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.

Einstein’s bees, sound bites and vitamins

By Athayde Tonhasca

If you have been following the news about bees’ decline in the newspapers and social media, you’ve probably come across variations of this quote, attributed to Albert Einstein: “If the bee disappears from the surface of the earth, man would have no more than four years to live.” This insight from one of the greatest scientist who ever lived seems to corroborate another mantra: “one in every three bites of food we eat depends on bees”. So the message from these sound bites is clear and dire: bees’ extinction would lead to food shortages, widespread famine, and ultimately the extinction of mankind.

Considering the seriousness of the matter, we may feel a bit disappointed by Einstein’s vagueness: did he mean the honey bee alone as humanity’s saviour, or the other 20,000 or so known species as well? But don’t blame Einstein for this taxonomical oversight because the quote is a myth: he never said it. Which is not surprising, really; would it be reasonable to expect the man who revolutionized our understanding of space, time, gravity and the universe, to have the time and knowledge to lecture us about bees as well? Probably not. Could the eminent evolutionary biologist Richard Dawkins offer new insights about the Special Theory of Relativity? Probably not. Authority has boundaries, and experts generally know their limitations.

Einstein’s prophecy belongs to the extensive list of fake quotes attributed to him and the likes of Abraham Lincoln, Mark Twain and Winston Churchill. But at least we know that one of every three bites of food we eat depends on bees. Or do we?

The 1 to 3 ratio could be read as the amount of food we eat by weight or by volume, or the proportion of food items in our diet. The latter is the usual interpretation of the quote, which originated from a misinterpretation of a 1976 report by the American Department of Agriculture.

But here are the data. Nearly 90% of the world’s caloric intake comes from rice, maize, millet, barley, sweet potatoes, bananas, wheat, sorghum, rye, potatoes, cassava and coconut. Only the last crop may require some insect pollination. About 60% of global food production comes from crops that do not depend on animal pollination: they are wind-pollinated, self-pollinated or propagated asexually. 

But how about the number of food items? Around three-quarters of the world’s main crops benefit from animal pollination (insects, birds, bats, etc.). But ‘benefit from’ is a far cry from ‘depend on’; pollination is not an all-or-nothing scenario. Crops have diverse degrees of reliance on pollination (see figure), which does not necessarily reflect on yield, but sometimes on product quality or shelf life. Only about 12% of the main crops depend entirely on pollinators to produce the food we consume.

Level of dependence on animal pollination of the main crops produced in 200 countries. Data from Klein et al. 2007. Proc. R. Soc. B 274: 303-313

The ‘1 in 3’ formula ignores meat in our diet. It’s difficult to evaluate the contribution of pollination to meat production considering the range of animal species and production systems. But it is safe to say that the bulk of animal protein originates from plants that don’t need animal pollinators such as grass, maize, and soybean. 

The proportion of animal-pollinated food of course depends on cultural backgrounds, dietary preferences and economic status, but it is not likely to be that great. You can check it for yourself: make a list of non-meat items on your dinner plate and look it up as to whether they are pollination-dependent (you may exclude the pizza and fish & chips dinners).

None of the above undermines the importance of pollination. This ecological service is estimated to account for around 10% of the world’s annual agricultural output; we could expect losses of 5 to 8% in total crop production in the absence of animal pollination. In the EU, 15% of crop production involves pollination, which generates around 31% of the income from crops. These figures are far from inconsequential. And the importance of pollination stretches way beyond yields and income: nearly 90% of the world’s flowering plants require animal pollination, so the whole functioning of the planet is linked to pollinators.

Like any good sound bite, “one in three bites” is memorable and catchy; but as it is often the case with sound bites, it is unclear, inaccurate and simplistic. It also distracts us from pollination’s real contribution to food production, which is the quality of our diet.

Most of the vitamins A, C, and E we need come from animal-pollinated plants such as vegetables, nuts, seeds, and fruits. The same is true for a large portion of vital minerals such as calcium, fluoride and iron. A decline in pollination services would decrease the supplies of these crops, which inevitably would result in higher incidence of diet-related illnesses such as heart diseases, cancer and diabetes. Fewer animal-pollinated fruits and vegetables in our diet would also contribute to the ‘hidden hunger’, which is a form of malnutrition caused by a lack of vitamins and minerals in the diet. Close to 2 billion people worldwide suffer from ‘hidden hunger’; this figure could be brought down by the addition of minerals and vitamins to staple foods, and by protecting pollinators that provide this public health service for free.

