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    How farming could become the ultimate climate-change tool

    Scientists can measure the carbon-storage capacity of various types of soil.Credit: Patrice Latron/Eurelios/Look at Sciences/Science Photo Library

    When it comes to carbon, humanity has two pressing problems. First, there’s too much of it in the atmosphere. The atmospheric concentration of carbon dioxide has increased by about 50% since the start of the industrial age, from 280 parts per million to nearly 420 parts per million in 2023 (see Much of that comes from the combustion of fossil fuels, but agriculture is a major contributor. Each year, around 13.7 billion tonnes of CO2 or equivalent greenhouse gases is released into the atmosphere by agricultural processes, with more than one-quarter of global greenhouse-gas emissions arising from food production1.The second carbon problem is that there isn’t enough of it in the soil. Soil carbon has been drastically depleted around the world, thanks to intensive farming practices that have been developed to feed the growing population. One estimate suggests that around 133 billion tonnes of carbon — about 8% of total organic soil carbon — has been lost from the top 2 metres of soil since the advent of agriculture some 12,000 years ago. Around one-third of that loss has occurred since the Industrial Revolution in the 1800s2.This imbalance means that agriculture has an ace up its sleeve: although it’s currently a carbon source, it also has the potential to be a carbon sink, which could alter the planet’s climate-change trajectory (see ‘Green horizons’). It’s not only possible, but it’s relatively easy to recharge soil organic carbon stocks by supporting and enhancing the natural processes that draw and convert CO2 into soil carbon.

    Source: FAOSTAT for 2021 and model projections for future years

    The latest Intergovernmental Panel on Climate Change (IPCC) synthesis report3 puts carbon sequestration in agriculture as one of the highest potential contributions to reducing net emissions. At around 3.5 gigatonnes of CO2 or its equivalent greenhouse gases per year, this is greater than the emissions from the entire European Union in 2022 — exceeded only by a conversion of current energy supplies to solar or wind energy, or reduced destruction of natural ecosystems. The challenge is to ensure that this happens fast enough, and at a low enough cost, for it to make a substantial contribution to achieving global net-zero carbon emissions by 2050.The agricultural techniques that can help to increase soil carbon sequestration aren’t necessarily complex. But with the looming deadline of net-zero carbon emissions by 2050, as set by the Paris climate agreement, the pressure is on scientists to identify the most efficient, effective and rapidly scalable methods for soil carbon sequestration and how these can help to achieve the dual goals of mitigating climate change and improving soil health.Carbon farmingSoil organic carbon is the result of the CO2 that plants have extracted from the atmosphere and incorporated into their structure, especially root systems, being used to nourish other living organisms in the soil.
    Nature Spotlight: Agricultural sciences
    “Before soil carbon was even a thing from a climate-change perspective, people were promoting the increase of organic matter in the soil to improve its fertility, to improve water-holding capacity and resilience to droughts, and to prevent erosion,” says Peter Smith, a soil scientist at the University of Aberdeen, UK, and science director of Scotland’s ClimateXChange centre in Edinburgh, UK. “Nobody disagrees that increasing the amount of soil organic matter is a good thing,” Smith says.The good news is that increasing soil carbon isn’t high tech. Evolution has already done most of the hard work by giving plants the ability to extract CO2 from the atmosphere through photosynthesis, turning it into carbohydrates and oxygen. The plants assimilate that carbon into their cells and tissues, which eventually become integrated into the soil when the plant sheds matter in the form of leaves, branches, flowers or fruit, or when it is consumed by other organisms, or when the plant dies and decomposes.The biggest barrier to this process is humans and the bad habits that we have developed to squeeze better short-term yields out of soil. One of these is tilling, particularly the deep ploughing that is commonly used to prepare the soil for planting. “A century ago, one of the things that made the prairie regions across the globe so fertile is that when we tilled them, the organic matter degraded and that released tremendous amounts of nutrients and produced bountiful crops,” says David Burton, a soil scientist at Dalhousie University in Halifax, Canada. That process breaks up the soil, including the root systems of the crops and grasses, causing the release of CO2 into the atmosphere. Tilling also destroys the structure of the soil and increases the risk of erosion by wind or water, which can in turn cause more CO2 to be released.

