Bumblebee Colony Growth Research Articles

Gardens reduce seasonal hunger gaps for farmland pollinators.

Gardens can benefit pollinators living in surrounding farmland landscapes, but the reason for their value is not clear. Gardens are no different from many semi-natural farmland habitats in terms of the quantity of floral resources (pollen and nectar) they produce, but the timing of their resource supply is very different, which may explain their value. We show that gardens provide 15% of overall annual nectar in farmland landscapes in Southwest UK, but between 50% and 95% during early spring and late summer when farmland supplies are low. Gardens can therefore reduce seasonal nectar gaps experienced by farmland bumblebees. Consistent with this pattern, bumblebee activity increased in gardens relative to farmland during early spring and late summer. An agent-based model reinforces this point, showing that timing, not quantity, of garden nectar supply enhances bumblebee colony growth and survival in farmland. We show that over 90% of farmland in Great Britain is within 1 km of a garden and therefore positive actions by gardeners could have widespread spillover benefits for pollinators across the country. Given the widespread distribution of gardens around the world, we highlight their important interplay with surrounding landscapes for pollinator ecology and conservation.

Exposure to urban heavy metal contamination diminishes bumble bee colony growth

As a result of their industrial past, legacy cites often have elevated concentrations of soil heavy metal contamination. Metal pollution can have negative and prolonged ecosystem impacts, and bees that forage in these urban ecosystems are at risk of exposure. Legacy cities are known to support species rich bee communities, which highlights the importance of determining the impact of heavy metal contamination on wild bee health. We examined how oral exposure to concentrations of four metals found within the provisions of bees foraging within Cleveland, Ohio, USA influenced colony growth of Bombus impatiens Cresson (Hymenoptera: Apidae), a common species within legacy cities across the eastern United States. Colony weight and brood survivorship were compared among hives fed uncontaminated sucrose solution (hereafter nectar), nectar spiked with one metal (arsenic, cadmium, chromium, or lead), and nectar containing all metals, after 15 or 30 d of exposure within flight tents. Across both exposure periods, we found a significantly higher proportion of dead brood in metal exposed hives. Additionally, colonies fed all four metals had a significantly higher proportion of dead brood than those fed a single metal. Our findings illustrate that even low, environmentally relevant concentrations of metals collected by B. impatiens in legacy cities can negatively influence bee colony growth. We highlight the need to identify metal exposure routes for bees in contaminated landscapes to minimize risk and bolster conservation habitat initiative success.

Bumblebees Exposed to a Neonicotinoid Pesticide Make Suboptimal Foraging Decisions.

Bumblebees are important pollinators of agricultural crops and wildflowers, but many species are in decline. Neonicotinoid insecticides are the most commonly used insecticide globally and can have negative sublethal effects on bumblebee colony growth and reproduction. Individual bumblebees can visit hundreds to thousands of flowers a day to forage for their colony. As such, they are a model species for studying optimal foraging, and small impairments to an individual's foraging decisions may have compounding effects on the colony's nutritional intake. We exposed bumblebees (Bombus impatiens) to an acute, field-realistic dose of the neonicotinoid insecticide imidacloprid, before allowing them to forage on an artificial floral array. We found that neonicotinoid-exposed bumblebees made suboptimal foraging decisions, as they were more likely to visit flowers located further apart than control bees. This indicates that for a given flower patch, individual bees exposed to a neonicotinoid will likely use more energy and forage less efficiency than unexposed bees, although further studies that directly measure energetic cost are required to confirm this. Given the robust and growing body of evidence demonstrating negative sublethal effects of neonicotinoids on bees, sublethal assessments on non-Apis bees should be made mandatory within the regulatory process.

The Neonicotinoid Insecticide Imidacloprid Disrupts Bumblebee Foraging Rhythms and Sleep.

SummaryNeonicotinoids have been implicated in the large declines observed in insects such as bumblebees, an important group of pollinators. Neonicotinoids are agonists of nicotinic acetylcholine receptors that are found throughout the insect central nervous system and are the main mediators of synaptic neurotransmission. These receptors are important for the function of the insect central clock and circadian rhythms. The clock allows pollinators to coincide their activity with the availability of floral resources and favorable flight temperatures, as well as impact learning, navigation, and communication. Here we show that exposure to the field-relevant concentration of 10 μg/L imidacloprid caused a reduction in bumblebee foraging activity, locomotion, and foraging rhythmicity. Foragers showed an increase in daytime sleep and an increase in the proportion of activity occurring at night. This could reduce foraging and pollination opportunities, reducing the ability of the colony to grow and reproduce, endangering bee populations and crop yields.