The proportion of food production that is dependent on pollination for vitamin A (a) and iron (b) © Chaplin-Kramer et al. 2014. Proc. R. Soc. B 281: 20141799

Pollinators do not contribute significantly to our caloric necessities; the number of bites of food that depend on bees is relatively small. But these few bites are essential for our nutrition and consequently to our health. In a country where 1 in every 4 adults and 1 in every 5 children are estimated to be obese mostly because of poor diet and lack of exercise, reducing the number of bites we eat should be a national priority. But improving the quality of those bites is equally important, with more fruit, vegetables and nuts on our plates: here’s where pollinators make their greatest contribution to our wellbeing.

Smorgasbord or Spartan: the consequences of pollen diets

By Athayde Tonhasca

There is nothing visibly remarkable about the mining bee Andrena florea. This bee, one of the 67 Andrena species in Britain, is found in open scrubby areas, grassland and woodland edges of south-east England. But one thing makes this bee unusual; it only takes pollen from white bryony (Bryonia dioica).

Andrena florea, which is commonly and unsurprisingly called the white bryony mining bee, is a rare British example of a bee that forages on a single plant species. This dietary restriction is circumstantial, because white bryony is the only plant of this group occurring in Britain. In continental Europe, A. florea has other Bryonia species available. So in a wider geographical context, this bee is oligolectic (or an oligolege) that is, it collects pollen from a few related plant species (from the Greek oligo: few, scant; and lect: chosen, picked).

A white bryony mining bee and its pollen source, white bryony © Aiwok (L) and H. Zell (R), Wikipedia Creative Commons

Pollen specialisation can be a considerable drawback for a bee because food may be scarce even in a landscape full of flowers, and this may limit populations of some species. For example, until recently the white bryony mining bee was rare and threatened in Poland. This has changed with the spread of white bryony into the country’s urban areas. And yet, a considerable number of species are pollen specialists; in some habitats, they make up the majority of the bee fauna. So pollen specialisation must have its advantages, for example by allowing more efficient flower visitation and pollination rates, which benefits bees and plants.

Polylectic bees are at the other end of the spectrum: they collect pollen from various unrelated kinds of flowers. The advantages of being a pollen generalist seem evident: there is more food to choose from and it’s available for longer, as flowers blossom at different times. But these bees must also have an array of physiological adaptations to overcome a variety of chemical and physical barriers to different types of pollen. This could be too costly for a bee’s metabolism.

Pollen is a rich source of protein, lipids, vitamins and minerals. But it also contains secondary compounds that may be noxious to some bees, and pollen grains are often protected by indigestible coating. These barriers explain why few insect taxa rely on pollen alone for food, and could also explain why most polyleges (polylectic bees) exhibit a degree of pollen specialisation: for example, heather (family Ericaceae) and legumes (family Fabaceae) make up over 70% of the pollen collected by British bumble bees, despite local abundance of other pollen sources.

Experiments with the closely related red mason bee (Osmia bicornis) and horned mason bee (Osmia cornuta) show the effects of different types of pollen. Red mason bee larvae develop well on buttercup pollen (genus Ranunculus), but fail to do so on pollen from viper’s bugloss and related plants (genus Echium); the reverse happens for the horned mason bee. Both bees do well on field mustard pollen (genus Sinapis), while neither develop on pollen from tansies and related species (genus Tanacetum). But the story is a bit more complex: neither bee shows any negative effect as long as they are not restricted to ‘bad’ pollen. In fact, unsuitable pollen is part of the bees’ natural diet. Other bee species show similar patterns.

Viper’s bugloss (1), creeping buttercup (2), field mustard (3) and tansy (4): nutritious/poisonous food for the right/wrong bee. © Wikipedia Creative Commons

So what can we conclude from all this?

Oligolecty and polylecty are both successful evolutionary strategies. Some bees depend on a few plants, others have diversified pollen diets. The range of hosts can be narrow or wide, depending on the species, but setting aside a handful of exceptions, bees need pollen from different plants to complement nutritional imbalances or to mitigate the effects of harmful secondary metabolites. But even pollen of low nutritional quality or digestibility is taken, as long as it’s a portion of a balanced diet.

These aspects have important consequences for the conservation of bees. They need a diversity of flowers, and plenty of them. Habitats such as semi-natural grassland, hedgerows, field borders, cover crops, brown sites, road verges, wild gardens and weedy parks are all suitable. Planting is helpful, but except for the honey bee and some bumble bees, we know little about what plant species to use. The safest action is to let our wild plants go wild, so that we have bigger, and more diverse flower-rich habitats. That’s not much or too difficult a task to assure the future of our most important pollinators.  