    Agricultural practices such as ploughing release carbon dioxide into the atmosphere.Credit: Jonas Gratzer/LightRocket/Getty

    Therefore, one way to potentially keep that carbon in the soil is to reduce or eliminate tilling in what’s called no-till or zero-till agriculture. Instead of turning over large amounts of soil to plant seeds or seedlings, farmers use equipment that creates either a narrow channel or a hole into which the seed or seedling can be planted. The residue of the previous season’s crop — stubble, stalks and stems, for example — is left in the soil and on the surface. The idea is that this reduces the disturbance of the soil structure and leaves more of the soil organic carbon in place.Although carbon sequestration through no-till is promising, the evidence is mixed. Research suggests that the amount of soil carbon sequestered with no-till farming varies with climate and soil type. One analysis found evidence that the greatest increase in soil carbon with no-till agriculture occurred in warmer and wetter climates rather than in cooler and drier climates4. However, less tilling does mean less fuel consumption — because farmers don’t have to plough as often and as deep — and therefore lower emissions. For example, the use of low-till farming in the United States is estimated to have saved the equivalent of around 3,500 million litres of diesel annually, enough to offset the annual CO2 emissions of around 1.7 million cars5.Another method to increase the retention of soil carbon is to grow cover crops alongside the main crop, instead of manually pulling up or poisoning weeds that appear. This keeps the root structure and its soil carbon contribution intact and in place. A study of two Australian vineyards found that allowing grasses to grow in between the rows of grape vines was associated with a nearly 23% increase in soil organic carbon over a 5-year period compared with the conventional method of using herbicide to control grass growth6. The practice is gaining momentum in North American vineyards , and it is already well established in European ones, where cover crops such as clover and barley have been shown to improve soil carbon levels while reducing weeds7.There is also a growing interest in the carbon sequestration potential of adding inorganic, or mineral carbon, to agricultural soils through a process called enhanced weathering. This involves adding ground-up silicate rock, such as basalt, to the soil. The minerals in the rock dust — mainly magnesium and calcium — interact chemically with CO2 in the atmosphere to form carbonates, which remain in the soil in a solid form or dissolve and gradually drain out to the ocean through the water table8.A four-year study, which was published in February, of the US corn-belt region found that applying crushed basalt to maize (corn) and soya bean fields was associated with sequestration of an extra 10 tonnes of CO2 per hectare per year, while also increasing crop yields by 12–16%9. “It’s one of the most intensively managed areas of agricultural land in the world, so if it works there, then you’ve got kind of instant scalability,” says study co-author David Beerling, a biogeochemist and director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield, UK.Deforestation is another major contributor to agricultural sector carbon emissions, particularly in cattle farming10, in which forests are bulldozed to create pastures for animals. Agroforestry — the integration of trees into farming systems — is one way to mitigate this problem. Growing trees and shrubs among crops and pastures not only increases carbon sequestration in the soil and the tree biomass, but also provides further benefits including wind-breaks and shade for cattle. Agroforestry is well established in many parts of the world, including in tropical areas where trees provide shade for crops such as coffee beans.As promising as soil carbon sequestration looks on paper, it has a limit, says Smith. “If we’re chucking it all up from geological sources, the biological sinks aren’t enough to suck up all that carbon,” he says. It’s also finite — there is a limit to how much carbon an area of land can sequester. The question is: what is that limit?Measure, monetise, incentivizeSoil scientist Rattan Lal, director of the Lal Carbon Center at Ohio State University in Columbus, says that if the world switches to non-fossil-fuel sources of energy, it will be possible to achieve a long-term positive soil carbon budget in which more carbon is absorbed by agriculture than is generated by it. “By 2100, the [carbon] sink capacity of the land is about 150 to 160 gigatonnes of carbon, and another of the same amount for trees,” Lal says. That amounts to around two gigatonnes of carbon per year that could be sequestered in soils. Other studies suggest that number could be as high as 4–5 gigatonnes of carbon per year11. Given global emissions now sit at around 35 gigatonnes per year, this is a substantial proportion12.Even at the lower estimate, if the entirety of that atmospheric carbon removal is realized, Lal’s research suggests it could reduce global atmospheric concentrations of CO2 by around 157 parts per million13, which would completely remove all the extra CO2 emitted since the start of the Industrial Revolution. “Agriculture could be a part of the solution,” he says.

