Author
Brad G. Howlett
Bio: Brad G. Howlett is an academic researcher from Plant & Food Research. The author has contributed to research in topics: Pollinator & Pollination. The author has an hindex of 11, co-authored 45 publications receiving 2885 citations.
Topics: Pollinator, Pollination, Honey bee, Biology, Pollen
Papers
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National University of Río Negro1, University of Würzburg2, Rutgers University3, National University of Comahue4, Swedish University of Agricultural Sciences5, Commonwealth Scientific and Industrial Research Organisation6, University of California, Berkeley7, University of Leeds8, Naturalis9, University of Calgary10, Hebrew University of Jerusalem11, ETH Zurich12, Lüneburg University13, National University of Tucumán14, Federal University of Ceará15, Federal University of Bahia16, Plant & Food Research17, Michigan State University18, Agriculture and Agri-Food Canada19, The Nature Conservancy20, University of Göttingen21, University of Queensland22, Cornell University23, University of Reading24, Stockholm University25, University of Vermont26, Lund University27, University of Bern28, University of Koblenz and Landau29, Jagiellonian University30, Universidad de las Américas Puebla31, University of California, Davis32
TL;DR: Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation.
Abstract: The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.
1,881 citations
Wageningen University and Research Centre1, Rutgers University2, Spanish National Research Council3, Naturalis4, University of Leeds5, Institut national de la recherche agronomique6, Michigan State University7, University of Freiburg8, University of California, Berkeley9, University of New England (United States)10, University of Vermont11, University of California, Davis12, National University of Singapore13, Hungarian Academy of Sciences14, University of Göttingen15, Cornell University16, Swedish University of Agricultural Sciences17, Stellenbosch University18, Centre national de la recherche scientifique19, Simon Fraser University20, University of Reading21, University of Würzburg22, Plant & Food Research23, University of Giessen24, University of Texas at Austin25, University of Bern26, Hebrew University of Jerusalem27, Lund University28, Federal University of Bahia29
TL;DR: It is shown that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management Strategies to promote threatened bees.
Abstract: There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.
698 citations
University of New England (Australia)1, Spanish National Research Council2, National University of Río Negro3, University of Reading4, Plant & Food Research5, Rutgers University6, Commonwealth Scientific and Industrial Research Organisation7, University of Queensland8, Australian Bureau of Agricultural and Resource Economics9, Lund University10, Swedish University of Agricultural Sciences11, University of California, Davis12, University of Brasília13, University of Lisbon14, Naturalis15, National University of Tucumán16, University of Koblenz and Landau17, Federal University of Ceará18, United Nations19, ETH Zurich20, Federal University of Bahia21, University of Giessen22, University of Freiburg23, Wageningen University and Research Centre24, Hebrew University of Jerusalem25, American Museum of Natural History26, University of Bern27, Trinity College, Dublin28, Royal Holloway, University of London29, Jagiellonian University30, University of Agriculture, Faisalabad31, Universidad de las Américas Puebla32
TL;DR: It is shown that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use.
Abstract: Wild and managed bees are well documented as effective pollinators of global crops of economic importance. However, the contributions by pollinators other than bees have been little explored despite their potential to contribute to crop production and stability in the face of environmental change. Non-bee pollinators include flies, beetles, moths, butterflies, wasps, ants, birds, and bats, among others. Here we focus on non-bee insects and synthesize 39 field studies from five continents that directly measured the crop pollination services provided by non-bees, honey bees, and other bees to compare the relative contributions of these taxa. Non-bees performed 25–50% of the total number of flower visits. Although non-bees were less effective pollinators than bees per flower visit, they made more visits; thus these two factors compensated for each other, resulting in pollination services rendered by non-bees that were similar to those provided by bees. In the subset of studies that measured fruit set, fruit set increased with non-bee insect visits independently of bee visitation rates, indicating that non-bee insects provide a unique benefit that is not provided by bees. We also show that non-bee insects are not as reliant as bees on the presence of remnant natural or seminatural habitat in the surrounding landscape. These results strongly suggest that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use. Non-bee insects provide a valuable service and provide potential insurance against bee population declines.
620 citations
University of East Anglia1, University of Cambridge2, University of Reading3, National University of Comahue4, University of Calcutta5, Bogor Agricultural University6, University of Córdoba (Spain)7, National Scientific and Technical Research Council8, National University of Río Negro9, World Agroforestry Centre10, Prescott College11, Plant & Food Research12, University of São Paulo13, University of KwaZulu-Natal14, Kyungpook National University15, International Centre of Insect Physiology and Ecology16, University of Cape Town17
TL;DR: The authors evaluated the relative regional and global importance of eight drivers of pollinator decline and ten consequent risks to human well-being using a formal expert elicitation process, and concluded that global policy responses should focus on reducing pressure from changes in land cover and configuration, land management and pesticides.
