in the city of Munich in which the same plant species were cultivated in both years. No bee hives were present in the focal garden, and all bee hives in the adjacent area were closely monitored by interviewing the relevant bee keepers in both 2019 and 2020. Honeybee numbers were similar in April of both years, but increased from May to July 2020 compared to 2019. The higher densities correlated with a significant increase in shifts from wild bee to honeybee visits in May/June/July, while visitor spectra in April 2019 and 2020 remained the same. Most of the species that experienced a shift to honeybee visits in 2020 were visited mostly or exclusively for their nectar. There were no shifts towards increased wild bee visits in any species. These results from a flower-rich garden have implications for the discussion of whether urban bee keeping might negatively impact wild bees. We found clear support that high honeybee densities result in exploitative competition at numerous types of flowers.