    Soil scientist Rattan Lal at Ohio State University in Columbus says that a switch to non-fossil fuels should make it possible for more carbon to be absorbed by agriculture than is generated by it.Credit: The Ohio State University

    However, the soil-science community is divided over whether sequestering carbon in soils could be part of the climate-change remedy, says Alex McBratney , a soil scientist and director of the Sydney Institute of Agriculture at the University of Sydney, Australia. Even today, there are some people who think it’s simply too difficult because of the challenge of measurement.Soil carbon content varies a lot geographically, even over short distances, so getting a reasonably accurate measurement at a point in time means taking lots of samples — and that can add up financially. Soil carbon also fluctuates naturally, depending on weather conditions and other factors. And the change in soil carbon levels over time might also be small relative to the overall amount of carbon in the soil, which makes it harder to record a significant change.Soil carbon levels also change slowly. “We would say, as a rule of thumb, that it probably takes of the order of five years to show observable differences … that you can detect against the background of this natural variation,” McBratney says. Combined with variability, this makes it challenging to show that extra soil carbon has been sequestered, especially in a cost-effective manner.Cultivating changeDespite the uncertainties of soil carbon sequestration, it is a hot topic when it comes to emission reductions. Governments have leapt enthusiastically, and sometimes prematurely, into capitalizing on the possibility of buying and selling carbon credits from agriculture. These are credits earned from reducing carbon emissions that can be used to offset carbon emissions from other sources or sectors — a win-win situation, given the added benefits of improving soil health.Marit Kragt, an agriculture and resource economist at the University of Western Australia in Perth, became interested in soil carbon sequestration shortly after the Australian government introduced the Carbon Farming Initiative act in 2011. Her concerns were that the policy had been formulated with little scientific or economic data on, for example, the best practices for sequestering soil carbon, the impact of climate, the cost to farmers and whether soil carbon sequestration would truly increase overall soil carbon.This cost-benefit analysis will be crucial to overcoming the sociocultural barriers to change. There is resistance to changing farming practices, particularly when the advice to do so comes from scientists or policymakers, says Kragt. “Sociocultural change is actually really important in any society, but is often forgotten,” she says. “When you have a group of people advocating for something and they’re not part of the farming community or trusted peers, there is push back.”However, Kragt says that most farmers who implement carbon-positive farming techniques don’t do it for the credits. “I think most people that have taken up carbon farming practices will have done so because they wanted to regenerate their environment,” she says. Many farmers are also concerned about climate change because they can see the impact on their livelihoods. “They have seen the bushfires, droughts and extreme heat that’s affecting their harvests, so they know that something needs to change.” More

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    Wildfires are raging in Nepal — climate change isn’t the only culprit