Annual flowers strips benefit bumble bee colony growth and reproduction

Bumble bees are important crop pollinators but are negatively impacted by agricultural intensification and concomitant loss of floral resources. Flower strips can increase the abundance and sometimes the diversity of bumble bees at local scales, but the importance of flower strips for bumble bee populations at larger scales remains poorly understood. We investigated the effect of flower strips on bumble bee colony growth and reproduction at landscape scales. Commercial bumble bee colonies of a native species (Bombus terrestris) were placed and monitored at different distances from flower strips that were sown on existing ecological focus areas (European Common Agricultural Policy) in southern Sweden. Both the average colony growth (weight) and the production of reproductives (drones and queens) were highest for colonies adjacent to flower strips and declined with increasing distance. Colonies close to the flower strip also produced more reproductives per colony weight. Colony foraging activity was negatively related to the distance to flower strips whereas worker size was not affected. Annual flower strips in ecological focus areas benefit bumble bee colonies by increasing foraging success, colony growth and finally boosting sexual reproduction, demonstrating potential benefits for pollination within and between seasons. These effects were spatially limited but extended to foraging ranges of bumble bees. However, effects of increased colony growth on the abundance of foraging bees in the landscape may extend to larger distances because of forager movements within seasons and queen dispersal between seasons, suggesting that voluntary or incentivised collaboration between farmers may be needed to achieve optimal implementation of flower strips.

Multiple stressors interact to impair the performance of bumblebee Bombus terrestris colonies

Bumblebees are constantly exposed to a wide range of biotic and abiotic stresses which they must defend themselves against to survive. Pathogens and pesticides represent important stressors that influence bumblebee health, both when acting alone or in combination. To better understand bumblebee health, we need to investigate how these factors interact, yet experimental studies to date generally focus on only one or two stressors. The aim of this study is to evaluate how combined effects of four important stressors (the gut parasite Nosema ceranae, the neonicotinoid insecticide thiamethoxam, the pyrethroid insecticide cypermethrin and the EBI fungicide tebuconazole) interact to affect bumblebees at the individual and colony levels. We established seven treatment groups of colonies that we pulse exposed to different combinations of these stressors for 2weeks under laboratory conditions. Colonies were subsequently placed in the field for 7weeks to evaluate the effect of treatments on the prevalence of N. ceranae in inoculated bumblebees, expression levels of immunity and detoxification-related genes, food collection, weight gain, worker and male numbers, and production of worker brood and reproductives. Exposure to pesticide mixtures reduced food collection by bumblebees. All immunity-related genes were upregulated in the bumblebees inoculated with N. ceranae when they had not been exposed to pesticide mixtures, and bumblebees exposed to the fungicide and the pyrethroid were less likely to have N. ceranae. Combined exposure to the three-pesticide mixture and N. ceranae reduced bumblebee colony growth, and all treatments had detrimental effects on brood production. The groups exposed to the neonicotinoid insecticide produced 40%-76% fewer queens than control colonies. Our findings show that exposure to combinations of stressors that bumblebees frequently come into contact with have detrimental effects on colony health and performance and could therefore have an impact at the population level. These results also have significant implications for current practices and policies for pesticide risk assessment and use as the combinations tested here are frequently applied simultaneously in the field. Understanding the interactions between different stressors will be crucial for improving our ability to manage bee populations and for ensuring pollination services into the future.

