The birds and the bees
Plant sex is the ultimate form of a long-distance relationship, with animals co-opted into carrying out the act. The result: much of life on Earth depends on the habits of hungry insects, bats, reptiles and birds. But we don’t know exactly who’s doing what to whom, and when—and what might happen if they disappear.
Plants face a fundamental problem when it comes to sex: they’re rooted to the spot. Getting their male bits close enough to nearby female bits for reproduction to occur is a sticky issue. Luckily, they’ve had 400 million years to figure out how to do it. Back in the murky depths of evolution, seed-producing plants took a “spray and pray” approach to the job. Among these were the gymnosperms—the group that includes modern-day conifers. Their male cones produce an obscene amount of pollen, which they unleash upon the world every sun-drenched spring, relying on the wind to spread it. A minuscule portion of that pollen might find its way to a receptive female cone of the same species, but it all depends on blind luck. It is energy intensive, wasteful, and also means these plants can reproduce only with others in their immediate vicinity.
During the time of the dinosaurs, a new group called angiosperms cracked onto something big: they worked out how to outsource sex. It was a socio-technological leap that anticipated capitalism by 100 million years, and it changed the world. All they needed to do was entice the armies of sentient creatures they shared the planet with into providing endless amounts of labour in return for a small reward.
The ploy was simple in concept, but breathtakingly complex in execution and evolution. First, grow a colourful and attractive vessel: a flower. Keep the reproductive parts inside this vessel: pollen (the plant version of sperm) and the stigma (which receives the pollen and sends it to the plant’s ovary). Brew a reward: sweet nectar. Then wait.
The rest of the story is the stuff of primary-school biology. Animals who come to the flower seeking nectar inadvertently get pollen stuck to their bodies, which later brushes off on the stigmas of other flowers. And, with these highly mobile animals carrying the pollen exactly where it is needed, angiosperms can afford to produce far less of it. Pollinators spread the flowering plants’ genes much further across the landscape than the wind ever could, allowing them to expand into new markets and outcompete their gymnosperm rivals.
Angiosperms now comprise around 90 per cent of all plants on land, and animal pollination underpins the functioning of life on our planet. Pollinating insects are the hardest workers in agriculture. They’ve enabled us to grow the crops that have fed humanity. We have multiplied in our billions, and built empires on the back of free insect labour.
And the most important player in this global conquest? The honeybee, Apis mellifera, one of about 20,000 species worldwide. But honeybees didn’t exist in New Zealand until 1839. Before then, our plants found their pollinators in countless other species—some of which have been working without recognition. We’re only just beginning to understand the role these species play. The thing is, they’re not always easy to find.
My headlamp battles to pierce the sleety rain that sweeps in sideways off the Southern Ocean. In the distance, waves thunder against the battlements of Enderby Island’s volcanic cliffs, while birds shriek weirdly in the pitch darkness. It’s cold, wet, windy and hostile. A typical midsummer’s night in the subantarctic.
Along with University of Auckland researcher Max Buxton, I pick my way through the sodden vegetation, scanning the foliage with my torch. At this time of year, the megaherbs are in full bloom. Anisotome latifolia, the Campbell Island carrot, with its purple puppet-tufts standing proud above the tussock. Stilbocarpa polaris, the Macquarie Island cabbage, its plate-sized leaves cradling fists of tiny flowers. And out here on the exposed tundra of Enderby, great swathes of Bulbinella rossii, the yellow Ross lily, the flower on our $5 note.
Fat, fuzzy moths are clambering up the Bulbinella stems, water beading off their bodies as they probe the flower heads in search of nectar. Unlike moths back on the mainland, these ones rarely fly, and for good reason. In the fierce wind, an overly ambitious leap from one plant to the next might see a moth swept away to the oblivion of the open sea. Instead, they hold on tight and walk. When there are gaps in the wind, they make short hops between flowers.
This is not what pollination looked like in my school textbooks.
“When you think of pollination,” agrees Buxton, laughing, “you think of bees, and sunny, happy kind of things.”
Remote islands like Enderby usually have few insects. Flowers in these places tend to rely on the wind to carry their pollen to neighbouring plants, or they fertilise themselves—a trick some plants developed when help was hard to find. There are no bees in New Zealand’s subantarctic, but scientists have counted 89 species of moth.
