Bugs on the move: pollinators, pesticides and one epic migration

A recent study from a team of ecologists at the University of Exeter reveals an amazing insect migration from the Middle East to Cyprus. But globally, numbers are in decline – and the ‘emergency’ use of pesticides could have a devastating effect. 

The Karpaz Peninsula – the distinctive finger-like promontory on the north-east of the island of Cyprus – was the scene for a a new piece of research on the movement of insects from the Middle East to Europe.

Photograph by Alamy
By Lauren Jarvis
Published 13 Dec 2022, 09:28 GMT

“I HAD NEVER seen anything like it. The sky turned black and we were being pelted by what felt like tiny bullets – we had to dash for cover behind the car door.”

PhD student, Will Hawkes, from the University of Exeter’s Centre of Ecology and Conservation was studying insect migration in the Mediterranean, when a swarm of Biblical scale descended on the tiny tip of the Karpaz peninsula in north-east Cyprus.

In just over one month, lead researcher Hawkes, who is funded by The Royal Society, and a team of international researchers from insect migration groups led by Wotton & Chapman at the University of Exeter, recorded 39 million migratory insects arriving from the Middle East into Cyprus. Powered by the wind and using the sun as a compass, some of the tiniest creatures on the planet navigated safe passage across at least 105 kilometres of open ocean.

The scientists believe this migration could be part of a much larger movement, with billions of insects heading to Europe from locations including Syria, Iraq and Saudi Arabia. Their findings have been published in a paper in the journal Ecography: Huge Spring Migrations of Insects from the Middle East to Europe: Quantifying the Migratory Assemblage and Ecosystem Services.

“For me, it’s not just the numbers which are impressive,” says Hawkes, “but the diversity of insects migrating. We recorded huge numbers of vagrant emperor dragonflies and painted lady butterflies, but flies were the most numerous migrants by far – 86% were Diptera, while 10% were Lepidoptera.”

Using just one pair of wings to fly, and found around the world, the Diptera order of insects numbers more than 125,000 species, including hover flies, craneflies, mosquitoes, midges, house flies and horse flies. Lepidoptera, meaning “scaly wing” in Greek, is an order of 155,000 species which includes butterflies, moths and skippers, distributed across every continent except Antarctica. The remaining insects identified by Hawkes and his colleagues included bees and parasitic wasps (Hymenoptera, 2%), true bugs (Hemiptera, 1%), dragonflies (Odonata, 0.5%), beetles (Coleoptera, 0.3%), bark lice (Psocoptera, 0.06%) and lacewings (Neuroptera, 0.01%).

A marmalade hoverfly in flight. A well-known long-distance flyer that climbs to high altitude to take ...

A marmalade hoverfly in flight. A well-known long-distance flyer that climbs to high altitude to take advantage of tail winds, this species is one of many that enter and exit the U.K. each year. The total biomass of insects that arrive on our shores each year equals some 3,200 tons – or around 3.5 trillion insects.

Photograph by Will Hawkes
The crimson-speckled moth is a species native to southern Europe which also makes long migrations, sometimes ...

The crimson-speckled moth is a species native to southern Europe which also makes long migrations, sometimes – though rarely – as far as the U.K.'s southern coast.

Photograph by Will Hawkes
A wildflower meadow in Cyprus – one of the theatres of study for University of Exeter ...

A wildflower meadow in Cyprus – one of the theatres of study for University of Exeter research.

Photograph by Will Hawkes

‘Flyways’ and gene migration

These tiny migrating marvels perform a diverse range of vital environmental services, from driving cross-continental pollination, to transferring essential nutrients into soils, decomposing organic matter, providing an important food source for local insectivorous wildlife, and keeping pest numbers down. The long-distance transfer of genes by migrant insects also allows plants to maintain a diverse genetic pool and potentially mitigate changes in environmental conditions.