    Nepal’s wildfires are increasing in frequency and intensity, but it’s not just climate change to blame. Forest scientists say that Nepalis’ changing relationship with forests is also escalating the incidence of forest fire, but that better fire prediction and preparedness could minimize harm.This year alone, Nepal has already witnessed nearly 5,000 wildfires — the second worst since records began in 2002 and second only to its 2021 fire season, when the country recorded more than 6,300 outbreaks. More than 100 people have died from wildfires in the past 12 months. Kathmandu was engulfed in hazardous wildfire smog for days on end.Climate models suggest that Nepal will face more-frequent drought conditions into the future and that this will probably make wildfires worse. However, mismanagement of forests is more likely to be behind the recent blazes, say researchers.Nepal’s rural population grew rapidly in the early 1970s and the country’s heavy reliance on agriculture took its toll on the nation’s forests. In the hills, villagers cleared vast swathes of trees for firewood, fodder and timber. A 1979 World Bank report concluded that “the spectre of ecological disaster” was near, urging the country to undertake a large-scale tree-planting programme. The government took heed and decided to decentralize the management of its forests, granting locals control over nearly 1.8 million hectares of wooded land across the country. As a result, Nepal’s forest cover almost doubled in three decades, reaching 45% in 2016.Over this period, Nepal also went through major socio-political upheaval. Following the abolition of the monarchy in late 2008, the country transitioned into a federal system in 2015. “But this new political atmosphere didn’t prioritize the management of community forests like before,” says Uttam Babu Shrestha, an environmental scientist at the Global Institute for Interdisciplinary Studies in Kathmandu. Many community forests across the country are also still bound by rules that date to the 1990s, which prohibit the cutting of timber.The changes were further escalated by migration of people away from rural areas. In 2022, Sarada Tiwari, then a researcher for ForestAction Nepal in Patan, found that, in the previous year, more than 33% of locals that relied on the forests had left the country and that 63% of rural households had at least one member leave the village.Local peoples’ financial dependence on the forests dwindled. “With no clear benefits coming out of forests, the locals don’t feel the same ownership,” Shrestha says. They didn’t gather firewood or clear forest litter, which fuelled later forest fires. Shrestha says that even when the community-managed forests catch fire, locals don’t feel obliged to take action.In 2021, when Tiwari first visited the community forests in Bhumlu rural municipality, central Nepal, she was awestruck looking at the lush green regenerated pine forests. However, upon revisiting Bhumlu the following year, she couldn’t grasp how drastically the landscape had changed. “The forest had been completely transformed into an awful, blackened ash-covered terrain,” Tiwari says.Fire predictionIn 2021, when the country experienced its worst wildfires, Binod Pokhrel, a climate scientist at Tribhuvan University, Kathmandu, decided to study factors that might have contributed to them. He analysed trends of temperature, humidity and wind speed to calculate a drought index. As expected, a high drought index was often associated with a high number of wildfires in following weeks1.He found that the spread of wildfires is climate dependent, however “their origin, at least in Nepal, is mainly anthropogenic”, says Pokhrel. He suggests that informing community forest groups about the risk of forest fires ahead of time could drastically curb forest fires. There are more than 282 weather stations across Nepal. “By using weather station data, we could precisely forecast drought index up to a local ward level,” Pokhrel says.
    Why is Latin America on fire? It’s not just climate change, scientists say
    The International Centre for Integrated Mountain Development (ICIMOD), an intergovernmental research institute based in Lalitpur, already uses a similar framework to update its wildfire-monitoring portal. “We have added features that provide a two-day forest fire outlook, indicating which areas face high chances of forest fires based on weather data,” says Sudip Pradhan, a geospatial scientist at ICIMOD. Because people in most villages have access to the Internet and smartphones, Pradhan’s team is preparing to deploy mobile applications with real-time monitoring of forest fires.Pokhrel says that a smartphone-based forecast would reduce the chance of fires getting out of control and reaching the levels they did in 2021 and 2024. He and his team also surveyed locals and found that they would be better prepared to control local fires if they were informed at least a month in advance and were provided with tools such as fire trucks.Pokhrel says that although the work of organizations such as ICIMOD is useful, the Nepalese government also needs to be more involved in fire management. Pokhrel says the government could harness the existing community forest stewardship model and improved forecasting to help with fire preparedness. Without such measures, signs are clear that “the lack of management of increasing forest cover can easily lead to another disaster”, he says. More

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    I raise delicate butterflies on the mean streets of New York

    “Monarch butterflies (Danaus plexippus) are complex creatures, which is part of what makes them so interesting to me. Every breeding season there are four generations of these butterflies. Three live for only a few weeks, but the fourth survives for six to nine months. Some of this generation emerge from their chrysalises here in Queens, New York City, in September or October. They then begin a long migration to Mexico, before restarting their generational cycle and heading north in March or April.I became interested in butterflies by chance. I knew a little about their habitats from work I’d done at the wildlife conservation society at New York’s Bronx Zoo. One day in 2019, I saw a lawnmower going down the side of a highway in the city, and cutting through milkweed, which is the main habitat and food source for butterflies and their larvae. I knew that there in the weeds, thousands of eggs and caterpillars were being destroyed. That day was when I started my rescue mission. I set up a habitat in my backyard and started collecting eggs and bringing them home with me. From July through to September, that still takes me around six hours a day, seven days a week.In this photo, taken in August 2021, I’m in my backyard tagging one butterfly with a small sticker that will help to monitor the population’s progress south. I’ve released thousands of healthy monarchs from eggs I’ve collected by the roadside, which is mown regularly by the Department of Transportation (DOT) here in New York.Now, I’m working with the DOT to get better protection for monarch habitats. In the long run, this will help the butterflies more than my egg-rescue efforts can. As an animal lover, it’s hard to think about all those creatures that might never have made it to adulthood under a lawnmower’s blades on some random roadside. I do this for them and for their role in the wider ecosystem.” More