Agri‐environment schemes enhance pollinator richness and abundance but bumblebee reproduction depends on field size

Abstract Pollinators have experienced a dramatic decrease world‐wide due to agricultural intensification. In many countries, agri‐environment schemes (AES) have been introduced to counteract this current trend. However, until now, the relative importance of each AES for biodiversity and ecosystem services is still little understood and might change depending on landscape context. Complex landscape‐experiments are required to fill this knowledge gap, enabling the implementation of sustainable intensification of food production. In our study, we compared the effectiveness of the two most popular AES in Germany, organic farming and flower strips, in supporting pollinators and flower resources. We selected nine landscapes along a gradient of increasing field size, (configurational heterogeneity), each with a triplet of winter wheat fields: one organic, one conventional with flower strip and one conventional without flower strip as a control. We surveyed insect‐pollinated plants and pollinators (bumblebees, solitary bees and hoverflies). Additionally, we placed bumblebee colonies in the field edges to monitor their growth (colony weight gain) and reproduction (queen production). Flower strips stood out with the highest abundance and richness of pollinators. In contrast, bumblebee colony growth and plant richness benefited equally from organic and flower strip schemes. At the landscape scale, smaller fields had a positive effect on plant richness and bumblebee reproduction in flower strips. By contrast, bumblebee colonies in organic agriculture benefited most from large fields, as large organic fields provided much more flower resources than the narrow flower strips. Synthesis and applications. Our results showed that both local and landscape management shaped pollinator communities and their reproduction. Overall, organic farming and flower strips appeared to be effective tools to mitigate flower shortage in conventional cereal fields, with organic farming supporting the highest flowering plant cover per field. Flower strips enhanced local pollinator richness most, but increased bumblebee reproduction only when the surrounding landscapes had small fields with long field borders. Therefore, our results reveal that European Union policies need to take into account that the effectiveness of agri‐environment schemes depends on the structure of the surrounding landscape.

Urban heavy metal contamination limits bumblebee colony growth

Abstract Post‐industrial shrinking cities contain abundant vacant land and are increasingly recognized for their pollinator conservation potential. At the same time, the industrial legacies of these urban ecosystems have resulted in elevated levels of heavy metals in surface soils, which could negatively affect bee populations. We investigated whether foraging within heavy metal contaminated landscapes represents a fitness cost for the common Eastern bumblebee Bombus impatiens, by placing colonies in residential backyards along an urban to rural gradient extending south and east from the city of Cleveland, Ohio, USA. Bees foraged in the landscape for 3 weeks, after which time we counted the total number of workers and larvae present in the colony and analysed castes for the presence of heavy metals. We then assessed the relationship between landscape composition, heavy metal loads and caste abundance. Colonies located in urban landscapes were more likely to be exposed to lead (Pb). Elevated concentrations of Pb within workers were negatively correlated with both the number of workers and the number of larvae present. Synthesis and applications. Our findings raise concern that lead (Pb) contamination could represent a significant challenge to bee conservation in cities. To elucidate risks posed by this pollutant, we highlight a need to quantify lethal and sub‐lethal effects of Pb exposure using laboratory and field‐based studies. Further, identifying routes of exposure and landscape factors that influence exposure risk is necessary to implement mitigation strategies as part of urban conservation initiatives.

Maize‐dominated landscapes reduce bumblebee colony growth through pollen diversity loss

Abstract Bumblebees are important pollinators for a wide range of crops and wild plants. Performance of their colonies depends on pollen and nectar as food resources, but flowering plants are scarce in modern agricultural landscapes. It is well‐known that semi‐natural habitats can enhance floral resources and bumblebee abundance, but the impact of different crop types and their heterogeneity at the landscape scale remains unclear. We tested the effect of two different crop types (oilseed rape [OSR] and maize) and of configurational (field border density) and compositional heterogeneity (crop diversity) on weight gain of buff‐tailed bumblebee colonies (Bombus terrestris) and the pollen diversity collected by them in 20 landscapes in Central Germany. We found that augmenting maize cover had a detrimental effect on pollen diversity collected by bumblebees, probably due to intensive management resulting in low plant diversity. This low pollen diversity translated into reduced colony growth, since colonies with high pollen diversity gained more weight than colonies with low pollen diversity. In contrast, OSR cover and configurational and compositional heterogeneity did neither affect colony growth nor pollen diversity. However, for OSR, the timing of the flowering period was important. When OSR fields had a high flower cover at the end of the OSR blooming period, colonies showed increased growth rates. Synthesis and applications. Our results complement previous laboratory studies by showing that high pollen diversity leads to better colony performance under field conditions. Therefore, the maintenance of floral diversity in agricultural landscapes is crucial to ensure that bumblebees can fulfil their nutritional needs. However, the heterogeneity of crops, at least under the currently very low levels of crop rotation, does not contribute to this aim. In contrast, crop identity and timing of mass‐flowering crops turned out to be important factors, as maize reduced pollen resources, while late blooming oilseed rape (OSR) was beneficial to bumblebee colonies. Hence, maize cover per landscape should be reduced and strategies to enhance landscape wide flower diversity, especially towards and after the end of oilseed rape bloom, should be promoted to support bumblebee colonies that provide important pollination services.

