Just the facts, Ma’am

By Athayde Tonhasca

The biodiversity crisis is the main theme of a recent assessment by The Joint Nature Conservation Committee (JNCC), the UK’s government advisory body on conservation (Nature Positive 2030 – Evidence Report). Among many interesting facts and statistics, we are told that over 40% of UK species are in decline, a figure extracted from the State of Nature 2019 report.

A 40% reduction in species abundance is an alarming number; it signals a substantial impoverishment of our natural world. This figure was calculated from the abundance data on 697 species of birds, mammals, amphibians, reptiles, butterflies, and moths. Lepidoptera (butterflies and moths) contributed most: 499 species (about 71%). The focus on a single group may seem disproportionate, but Lepidoptera makes up about 77% of all the British fauna taken into account in the report. In fact, about 90% of all species of animals in the world are insects, therefore assessments of the state of nature require a finger on the pulse of insect populations.

There are more insect species (light grey, outer circle) on Earth than all other animal groups combined © Dow, J.A. et al. 2018. Drosophila as a model for neuroendocrine control of renal homeostasis

From 1970 to 2016, the 499 butterflies and moths experienced average declines of 16 and 25%, respectively. This sample represents about 20% of all Lepidoptera and 2% of all insects recorded in Britain. The true contribution of Lepidoptera to our entomological fauna is likely to be smaller because the diversity of certain groups such as parasitic wasps is believed to be greatly underestimated. 

The number of Lepidoptera species analysed is relatively small, but that’s not necessarily a problem. We can draw correct conclusions about much bigger populations the same way responses from a few hundred people can be used to accurately predict the intentions of millions of voters. All it takes is representative sampling. The question then is whether trends from a sample of butterflies and moths reflect the insect fauna; in other words, can we infer overall insect decline if Lepidoptera species are declining?

The best way to answer this is to look up what’s happening with other insects. Some studies have measured biomass or area of occupancy instead of numbers because it’s hard to count insects. Whatever the methodology, numerous reports have shown increases, decreases or no changes for solitary bees, social bees, social wasps, aphids, dragonflies and freshwater invertebrates, among other groups. Similar hotchpotches have been reported for continental Europe and America. So the body of evidence is far from uniform. 

Over 30 years, there was no significant decline in insect biomass at three out of four sites in England
© Shortall, C. et al. 2009. Insect Conservation and Diversity 2: 251 – 260

Mixed results do not refute the gravity of the problem; many populations of insects and other animals are decreasing in the UK and elsewhere. And the relentless loss of habitats worldwide is likely to make things worse. But unqualified generalisations about insects’ decline are not supported by the information we have. 

Trends of terrestrial (brown) and freshwater (blue) insect biomass from 166 long-term surveys. Bar thickness indicates credible intervals (±80, 90, and 95%), and overlaps with the dotted line mean statistically non-significant results. © Van Klink, R. et al. 2020. Science 368: 417-420

The State of Nature report is an exceptional compilation of information, reflecting the enviable tradition of biological recording in the UK. But the abundance data set covers a segment of the British terrestrial fauna; it is not representative of all insects, and does not contain important groups such as spiders – which comprise more species than birds – other arthropods, molluscs, etc. (bacteria, protozoa and other life forms are traditionally excluded from biodiversity assessments). The analysis was about terrestrial animals; it did not address plants and fungi, which make up the bulk of the planet’s biomass, or the aquatic fauna. 

‘Forty percent of all British species’ is an unpolished generalisation, which may have been used for the sake of brevity. But soundbites underplay successes: for example, agri-environmental initiatives have reduced or reversed declines of some plants and insects in Europe. Soundbites also oversimplify and distort, intensifying the magnitude of a problem. This harms credibility and promotes cynicism. 