“This research sheds new light on the little-studied Eastern Mediterranean ‘flyway’ of insect migrants, revealing how many species colonise Europe each year from the Middle East,” explains Hawkes. “So many of these insects play vital ecological roles. They are pollinators, decomposers, nutrient transporters, pest controllers – and sometimes pests themselves. If we know the routes they take around the globe, we can inform farmers how best to manage their land to make use of the insects' natural behaviours. With eight billion people now on the planet, having efficient and sustainable food systems in place is more important than ever, and insects definitely have a role to play in achieving that.”

Fully understanding the contribution made by migratory insects is a challenge for scientists as they are difficult to track, with migration often taking place at high altitude. Migration ‘hotspots’ like the Karpaz Peninsula offer a great opportunity to study insect movements at ground level.

The Exeter University team set up their study in spring 2019, and used a combination of camera traps, netting and timed counts to collect their data, documenting insects arriving at a rate of nearly 6,000 insects per metre per minute. Mass arrivals coincided with higher temperatures and easterly winds, and satellite imagery to assess the amount of winter vegetation growth allowed the research team to track the migrants’ origins to Syria, Iraq and Saudi Arabia.

Small but smart

Insects make up over half the species on earth, but with populations in decline around the world and 40% of species facing extinction in the coming decades, it’s more important than ever to have an understanding of their journeys and their contribution to terrestrial ecosystems.

“We know a lot about the migrations of land mammals and birds, but not much about insects apart from a few well-known examples, such as the monarch butterfly, desert locust and bogong moth,” says TV and radio presenter Dr George McGavin, President of the Dorset Wildlife Trust, Honorary Research Associate at Oxford University Museum of Natural History, and one of the UK’s foremost entomologists. McGavin was not involved in the work. “Before this study, we really didn't know a whole lot about fly migration. It’s really new, important stuff.” 

A locust blowfly, a migrant known to be an important natural controller for locusts – by ...

A locust blowfly, a migrant known to be an important natural controller for locusts – by feeding on its eggs. This serves both fly, and indirectly, humans; a 2021 plague of locusts in East Africa decimated crops. The use of millions of litres of broad-spectrum pesticides to control the locusts is therefore paradoxical given the locusts would probably have been less of a menace had biodiversity been less depleted, or climate change not complimented conditions conducive to their breeding.

Photograph by Will Hawkes
A drone fly smeared with orchid pollen. Migrants such as this typically enter their destinations carrying ...

A drone fly smeared with orchid pollen. Migrants such as this typically enter their destinations carrying 10 grains of pollen from an average of 3 different plant species; this is much less than bees, but given the greater number of flies, their service as a long-distance pollinator is considerable.   

Photograph by Will Hawkes
An ant feeds on the corpse of a painted lady butterfly. Butterflies are effective pollinators with ...

An ant feeds on the corpse of a painted lady butterfly. Butterflies are effective pollinators with a longer range than bees, and pollinate primarily vegetables as opposed to fruit crops typically pollinated by bees. 

Photograph by Will Hawkes

Insects generally migrate to exploit seasonal resources and continue to breed all year. In the northern hemisphere, insects migrate north in spring as flowers bloom progressively northwards. In the autumn, insects will migrate back south again to warmer wintering grounds. In a research study led by Richard Massy, a team including Hawkes, Wotton and Chapman discovered that insects as small as hover flies use the sun as a compass to orientate on their autumn migration, while another by Boya Gao and the team found that hover flies will actively choose winds blowing in beneficial directions for them to migrate.

The Karpaz study showed that the insects migrating from the Middle East into Cyprus were performing vital cross-continental pollination services, diversifying gene pools and sustaining local wildlife. “These migratory insects are really important at a local ecological level,” says Hawkes. “We saw ants eating painted lady butterflies, and migratory locusts and butterflies being eaten by turtles.”

While the discovery of millions of insects visiting one narrow spit of land in the Mediterranean is a much-needed positive find, scientists and conservationists remain concerned about the global decline of insect populations. Vital for keeping ecosystems in balance, as Sir David Attenborough has commented: “If we and the rest of the back-boned animals were to disappear overnight, the rest of the world would get on pretty well. But if the invertebrates were to disappear, the world’s ecosystems would collapse.”

