Heat punches

By Athayde Tonhasca

The recent record-breaking temperatures have been welcomed by many of us, deprived for so long of sunny beaches and bright skies abroad. Canadians and Americans, though, have been less thrilled by summer’s temperatures, which have reached life-threatening levels. And it’s not only the sizzling heat: wild fires, power failures, transport disruption and water shortages for people, livestock and crops have added to the summer misery of many in the northern hemisphere. Heat waves are one of the extreme climatic events that seem to have become more frequent, as predicted by those pesky climate scientists.

Heat waves are a growing risk to people, and to bumble bees too. For the last 10 years or so, researchers have noticed accentuated slumps in the numbers of bumble bees in several European countries following a heat wave – which happens when the daily maximum temperature is 5 °C higher than the average maximum for more than five consecutive days, as defined by the World Meteorological Organisation.

Areas of bumble bee scarcity following a heat wave © Rasmont & Iserbyt. 2012. Annales de la Société Entomologique de France 48: 275-28

Bumble bees are cold-adapted animals, and some species live comfortably in harsh alpine and arctic environments. This cold-hardiness is partially explained by their ability to generate internal heat: bumble bees cannot take off until their flight muscles reach 30^oC: once they are airborne, their body temperature can go up to 40^o C. This energy output may give the impression that bumble bees are heat resistant, but that is not the case. Internal heat is good, external heat is not. High air temperatures interfere with their metabolism, quickly leading to overheating and neuromuscular collapse (heat stupor). 

Unsurprisingly, species from colder habitats seem to be more sensitive to hot spells. And species that reproduce later in the season are also more affected by heat waves because these events tend to occur towards the end of summer. What are the implications of these observations for our bumble bees? Certainly a sombre outlook for species such as the great yellow bumble bee (Bombus distinguendus), Britain’s most endangered bumble bee. Once widespread, this species has been pushed to the northern fringes of Scotland, where it’s active between May and September. As a cold-adapted, late-nesting bumble bee, it could see heat waves added to its woes.

Average heat stress resistance, measured as time (min) before heat stupor, for bumble bee individuals across biotopes © Martinet et al. 2020. Conservation Biology DOI: 10.1111/cobi.13685

Most studies about the consequences of climate change have focused on the gradual increase in average temperatures, and the overall conclusion is that many plants and animals in the northern hemisphere are responding to a hotter world by expanding their ranges northwards and upwards (to higher elevations). However, bumble bees have not been very successful in tracking a changing climate; they tend to stay put, thus becoming increasingly exposed to the risks of heat stress and food shortages. The creation, protection and expansion of suitable habitats can improve species’ endurance and facilitate their escape to better areas, but these mitigation strategies will not be as effective against heat waves and other extreme climatic events. Intense and frequent temperature variations are immediate threats: species may not have enough time to move towards better climatic conditions.

People in Britain will have to adapt to a higher frequency of sizzling summers, destructive floods and paralysing snowstorms. And very possibly, become used to a different bumble bee fauna: some species may be squeezed out of their current area, heat-tolerant species such as the buff-tailed bumble bee (Bombus terrestris) may become much more abundant. The consequences of these changes to pollination services are impossible to predict. 

Although the damage of climate change to people and nature cannot be reversed, it can be contained. But time is running out.

The great yellow bumble bee, a species particularly vulnerable to heat waves © Arnstein Staverløkk/Norsk institutt for naturforskning, Wikipedia Creative Commons

The Thyme is right

When it comes to fragrance and the ability to attract bees you have to hand it to thyme.  One of our most popular herbs, it is both easy to grow and undemanding of space.  No wonder those who want to help pollinators love this little herb.

Herbs are a great option for those who can only have a window box or a container. Garden thyme in particular offers so much.  The leaves have a lovely scent, the flowers are vivid and draw pollinators in good numbers, and when it comes to cooking, it has long been on the top of the herb list. The leaves can be added fresh or dried in a range of dishes. 

When you dig into the reference books to find out more about thyme, you quickly discover that there are many varieties. It is reckoned that our garden thyme originated in the Mediterranean area, and it certainly seems to prosper in well-drained sites and low nutrient soils. 

We are fortunate to have a relative of garden thyme in Scotland. I’ve been seeing it whilst out on hill walks so our species must tolerate cold and wet Scottish winters. Like its garden relative our wild thyme is a magnet for pollinators.