In 2006, news about the imminent extinction of the honey bee hit the headlines. The media warned us about failed crops, famine, and the very survival of mankind. Hardly a day would go by without a new scare. There were protests, marches, petitions and parliamentary motions; the announced calamity inspired books, films and documentaries. However, the authors of those jeremiads hardly ever mentioned that honey bee declines were mostly American and European problems; worldwide, the number of bee hives and beekeepers had been growing steadily, so extinction was not remotely likely. Eventually fear fatigue settled in, and the ‘honey bee demise’ has disappeared from the news. Except from some anti-environmentalist sources, who cite the episode as proof of conservationists’ alarmism, exaggerations and penchant for half-truths.

In this age of “alternative facts” and politically inspired scepticism, scientists and other experts should go out of their way to avoid erosion of trust by adhering to data, explaining caveats and acknowledging uncertainties. Reasonable people understand that nature is complicated, and specialists often can offer partial explanations.

By an unfortunate coincidence, 40% is the percentage of insect species threatened with extinction globally, according to a widely publicised but methodologically flawed and debunked paper. So “40%” may very well become the mystic omen of biodiversity calamity.

‘We need to be realistic in what science can offer and the speed in which developments take place. This needs not only be communicated to the general public but also to news media. They sometimes unthinkingly write on science results without proper context and without the nuances and limitations that are essential for a correct understanding and interpretation of scientific results’. Christiaan Vinkers. Image by Frederick Burr Opper, 1894 (public domain)

Sunflower riches

Until recently sunflowers for me conjured up either images of the ever-impressive backdrops to the Tour De France, or the work of the enigmatic Dutch artist Vincent Van Gogh when he lived in Arles.  Lately however I’ve seen so many of them in Scotland that my ‘French connection’ has been, if not broken, certainly lessened.

Provence is a European heartland for the sunflower. Although when I say sunflower, I should quickly acknowledge that there are actually many, many varieties out there.  On closer inspection, rather like Van Gogh’s sunflower paintings, there are more sunflowers than first meets the eye.

A few months ago I was returning from Dundee having enjoyed a stroll around the Ninewells Community Garden, my route back to Perth took me via Errol.  Here I came across several field margins given over entirely to a sea of glowing sunflowers.  

That wasn’t the first time this summer that I’ve come across a field margin awash with these yellow beauties, so beloved of pollinators. In Islay I stumbled across more striking field margins around Balinaby near Loch Gorm. They are popular as they offer so much for bees and other pollinators as well as bringing a smile to passers-by.

Van Gogh can’t take sole credit for making sunflowers popular, but he certainly elevated their status. His painting ‘Vase with15 Sunflowers’ sold for several millions  in 1987 but it is was only one of several paintings made by the Dutch master that feature these bold and unmistakable yellow flowers. He loved sunflowers so much that he made a series of paintings featuring this striking flower one summer week in 1888 when he was forced indoors for several day by poor weather.  Less than a decade later Gustav Klimt also produced a notable painting featuring the sunflower. 

I doubt Van Gogh ever made it to Clydebank but if he was dropped into Melfort Park this summer he would have spied a few of his beloved sunflowers. The Melfort Park sunflowers were large enough to test my tip toes when it came to photographing them, but not quite the giddy 30 feet or so that the world’s largest sunflower grew to. 

But size isn’t everything when it comes to sunflowers. Regardless of height they certainly do their bit for bees crammed as they are with a rich harvest of pollen and nectar. So as well as enchanting children with an impressive spurt of growth to an absurd height the sunflower can be a fine introduction for youngsters seeking to watch pollinators go about their business.

The flower head of the sunflower is heliotropic (meaning it can follow the path of the sun). This was something that the poet William Blake noted in his ‘Ah, Sunflower!’

Ah Sun-flower! weary of time,

Who countest the steps of the Sun:

If all of this talk of sunflowers entices you to try growing your own then fear not, there is a lot of encouragement out there. The excellent Friends of the Earth pollinator pages recommend two types of sunflower which also feature on the Royal Horticultural Society’s Perfect for Pollinators plant list – the common sunflower (Helianthus annuus) and the cucumber leaf sunflower (Helianthus debilis).

Given that mixing your variety of sunflowers means you could have flowering versions from June through to October there is much fun to be had.  

You won’t reap the financial rewards that await the owners of Van Gogh or Klimt’s masterpieces, but you will be making space for nature and giving bees in particular a rich helping hand.

