The critical role of our wild pollinators for agriculture and biodiversity has been overlooked, but this is changing. Scientists are now cottoning on to the usefulness of wild pollinators, and arguing that we are missing a trick in not doing more to help them.
“Honeybees are really important, and we can move them around and manage them, but we’ve begun to appreciate that the vast majority of pollination in wild plants and crops is coming from wild pollinators,” says Dr Tomás Murray at the National Biodiversity Data Centre in Co Waterford.
There are 20 species of bumblebee and one species of honeybee in Ireland, but there are 76 kinds of solitary bee. Honeybees live in hives of thousands, bumblebees can have nests a few hundred strong. Solitary bees live, well, solitary lives, but make big contributions. Together, they all boost crop production.
One ginger-coloured mining bee (Andrena haemorrhoa) is increasingly recognised as a truly important pollinator of apples in Europe. Female mining bees dig tunnels, lay eggs and leave behind "bee bread" for larvae, made from a recipe of pollen and nectar. Young bees crawl out later in summer. Some solitary bees look large and fluffy like bumblebees, others look like wasps, some are like flying ants, and still others are simply small, black and nondescript.
“What makes bees great pollinators is that their entire life cycle is concerned with feeding on flowers. Both adults and larvae feed on nectar and pollen,” says pollination scientist Dr Jane Stout, of Trinity College Dublin.
Bumblebees and honeybees are excellent at collecting pollen for bee babies, often in special leg pouches. But some solitary bees are incredibly good pollinators because they are so bad at it. Mason and leafcutter solitary bees store pollen on their undercarriage, dropping it here, there and everywhere. One red mason bee can match the pollination work of more than 100 honeybees, research indicates.
Crop boost
A study of 41 crop systems in 600 fields around the world, reported in the journal Science in 2013, found that fruit set spiked upwards with visits by wild insects. Quantities of sweet peppers, apples, strawberries and raspberries rose significantly with more wild insect visits in all cases.
“That was shocking,” says Dr Murray. “We assume more honeybees mean greater yield, but that happened in only 14 per cent of the 600 fields, whereas it happened in all cases with wild insects. So they really are having a much bigger impact than we’d thought.”
Wild pollinators have been undervalued and understudied, partly because some are difficult to identify in the field.
And it’s not just bees. Only half of the flower visitors Dr Stout observes in agricultural fields are bees; the other half are hoverflies. “These are probably relatively important as pollinators, but we just don’t know how important. They have been largely ignored,” she says.
There are 180 species in Ireland. It is thought that they are not as efficient pollinators as bees because they sip nectar and eat pollen but do not collect pollen for their young. Without specialised mouth parts to feed on complicated flowers, they focus on flat, open flowers, such as bramble, hogweed, rape and hawthorn.
About 10 Irish hoverflies mimic bumblebees to con predators, and these hairy creatures are probably the best at moving pollen from one flower to the next.
"You really can be sold quite easily if you just get a glance. They get the protection of [looking like] bees, which predators like birds tend to avoid," says Dr Úna FitzPatrick of the National Biodiversity Data Centre. On the upside, hoverfly larvae eat all sorts of agricultural and garden pests. The centre plans to host hoverfly identification workshops, and true aficionados can read a new field guide, Britain's Hoverflies.
The centre has helped draw up an All-Ireland National Pollination Plan 2015-20, aimed at honeybees and wild pollinators. “We need to build pollinator habitat back into the landscape, because it has been almost entirely lost. There are steps you can take in your garden, your park, your school and on a farm, as well as along roadsides,” says Dr FitzPatrick. She is concerned that, with the milk quota gone, more intensely grazed grasslands may hurt Ireland’s pollinators, which could be bad for agriculture in the long run.
“Farmers want to do what’s profitable, but the situation might change, and it is hard to predict what a farmer’s children or grandchildren might want to grow on the land. If you want to grow a pollinator- dependent crop in future, and they are not there any more, it’s hard to bring the insects back,” she says.
Pollinators matter
Adding a wildflower strip to blueberry fields in Canada bumped yields by 10 per cent within four years, a study published last year showed. The net profit to the farmer was the equivalent of €8,000 per hectare of wildflowers after 10 years.
“We need that kind of research done here on strawberries, apples and other crops in Ireland,” says Dr Murray. “We can have a win-win situation where you increase your wild pollinators, and farmers get greater yields.”
Individuals can help by letting garden areas go wild. “Have some areas with more wildflowers, native plants especially, that flower at different times of the year,” says Dr Murray, or choose pollinator-friendly plants around farms and be judicious with herbicide and pesticide sprays. Roadside verges can be left unmown.
Fifty organisations have signed up for the pollinator plan, including Irish Rail, which has railway embankments perfect for attracting solitary bees. The plan will also offer advice to local authorities, with biodiversity advocates making specific recommendations. They could, for example, plant certain native meadow flowers in our parks and let some areas run wilder.
But local actions are already under way, with Tidy Towns committees promoting biodiversity-friendly areas. Wexford Tidy Towns, for example, has a brochure on pollinator-friendly flowers and when to plant them.
MAD HONEY: POISON NECTAR THAT KILLS HONEYBEES
A flowering rhododendron bush is often smothered in bumblebees in summer, but you will struggle to find any honeybees. Dr Jane Stout of Trinity College has figured out why: the plant’s nectar poisons them.
“The nectar is toxic to honeybees, but it doesn’t seem to have any lethal effects on bumblebees. Solitary bees are somewhere in between, and suffer sublethal effects,” she says.
This means that bees that are fed rhododendron nectar exhibit distress and “malaise behaviour”: they lie on their backs, waving their legs in the air. They appear to recover later.
In the wild, this would have an impact on their ability to avoid predators or even return to their nest. That’s not good for survival.
Honeybees were killed outright by the plant toxin. Perhaps unsurprisingly, when Dr Stout and her students carry out surveys in the field, honeybees are never seen foraging on rhododendron, and solitary bees are rarely seen. The toxin responsible has been identified as a grayanotoxin by Dr Stout ’s collaborators at Newcastle University and Kew Gardens. It is a compound that binds to important sodium channels in cell membranes and locks them into an excitable state.
Honey in some parts of the world is sometimes contaminated with this toxin via pollen. The Greeks reportedly used such toxic honey against their enemies, according to Greek historian Xenophon (430-355 BC). Consuming it reputedly causes temporary insanity and drunken behaviour. In Turkey, rhododendron honey is known as “mad honey”. It is produced in large quantities in the Black Sea region but is also used for treating medical conditions, such as high blood pressure.
It is not known why bumblebees are immune to the toxin. “It could be that their receptor targeted by the toxin does not react to it in the same way, or that they can detox it and excrete it. We don’t know yet,” says Dr Stout. Surprisingly, her team also found that bumblebees are not good at detecting nectar toxins – such as quinine, caffeine, nicotine and grayanotoxin – in bee-pollinated plants.