The Greeks must have enjoyed the scent of burnt thyme as it found its way into their religious ceremonies. Indeed its name originates from ‘thymos’, which translates as ‘perfume’.  Others found alternative uses for thyme, for example placing it under pillows in the belief that it would help to fend off maladies ranging from the plague to bad dreams.

There are cultural associations in Scotland too. In some quarters, many moons ago, thyme was associated with fairies and it was viewed as bad luck to bring it into a house. A more pleasant association is found in folk music where the song ‘Wild Mountain Thyme’ has been popular for many years. Indeed in 1965 Joan Baez performed it in Edinburgh, as YouTube will testify.

Thyme is an important element of Scotland’s machair, and, as with many wild plants, cropped up in traditional remedies, such as for settling stomachs and warding off nightmares.  Unconfirmed reports suggested it had antiviral, antibiotic, antiseptic properties, which in this current era of widespread use of hand sanitiser strikes a highly topical note.  Finally, thyme extracts are in some quarters viewed as part of a ‘tonic’ that beekeepers can feed to their honey bees in spring to get them up to strength after a long hard winter.

When I’ve sat down to photograph thyme and watch the insects visiting it, I’ve been impressed by the range of pollinators, which include honey bees, various bumble bees, and solitary bees.

Many of our favourite herbs are great for pollinators.  Lavender, rosemary, borage, sage, fennel, marjoram, mint, chives … the list is endless. Thyme as a member of the Lamiaceae, or mint, family of plants is a worthy addition to that list.

The silent and lethal majority

By Athayde Tonhasca

If you were to stroll around this garden and estimate which insects are most abundant, you may come up with flies, or perhaps beetles. These two groups will indeed be well represented, but chances are they pale in comparison to some other insects you will struggle to even notice: parasitoid wasps.  

We tend to think of wasps as large, social insects like paper wasps and hornets. But the great majority of them are small, solitary (i.e., they don’t live in colonies) parasitoids. A female parasitoid lays her eggs inside or on the surface of a host; the eggs hatch and the developing larvae consume the host, eventually killing it. Like a parasite, a parasitoid requires a single host for its development; but like a predator, it ultimately kills the host.

Parasitoid wasps comprise groups such as Darwin wasps, aka ichneumons or ichneumonids (family Ichneumonidae), braconids (family Braconidae) and chalcids (superfamily Chalcidoidea). These names may sound strange and unfamiliar, and in fact these insects are poorly known. It is hard to tell species apart and few entomologists work with them; trickier still, many species are miniscule and easily overlooked. But parasitoid wasps are one of the most speciose and abundant components of terrestrial ecosystems. Here are some figures to give a proper perspective: it is believed that the 50,000 or so described species represent a small fraction of the total number (for comparison, birds and mammals are in the order of 10,000 and 5,000 species, respectively). Over 6,000 species have been recorded in Britain, which makes up about 25% of all insect species. In a suburban garden in Leicester alone, 455 species were collected in a two-year period.

At 0.15 mm, the parasitoid wasp Kikiki huna is the smallest flying insect. Its name comes from Hawaiian words meaning ‘tiny bit’. © Huber & Noyes, 2013. Journal of Hymenoptera Research 32: 17–44.

Inevitably, such dominance has important consequences. Parasitoid species – wasps and other groups such as flies – keep populations of their hosts under control. Some insects are attacked by 5 to 10 species of parasitoid wasps, so many of them can’t even make themselves noticed because of relentless pressure from their natural enemies. If unchecked by parasitoids, the numbers of some plant feeders would quickly grow to outbreak levels and become agriculture or forestry pests. 

A braconid wasp © Richard Bartz, Wikipedia Creative Commons

We have learned to tap into this biological control potential by rearing large numbers of parasitoid species and releasing them in fields and forests. In West Africa, the cassava mealybug (Phenacoccus manihoti) threatens the production of cassava, a vital staple food. The introduction of Anagyrus lopezi, a parasitoid wasp native to Central America, reduced pest populations by 80 to 90%.