Further information:

Find out more about the world of heliotropic plants

Alys Fowler talks sunflowers in The Guardian @

Judicious poisoning

By Athayde Tonhasca

Bright lemon-yellow globeflowers (Trollius europaeus) bring a bit of gaiety and colour to damp and shady areas such as woodlands, river banks, upland pastures and meadows across Scotland, northern England and northern Wales. These globe-shaped flowers are unusual: they have tightly-closed sepals that encase the true petals, which have nectaries at their base. They look like big yellow buds at the top of long stems, and rarely open fully. 

Globeflowers © BerndH, Wikipedia Creative Commons

This type of arrangement does not encourage most pollinators because they have hard times getting to the pollen and nectar. But one group of insects doesn’t mind: the root-maggot flies of the genus Chiastocheta, of which five species have been recorded in the UK. These are anthomyids – from the family Anthomyiidae, a name derived from the Greek anthos (flower) and myia (fly). The less flattering ‘root-maggot flies’ comes from the fact that their larvae grow inside stems or roots of various plants.

A fly investigating a globeflower © Uoaei1, Wikipedia Creative Commons

Male and female flies wiggle their way towards the flower’s nectaries. Once inside, they feed and mate, pollinating the flower in the process. Male and female are hairy, so pollen gets attached all over their bodies. But females need more than food: as true root-maggot flies, they deposit their egg on the carpels (the flower’s seed-bearing structures), and the resulting larvae develop and feed on the seeds. So Chiastocheta spp. are simultaneously pollinators and seed predators.

A female Chiastocheta setifera © Janet Graham, Wikipedia Creative Commons

Insect pollination is a mutualistic relationship, where each partner benefits from the other: the pollinator gets food or some other reward, while the plant gets fertilized. Another way of seeing it is as reciprocal exploitation: flowers produce as little pollen and nectar as necessary to attract pollinators, and insects would take away as much of those resources as flowers allow. So flowers must maintain a fine equilibrium between attractiveness and the metabolic costs of producing pollen and nectar. In the case of globeflowers, there is the added burden of seeds lost to root-maggot flies.

Seed head of a globeflower: cosy growth chambers for root-maggot flies © Ivar Leidus, Wikipedia Creative Commons

To avoid over-exploitation by Chiastocheta spp., globeflowers resort to chemical defence. Like other species of the buttercup family (Ranunculaceae), globeflowers are slightly poisonous: they produce compounds that discourage plant feeders. One of these chemicals, adonivernith, plays a regulatory role in the pollination/seed parasitism balance. Adonivernith is spread all over the plant, but concentrates in the flowers (it contributes to their bright yellow coloration). If the number of larvae growing inside the flower increases, the amount of adonivernith also increases, eventually inhibiting larval growth and feeding. It’s the globeflower’s way to regulate the loss of valuable seeds for the sake of pollination: when flies become a liability, they are curtailed by intoxication.  

Male flies are also important for maintaining the right balance between pollination and seed predation. They are smaller and transport less pollen than females, but make about twice as many flower visits during the same time period. Male pollination incurs no seed losses, so they help reduce the pressure on their host. 

In nature, it’s often a matter of harmonizing antagonistic interests.   

Utrecht’s new treaty

Perhaps not since 1474, when the Treaty of Utrecht signalled the end of the Anglo-Hanseatic War, has the ancient city of Utrecht been so prominently in the news. I exaggerate of course, but the war on biodiversity loss and climate change has thrust this old university town into the public eye once more. Today bus shelters rather than naval power are amongst the weapons of choice.

In a bold and innovative move to help pollinators Utrecht city council has teamed up with partners to transform over 300 bus stops into ‘bee stops’. This has been achieved by giving the roofs of the adjacent bus shelters a make-over which includes pollinator-friendly sedum planting.

There is a climate change mitigation bonus beyond this as the plants have the capacity to capture fine dust particles and store rainwater.  And we shouldn’t overlook the health and wellbeing angle as the additional greenery in the city makes for a visually more appealing urban view.

