Category Archives: Pollination

Garden pollinators for PAW no. 6 – Buff-tailed bumblebee (Bombus terrestris)

It would be impossible to write a series of blog posts about garden pollinators for Pollinator Awareness Week without considering the bumblebees (genus Bombus) and I intend to devote the last two posts to that group of bees. The bumblebees are arguably the UK’s most important pollinators of both wild and crop plants, certainly later in the season when colony numbers have increased. Earlier in the season it’s the solitary bees such as the Orange-tailed mining bee that are predominant.

Although common and widespread in gardens, the Buff-tailed bumblebee (Bombus terrestris) belongs to a group of bees in which the workers are rather variable in appearance and can be very difficult to distinguish from those in the Bombus lucorum group, which includes two other species (B. cryptarum and B. magnus).

This is a truly social species with an annual nest comprising workers and a queen. Nests are founded by queens that have mated the previous year and hibernated. They usually choose old rodent nests in which to begin their colonies, which is why they are sometimes found in garden compost bins. An interesting question that I’ve not seen answered is whether the queens actively displace mice or voles from such nests: does anyone know? This association between bumblebees and mice led Charles Darwin and Thomas Huxley into some speculation as to the role of spinsters in the British Empire.

In my garden the Buff-tailed bumblebee pollinates a range of crops including strawberries, squashes, courgettes, blackberries, runner beans, french beans, tomatoes, and raspberries. As the photo above shows they also visit the flowers of passion fruit, where they seem to be more effective than the smaller honey bees and solitary bees.

Garden pollinators for PAW no. 5 – Orange-tailed mining bee (Andrena haemorrhoa)

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The Orange-tailed mining bee (Andrena haemorrhoa) is also referred to as the Early mining bee due to its habit of emerging from over-wintered nests as early in the year as March. In truth, however, many Andrena species put in an early appearance, making them important pollinators of orchard fruit such as apples, which you can see from the photograph above, taken in my urban garden earlier this year. So “Orange-tailed” is a more descriptive name.

Thanks to the Orange-tailed mining bee and other early bees, this unnamed apple variety (which Karin and I rescued from the bargain area of a local garden centre) has gone on to produce a heavy crop of eating apples (see below). There’s considerable interest in the role of wild bees such as these as pollinators of fruit in commercial orchards, not just in Europe but in the USA too, where other Andrena spp. also pollinate apples.

The epithet “Mining bees” refers to the fact that these solitary species of the genus Andrena usually make their nests in soil, excavating deep tunnels in which to construct individual cells. It’s another generalist, taking pollen and nectar from a wide variety of garden and wild flowers. Dandelions are particularly important early in the year – so don’t over-manage your lawn and allow some to flower!

Garden pollinators for PAW no. 4 – Gatekeeper butterfly (Pyronia tithonus)

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For my fourth contribution to Pollinator Awareness Week I’m going to highlight the Gatekeeper (Pyronia tithonus), a butterfly that I featured on this blog last year. As I noted in that post, it’s fairly rare to have Gatekeepers in an urban garden which indicates that the shrubs and hedges grown by myself and my neighbours are providing the right microclimate for the adults. In addition the overgrown lawns of some adjacent gardens give opportunities for egg laying as the caterpillars are grass feeders.

Adult butterflies are very well camouflaged when resting with their wings folded. They take nectar from a range of plants in my garden but particularly love the dark, heavily scented infloresences of the buddleia variety pictured here. They also visit the wild blackberries scrambling through the hedge that separates us from next door’s garden and probably pollinate those flowers. Although it’s often said that butterflies are poor pollinators compared to bees, due to their general un-hairiness and habit of holding themselves above the stamens and stigmas in a flower, it very much depends on the type of flower. We have an unpublished manuscript that I hope to submit to a journal later this year showing that butterflies are actually better pollinators of one grassland plant than bumblebees.

