Combined stress from parasites, pesticides and lack of flowers drives bee declines

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

Bumblebees

Since bumblebees are a group associated with cool climates, Britain supports a large proportion (~10%) of the world's bumblebee fauna. However, three of our 25 species have become extinct, and seven species are Biodiversity Action Plan (BAP) listed, a higher proportion than for any other insect group. Declines are primarily driven by habitat loss and declines in floral abundance resulting from agricultural intensification, notably the loss of ~97% of all species-rich grasslands (haymeadows, calcareous grasslands) in the last 60 years. The decline in the abundance of Red Clover, once a common fodder and ley crop and a major source of pollen and nectar for many bumblebee species, is likely to have had a significant impact. Effects of habitat degradation and fragmentation are compounded by the social nature of bumblebees and by their largely monogamous breeding system, which means that they have a very low effective population size (most bumblebees are sterile workers). Hence, populations are susceptible to chance extinction events and inbreeding. Given the importance of bumblebees as pollinators of crops and wildflowers, their declines have broad ecological and economic significance. Suggested measures for their conservation include tight regulation of commercial bumblebee use and targeted use of agrienvironment schemes to enhance floristic diversity in agricultural landscapes

Causes of colony mortality in bumblebees

Despite considerable interest in bumblebees and their conservation, few data are available on basic life history parameters such as rates of nest predation and the proportion of wild nests that survive to reproduction. Here we use a combination of data collected by volunteers and our own direct observations which together describe the fate of 908 bumblebee nests in the UK between 2008 and 2013. Overall, 75% of nests produced gynes, with marked differences between species; the recently arrived species, B. hypnorum, had the highest proportion of colonies surviving to gyne production (96%), with the long-tongued B. hortorum having the lowest success in reaching gyne production (41%). There were also large differences between bumblebee species in the timing of nesting, gyne production and nest mortality, with B. hypnorum and B. pratorum nests starting early, producing most gynes before mid-summer, and then dying off in June, while at the other end of the spectrum B. pascuorum nests started late and produced gynes mainly in August. There was evidence for the partial or complete destruction of 100 nests. The main reported causes were excavation by a large mammal, probably primarily Meles meles (50%). Human disturbance was the second greatest cause of nest mortality (26%), followed by flooding (7%). Wax moth infestations were common (55% of nests), with Bombus hypnorum nests most frequently infested. However, infestation did not results in reduced likelihood of gyne production, perhaps because infestations often do not become severe until after some gynes have been produced. Our study provides novel insights into the little-studied biology of wild bumblebee nests and factors affecting their survival; collecting similar data sets in the future would enable fascinating comparisons as to how parameters such as nest survival and reproduction are changing over time, and are affected by management interventions for bees

The neonicotinoid insecticide Imidacloprid repels pollinating flies and beetles at field-realistic concentrations

Neonicotinoids are widely used systemic insecticides which, when applied to flowering crops, are translocated to the nectar and pollen where they may impact upon pollinators. Given global concerns over pollinator declines, this potential impact has recently received much attention. Field exposure of pollinators to neonicotinoids depends on the concentrations present in flowering crops and the degree to which pollinators choose to feed upon them. Here we describe a simple experiment using paired yellow pan traps with or without insecticide to assess whether the commonly used neonicotinoid imidacloprid repels or attracts flying insects. Both Diptera and Coleoptera exhibited marked avoidance of traps containing imidacloprid at a field-realistic dose of 1 μg L-1, with Diptera avoiding concentrations as low as 0.01 μg L-1. This is to our knowledge the first evidence for any biological activity at such low concentrations, which are below the limits of laboratory detection using most commonly available techniques. Catch of spiders in pan traps was also slightly reduced by the highest concentrations of imidacloprid used (1 μg L-1), but catch was increased by lower concentrations. It remains to be seen if the repellent effect on insects occurs when neonicotinoids are present in real flowers, but if so then this could have implications for exposure of pollinators to neonicotinoids and for crop pollination. © 2013 Easton, Goulson

Quantifying the attractiveness of garden flowers for pollinators

There is great interest in planting urban areas to benefit pollinating insects, with the potential that urban areas and gardens could act as an extensive network of pollinator-friendly habitats. However, there are a great many different plant cultivars available to the gardener, and a paucity of evidence-based advice as to which plants are truly most attractive to flower-visiting insects. Here, we report insect visitation to metre square plots of 111 different ornamental plant cultivars at a site in central UK. Data were collected over 5 years, and comprise over 9000 insect observations, which were identified to species (for honeybees and bumblebees) or as ‘solitary bees’, Syrphidae, Lepidoptera and ‘others’. Unlike some previous studies, we found no difference in numbers of insects attracted to native or non-native species, or according to whether plants were annuals, biennials or perennials, but we did find that native plants attracted a significantly higher diversity of flower-visiting insects. Overall, the most-visited plants were Calamintha nepeta, Helenium autumnale and Geranium rozanne. However, patterns of visitation were quite different for every insect taxa examined. For example, different species of short-tongued bumblebees showed little overlap in their most-preferred plant cultivars. Interestingly, very similar plant cultivars often attracted different insect communities; for example, 72% of visitors to Aster novi belgii were honeybees or bumblebees, while the related Anthemis tinctoria, which also has daisy-like flowers, did not attract a single honeybee or bumblebee but was popular with solitary bees, hoverflies, and ‘other’ pollinators. Some plant cultivars such as Eryngium planum and Myosotis arvensis were attractive to a broad range of insects, while others attracted only a few species but sometimes in large numbers, such as Veronicastrum virginicum and Helenium autumnale which were both visited predominantly by honey bees. It is clear that we do not yet fully understand what factors drive insect flower preferences. Recommendations are made as to which flower cultivars could be combined to provide forage for a diversity of pollinator groups over the season from early spring to autumn, though it must be born in mind that some plants are likely to perform differently when grown in different environmental conditions

Quantifying the impact and relevance of scientific research

Qualitative and quantitative methods are being developed to measure the impacts of research on society, but they suffer from serious drawbacks associated with linking a piece of research to its subsequent impacts. We have developed a method to derive impact scores for individual research publications according to their contribution to answering questions of quantified importance to end users of research. To demonstrate the approach, here we evaluate the impacts of research into means of conserving wild bee populations in the UK. For published papers, there is a weak positive correlation between our impact score and the impact factor of the journal. The process identifies publications that provide high quality evidence relating to issues of strong concern. It can also be used to set future research agendas