Bees in the sun, bees in the rain

By Athayde Tonhasca

For most animals and plants, the number of species increases from the poles to the Equator. This pattern, known as the latitudinal diversity gradient (LDG), is one the best documented features of life on Earth. At one extreme, lush and species-rich tropical rainforests and coral reefs; at the other, species-poor, barren polar areas. Ecologists have proposed several theories to explain the causes of LDG, which include solar radiation, competition, predation, rates of speciation (the formation of new species in the course of evolution) and other factors. But the debate is far from settled.

However, as is the case for many biological patterns, there are exceptions. And bees are one of them.

Time and time again, regional surveys around the globe have shown more bee species in dry and warm regions than in the humid and warm tropics. Despite the scarcity of data for some countries, these results have been consistent; there are many more bees in the deserts of South-western USA and the Mediterranean Basin than in the South American and African jungles. Recently, a group of scientists put together over 5.8 million records of the 20,000 or so known species of bee around the world to map their global distribution. The resulting image is an exceptional snapshot of the world’s biodiversity, and it confirms the pattern found in several independent, smaller-scale surveys: bee species richness is highest in dry, temperate and mid-latitude areas, decreasing sharply towards the equator. Israel for example, with very hot, dry summers and few rainy days, has the highest number of species per area of any country.

Bee species richness projections © Michael C. Orr et al. Global patterns and drivers of bee distribution. Current Biology, 2020; doi: 10.1016/j.cub.2020.10.053

Ecologists have mulled over explanations for such an unusual biodiversity pattern. It could be that bees don’t cope with high humidity. Most species store their larval food (usually pollen mixed with nectar) in cells excavated in the soil. The cells are lined with waxy or paper-like materials, but these barriers are thin and may not prevent fungal attacks in humid environments. Also, larval food stores may deteriorate more easily because of moisture absorption. 

Bee species concentrate on areas of high solar radiation and high plant productivity, as long as they are not forests. Perhaps because forests offer less pollen and nectar, and fewer nesting sites (e.g., bare earth on sunny spots). Predation on bee larvae by ants may be more intense in forests, especially in the tropics, where ants have the highest diversity and biomass. These are hypotheses: we don’t know for sure the factors determining bee species distribution.

A South African desert in bloom, a bees’ haven © Winfried Bruenken, Wikipedia Creative Commons

While bees differ from most life forms in their latitudinal diversity gradient, British bees differ from most bees. They live in habitats of short seasons, thus with a low incidence of solar radiation, and face a harsh climate of cold and humid winters. Our solitary bees adapt by passing most of the time tucked away in their nests as larvae or as adults encased in cocoons, to emerge in spring. Their flying stage is very short, lasting from a few weeks to a couple of months, which they spend frantically collecting food for their young. Bumble bees also hibernate to go through unfavourable conditions (only the queens: all workers die at the end of the season), and are better adapted to the cold. Bumble bees produce internal heat, and their chunky and hairy bodies are well suited to maintaining their body temperature.

A British landscape: not very sunny, not very dry, but good enough for our bees. © Tim Niblett, Wikipedia Creative Commons

Surveys and the map of global diversity tell us that bees are creatures of dry, sunny and open surroundings. Our bees share none, or very little, of this Mediterranean paradise. But they have evolved to cope with the cold, damp and long winters, and to the seasonal scarcity of food. So they thrive, regardless of their hardships. That is, as long as we don’t mess up their habitats.   

May the Force be with the bee

By Athayde Tonhasca

If we are asked how a bee finds a flower, we think of smells, colours, shapes and textures. These are important sensory signals, but there is another one whose relevance is just beginning to be understood: electricity.

It has long been known that the platypus, some fish and amphibians, as well as some ants, cockroaches, mosquitoes and fruit flies have the ability to detect external electric forces. However, vertebrates need water as a conductive medium, while most insects respond only to unusually strong electric fields such as those generated by high voltage power lines. Bumble bees however have a sparking story to tell. 

We do not notice it, but our planet is an immense electrical circuit. On a calm day, the air is positively charged, while the ground surface has a negative charge. Now and then the equilibrium of charges is disturbed by lightning bolts or a minor shock from a car door, reminding us we are surrounded by electricity.

The negative charges accumulated on the planet’s surface extend to any object connected to the ground, plants included. So flowers have a slight negative charge in relation to the air around them. As a bee buzzes along in search of food, electrons are stripped off its body by friction with the air, leaving the bee positively charged. When the bee lands on a flower, some of the negatively charged pollen grains stick to the bee, sometimes jumping from the flower even before the bee makes contact. So electrostatic forces are a great aid to pollination.