Exploring the relationships between landscape complexity, wild bee species richness and reproduction, and pollination services along a complexity gradient in the Netherlands

Pollinator communities exhibit variable responses to changing landscape composition. A general expectation is that a decreasing cover of semi-natural habitats negatively affects pollinator reproduction, population size and pollination services, but few studies have investigated the simultaneous effects of landscape complexity on different aspects of pollinator communities and functioning.In 20 agricultural landscape plots the size of an average Dutch farm, we studied how changing landscape complexity affected wild bee abundance, species richness and reproduction. To measure pollination, we placed potted strawberry plants as phytometers in landscapes. Landscape complexity was characterized as the area of semi-natural habitats. In addition, we estimated floral resource abundance in each landscape plot. We expected that i) bee species richness, reproduction and pollination would be positively related to area of semi-natural habitats and flower abundance, and that ii) species richness and reproduction would be positively related to pollination.An increase in semi-natural habitats in landscapes increased both the abundance of cavity-nesting bees colonizing trap nests, and the growth rates of experimental Bombus terrestris L. colonies, but not the species richness of wild bees measured by pan traps. There was only a tendency for higher pollination levels of strawberry plants with higher cover of semi-natural habitats. There was no relationship between species richness and bee reproduction in a landscape and the pollination services. Estimated flower abundance in landscape had a positive effect on bumblebee colony growth only and not on the other variables.Our results suggest that, by improving habitat quality on their farms through establishing more semi-natural habitats or enhancing the flower availability in semi-natural habitats, farmers can promote reproduction of a number of functionally important bee species and the pollination services they provide. Bee species richness, however, seems to be more difficult to enhance and requires more than just creating more of the same type of habitats or flowers.

Bumble bee colony growth and reproduction on reclaimed surface coal mines

AbstractReclamation of coal mine lands in the eastern United States creates pockets of grassland habitat in an otherwise predominantly forested region. These sites may represent an opportunity for pollinator conservation if they provide valuable foraging habitat for wild bees. To determine site characteristics that influence bee success on reclamation lands, we monitored growth and reproduction of 24 commercially reared bumble bee (Bombus impatiens) colonies placed on 12 former coal mines (aged 2 to 30+ years post‐reclamation) in Ohio, U.S.A. Twenty colonies survived the duration of the experiment (May–August 2014). All colonies produced both new queens (mean 21.0 ± 37.0 SD) and males (36.5 ± 36.5), in proportion to overall colony size. Results of generalized linear models indicate that colony growth and reproduction increased with floral diversity and species turnover, and declined with site area and the proportion of forest in the surrounding landscape. The sex ratio of reproductive offspring was significantly more male‐biased on sites with low flower diversity, underscoring the importance of floral diversity for meeting the higher resource demands of queen production. Floral resource composition and consistency were influenced by site age and surrounding landscape. Older sites had higher floral diversity and species turnover throughout the season than younger sites, and included high‐quality native bee forage plants. We discuss the implications of this study for reclamation project managers seeking to promote bee reproduction and conservation.