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    ‘Rainbow’, ‘like a cricket’: every bird in South Africa now has an isiZulu name

    The African pitta’s isiZulu name unothingo — meaning rainbow — is a reference to its brightly coloured plumage.Credit: Richard Flack/NaturePL

    Researchers hope that the Rudd’s lark’s new isiZulu name — unonhlozi — could bolster conservation efforts to protect the small endangered lark (Heteromirafra ruddi). Unonhlozi means eyebrows, a nod to the bird’s wizard-worthy eyebrows, and it is one of many new isiZulu words that researchers have created for South Africa’s birds.“We must all engage with our natural heritage in any language we choose,” says Nandi Thobela, a manager at the non-governmental organization BirdLife South Africa in Johannesburg, and co-author of a paper published last week in the South African Journal of Science1. The article describes how the researchers developed isiZulu terminology for all 876 wild bird species found in the country.The effort took more than a decade and involved numerous meetings to agree on the names, which were also made available for public comment before inclusion in the definitive list.Lolie Makhubu-Badenhorst, director of the Multilingualism Education Project at the University of Cape Town, South Africa, welcomed the research. “Such a publication contributes and affirms the use of our South African Indigenous languages, particularly in the field.”New terminologyIsiZulu is one of about 2,000 languages spoken in Africa, the overwhelming majority of which have been ignored by modern science. This can hamper research in many disciplines, including conservation science. Monitoring wild birds is a good way to gauge ecosystem health. But many African languages, including 10 of South Africa’s 12 official languages, do not have official names for different species, which can cause confusion.Since 2011, a team of scientists, language specialists and Zulu bird guides have been working with Birdlife South Africa to create a complete list of South African bird names in isiZulu.There were already isiZulu names for some birds, such as sparrow (ujolwane) and owl (isikhova), but the team adapted them to describe specific species. For some birds, the team had to coin entirely new names: the African pitta (Pitta angolensis), for example, was given the isiZulu name unothingo (which means rainbow), because of its green back, red undertail, yellow chest and striking face and wing markings. The barred wren-warbler (Calamonastes fasciolatus) is isanyendle, which means ‘like a cricket’, because of its cricket-like call. The names have been added to Cornell University’s global bird-identification app Merlin.The 18 bird guides involved in the naming and their Indigenous knowledge were “absolutely essential” to the project, says co-author Eckhart Buchmann, a retired reproductive-health researcher and avid bird watcher based in South Africa. “How can you choose a bird name if you don’t have in-depth working knowledge of the isiZulu language in environments where birds are appreciated?” he says. “You can only do this if you’re a Zulu person who’s grown up with these creatures around you.”Birdlife South Africa is now turning its attention to Sotho, a language spoken in the north of the country, says Buchmann. More

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    I breed and release Arctic foxes to boost their numbers in the wild

    “Here in Norway, red foxes (Vulpes vulpes) are all over the place. But Arctic foxes (Vulpes lagopus) — the fluffy white cousins of red foxes — survive only high up in the mountains, and meeting one is a really rare occurrence.Researchers estimated that, in 2000, just 40 to 60 Arctic foxes remained in Norway and Sweden. A combination of factors probably explains why the population has collapsed since the start of the twentieth century. For example, fur hunting occurred until the 1930s, and reductions in the numbers of lemmings — a crucial prey animal for the foxes — have also had an impact. Moreover, Arctic foxes live in a fragmented mountain habitat, and the construction of roads has increased the risk of the animals being killed as they disperse from one area to another.Steps taken by the Norwegian Institute for Nature Research are starting to turn things around. These include supplementary feeding of the wild population and running a captive breeding station. Now there are an estimated 560 Arctic foxes across Norway, Sweden and Finland.We have 15 foxes at our captive breeding station near Oppdal in Norway’s Trøndelag county. In this photo, I’m crouching down helping a colleague to transfer a pup from a trap into a handling bag for a health check. We try not to handle them more than we have to, and we prepare them as much as possible for life in the wild. As cute as they are, they are not tame. The 464 young foxes we’ve released since 2006 have done really well. They’ve survived and bred in the wild.At this point, we’ve progressed from trying to save the Arctic fox from extinction in Scandinavia to working on getting its population to be sufficiently large and genetically diverse to sustain itself. We’ve still got a way to go, however, before we can say the species is saved.” More