Over four nights Buxton, along with the University of Otago’s Janice Lord and Barbara Anderson from the Otago Museum, set traps to capture some of them. Later, they analyse the moths under a microscope, looking for pollen grains stuck to their hairy heads and bodies. It’s this work that’s provided the first evidence that moths are playing an important role in subantarctic pollination, particularly for Bulbinella and Dracophyllum species on Enderby Island.
Lord has long been working on the puzzle of pollination in the subantarctic. In 2010, she travelled to Campbell Island to figure out how its megaherbs reproduced. She wondered if flies were visiting the plants during the day, but reading the visitors’ book in the hut led her to an unexpected discovery. “There was a comment about these wētā coming out and crawling over the flowers at night. So I rounded everyone up, we put on our head torches and went out at midnight.
“Wētā were swarming over the Bulbinella and Anisotome and carrying pollen—there were up to 15 wētā crammed on one flower, fighting each other and falling off.
“It just goes to show—in a weird environment, weird combinations of species come up with weird interactions.”
Similarly, on the mainland, scientists are only just starting to understand the ins and outs, so to speak, of plant sex in Aotearoa. And gaining an intimate understanding of who is doing what to whom—and when—is crucial. With many of our native plant species on the brink of extinction, and with our multibillion-dollar agricultural and horticultural export trades dependent on pollination, scientists are trying to figure out how we can bolster our insect allies against what is potentially a looming crisis.
Before honeybees arrived in New Zealand with European settlers, the country already had its own native bees (see sidebar on page 54). They’re far more common than most people realise—including me.
In fact, I’m not even sure I’ve ever seen one. So, on a beautiful, warm, early spring day, I head down to the Dunedin Botanic Garden for a look. Enquiries with volunteer staff about where to find native bees draw a blank. Obviously, this is not a question they get asked very often.
Wandering into a grove of native plants, I spot a koromiko in full bloom by the side of the path and get down for a closer look. To my surprise I quickly spot several tiny bees at work. They’re jet-black, and about a third of the size of a honeybee. I realise I have in fact seen these insects before—they’re the little black bugs that occasionally hover across my field of vision while I weed the garden.
All our bee species are solitary. They don’t form hives and don’t produce honey. They nest in burrows in the ground, and can only be seen working flowers in the spring and summer. We also don’t have many of them—our 28 native bee species pale in comparison to Australia’s 2000.
“Most countries have a high diversity of bees,” says David Pattemore, a scientist with Plant & Food Research. “We have a lot of moths, beetles and flies.”
Before New Zealand was colonised, birds, bats and lizards were probably also a vital part of the pollination effort—perhaps more so than elsewhere in the world. Sandra Anderson, a pollination researcher based at the University of Auckland, believes honeyeaters like tūī and korimako/bellbirds, along with hihi/stitchbirds, are much more important than scientists have previously recognised.
“Many of our native trees and shrubs produce small white flowers,” she tells me. “Until now, those flowers have been regarded as insect-pollinated, because in the northern hemisphere that’s what an insect-pollinated flower should look like.”
But on predator-free islands such as Tiritiri Matangi, in Auckland’s Hauraki Gulf, native birds can be seen swarming all over the tiny-flowered plants. “They flower at times when the birds really need them and other resources aren’t available,” Sandra Anderson says.
However, many native birds are mostly gone from our mainland forests—as are pekapeka-tou-poto/lesser short-tailed bats, also thought to have been important pollinators.
“We’ve got plants that have almost entirely lost their pollinators,” says Pattemore.
These include some native mistletoes and the parasitic wood rose Dactylanthus taylorii, which is pollinated by ground-foraging bats.
A number of native plants have long, tube-shaped flowers—think fuchsias, flax and kōwhai—which means their pollinators need a beak and a long tongue to reach the nectar.
“So if we’ve lost native birds in that area,” says Pattemore, “we don’t have another species that can easily pollinate that plant.”
We will probably never know how many plant species have been lost because they couldn’t be pollinated.
“How would you know?” says Lord. “We know some plant species have gone extinct, because they were recorded by early Europeans. Certainly, there’s a lot of very rare species.
“There’s also a lot of rare tree daisies. They’re visited by moths at night, but often the seed isn’t viable, so maybe the moths aren’t moving around enough, or there’s not enough trees, or some other part of the whole system is missing.
“It’s scary that there are still great gaps in our knowledge, when there are species that are rare and not regenerating.”