Why has Utrecht gone down this route?

The city, the fourth largest in the Netherlands, has declared an intention to deliver a circular economy and is striving to reach a net-zero position as quickly as possible. The buses that call at these bus stops are increasingly electric and by 2028 Utrecht’s administrators predict they will have a ‘clean’ urban transport system.  

Not surprisingly perhaps, the energy for these buses taps into the numerous windmills and turbines that pepper the local landscape.  Even the wildflowers and grasses on the roofs of the city bus shelters are watered by a team using electric vehicles. By using sedums widely in the planting schedule that watering is effectively minimised and supplements the service offered by rain.

Much of the progress here leans heavily on the expertise and drive of the EIS Insect Knowledge Centre. They have monitored the bus stops and made an inventory of 30 of the shelters to see just which insects are making use of this new resource.

The EIS team visited their chosen shelters twice between May and August and counted a total of 8 bee species and 5 hoverfly species. It’s important to bear in mind that a very dry and warm summer will contribute to dry roofs and late blooming of flowers. This, and the fact that the sedum roofs are relatively small, helps account for the smallish numbers (the Netherlands does indeed have around 360 species of bee).

The Utrecht project was born out of seizing the moment. When the local authority realised that 481 of its shelters needed to be renewed they saw a moment of opportunity and elected to cover 316 of them with a sedum roof. It’s a low maintenance solution to tackle issues around potentially damaging rainwater incidents, pollinator pressures and air quality concerns. 

Mind you there was nothing low maintenance about the survey challenges for John Smit and Tjomme Fernhout who often found themselves at the end of a ladder waving a large inset net around to collect samples.

The role of EIS is important to Utrecht’s council in helping to take stock of the success, and challenges, behind bus shelter greening.  Monitoring and research are essential if we acknowledge that not everything succeeds first time.  

Given that the roofs are in an urban setting and that many bees look to feed near their nesting site the smaller than anticipated pollinator numbers is perhaps not such a surprise. It’s also worth bearing in mind that a lack of bloom wasn’t ideal, nor have three consecutively particularly dry spring and summer seasons helped.  However, such problems – which the EIS team picked up – can be tackled in coming years with a little more watering than initially anticipated, and perhaps a wider mix of plants. The council has tweaking the composition of plants on some bus stop rooftops in hand already.

187 km to the north of Utrecht lies the city of Groningen which revels in the strapline ‘Nothing surpasses Groningen’. As far as cycling is concerned that is a fair claim. But the city does much more than encourage that healthy and booming form of transport to adapt to the challenges of climate change. For example, the intriguingly-titled promote green facades is part of their forward-thinking climate policy. The council and major employers have worked hard to make building facades in the city greener. Where walls were once uniformly harsh brick and concrete they are increasingly vibrant green vertical gardens. That’s another step along the road to cleaner air and better flood management systems.

Groningen and Utrecht are all fine urban examples. They fall within a nation where, since 2015, the national government has been committed by law to cutting emissions and ensuring greater climate change mitigation efforts are enshrined in law. Back in 1953 1,835 people died in a catastrophic flood. It’s instilled a belief that prevention is better than tackling any aftermath.

What’s happening in the Netherlands is now gaining momentum in other European cities.

Nature based solutions are a win-win. The introduction of porous pavements, restoration of wetlands, and increasingly greening of our cities not only slows down surface water, it connects people with nature and creates more pleasant urban environments. And for wildlife all of the above is a triumph.  For pollinators in particular Utrecht’s new treaty promises to help address many issues they face.

All images courtesy of Tjomme Fernhout (except the one of him swinging the net)

FURTHER READING:

Find out more about the Utrecht bus shelter project

Find out more about the EIS knowledge centre

Quietly riding off into the sunset

By Athayde Tonhasca

In 2019, four American and Australian enthusiasts set off to Indonesia on a bold mission: to find the Wallace’s giant bee, Megachile pluto. This bee was first described in 1858 by naturalist, explorer and co-author of the theory of evolution Alfred Russel Wallace (1823-1913). After its official discovery, the Wallace’s giant bee – aka the giant mason bee – disappeared from the records and was thought to be extinct until it was rediscovered in 1981. The bee vanished again for the next 37 years, until the 2019 search expedition: the team found and filmed the Wallace’s giant bee. 