Abstract: Pollinator decline has attracted global attention and substantial efforts are underway to respond through national pollinator strategies and action plans. These policy responses require clarity on what is driving pollinator decline and what risks it generates for society in different parts of the world. Using a formal expert elicitation process, we evaluated the relative regional and global importance of eight drivers of pollinator decline and ten consequent risks to human well-being. Our results indicate that global policy responses should focus on reducing pressure from changes in land cover and configuration, land management and pesticides, as these were considered very important drivers in most regions. We quantify how the importance of drivers and risks from pollinator decline, differ among regions. For example, losing access to managed pollinators was considered a serious risk only for people in North America, whereas yield instability in pollinator-dependent crops was classed as a serious or high risk in four regions but only a moderate risk in Europe and North America. Overall, perceived risks were substantially higher in the Global South. Despite extensive research on pollinator decline, our analysis reveals considerable scientific uncertainty about what this means for human society.
92 citations
TL;DR: It is shown that pollinator hairiness is strongly linked to pollination—an important ecosystem function, and a rigorous and time-efficient method is provided for measuring hairiness.
Abstract: BACKGROUND Functional traits are the primary biotic component driving organism influence on ecosystem functions; in consequence, traits are widely used in ecological research. However, most animal trait-based studies use easy-to-measure characteristics of species that are at best only weakly associated with functions. Animal-mediated pollination is a key ecosystem function and is likely to be influenced by pollinator traits, but to date no one has identified functional traits that are simple to measure and have good predictive power. METHODS Here, we show that a simple, easy to measure trait (hairiness) can predict pollinator effectiveness with high accuracy. We used a novel image analysis method to calculate entropy values for insect body surfaces as a measure of hairiness. We evaluated the power of our method for predicting pollinator effectiveness by regressing pollinator hairiness (entropy) against single visit pollen deposition (SVD) and pollen loads on insects. We used linear models and AICC model selection to determine which body regions were the best predictors of SVD and pollen load. RESULTS We found that hairiness can be used as a robust proxy of SVD. The best models for predicting SVD for the flower species Brassica rapa and Actinidia deliciosa were hairiness on the face and thorax as predictors (R2 = 0.98 and 0.91 respectively). The best model for predicting pollen load for B. rapa was hairiness on the face (R2 = 0.81). DISCUSSION We suggest that the match between pollinator body region hairiness and plant reproductive structure morphology is a powerful predictor of pollinator effectiveness. We show that pollinator hairiness is strongly linked to pollination-an important ecosystem function, and provide a rigorous and time-efficient method for measuring hairiness. Identifying and accurately measuring key traits that drive ecosystem processes is critical as global change increasingly alters ecological communities, and subsequently, ecosystem functions worldwide.
74 citations
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TL;DR: The stresses bees are experiencing from climate change, infectious diseases, and insecticides are reviewed, with concern that the authors may be nearing a “pollination crisis” in which crop yields begin to fall.
Abstract: Bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.
2,526 citations
01 Jan 2009
TL;DR: In this article, the effects of cross-fertilisation and self fertilization on the production of seeds are discussed. But the main difference between cross-and self-flowered plants is the height and weights of the crossed and self-flowering plants.
Abstract: 1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.
1,224 citations
TL;DR: There are well-documented declines in some wild and managed pollinators in several regions of the world, however, many effective policy and management responses can be implemented to safeguard pollinators and sustain pollination services.
Abstract: Wild and managed pollinators provide a wide range of benefits to society in terms of contributions to food security, farmer and beekeeper livelihoods, social and cultural values, as well as the maintenance of wider biodiversity and ecosystem stability. Pollinators face numerous threats, including changes in land-use and management intensity, climate change, pesticides and genetically modified crops, pollinator management and pathogens, and invasive alien species. There are well-documented declines in some wild and managed pollinators in several regions of the world. However, many effective policy and management responses can be implemented to safeguard pollinators and sustain pollination services.
1,121 citations
TL;DR: It is shown that a commonly used insecticide seed coating in a flowering crop can have serious consequences for wild bees, and the contribution of pesticides to the global decline of wild bees may have been underestimated.
Abstract: 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.
812 citations
Wageningen University and Research Centre1, Rutgers University2, Spanish National Research Council3, Naturalis4, University of Leeds5, Institut national de la recherche agronomique6, Michigan State University7, University of Freiburg8, University of California, Berkeley9, University of New England (United States)10, University of Vermont11, University of California, Davis12, National University of Singapore13, Hungarian Academy of Sciences14, University of Göttingen15, Cornell University16, Swedish University of Agricultural Sciences17, Stellenbosch University18, Centre national de la recherche scientifique19, Simon Fraser University20, University of Reading21, University of Würzburg22, Plant & Food Research23, University of Giessen24, University of Texas at Austin25, University of Bern26, Hebrew University of Jerusalem27, Lund University28, Federal University of Bahia29
TL;DR: It is shown that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management Strategies to promote threatened bees.
Abstract: There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.
698 citations