Bumblebee colony development following chronic exposure to field-realistic levels of the neonicotinoid pesticide thiamethoxam under laboratory conditions

Neonicotinoid pesticides are used in agriculture to reduce damage from crop pests. However, beneficial insects such as bees can come into contact with these pesticides when foraging in treated areas, with potential consequences for bee declines and pollination service delivery. Honeybees are typically used as a model organism to investigate insecticide impacts on bees, but relatively little is known about impacts on other taxa such as bumblebees. In this experiment, we chronically exposed whole mature bumblebee (Bombus terrestris) colonies to field-realistic levels of the neonicotinoid thiamethoxam (2.4ppb & 10ppb) over four weeks, and compared colony growth under laboratory conditions. We found no impact of insecticide exposure on colony weight gain, or the number or mass of sexuals produced, although colonies exposed to 2.4ppb produced larger males. As previous studies have reported pesticide effects on bumblebee colony growth, this may suggest that impacts on bumblebee colonies are more pronounced for colonies at an earlier stage in the reproductive cycle. Alternatively, it may also indicate that thiamethoxam differs in toxicity compared to previously tested neonicotinoids in terms of reproductive effects. In either case, assessing bumblebee colony development under field conditions is likely more informative for real world scenarios than tests conducted in laboratory conditions.

Bumble bee colony growth and reproduction depend on local flower dominance and natural habitat area in the surrounding landscape

Conservation measures for bees often focus on increasing the diversity and abundance of floral resources. But it has not been clear if observed benefits of floral enhancements result from greater population growth, which is critical for the long-term success of conservation, or from mobile foragers aggregating in high-resource locations. Experimental evidence is only beginning to emerge in favor of the former mechanism and it is not well-established how different aspects of floral resources affect population growth. For example, bumble bee colonies may benefit from greater overall floral abundance, richness, or relative dominance of resource species. Because bumble bees are highly mobile, resource variability in the surrounding landscape is also important for colonies and may mediate local-scale effects. We experimentally assessed the growth and reproduction of bumble bee colonies (Bombus impatiens) deployed in grasslands in different local- and landscape-scale resource environments. We found that floral dominance, rather than the overall abundance or richness of floral resources, was the most important local factor for colony growth and reproduction. This may reflect more efficient foraging on a few numerically dominant and abundant resource species. Local- and landscape-scale predictor variables had interacting effects on colony growth and reproduction, suggesting that foraging distance depends on where in the landscape efficiently used resources are located. Our results provide further evidence that conservation strategies aimed at enhancing floral resources can increase bumble bee population growth. However, the most effective form of floral enhancement may vary among bee species.

Pesticide use within a pollinator-dependent crop has negative effects on the abundance and species richness of sweat bees, Lasioglossum spp., and on bumble bee colony growth

Pesticides are implicated in current bee declines. Wild bees that nest or forage within agroecosystems may be exposed to numerous pesticides applied throughout their life cycles, with potential additive or synergistic effects. In pollinator-dependent crops, pesticides may reduce bee populations, creating trade-offs between pest management and crop pollination. In this three-year study, we examined the effects of pesticides on the abundance and species richness of wild bees within apple orchards of southern Wisconsin. We additionally deployed colonies of Bombus impatiens, a native and common species, in order to relate colony performance to orchard pesticide use. Utilizing grower spray records, we developed “toxicity scores” as a continuous index of pesticide use for each orchard, a measure that incorporated each pesticide’s relative toxicity to bees, its residual activity, and its application rate. While there was no relationship between total wild bee abundance and species richness with toxicity scores, there was a significant, negative effect on sweat bees, Lasioglossum spp. Many of these sweat bees are small-bodied, have short foraging ranges, are social, and have long foraging periods, all traits that could increase bee exposure or sensitivity to orchard pesticides. In addition, sentinel bumble bee colonies at orchards with high toxicity scores produced fewer, and smaller, workers. Bumble bees may also have a greater sensitivity and exposure to orchard pesticides due to their sociality and long foraging periods. Our results demonstrate that certain bee taxa may have a higher exposure or sensitivity to on-farm pesticide applications, and could therefore be vulnerable in agroecosystems.

Colonies of Bumble Bees (Bombus impatiens) Produce Fewer Workers, Less Bee Biomass, and Have Smaller Mother Queens Following Fungicide Exposure.