A female Wallace’s giant bee and a worker honey bee © Abalg, Wikipedia Creative Commons

Denizens of tropical jungles are expected to be elusive and mysterious, but the Wallace’s giant bee lives up to its name: it is the largest bee on Earth. If a bee of this size can go unnoticed and believed to be extinct for most of its recorded history, it’s not surprising that less spectacular species can go unrecorded for a long time. The bee Pharohylaeus lactiferus, sighted this year in Australia, was previously seen in 1923; the bone skipper fly (Thyreophora cynophila) was first described in 1794, remained undetected until 1850, then disappeared again until its rediscovery in Spain in 2009. There are many other examples of what is known as ‘Lazarus fauna’: species believed to be gone, only to ‘come back from the dead’ when rediscovered.

Extinct… Not. The bee P. lactiferus (© Natural History Museum, Wikipedia Creative Commons) and the fly T. cynophila (© Carles-Tolrá et al. 2011, Boletín de la Sociedad Entomológica Aragonesa 48: 217‒220)

Small size and secretive lives are only partially responsible for the patchy or absent recording of insect species: rarity is a huge factor. 

Rarity is one of the quirks of life on Earth; for almost every ecological community (a group of species living in the same location), most species are represented by few individuals, and most individuals belong to a few common species. Reams of paper and gallons of ink have been spent trying to explain why it is so, with no consensus so far. Whatever the explanation, there are many rare species and only a few common species.

Relative species abundance of beetles sampled from the river Thames © Aedrake09, Wikipedia Creative Commons

Rarity is a big headache for conservationists because for most species it is difficult to say with confidence they are declining or no longer present (i.e., extinct): some of them may just have been overlooked because of low numbers or obscure existences. The International Union for Conservation of Nature (IUCN) considers a species extinct when ‘there is no reasonable doubt that the last individual member has died’. This is a sensible approach, but ‘no reasonable doubt’ is a tall order for insects. So it is not surprising that the IUCN has registered fewer than 50 extinct insect species worldwide, and that the list of 23 American species declared extinct last month by the Fish and Wildlife Service does not include any insects: conservationists just don’t have enough data.

The Wallace’s giant bee may be a naturally rare species, but much of its habitat has been wiped out and replaced by crop fields and palm oil plantations. So it may very well become extinct. But if it does, it will take us many years to know. 

These uncertainties are vexing and underplay the trouble faced by insects. The only way to deal with the problem is by keeping a finger on the pulse of populations to notice signs of decline, and this is done by meticulous, long-term monitoring. Thanks to the work of enthusiastic and determined volunteers, we know that in Britain at least thirty species of larger moths have become 40% less abundant in the last 10 years, on average the distribution of 112 species of solitary bees have contracted between 1980 and 2013, and over 40% of dragonfly species have increased since 1970. As incomplete and tentative as these figures are, they reflect Britain’s long tradition of biological recording. We have only a nebulous idea of what’s happening in most of the world. 

Serendipitous rediscoveries of species thought to be extinct are heart-warming, but they are far and between. Considering the relentless shrinkage of natural habitats across the globe, species vanishings are more likely to be permanent. By monitoring, we can raise the alarm and trigger action. If we don’t monitor, inconspicuous species, the very fabric of biodiversity, may slip quietly into oblivion. 

The Franklin’s bumblebee (Bombus franklini), last seen in the western United States in 2006: perhaps gone forever © Project Noah

Garnock’s Buzzing

In conversation with … Lorna Cole of SRUC, and Gill Smart of the Scottish Wildlife Trust, working together on Garnock’s Buzzing.

Garnock’s Buzzing is one of 28 projects being undertaken by Garnock Connections, a landscape partnership funded by the National Lottery Heritage Fund.  The project will enhance, improve and promote both natural and cultural elements of the area around the River Garnock. As Lorna and Gill explain, great strides have been made for people and pollinators through targeted habitat creation and citizen science in the Garnock Connections study area. 