An electrifying encounter: a positively charged bee approaches a negatively charged flower. Images in the public domain.
Pollen clinging to a sweat bee. © Pixabay.

But flower power reaches shocking levels for the buff-tailed bumble bee (Bombus terrestris), and probably for other bumble bees as well: they are able to sense the weak electric field around a flower. No one knows exactly how they do it, but mechanoreceptive hairs must be involved. These special hairs are innervated at their base, so they detect mechanical stimuli such as air movement and low frequency sounds. Apparently, the flower’s electrical field moves the mechanoreceptive hairs of an approaching bee, similar to the way a rubbed balloon makes your hair stand on end. This hair movement is processed by the bee’s central nervous system and gives information about the shape of the electric field. It is as if the bee ‘sees’ the flower’s electrical aura. 

Bumble bees’ hairs provide thermal insulation, collect pollen and help bees sense air motion, sounds and electricity. ©Kevin Mackenzie, University of Aberdeen. Attribution 4.0 International (CC BY 4.0).

But bumble bees’ capacity to detect electric forces may go beyond recognising flowers’ sizes and shapes: they could use the information to maximise foraging trips. Once a positively charged bee lands, the flower’s electric field changes and remains changed for about two minutes after the bee leaves. Researchers believe that an altered field warns the next bee that the flower is temporarily depleted of nectar; it’s like turning off a ‘we are open’ neon sign. So the next bee may as well buzz off to another flower with sufficient negative charges and a decent volume of nectar. 

Bees and other insects detect ultraviolet and polarized light, and use magnetic fields for navigation. Sensing electricity is one more way their world is experienced radically differently from ours.

Insect inspiration

Insects and football don’t often mix. An influx of flies when England met Tunisia in Volgograd during the 2018 World Cup was a rare occasion. It wasn’t warmly welcomed by players or spectators. Two years earlier at Euro 2016, Silver Y moths were clearly visible as Portugal and France contested the final. But there are a few insects embedded in ‘the beautiful game’ in a more celebrated fashion – in club nicknames.

The recent televised FA Cup tie between Brentford and Leicester City featured several shots of the London club’s badge – which features a bee. Brentford are nicknamed ‘The Bees’ and football writers have long loved the opportunity to craft match headlines centred around that favourite old phrase about a game having a ‘sting in the tail’. A late goal at Brentford is almost sure to provoke this phrase in some guise or other.

At one time the Brentford crest resembled a shield, and featured a traditional skep hive and a couple of impressively stout bees.  A recent make-over has delivered a modern round badge featuring a single bee which is now the proud focal point.

Screenshot 2020-02-10 at 17.28.16

Brentford are pushing for promotion to the top flight, about to move to a sparkling new stadium, and football headline writers may go into overdrive if there they were to meet Watford who go by the nickname of ‘The Hornets’.

We can presume Watford’s nickname is intended to denote a menacing and powerful force. The connection can seem confusing when the club badge is clearly dominated by an image of a ‘hart’ or stag. Their ‘hornets’ nickname appears to date to the 1960s and is likely based simply on their predominantly yellow and black colours; there was only a brief window when the badge on their strip actually featured a hornet.

England doesn’t have a monopoly on insect nicknames.

In Scotland championship club Alloa Athletic are well known as The Wasps and their vivid gold and black hooped jerseys make the choice of this nickname an easy one to appreciate. Their Recreation Park home enjoys lovely views of the Ochils and Alloa may have had their nature inspired nickname since around the 1880s.

Perhaps not surprisingly the current Alloa club crest prominently features a wasp. It’s not a slavish representation by any means, and indeed has a cartoon element with the wasp depicted in a ‘superman’ pose complete with bulging muscles.  But the nickname has stuck over the years, as have the club’s colours, and as a consequence Alloa have a distinctive identity.

Football is game steeped in tradition, and the retaining of insects in these nicknames and club crests is evidence of the importance of history to many football clubs. It also shows that folk notice insects in many different ways.

It is one thing to have an insect nickname, what about when the actual club is named after an insect?

Since 1886 that’s been the case in the Swiss city of Zurich, where one of the local football clubs is called Grasshoppers. It’s a fitting note to end on as they were in fact formed by a Scotsman – albeit going by the rather Welsh sounding name of Tom Griffiths. The name Grasshoppers is said to have reflected an energetic style of play and lithe athleticism. They visited Scotland in 1958 to play a floodlit friendly match in Glasgow, but apparently it was so foggy that evening it was hard to see from one end of the pitch to the other, let alone determine if the Swiss side lived up to their ‘springy’ name.

So insects and football.  Not an obvious relationship, but there nevertheless.