Moths often lay their eggs on specific native plants, which the larvae then feed on. As those plants vanish from our landscape, the moths’ ability to reproduce is greatly diminished. Barbara Anderson, who runs Ahi Pepe MothNet, an outreach project based in Dunedin, is concerned a catastrophic moth decline is occurring right under our noses.
Electric lights may also be disrupting moths’ ability to be effective pollinators. “Moths are drawn to the light,” she explains, “so they’re buzzing around the light, not doing what they’re meant to be doing, which is mating, laying eggs and feeding.”
The effects on our flora of a pollinator decline may take many years, or even decades, to become apparent, a phenomenon referred to as “extinction debt”.
“If a plant’s pollinator goes extinct, you might not know it straight away,” says Barbara Anderson, “because plants have a long lifespan. You could have a tree that’s moth-pollinated which lives for a hundred years. The pollinator could go extinct, but you wouldn’t necessarily know that the plant was unable to be pollinated and was going to go extinct.”
Fortunately, however, most New Zealand plants take a much more “come-all-ye” approach to passing on their pollen.
“If you look at pollination systems in New Zealand,” says Lord, “virtually everything can benefit from different types of insects. It’s rare for a plant to depend on just one type of insect, because it makes them very vulnerable. A plant that’s visited by moths at night will most likely be visited by flies during the day.
“It would take more than just one species’ extinction to cause the extinction of the plant,” she tells me. “But if there’s a general decline, that could be a tipping point in the ability of a rare plant to regenerate in the wild.”
Is there an “insect apocalypse” happening here? Reports of pollinator declines overseas have triggered fears that a similar pattern is happening in New Zealand. But ascertaining whether a mass insect die-off is happening is not easy.
Many of our native plant species go through “mast” years, when they collectively produce huge amounts of seed, then won’t produce any in the following years. This, along with our country’s volatile climate, distorts the picture, and makes studying long-term trends in insect numbers very difficult.
“We’re only just breaking the surface of New Zealand’s pollination problem,” says Lord. “There’s a lot we don’t know, and only a handful of people working on the problem.
“Finding out what insects visit a plant, then which of those are the key pollinators, can take a lot of determined patience and effort.”
Long-term data sets are crucial, and while some universities and institutes like Manaaki Whenua/Landcare Research fund some long-term site monitoring, very often the work falters when the person leading the project moves on.
“There’s lots of examples of long-term monitoring plots that have just gone by the wayside because whoever was the passionate person behind it has retired,” says Lord. “But without that historical data we’ve got nothing to compare it to.”
To counter this problem, some researchers are now using novel methods to track pollination changes through time. Deep in the bowels of Te Papa, terrestrial invertebrates curator Julia Kasper is dusting off old drawers full of native and introduced bees that have been collected since the early 1800s. She’s painstakingly removing microscopic grains of pollen, then analysing it to determine what plants it came from. “It gives us a view back into the past,” she says.
The pollen record captured on the hairs of these bees, she explains, will paint a picture of changing land use over the years. “We can go back and look at the insects that have been collected when the bush was still very original and native and compare it with insect samples from later, when we know there was lots of farming going on. Then we can model scenarios that predict the future.”
Barbara Anderson is doing similar work at the Otago Museum, using a massive collection of more than 23,000 moths collected by former curator Brian Patrick. She plans to compare moth species collected at certain localities with moth species that are found in those places now, in order to detect changes in moth populations.
What we do know is that native pollinators are disappearing in areas of unbroken pasture. “Where you get the really intensive farming areas, there are almost no native pollinators at all,” says Jamie Stavert, a Department of Conservation science advisor, who wrote his PhD thesis in 2018 on the subject.
When land is completely given over to pasture, Stavert found, native bees disappear entirely. “They reproduce once a year,” he explains, “and they nest in the soil, so you can imagine if you get a farm doing a whole lot of grazing cattle and sheep, tilling the ground and disturbing it all the time, then trying to nest in that sort of environment’s not going to work.
“Removing native plants also denies our native bees a critical food source, without which they can’t build up enough food reserves to survive the winter.”
For Barbara Anderson, it’s time New Zealand woke up and started taking more care of its insect pollinators.
“The thing about pollination is everyone thinks bees,” she says. “They think in a very British mode.”
Pollination networks and plant ecologies, I’m beginning to understand, are tightly interwoven and complex. They’re like the source code that underlies a computer’s operating system. Tinker with one part of it and the program changes, sometimes in unpredictable ways. Some facets may stop working. Unlike a computer, however, there’s no ‘undo’ button for nature, no previously saved version. The parts you erase can never be rewritten.