Why would you say projects like Garnock’s Buzzing are important?

Since the end of the Second World War it is reckoned that we have lost 97% of our wildflower meadows. As a result we are losing the joy of seeing an explosion of colour during the summer months, and leaving some of our most precious bees, and other pollinators short on food and habitat. Through the Garnock’s Buzzing project we aim to do our bit to change this and make the Garnock Connections landscape a haven for pollinators.

What sort of projects have you developed?

Well, where to begin? There have been so many successful elements that the list is quite lengthy. So far, we have actively involved almost 100 school pupils and trialled different cutting regimes to identify pollinator friendly verge management practices.   We’ve also put up around a dozen information signs, created many new meadows, put up 14  bee hotels or bee banks and created 0.9ha of bare earth habitat for mining bees.

The white rectangle to the top right of this image is a wonderful wildflower meadow in Irvine

Where can people go to see these new meadows for themselves?

Meadow areas have been established on both Irvine Beach Park and Stevenston Beach Park, giving large numbers of people access to enjoy the flowers and insects.

Lochshore in Kilbirnie is another large public open space with an area given over to wildflowers. 

Which element are you, Lorna, most pleased about with your Garnock’s Buzzing work?

Garnock’s Buzzing kicked off just about the same time as COVID 19. With the country in lockdown we were no longer able to undertake the visits to schools we had originally planned. To help teachers and pupils alike SRUC developed a wobbly apple experiment to highlight the important role that insects play in pollinating crops. This allowed us not only to engage with children in the Garnock Connections area, but also throughout Scotland.

I’ve seen the stunning meadow near the boating pond at Irvine Beach Park. That’s a fantastic resource for pollinators. Can you tell us a little about how that area was created and how you manage it?

This was collaboration between the Scottish Wildlife Trust and North Ayrshire Council, made possible by Garnock Connections.  In autumn 2020, a tractor was used to lightly plough the ground and mechanically sow a wildflower mix containing both annual and perennial species.  The annuals flowered profusely in summer 2021 and we could see the leaves of future perennials developing.  The trick to keep the flowers blooming is to cut in autumn and remove the clippings while allowing lots of seeds to fall to the ground.  We plan to use some of the clippings, which will still contain plenty of seeds, to start new meadow areas nearby.

If anyone reading this wants to help with Garnock’s Buzzing and get involved in projects, what should they do?

Email Garnock Connections Natural Heritage Officer, Neal Lochrie neal.lochrie@rspb.org.uk or visit their website https://www.garnockconnections.org.uk/

Find out more:

Garnock’s Buzzing is led by SRUC, the Scottish Wildlife Trust and Buglife.

Garnock’s Buzzing

Note:

The Green Infrastructure Fund is part of the Scottish Government’s current European Regional Development Fund programme, which runs through to 2023.  This is one of two ERDF Strategic Interventions led by NatureScot – the other is the Natural & Cultural Heritage Fund.

You can follow the European Structural Funds blog for ESF activities, news and updates. For twitter updates go to @scotgovESIF or use the hashtags #ERDF and #europeanstructuralfunds

Hazardous neighbours

By Athayde Tonhasca

Since their discovery in the 1800s, viruses have confounded scientists and philosophers because they raise questions about the very nature of life. Viruses consist of genetic material (DNA or RNA) coated with protein, and that’s about it. They draw a blank on six of the seven fundamental indicators of a living organism: movement, respiration, response to stimuli, feeding, excretion, and growth. They do better on the seventh – reproduction – but to a point. They do multiply, although only by seizing the cell machinery of a host to make copies of themselves. But viruses have one essential asset: genetic heredity, which allows them to evolve. So viruses are considered living or non-living, depending on who you ask. That’s why they have been defined as ‘biological entities’, ‘at the edge of life’, and ‘existing at the border between chemistry and life’. Considering the viral upheaval that hit us in 2019, we could settle for the definition offered by immunologist and writer Peter Medawar (1915-1987): ‘a virus is a piece of bad news wrapped up in protein’ (although you may be surprised to hear that viruses are fundamental to life on Earth). 