Cocoons of the braconid wasp Glyptapantheles liparidis attached to a gypsy moth caterpillar (Lymantria dispar) © György Csóka, Wikipedia Creative Commons

Caterpillars are the main victims of parasitoid wasps, but bees are not immune to them. Chalcids are a particular headache for solitary bees: they invade bees’ nests and pierce the brood cell walls with their elongated ovipositors. The wasp stings and immobilises the bee larva, then lays her eggs inside the nest cavity. The wasp larvae hatch in one or two days and slowly devour the paralysed host. Monodontomerus spp., chalcid wasps whose big name belies their small size, can be a problem in artificial bee houses, which create unnaturally high concentrations of nests. In these situations, chalcid wasps reproduce quickly and can cause havoc among their hosts. Watch chalcid wasps in action.

Monodontomerus sp., a chalcid wasp © Robert Webster, Wikipedia Creative Commons

In the natural environment, bee mortality by wasp parasitoids is believed to be relatively low, perhaps around 1%. But these tiny creatures are there in the background, shaping the structure of whole insect communities and regulating plant-herbivore interactions. The consequences of this powerful instrument of population control on pollen and nectar production are not completely known, but certainly are not negligible. 

It’s good to talk

Local Authorities are essential to the implementation of the Pollinator Strategy for Scotland. This is good news, as many of them are enthusiastically carrying out pollinator-friendly work. So much so that last month we hosted an online conference to share experiences and learn about one or two challenges.

Scotland’s 32 local councils own about 81,000 acres between them. Their biodiversity officers know their estates well, and are adept at making changes and embedding practices that are good for nature and good for people. 

Below is a summary of what was said over 90 minutes worth of presentations.

Our very own Athayde Tonhasca set the scene with a look at pollinators and pollination with an emphasis on the most significant group – bees. Then, in quick succession, Lindsay Grant, Carol MacLean, and Louisa Maddison gave an insight into how Edinburgh, Glasgow, and South Lanarkshire Councils have made a mark for pollinators. In order to compare and contrast, Phil Sterling, the highly respected and much admired Butterfly Conservation officer from Dorset, and Philipp Unterweger, from Tubingen in Germany, closed proceedings with a view from beyond our own border.

Lindsay Grant, of Edinburgh Living Landscape, gave an insight into Edinburgh’s approaches and techniques to pollinator-friendly public spaces, with an emphasis on community engagement. He revealed how the capital city has gone about delivering a more pollinator-friendly vision. As part of the wider Edinburgh Living Landscape project, a range of approaches and techniques were applied to managing public spaces differently. The role of community engagement was strongly highlighted. Good dialogue can prove a powerful tool in transforming poor amenity grassland areas into something more biodiversity-friendly, especially as the early stages of this work can create an impression of abandonment.

The development of perennial meadows, reduced mowing regimes, use of spring bulbs, and native seeding ultimately proved popular with the public. Trickier was the realisation that, without intervention, perennial meadow areas could become overwhelmed by one or two dominant species. Lindsay spoke too about the required change in machinery and its impact on budgets. 

The mistakes weren’t glossed over, and these included the cutting of some Living Landscape sites, and an initial ‘historic calendar’ approach to mowing rather than ‘site specific’ cuttings. It was a frank look at the objectives, successes, and false steps. 

Carol MacLean, from Glasgow, built on Lindsay’s presentation with a view that having a Pollinator Plan, which dovetailed with the National Pollinator Strategy, had been a welcome move towards biodiversity objectives. Carol also stressed the value of having knowledgeable partners such as Bumblebee Conservation Trust, Buglife Scotland, and Butterfly Conservation involved.

Periodic ecological surveys were seen as essential for the long-term success of meadow creation. Through both a three-year bulb planting project and an ambitious tree planting programme, Carol was able to demonstrate impressive progress. Like Lindsay, Carol emphasised the role of communication and community involvement. The Health and Wellbeing agenda was also central to the works in Glasgow, and green and biodiverse corridors were part of what came over as a cohesive plan of action.

Louisa Maddison was keen to emphasise the value of collaboration and communications too. She rounded off the look at Scottish actions with a report from South Lanarkshire. 

The very title of ‘Pollinators and People Power’ was a taster of what was to come, for  the presentation covered the creation of meadows, thriving community parks, and liaison with community groups. As with Edinburgh and Glasgow, there was an acknowledgement of the role of environmental bodies, and one of the highlights was the role played in helping Buglife Scotland with their B-Lines project. 