Introduce new code, however, and you might be able to get some of the old jobs done. As our native pollinators have disappeared from our landscape, introduced pollinators have been hard at work in our native bush. Honeybees, in particular, are thought to be, at least to some extent, replacing vanished birds, bats, beetles and lizards.
“A lot of native flowers are very generalised and can be easily accessed by anything,” says Pattemore. “So honeybees and bumblebees are well equipped to pollinate those plants.”
Recent research by Pattemore and David Wilcove, an ecology professor at Princeton University, has shown that some plant species, including pōhutukawa and rewarewa, are now being pollinated by ship rats. Some of these plants may even depend on rats for survival—which means that eradicating rats without also encouraging native animals back could have negative consequences for native plants.
Bees are very good at transferring pollen, and as “super-generalists” they are able to pollinate many different plant species—but what really gets the job done is their sheer numbers. A honeybee hive maxes out at around 60,000 bees, with each queen producing armies of workers ready to die for the cause of gathering food.
The four species of bumblebee in New Zealand are also important pollinators for certain crops, although their colonies number only a few hundred individuals. Between, them, honeybees and bumblebees keep us in clover, and apples, and pears, and apricots, and kiwifruit, and… well, the list goes on.
It’s thought pollination of food crops, fruit and arable pastures by introduced bees contributes billions of dollars to New Zealand’s economy.
But being so heavily dependent on a handful of species makes us vulnerable, especially as disease threatens bees. If anything happened to honeybees, New Zealand would face a pollination crisis. Could native insects come to the rescue?
Pattemore is interested in trying to reduce our dependence on Apis mellifera by bolstering native pollinators. The problem with honeybees, after all, is that you can’t herd them.
“You might go to the expense of getting hives into your orchard and if there happens to be a more attractive flower open two kilometres away in the opposite direction, those hives could easily decide to go and forage there instead,” says Pattemore. “Whereas if you’ve actually maintained populations of wild pollinators in your orchard, they are much more likely to forage within your orchard. It builds resilience into our farming systems.”
Native insects may also be able to bolster our agricultural systems against a changing climate.
“If you rely on just one species to do all your pollination,” says Stavert, “and there’s a change in the environment and it disappears, then you’ve lost that service. But if you’ve got half a dozen species that are all providing that service, some might drop out, but others will persist.”
Since 2003, Brad Howlett of Plant & Food Research has been studying the importance of native pollinators to New Zealand crops.
“Diversity of pollinators is really important,” he says, “because honeybees are active when it’s warm and sunny, but other pollinators will be active when it’s cooler. So trying to get pollinator diversity hedges your bets. If you can encourage that, you’re likely to get more even pollination in your crop.
“It’s just assumed that because honeybees are managed, they’re the best pollinators for everything. But in reality, some of the crops we grow, such as avocado, haven’t even evolved with honeybees present.”
And sometimes native bees, bumblebees, moths or even flies are better pollinators than honeybees.
“There are certain crops that flies are quite good at pollinating,” says Howlett. “They’re quite attracted to carrot, whereas bees often aren’t.”
Howlett and his colleagues are investigating the efficacy of using native hoverflies in orchards. The key to a good diversity of pollinators, he says, is planting native species.
Says Stavert: “The farming landscape needs to have native habitat interspersed and areas that are refuges for native species.”
Trying to put into words the importance of animal pollination is not easy. You can mention specifics, like the 31 billion honeybees needed to pollinate California’s almond orchards each year, or the critical role bats play in pollinating Indonesia’s durian trees. You can talk about the four billion hoverflies that move like a tide over the summer fields of the United Kingdom, ensuring that country’s crops and wildflowers reproduce, or how animal pollination is worth $260 billion a year to the global economy.
But even then, you don’t really get close, as these facts and figures ignore the vast role pollinating animals play in maintaining Earth’s wild ecosystems and forests—the lungs of the planet that keep us breathing. In the end, trying to quantify the importance of animal pollination to life on Earth becomes a bit like trying to describe the value of oxygen, or water—because we live in a world that has been utterly shaped by it.
In today’s New Zealand, it’s all about striking a balance—between native and introduced, wild and domestic, forest and farm. It’s been that way since the first human set foot on the shores of Aotearoa. But as we look down the barrel of a global insect decline, the stakes of getting it right are as high as they’ve