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    Why cicadas shriek so loudly and more: your questions answered

    A periodic cicada in Illinois, where two broods are emerging this month at once.Credit: AJ Mast for Nature

    As spring turns to summer in the United States, warming conditions have started to summon enormous numbers of red-eyed periodical cicadas out of their holes in the soil across the east of the country. This year sees an exceptionally rare joint emergence of two cicada broods: one that surfaces every 13 years and another with a 17-year cycle. They last emerged together in 1803, when Thomas Jefferson was US president. This year, billions or even trillions of cicadas from these two broods — each including multiple species of the genus Magicicada — are expected to swarm forests, fields and urban neighbourhoods.To answer readers’ cicada questions, Nature sought help from three researchers. Katie Dana is an entomologist affiliated with the Illinois Natural History Survey at the University of Illinois at Urbana-Champaign. John Lill is an insect ecologist at George Washington University in Washington DC. Fatima Husain is a cognitive neuroscientist at the University of Illinois at Urbana-Champaign. Their answers have been edited for length and clarity.Why do periodical cicadas have red eyes?JL: We’re not really sure. We do know that cicadas’ eyes turn red in the winter before [the insects] come out. The whole coloration pattern in periodical cicadas is very bright: red eyes, black and orange wings. They’re quite different from the annual cicadas, which are green and black, and more camouflaged. It’s a bit of an enigma why the periodical ones are so brightly coloured, given that it just makes them more obvious to predators. There are no associated defences with being brightly coloured — it kind of flies in the face of what we know about bright coloration in a lot of other animals, where usually it’s some kind of signal for toxicity. There also exist mutants with brown, orange, golden or even blue eyes. People hunt for blue-eyed ones; it’s like trying to find a four-leaf clover.

    Entomologist Katie Dana collects cicadas in Monticello, Illinois.Credit: AJ Mast for Nature

    Can periodical cicadas see in colour?JL: They do see colour. But their eyes are basically non-functional when they’re underground. They’re not investing a lot of energy in making the sort of proteins associated with vision when they’re not needed. And so there’s some dramatic, abrupt developmental switch that happens, that probably coincides with the eye colour changing to red. They now need to be able to use their eyes in a new habitat, which is above ground.Can the two cicada broods interbreed?KD: We know that they can interbreed when introduced to each other in the lab, but it remains to be seen if it actually happens in a wild setting.Do cicadas compete to be heard?JL: Cicadas get together in all-male groups called choruses, and usually in a given tree. Cicadas of a particular species congregate together, put on a big show, and the females are hanging out around the periphery, judging the quality of potential mates. So that’s the reason it’s so loud, but I don’t know the degree to which they’re competing to be heard. They’re obviously trying to distinguish themselves among an already loud group, for the females. And the females are judging something about the quality of the call. But I think the loudness is probably correlated with how vigorous that male is, and might indicate [for a female] good genes to pass on to her offspring, so that she can, in turn, have loud-calling sons that would pass on those genes.
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    Can the incessant din of cicadas cause people to develop conditions such as temporary psychosis?FH: I highly doubt that the loud noise of the cicadas causes temporary psychosis. At least, I have not heard of any such cases. People do have hypersensitivity to loud sounds and may find the cicada noises bothersome. Some may find that the noise exacerbates their tinnitus. But for some others, the cicada noise can actually mask their tinnitus.If cicada males buzz to attract females, is it possible that females of one species will be attracted to males of the other species?KD: Noise absolutely brings female cicadas. If you run a lawnmower these days, all the cicadas will flock to you. But once they get closer to each other, there’s a call-and-response that’s more species-specific. The other thing is that in insects, we often talk about lock and key: the male [reproductive organ] is the key and the female [reproductive organ] is the lock, and they have to fit together perfectly. That’s how a lot of insect species make sure they’re mating with the right species.Do any insects thrive on periodical feasts of cicadas?JL: The cicada killer [Sphecius speciosus] is one of the largest native, stinging wasps that we have in this area [the eastern United States]. But the wasps don’t really start foraging until after the periodical cicadas are mostly gone. They mostly feed on the larger, green annual cicadas [family Cicadidae] that come out later in the year. The wasps capture cicadas and paralyse them with their venom and then bring them back to a pre-dug nest in the ground, where they lay an egg upon them. And the cicada serves as live meat for the developing wasp larva that will feed underground on the hapless cicada that gets eaten alive by the wasp larva. More