Louisa also emphasised how important a few simple, yet explanatory, signs could be in converting the local communities to the value of changes in management practices. When the actions were explained, there was public support. Louisa set the scene nicely for Phil Sterling by ending her presentation with an image that looked at the vital practice of ‘cut and collect’.

Not many people will come away from a Phil Sterling presentation feeling anything other than bowled over by his enthusiasm, clarity, and experience. One of the most interesting elements of Phil’s talk was the realisation that over-zealous mowing is a carbon-related environmental impact as well as a biodiversity problem. He devoted a deal of time to his ‘cut and collect’ philosophy, which ensures low levels of soil nitrogen.  By carrying out repeated short-term cut and collecting in the initial stages, you can expect a huge dividend later, let alone cost savings from reduced mowing.  Phil added a plea to not move soil around needlessly out of habit with the fuel use this entails. 

It was left to Philipp Unterweger of Tubingen, Germany, to bring proceedings to a close with a video that demonstrated the environmental drive embedded in German culture. His talk began with a look at insect losses and a plea that insects should be seen as being more important than nurturing neat lawns and gardens. 

Philipp celebrated the work of students at the University of Tubingen in persuading the university authorities to transform swathes of lawn into flower-rich areas ripe for pollinators and insects in general. This model was rolled out in housing areas too, with considerable success. The paradox of enrichment, in that more nutrition results in lower biodiversity, was covered, as was the importance of communicating change. Indigenous plants and seeds, and taking care of existing meadows, also fell under Philipp’s spotlight.

The insect fix we need isn’t going to be an overnight job, but on the evidence of what we heard last month we are heading in the right direction.

Fungus therapy

By Athayde Tonhasca

About 12,000 years ago, mankind took a mighty leap forward by adopting agriculture; peoples in different parts of the world abandoned nomadic, hunting-gathering existences to take up farming and animal husbandry. Cities multiplied, populations grew dramatically, and civilizations flourished. Not bad for the bipedal primate Homo sapiens, but agriculture was already old news – in fact, at least 40 million years old – for some insects.

Agriculture, or the practice of producing crops, has long evolved as the way of life for about 80 species of leaf-cutter ants, 330 species of termites and 3,400 species of ambrosia beetles: these insects get their food by cultivating fungus gardens. Ants and termites collect plant material to provision their fungi, which convert the vegetable substrate into nitrogen-rich fungal biomass. Ambrosia beetle fungi extract nutrients directly from the host plant. These farming insects propagate and control the growth of their fungi, weed out contaminants and pests and take spores with them to start new colonies. And without their gardeners, these fungi quickly die.

Leaf-cutter queen and workers on their fungus garden © Christian R. Linder, Wikipedia Creative Commons

Recently, a bee was found to belong to this insects’ farming union: the South-American stingless bee Scaptotrigona depilis. Its larvae feed on a fungus in the genus Monascus, bits of which adult bees transfer between brood cells and take to newly founded nests. Without the fungus, few larvae survive. The need to eat a fungus seems puzzling because inside each brood cell, a larva floats in a pool of abundant, nourishing food. The reason appears to be protection rather than nutrition. The fungus may produce chemical compounds that defend the larvae and their food from harmful fungi and bacteria. Monascus fungi are used to preserve meat and fish in Southeast Asia because of their antibacterial and antifungal properties, so the hypothesis is plausible.

A. A Scaptotrigona depilis egg floating on the semi-liquid brood food; B. 1-day old larva: fungal mycelia growing from cell wall onto larval food; C. 3-day-old larva: dense fungal mycelia on cell wall © Menezes, C. et al. 2015. Current Biology 25: 2851-2855

These tropical fungus gourmets may seem of little relevance to our pollinators, but they suggest that cases of insect-fungus symbiosis – from the Greek syn (together) and biosis (living) – are more common and relevant than what we know. Some Aspergillus, Penicillium, Cladosporium and Rhizopus fungi protect the honey bee (Apis mellifera) against diseases such as chalkbrood and contribute to the fermentation of pollen to produce ‘bee bread’ (the main food of larvae and workers, comprising a mixture of pollen and honey). Fungi are known to produce chemicals that work against other fungi, bacteria and viruses. In fact, honey bees that feed on Fomes and Ganoderma mushrooms have reduced levels of infestations of some destructive viruses such as the deformed wing virus and the Lake Sinai virus. We have much less information on beneficial fungi in relation to other bee species. 