Garden pollinators for PAW no. 2 – Marmalade hoverfly (Episyrphus balteatus)

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One of the most frequently encountered of hoverfly species in urban gardens is the beautifully named Marmalade hoverfly (Episyrphus balteatus). This insect is a “true fly” of the order Diptera that is sometimes confused with superficially similar wasps (order Hymenoptera), though (as the common name suggests) the species is translucent orange and black in colour rather than waspish yellow and black. It also has a very flat abdomen whereas wasps are rounded, and they certainly don’t sting.

Individual insects are relatively ineffective as pollinators – they are small and not very hairy, so carry little pollen compared to bumblebees for instance. However they can be extremely abundant and that abundance makes up for any individual ineffectiveness. It’s a real generalist, visiting lots of different types of flowers, and in my garden they visit radishes (as I noted last year) and raspberries.

I often see individuals patrolling crops such as runner beans, not visiting the flowers but laying eggs on leaves and stems: the larvae of the Marmalade hoverfly is carnivorous and feeds on aphids, so it plays an interesting dual role of both pollinator and pest controller. Definitely a gardener’s friend!

Garden pollinators for PAW no. 1 – Patchwork leaf-cutter bee (Megachile centuncularis)

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As promised, here’s the first of my posts for Pollinator Awareness Week and I’m going to start with one of my favourite groups of bees – the leaf-cutters of the genus Megachile. The UK has only nine Megachile species recorded, several of which are quite frequently found in gardens.

In my urban garden in Northampton I’ve often encountered the Patchwork leaf-cutter (Megachile centuncularis) this summer. As you can see from the link to Steve Falk’s excellent photographs and description of the species, it’s quite distinctive with a brush of orange hairs that extends right to the tip of the abdomen (see the first picture, though the colour of this can fade with age so it’s not always so apparent). The brush is used for collecting pollen from flowers to take back to provision its nest, which is constructed from leaf segments lining a tubular cavity in old walls, wood or occasionally soil (hence “leaf-cutter” bees). The leaf-cutters (as with 90% of bee species) are “solitary” in the sense that they don’t have a social structure with a communal nest, a queen, etc. It’s the female bees that are solely responsible for nest building; the purpose of the males is simply to mate.

I’ve seen this species visiting my runner beans in the garden and, given their size, they probably pollinate that crop, though not as effectively as bumblebees which are much more abundant.

In the image above you can clearly see the pollen that’s been collected by this bee under its abdomen.

In my garden the Patchwork leaf-cutter is very fond of Lamb’s ear (Stachys byzantina), but I’ve seen it collecting nectar and pollen on a wide range of other plants too.

Pollinator Awareness Week – 13th – 19th July 2015

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Next week has been designated Pollinator Awareness Week (PAW) by Defra and there are events and profile-raising activities going on all over the country.

The motivation behind the PAW is (quote) “to bring attention to the essential needs of pollinators and the simple actions that we can all take to help pollinators survive and thrive”.

With that in mind, next week I intend to produce one blog post a day that highlights, with photographs, a pollinator (or group of pollinators) that I’ve found in my own urban garden in Northampton. The purpose is to illustrate the diversity of pollinators that even a town garden can support, something about their fascinating life histories, and the different ecological requirements of these pollinators that our gardens can provide. For some of them I’ll even discuss the garden crops that they pollinate. First post will be on Monday.

If you, or the group you work with, are doing something for Pollinator Awareness Week feel free to share it in the comments section below.

How can an understanding of plant–pollinator interactions contribute to global food security? A new discussion paper

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A new discussion/review paper that I contributed to has just been published in the journal Current Opinion in Plant Biology. Entitled “How can an understanding of plant–pollinator interactions contribute to global food security?” the paper was written in collaboration with Professor Beverley Glover and her PhD students Emily Bailes and Jonathan Pattrick at the University of Cambridge.

The abstract and highlights are copied below; if anyone wants a PDF of the full paper, send me an email or ask in the comments section.

Abstract:

Pollination of crops by animals is an essential part of global food production, but evidence suggests that wild pollinator populations may be declining while a number of problems are besetting managed honey bee colonies. Animal-pollinated crops grown today, bred in an environment where pollination was less likely to limit fruit set, are often suboptimal in attracting and sustaining their pollinator populations. Research into plant–pollinator interactions is often conducted in a curiosity-driven, ecological framework, but may inform breeding and biotechnological approaches to enhance pollinator attraction and crop yield. In this article we review key topics in current plant–pollinator research that have potential roles in future crop breeding for enhanced global food security.