Bees provide vital pollination services to the majority of flowering plants in both natural and agricultural systems. Unfortunately, both native and managed bee populations are experiencing declines, threatening the persistence of these plants and crops. Agricultural chemicals are one possible culprit contributing to bee declines. Even fungicides, generally considered safe for bees, have been shown to disrupt honey bee development and impair bumble bee behavior. Little is known, however, how fungicides may affect bumble bee colony growth. We conducted a controlled cage study to determine the effects of fungicide exposure on colonies of a native bumble bee species (Bombus impatiens). Colonies of B. impatiens were exposed to flowers treated with field-relevant levels of the fungicide chlorothalonil over the course of one month. Colony success was assessed by the number and biomass of larvae, pupae, and adult bumble bees. Bumble bee colonies exposed to fungicide produced fewer workers, lower total bee biomass, and had lighter mother queens than control colonies. Our results suggest that fungicides negatively affect the colony success of a native bumble bee species and that the use of fungicides during bloom has the potential to severely impact the success of native bumble bee populations foraging in agroecosystems.

Tasteless pesticides affect bees in the field

Two studies provide evidence that bees cannot taste or avoid neonicotinoid pesticides, and that exposure to treated crops affects reproduction in solitary bees as well as bumblebee colony growth and reproduction. See Letters p.74 & p.77

Seed coating with a neonicotinoid insecticide negatively affects wild bees.

Understanding the effects of neonicotinoid insecticides on bees is vital because of reported declines in bee diversity and distribution and the crucial role bees have as pollinators in ecosystems and agriculture. Neonicotinoids are suspected to pose an unacceptable risk to bees, partly because of their systemic uptake in plants, and the European Union has therefore introduced a moratorium on three neonicotinoids as seed coatings in flowering crops that attract bees. The moratorium has been criticized for being based on weak evidence, particularly because effects have mostly been measured on bees that have been artificially fed neonicotinoids. Thus, the key question is how neonicotinoids influence bees, and wild bees in particular, in real-world agricultural landscapes. Here we show that a commonly used insecticide seed coating in a flowering crop can have serious consequences for wild bees. In a study with replicated and matched landscapes, we found that seed coating with Elado, an insecticide containing a combination of the neonicotinoid clothianidin and the non-systemic pyrethroid β-cyfluthrin, applied to oilseed rape seeds, reduced wild bee density, solitary bee nesting, and bumblebee colony growth and reproduction under field conditions. Hence, such insecticidal use can pose a substantial risk to wild bees in agricultural landscapes, and the contribution of pesticides to the global decline of wild bees may have been underestimated. The lack of a significant response in honeybee colonies suggests that reported pesticide effects on honeybees cannot always be extrapolated to wild bees.

Hive weight as an indicator of bumblebee colony growth

Hive weight as an indicator of bumblebee colony growth

Hive weight as an indicator of bumblebee colony growth

Recommendations for using bumblebees for pollination areexpressed as the number of hives or workers per unit area. Ingreenhouses, however, growers consider only the age ofbumblebee colonies when managing the number of pollinators.They consider an 8-week-old colony as optimal and an 11-week-old colony as too old and inefficient. However, this parameter isnot reliable. Whereas the number of workers in young colonies(4 weeks old) is generally well estimated by directly observing thebees within the hive, future projections of the worker populationare uncertain because of the variability of the colony growth rate(Beekman, 1998; Alaux, 2001; Goulson

The Natural History of Bumblebees: A Sourcebook for Investigations. By Carol A Kearns and , James D Thomson. Boulder (Colorado): University Press of Colorado. $65.00 (hardcover); $24.95 (paper). xv + 130 p; ill.; index. ISBN: 0–87081–565–2 (hc); 0–87081–621–7 (pb). 2001.

Previous articleNext article No AccessAnimal SciencesThe Natural History of Bumblebees: A Sourcebook for Investigations. By Carol A Kearns and , James D Thomson. Boulder (Colorado): University Press of Colorado. $65.00 (hardcover); $24.95 (paper). xv + 130 p; ill.; index. ISBN: 0–87081–565–2 (hc); 0–87081–621–7 (pb). 2001.Bernd HeinrichBernd HeinrichBiology, University of Vermont, Burlington, Vermont Search for more articles by this author Biology, University of Vermont, Burlington, VermontPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 77, Number 2June 2002 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/343965 Views: 20Total views on this site Citations: 1Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Sarah B. Scott, Frances S. Sivakoff, Mary M. Gardiner Exposure to urban heavy metal contamination diminishes bumble bee colony growth, Urban Ecosystems 25, no.33 (Jan 2022): 989–997.https://doi.org/10.1007/s11252-022-01206-x