The stingless bee Scaptotrigona depilis © Cristiano Menezes, Agência FAPESP

Most bees nest and store nutrient-rich food underground, which makes them vulnerable to pathogens and parasites. Many of these bees – and the honey bee as well – are protected to some extent by gut microbiotas, and bacteria are the better known components of these symbiotic fauna. In time, we may find that fungi have a greater protective role than is currently recognized.

Enjoying a natural high

Beinn Eighe is Britain’s oldest National Nature Reserve. It’s also a vast site, covering in the region of 48 square kilometres. Rugged peaks, towering ridges and scree-covered slopes, along with swathes of ancient Scots pinewood, draw visitors year after year.  But now those who like the smaller things in life have an attraction they too can revel in – the Beinn Eighe pollinator trail. 

Increasingly some visitors happen upon Beinn Eighe NNR almost by accident. Often that’s thanks to the North Coast 500, which runs right past the front door at Beinn Eighe’s visitor centre, and what a fantastic visitor centre it is. The road outside the centre is as dramatic as any, rather like Les Corniche on the Côte d’Azur, South of France (which features in the classic film ‘To Catch a Thief’)  mesmerising scenery draws the eye irresistibly.

But whilst our eyes are accustomed to the big views and the grand scenery, the pollinator trail here aims to explain why the very little things in life matter deeply.

Our appreciation of the role of insects in the world is clearly ever increasing. There are plenty of them around Beinn Eighe, and the pollinator trail highlights some of them by tagging onto the Buzzard Trail which starts from right outside the popular visitor centre.

Mind you, that said, walkers, cyclists and motorists will actually spy their first pollinator sign before they have even settled, for it sits on the grass verge immediately outside the visitor centre. This is a wildflower patch that nestles in between the road, the large welcome sign and the centre.  Here the pollinator trail panel ‘Mow less, give more’ explains the benefit of the reduced mowing principle. 

Once you join the pollinator (or buzzard) trail you come quickly to a sign explaining the virtues of helping pollinators. On a lovely, even, path you are soon invited to consider hoverflies, and role of trees and shrubs in helping pollinators.  The information panels are housed in local wood and both sensitive to the special surroundings and easy on the eye.

As the trail meanders beneath the trees the role of deadwood in providing insects with hibernation, shelter and nesting opportunities is followed by a panel that takes a closer look at the early season value of willow as a food source for emerging insects in spring.

Up to this point the trail has been in calming woodland, but things get a bit more dramatic when a series of beautifully laid, and easy to negotiate, steps take the visitor higher up the reserve. When you emerge from the smell of pine trees it is fitting that you quickly come across a sign devoted to another Scottish icon – heather.

Visitors will surely enjoy a sign that celebrates this widespread plant and the chances are they will be equally captivated by the next panel which is intriguingly titled ‘The Hardy Highlander’. It takes a look at the blaeberry bumble bee, also known as the bilberry or mountain bumble bee. It’s a subject you can read more about on our blog.

As the trail gradually descends back into the woodland there is time for one more sign – devoted to the power of flowers. Having something pollinator-friendly in flower from early spring to autumn is crucial for emerging pollinators and those heading into hibernation. 

The trail went out at the start of April, when the primroses were in flower, but it wasn’t feeling very spring-like with snow on the ground. It will stay out over the summer and right through to the end of October, so there is still plenty of time to pay a visit, talk a walk around and pick up some interesting facts. If you are out visiting the pollinator trail be sure to take your camera and submit photos to the Beinn Eighe photo competition that is running over summer to celebrate Beinn Eighe’s 70th anniversary.

The aim of the trail is to raise awareness of species and habitats, and to encourage folk to go home with an idea or two on how they could improve their local patch for bees and other pollinators.

There is of course so much more to see at Beinn Eighe than the pollinator trail. The stunning Mountain Trail, the calming Woodland Trail, and the sheer pleasure of relaxing in such nature-rich surrounds are a fantastic way to spend time. But we are rather taken by reserve manager Doug’s excellent pollinator trail, and – returning our earlier Mediterranean analogy – it surely glitters as brightly as the jewels in ‘To Catch a Thief’.

Find out more about Beinn Eighe National Nature Reserve