Bacteriophages (viruses that infect bacteria) mobbing a bacterium © Graham Beards, Wikipedia Creative Commons

Living or non-living, viruses act as intracellular parasites, and insects certainly are not immune to them. Some viruses are used as biological control agents against agricultural pests and vectors of diseases, but others are harmful to insects that benefit us, such as the European honey bee (Apis mellifera).

Beekeepers have to deal with a number of pests and diseases, including RNA viruses with ominous names such as acute bee paralysis virus, black queen cell virus, Israeli acute paralysis virus and slow bee paralysis virus. Among this disagreeable family, the deformed wing virus (DWV) is particularly damaging to apiaries in Europe and other temperate zones; DWV variants are among the world’s most widely distributed and contagious insect viruses. Infections are generally detected in workers with shortened abdomens and deformed or missing wings.

A honey bee with deformed wings © Shawn Caza, Wikipedia Creative Commons

The virulence (i.e., the capacity for causing disease) of DWV and other viruses is dramatically heightened by another honey bee scourge: the varroa mite (Varroa destructor). This pest transferred – ‘host jumped’ – from the Asian honey bee (Apis cerana) to the European honey bee in the early 1900s, and since then it has caused havoc to the beekeeping industry around the world. The mite depletes bees’ reserves by sucking up their fluids, and it also injects virus particles into its hosts. The synergistic combination of varroa mite and DWV has had a devastating impact on managed honey bees, with sharp increases of overwintering mortality and colony losses.

A honey bee pupa infested with the varroa mite, a vector of DWV. Image in the public domain

Harm to honey bees is bad enough, but DWV can do much worse. It has been found in bumble bees, mason bees, mining bees, wasps and at least one species of ant and one species of beetle. We don’t know how badly DWV affects most of these non-Apis hosts because infections are typically asymptomatic. Hosts’ immune system may suppress viral replication, or the virus may just be picked up accidentally by feeding on pollen or nectar. But some bumble bees are not so lucky: they die or develop wing deformities when infected by DWV. 

Bumble bees are not parasitized by varroa mites, so they get infected by DWV some other way. The most likely route is through feeding; bumble bees pick up the virus when collecting nectar or pollen from a flower that was visited by a diseased insect – probably a honey bee. Direct virus transmission from honey bees to bumble bees has not been demonstrated, but there is plenty of circumstantial evidence to suggest it: honey bees deposit viruses on the flowers they visit, and apparently viruses occur mostly on flowers near apiaries; bumble bee rates of infection are higher when honey bees are present and almost non-existent when honey bees are not around. 

A dangerous encounter: a bumble bee and a honey bee sharing a flower © Uroš Novina, Wikipedia Creative Commons

Putting all the clues together, flower sharing seems to be responsible for honey bee to bumble bee ‘pathogen spillover’, which happens when a pathogen transfers – or ‘spills over’ – from a reservoir species to another receptive species. There is much to be discovered about bee viruses and hosts’ responses, but what we know suggests we should keep honey bees apart from bumble bees and other pollinators, especially when rare or endangered species are involved. That’s one of the reasons why some countries such as Australia and the United States restrict beekeeping in national parks and other conservation areas.  

Honey bees are incredibly important and valuable: but they can also be a health hazard to fellow pollinators. Awareness of this risk can help us manage bee hives and pollinators’ habitats, for example by planting more flowers throughout the growing season so that the likelihood of spillover is reduced. Which is good for honey bees, for wild pollinators, and for us.

The apple bumble bee

Given the popularity of apples in Britain you could be forgiven for expecting the apple bumble bee (Bombus pomorum) to be one of the species found here. However, think again. The Bumblebee Conservation Trust’s website records sightings on the south coast in the mid-1800s, whilst the equally highly-reputable NBN Atlas, which holds more than 198 million UK species records, has only two mentions for the apple bumble bee. They are both historic sightings.