Chemical threats

Around the world, habitat loss, climate change and pesticide use have caused alarming reductions in numbers of butterflies, moths and bees, essential pollinators for the 75% of crop species that rely on animals to propagate. In the UK, flying insects have declined by 60% in just 20 years.

“The threats to our insects here in the United Kingdom are the same as those threatening the rest of our planet's biodiversity,” says Dr George McGavin. “Climate change and associated extreme weather events such as floods and drought; habitat loss, largely due to intensive agriculture; fields planted with monoculture crops treated with powerful toxic pesticides; and the loss of our wildflower meadows. England has lost 97% of its meadows since the 1930s and the UK is sadly no longer a ‘green and pleasant land’: it is one of the most nature-depleted countries in the world.” 

With the UK’s departure from the European Union, wildlife NGOs and Europe’s only conservation organisation for invertebrates, Buglife, have expressed concerns over the Government’s Retained European Union Law (Revocation and Reform) Bill – or REUL – which could see the removal of pesticide regulations: a huge backwards step which could put insect populations, other wildlife and human health in danger.

In a recent statement, Buglife said that the UK Government missed commitments to introduce a National Action Plan on the Sustainable Use of Pesticides in 2018, and has repeatedly overruled the independent UK Expert Committee on Pesticides (ECP) to allow the use of banned products known to cause harm – including neonicotinoids – on sugar beet crops.

“The threats to our insects here in the United Kingdom are the same as those threatening ...

“The threats to our insects here in the United Kingdom are the same as those threatening the rest of our planet's biodiversity.” Entomologist Dr George McGavin.

Courtesy of George McGavin

Insects vs. humans

Chemically similar to nicotine, neonicotinoids have been widely used on crops around the world since the 1990s and are systemic pesticides, meaning that unlike contact pesticides – which remain on the surface of treated plants – they are usually applied to seeds or sprayed on the foliage and permeate the entire plant, including the leaves, roots, stems, flowers, pollen and nectar. Highly toxic to invertebrates including bees, they attack their central nervous system, leading to paralysis and death.

The European Union banned the outdoor agricultural use of three neonicotinoids in 2018 – clothianidin, imidacloprid and thiamethoxam – but by 2020 at least 67 ‘emergency’ authorisations had been issued to use the insecticides on European crops including sugar beet, maize, oilseed rape and lettuce. In March 2022 George Eustice, Secretary of State for Environment, Food and Rural Affairs approved the National Farmers Union and British Sugar’s joint application for an emergency authorisation for the use of thiamethoxam (Cruiser SB) on England’s sugar beet crop to protect it from aphid-transmitted yellows virus (YV). Controlled by neonicotinoid seed treatments prior to the ban, 25% of the national crop succumbed to YV in 2020, with growers losing £43 million in revenue. The race is on to develop YV-resistant strains of beets and less toxic treatments, but in these challenging economic times, farmers are looking for swift solutions.

Neonicotinoids are still widely – and legally – used in greenhouse food production, which studies have shown pollutes surface and groundwater, despite being considered a low-risk, enclosed system. They are also found in high concentrations in flea and tick treatments for pets in the UK, including collars. One flea treatment of a medium-sized dog with the neonicotinoid imidacloprid – found in multiple products – contains enough pesticide to kill 60 million bees. Bathing pets flushes the chemicals into the water system, while dogs swimming in rivers and lakes is adding to the toxic soup: a study by researchers at the University of Sussex found that 99% of samples taken from 20 English rivers were chronically contaminated with insecticides which are hazardous to aquatic ecosystems, and highly toxic to invertebrates, fish and birds.

A pesticide sprayer treats crops on a German field. While neonicotinoids were banned by the EU, ‘emergency authorisations’ to protect crops including sugar beet, maize, oilseed rape and lettuce from insect-borne threats have resulted in the pesticides being used again. 

Photograph by Canetti / Alamy

“In recent times, increasing pesticide use has caused localised extinctions of bee populations and has made our rivers toxic,” said TV Presenter and Buglife President, Steve Backshall in the organisation’s statement. “This is a time for our Government to protect wildlife and people from pesticide harm. I would urge our new government to reconsider removing pesticide regulation.”