Highlights:

Animals are globally, and increasingly, important for the improved yield and quality of many crops.
Floral traits are a promising and little explored avenue for the improvement of crop yields.
Work surrounding plant–pollinator interactions can inform us on the best strategies to do this.
Coordinating crop flowering time with key lifecycle stages of pollinators could benefit both crop yields and pollinators.

How good is the evidence base for pollinator declines? A comment on the recent Ghazoul and Goulson Science correspondence

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In a recent issue of the journal Science, Dave Goulson and colleagues presented a review entitled “Bee declines driven by combined stress from parasites, pesticides, and lack of flowers”. This stimulated Jaboury Ghazoul to submit a letter to Science criticising the Goulson et al. paper from a number of perspectives, but particularly the paucity of the evidence base for pollinator declines. Dave and his co-authors robustly responded to that letter, as you might imagine. In some respects this was an unsatisfactory exchange, however, as the focus was largely on agricultural pollinators, rather than pollinators of all plants (including the majority non-cultivated species) and I think that (perhaps with more space?) Dave could have outlined the evidence in more depth.

The most striking statement in Jaboury’s letter was that the “evidence for pollinator declines is almost entirely confined to honeybees and bumblebees in Europe and North America”.

Now, even given the fact that Jaboury was possibly referring specifically to agricultural pollinators, that is a very extreme statement to make. Underlying it is the suggestion that global concerns about declining pollinator biodiversity (a subject I’ve discussed repeatedly on this blog) is underpinned by a taxonomically and geographically thin evidence base. Is that really true? I don’t believe so and I think it’s worth presenting a brief overview of the evidence, not least because Dave’s review and the resulting correspondence is pay-walled at the Science site (though if you Google the titles you might, just might, find copies posted on the web…)

Let me state from the outset that I have considerable respect for both Jaboury and Dave, as individuals and as scientists. I’ve known Dave since we were postgrads together in the early 1990s, and have had occasional contact with Jaboury through conferences and via email. So this isn’t meant to be a criticism of either of them. But I do believe that the evidence for pollinator declines is considerably more robust than Jaboury acknowledges, and even more wide ranging than Dave and colleagues describe in their response (though in fairness, most of the bee evidence was cited in their original review).

Here’s a summary of where I see the evidence base at the moment; it’s not meant to be a full review, by any means, but rather to give a flavour of the taxonomic and geographical breadth and depth of the evidence as it currently stands:

Wild bees (including bumblebees, and solitary and primitively eusocial bees) – significant reduction of abundance and diversity at local, regional and country-levels documented in Britain (Biesmeijer et al. 2006, Ollerton et al. 2014), Holland (Biesmeijer et al. 2006), Europe as a whole (Kosier et al. 2007, the recent IUCN Red List by Nieto et al 2014), North America (Grixti et al. 2007, Cameron et al. 2011, Burkle et al. 2013), South America (Morales et al. 2013; Schmid-Hempel et al. 2013), China and Japan (Xie et al. 2008; Williams et al. 2009; Matsumura et al. 2004; Inoue et al. 2008), and South Africa (Pauw 2007).

Honey bees – colony declines documented in Europe and North America (see reviews by NRC 2007, Potts et al. 2010) and evidence that global demand for honey bee pollination services is outstripping supply (Aizen and Harder 2009).

Hoverflies (Syrphidae) – diversity declines documented in Holland and Britain (Biesmeijer et al. 2006).

Butterflies and moths – diversity and abundance of Lepidoptera has declined in the UK (Gonzalez-Megias et al. 2008, Fox 2013), whilst in North America some 50 species are IUCN criteria Red Listed and there is particular concern about the iconic Monarch butterfly. Likewise a significant fraction of butterflies in other parts of the world are of conservation concern, e.g. Southern Africa, Australia, and Europe.

Flower-visiting wasps – reduction in country-level diversity in Britain (Ollerton et al. 2014).