The apple bumble bee (Bombus pomorum) © Picto Sauvignet louis didier, Wikipedia Creative Commons

Dave Goulson’s highly regarded and hugely enjoyable ‘A Sting in the Tale’ makes reference to the apple bumble bee as maybe having never been resident in the UK. The four specimens known were, he explains, found on the dunes near Deal (Kent) in 1865. And whilst he reckons the sightings likely to be genuine, given the stature of the recorder and the existence of specimens, no further records have been confirmed in the 150 plus years since.

We can surmise with some confidence that this isn’t down to under-recording. Given the long-standing and very efficient history of studying bumble bees on these shores it would hardly be missed. As things stand you need to visit central and eastern Europe to catch a glimpse.

In 1999 Lithuania marked several important events on postage stamps. The 400^th anniversary of the printing of the first book in the Baltic state was one, two bumble bees which featured on their red list – one being the apple bumble bee – were also of sufficient national interest to feature. 

Bombus pomorum has seen its range alter on the continent. It hasn’t been recorded in Denmark, Spain, or Belgium in recent years. Unlikely to be found near the coast, it is fond of flowers such as thistles, and as agriculture continues to intensify, and so-called weeds are marginalised, it is now viewed as being in an unfavourable or vulnerable condition within its current range.  Additionally, the species is considered to be at risk due to the threat of climate change.

That said there was interesting news recently when two specimens were collected in Siberia.  This was a first for this species, although it could be that rather than expanding its range it had simply gone unnoticed previously.

Apple blossom in the Battleby orchard. ©Lorne Gill/SNH.

We can’t always take a species name as definitive or too literally. Why was the apple bumble bee so named?  That may be lost in time. Sometimes even well known names can be plain misleading, rather like the Koala Bear (which isn’t a bear) or, stepping beyond nature, the Hundred Years War (which lasted 116 years). In the case of the apple bumblebee the name almost suggests it specialises exclusively on apple blossom, which is unlikely given the very limited flowering period.

On Steven Falk’s splendid Flickr Album (a hugely informative and enjoyable resource) he has images of Bombus pomorum and says this: “Only ever known in Britain from Deal Sandhills and adjacent Kingsdown area (three males thought to date from 1857 and a queen from 1864). Considered by some to be a windblown vagrant or temporary colonist rather than a permanent resident, though the Kent population might also have represented a relic population from the pre-agricultural revolution landscape.”

It is estimated that we import around 476,000 tonnes of apples, a figure perhaps made higher than expected because of an apparent 36% decline in the number or orchards here since the mid-1980s. But as a fruit that can be easy to store, is a key element of many ciders, and in a nation where apple pies and apple crumbles are popular winter-warmers, their popularity shows no signs of waning.

In our own apple industry names such as Cox, Smith and Bramley are indelibly linked to our appreciation of apples. The Bramley apple alone, for example, is produced in impressively huge numbers (reckoned in some quarters to be around 83,000 tonnes each year).

There have been many studies looking at how apples are pollinated. All agree that insect pollination is key to apple production, but there is still some way to go in identifying the most successful pollinator of this fruit.  

There are a variety of reasons for scientists being cautious in making sweeping statements. Apples are many and varied. Firstly, there is a widely acknowledged varying nectar and pollen availability between different apple blossom varieties, thus making them more or less attractive to particular species. Secondly the four main guilds of apple pollinators – bumble bees, honey bee, solitary bees, and hoverflies – have different feeding specialisms so will have certain preferences. Thirdly, apples flower at a time when the weather is hugely variable, so the range of species visiting is likely to vary considerably between years.

Science will undoubtedly unravel the mysteries. 150 years on from those sightings in Kent scientists continue to discover more about species. Research examining pollen preserved on the hairs of Natural History Museum specimens has made it possible to gain a better insight on many species’ foraging preferences.

What isn’t in dispute is the major contribution made by a range of insects, especially bees, to apple production, even if we don’t have the services of the apple bumble bee on our shores. When you next bite into an apple remember to thank our insect pollinators.