A regulatory minefield

Responding to these concerns, a spokesperson at the UK’s Department for Environment, Food and Rural Affairs (DEFRA) told National Geographic:  “The United Kingdom upholds strict food safety, health and environmental standards, and our first priority regarding pesticides is to ensure that they will not harm people or pose unacceptable risks to the environment.” The 2022 emergency authorisation of thiamethoxam was issued with strict conditions attached to ensure that potential risks to pollinators are minimised, DEFRA's spokesperson said, including conditions being imposed on the planting of any flowering crops within 32 months of the sugar beet crop, an industry-recommended herbicide programme to limit flowering weeds, and an independent monitoring programme of soil and plants in and around treated fields. 

The spokesperson added, “The UK Government has an excellent record on the environment enshrined in law in our landmark Environment Act. Any decision on preserving, repealing or amending Retained EU Law (REUL) will not come at the expense of these high standards – and we are working to publish an updated UK National Action Plan for the Sustainable Use of Pesticides (NAP).” They also said that while pesticides in soil can enter water bodies, an assessment carried out by the Health and Safety Executive found that levels of neonicotinoids in water were unlikely to harm aquatic life. However, the extensive risk assessment by the European Food Safety Authority is clear on the dangers, and the UK Expert Committee on Pesticides (ECP) advises that keeping neonicotinoid use to an absolute minimum is critical for insect population recovery.

“We now know that insect species aren’t blown randomly around the globe, but intentionally select favourable winds and orientate adaptively. ”

“To maintain balanced, healthy ecosystems, we urgently need to rethink agricultural practices,” says Exeter University’s Will Hawkes. “Intensive monoculture farming provides ‘nuisance’ insects with the perfect conditions they need to thrive. For example, aphids do well in monotypic crops such as sugar beet. ‘Useful’ insects, such as migrating hover flies, eat aphids, but they also need to feed on flowers, so the loss of our wildflower meadows – or deliberately stripping out flowers from a beet-growing region – is driving away the aphids’ natural predators. It’s a destructive cycle. If you're a farmer, intercropping with wildflower strips is very helpful – to both you and the insects.”

A natural transport network

In 2019, a study performed by Dr Karl Wotton and University of Exeter Associate Professor and ecologist Dr Jason Chapman, who both worked on the Cyprus migration study with Hawkes, discovered that hundreds of millions of hover flies migrate north from continental Europe to southern Britain England each spring – rivalling the number of managed honeybees across the whole of the UK during the summer and providing a vital pollination service for farmers. Once there, they lay their eggs, and their larvae feast on trillions of aphids – a natural, non-invasive form of pest-control – before the newly emerged adults head back to Europe in the autumn.

A man holds a grey heron poisoned by aerial-sprayed pesticides in Bunyala, Kenya. Pesticide use interfering with wider ecosystems is a global problem – affecting insects in the first instance but frequently crossing into aquatic environments and poisoning fish, birds and invertebrates.  

 

Photograph by Charlie Hamilton James

"Insect migration is happening globally on a massive scale,” says Chapman, who used narrow radar beams to track the insects’ journey. “It's a huge, under-appreciated phenomenon." Advances in radar entomology is helping scientists to understand high-altitude and night-time insect migrations, which have previously been difficult to document.

Trillions of bugs are annually on the move, and knowing which insects are migrating and where they are going is incredibly important, agrees Will Hawkes. “Without this information, we cannot even begin to understand what effects their movements have on the planet.”

Thanks to research by Hawkes, Wotton, Chapman and their fellow scientists, we now know that insect species aren’t blown randomly around the globe, but intentionally select favourable winds and orientate adaptively. Effective conservation of migratory species relies on protection throughout their annual cycle, and global coordination on establishing or maintaining protected areas (PAs) along their migration routes.

“Migratory insects are vulnerable to habitat loss beyond the boundaries of one country,” says Hawkes. "Human activity and climate breakdown could affect the migration routes and ranges of these insect species, so we need to take a more global, holistic view of conservation. If we all take an interest in these remarkable little creatures, we can not only protect them, but reap the huge and long-lasting rewards for doing so.”

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