Birds and mammals – the major vertebrate pollinators have recently been assessed at a global level by Regan et al. (2015) using IUCN Red List criteria. They concluded that: “overall, pollinating bird and mammal species are deteriorating in status, with more species moving toward extinction than away from it. On average, 2.5 species per year have moved one Red List category toward extinction in recent decades, representing a substantial increase in the extinction risk across this set of species”.

Of course a number of the studies cited above have shown that some species are doing better than others and a proportion of the taxa they have assessed are stable or even increasing in abundance (including managed honey bee colonies in some parts of the world). But the current evidence base, as I see it, is pointing towards significant declines in pollinator abundance and diversity at multiple spatial scales across all regions that have so-far been assessed with any rigour, for a wide range of taxa.

I’m happy to receive comments on this topic, particularly pointing me to major sources of evidence that I’ve not covered, or if you disagree with my conclusions.

References

Aizen and Harder (2009) The global stock of domesticated honeybees is growing slower than agricultural demand for pollination. Current Biology 19: 915–918.

Biesmeijer et al. (2006) Parallel declines in pollinators and insect-pollinated plants in Britain and the Netherlands. Science 313: 351–354.

Burkle et al. (2013) Plant-pollinator interactions over 120 years: Loss of species, co-occurrence, and function. Science 339, 1611–161.

Cameron et al. (2011) Patterns of widespread decline in North American bumble bees. Proc. Natl. Acad. Sci. U.S.A. 108: 662–667.

Fox (2013) The decline of moths in Great Britain: a review of possible causes. Insect Conservation and Diversity 6: 5–19.

Gonzalez-Megias, A. et al. (2008) Changes in the composition of British butterfly assemblages over two decades. Global Change Biology, 14: 1464-1474.

Grixti (2009) Decline of bumble bees (Bombus) in the North American Midwest. Biol. Conserv. 142, 75–84 (2009).

Inoue et al. (2008). Displacement of Japanese native bumblebees by the recently introduced Bombus terrestris (L.) (Hymenoptera: Apidae). J. Insect Conserv. 12: 135–146.

Kosior (2007) The decline of the bumble bees and cuckoo bees (Hymenoptera: Apidae: Bombini) of Western and Central Europe. Oryx 41, 79–88.

Matsumura et al. (2004) Invasion status and potential ecological impacts of an invasive alien bumblebee, Bombus terrestris L. (Hymenoptera: Apidae) naturalized in Southern Hokkaido, Japan. Glob. Environ. Res. 8, 51–66.

National Resource Council (2007) Status of Pollinators in North America. National Academies Press, Washington, DC.

Nieto et al. (2014) European Red List of Bees. Publication Office of the European Union.

Ollerton et al. (2014) Extinction of aculeate pollinators in Britain and the role of large-scale agricultural changes. Science 346: 1360-1362.

Pauw (2007) Collapse of a pollination web in small conservation areas. Ecology 88: 1759-1769.

Potts et al. (2010) Declines of managed honey bees and beekeepers in Europe. Journal of Apicultural Research 49: 15–22.

Regan et al. (2015) Global Trends in the Status of Bird and Mammal Pollinators. Conservation Letters DOI: 10.1111/conl.12162

Schmid-Hempel et al. (2013) The invasion of southern South America by imported bumblebees and associated parasites. Journal of Animal Ecology 83: 823–837.

Williams et al. (2009) The bumblebees of Sichuan (Hymenoptera: Apidae, Bombini). Syst. Biodivers. 7: 101–189.

Xie et al. (2008) The effect of grazing on bumblebees in the high rangelands of the eastern Tibetan Plateau of Sichuan. Journal of Insect Conservation 12: 695–703 (2008).

Urban bee diversity – a new study

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Over the past couple of years I’ve mentioned urban pollinators, and specifically the work of my PhD student Muzafar Hussain Sirohi, several times; for example here and here. Muzafar is currently finishing off the writing of his thesis, and during that time he’s also managed to publish the first paper from the study.

We are really pleased with this paper because not only is it the product of a lot of hard work to systematically sample and identify the bees, but the results are really exciting: Muzafar has shown that the centre of Northampton is home to a more diverse set of bee species than expected. In fact at least 50 species of bees are thought to live within a 500m radius of All Saints Church, which is significantly more than are found in the nature reserves at the edge of the town.

Muzafar’s work involved surveying the small gardens, road verges, traffic islands, and other patches of plants in the urban centre of Northampton. These areas provide important nectar and pollen sources for the bees, whilst old stone walls and bare soil offer opportunities for nesting sites. This community of bees includes one nationally rare Red Data Book species called Coelioxys quadridentata that is known from rather few sites.

Our estimate of about 50 species of bees is certainly too low because we focussed on the more neglected groups of bees and didn’t include the social bumblebees. The true figure is likely to be over 60 species, a remarkable number given the small area surveyed.

As I’ve discussed many times on this blog, pollinators such as bees are hugely important both ecologically (most plants require them for reproduction) and economically (much of our food production relies directly or indirectly on pollination by animals). However a significant proportion of bee species in the UK are declining in abundance, and some have gone extinct. Understanding how these bees are distributed across the landscape, including urban areas, is crucial to the conservation of such pollinators in a rapidly changing world. The project therefore has implications not only for conservation of biodiversity, but also food security, given the number of urban gardeners who grow their own food, and the ability of many bees to travel significant distance from urban to rural areas.

The research is published in the international, peer-reviewed Journal of Insect Conservation. The full reference (with a link to the abstract) is:

Sirohi, M.H., Jackson, J., Edwards, M. & Ollerton, J. (2015) Diversity and abundance of solitary and primitively eusocial bees in an urban centre: a case study from Northampton (England). Journal of Insect Conservation DOI 10.1007/s10841-015-9769-2

If anyone would like to receive a PDF of the paper, please leave a comment below or drop me an email: jeff.ollerton[at]northampton.ac.uk

Should biodiversity scientists be campaigners and polemicists?

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Earlier this week I attended a two day research funding workshop intended to develop initial project ideas to address evidence gaps in the recent National Pollinator Strategy. It was a productive meeting from which will hopefully emerge some important, focused science. As is so often the case at scientific meetings, many of the most interesting conversations occurred after the end of the day’s formal work, in the pub. There was a little bar stool criticism of some of the recent published work on the effects of neonicotinoid pesticides on pollinator health, and specifically whether or not researchers engaged in this kind of controversial science should be polemicists, stirring up controversy, or even activists with particular agendas that they wish to promote.

Whilst I agree that there is a difficult line to walk between scientist as campaigner and scientist as neutral presenter of facts, I also think that polemicist/activist is quite an admirable position for a scientist to take in many ways, as long as the rhetoric is backed up by sound science. It’s also brave given that perceptions of scientists can change the likelihood of their research being funded or even published – reviews and reviewers are rarely as objective as we would like to believe.

So should scientists, and specifically those, like myself, who are engaged with biodiversity science in all its myriad forms, be also engaged in campaigns and polemics? Is this what wider society wants from its scientists? How do other scientists feel about this? I’d really be interested in your views.

In this blog I’ve made no secret of the fact that I take certain positions on subjects such as the impact of poorly conceived development on nature reserves, the fallacies of political spin, and future developments in UK nature conservation. Those are positions that are predicated as much by my personal motivations as an “environmentalist” (a term I don’t like but which is widely understood and will do for now) as they are by my professional role as a university scientist who does research and teaches. I am not a neutral observer, though I hope that I’m an objective one.

There’s a lot of questions that can spin off from reflecting on the role of biodiversity science and scientists in the modern age, which I don’t have time to properly explore but which I hope will emerge in the comments. I was prompted to write this by a really interesting post by Joern Fischer over at the Ideas for Sustainability blog entitled “Losing humanity and other questions science doesn’t ask“. In it Joern develops some ideas about the kind of science that we should be doing “for it to be of use in the sense of creating a better, more sustainable world”. I’d add that what is important is not just the science that we do, it’s how we present that science (the passion and the story telling) to a range of audiences, and also the personal positions we take on the issues that the science illuminates.