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    The cicadas are here! Why US researchers are swarming to study them

    The emergence is in full swing. Periodical cicadas (Magicicada) are crawling out of the ground in vast numbers — in their trillions, maybe — across swathes of the southeastern and midwestern United States. And researchers, many of whom usually study other insects, are dropping everything to race to sites where they’ve popped up, eager to collect samples and observe the ecological spectacle.“There’s an awful lot that we don’t know” about these insects that spend most of their lives about 60 centimetres underground “in a little mud hole in the dirt”, says Martha Weiss, an entomologist at Georgetown University in Washington DC.This year’s emergence also ups the ante for researchers. Two particular broods — groups of multiple cicada species with the same life cycle appearing above ground in the same year — will sync up for the first time in 221 years. That means the last time they saw daylight together was when the United States was being led by its third president, Thomas Jefferson. Brood XIX, also known as the Great Southern Brood, has been emerging for the past few weeks after 13 years underground, and the more northerly brood XIII has just started popping up after 17 years.Separate territoriesGeographically, the two broods don’t overlap much, although “they come really close together” in central Illinois, near the city of Springfield, says Chris Simon, an evolutionary biologist and entomologist at the University of Connecticut in Storrs. Brood XIX spans the largest area of any known cicada brood, from Maryland to Georgia in the southeast and from Iowa to Oklahoma in the Midwest. Brood XIII, meanwhile, covers northern Illinois, including Chicago.But there is a possible contact zone, and some scientists are flocking to it. Katie Dana, an entomologist affiliated with the Illinois Natural History Survey at the University of Illinois Urbana-Champaign, is hoping to investigate how the two broods might interact and how their mating songs differ. Normally, the pitch of these songs is one way to distinguish between the multiple, visually similar, cicada species that make up a single brood.

    One way to distinguish between species of cicada is to collect specimens, freeze them and later sequence their DNA.Credit: AJ Mast for Nature

    It could also be a way to distinguish between broods XIX and XIII. They, too, are closely related and look the same, Dana says, making interbreeding possible but really challenging to study in the field.So Dana is now observing their interactions and collecting as many samples as possible, then flash-freezing them for storage. This will allow her and her colleagues to sequence the insects’ DNA later, to help them to distinguish between the broods.“There are gonna be so many graduate-student projects that we’ll have in our freezer after this year,” says Dana, who enthusiastically signs her e-mails “Dr. Ci-Katie-Dae”.Telling the time undergroundOne of the big questions that researchers will seek to answer during this emergence is, how do cicadas keep track of time?When they are above ground, periodical cicadas have a loud and frenzied mating season, after which the females lay eggs in small slits in tree branches. Once the eggs hatch weeks later, the white nymphs fall to the ground like snowflakes, burrow down into the soil and stay there, sucking sap from tree roots for nutrition. They survive and grow like this for a long time — usually prime-numbered stretches of years. The cicadas somehow know to emerge in a particular year once the soil warms up to a balmy 18°C.

    Periodical cicadas typically have red eyes, black bodies and orange-tinted wings.Credit: AJ Mast for Nature

    Researchers think that having prime-numbered reproduction cycles puts the cicadas conveniently out of sync with the life cycles of various predators that might stalk them. Emerging all at once, in vast numbers, also means that at least some members of a particular brood will survive to have offspring for the next reproduction cycle.But how exactly the insects work out whether 13 or 17 years have passed underground is a mystery. Certainly, they can clock seasonal changes in the trees they feed on, but that can’t be the whole story, Simon says. She suspects that epigenetics — chemical modifications of DNA that control how various genes are expressed — wind the insects’ internal clocks. Specifically, she thinks methyl groups (carbon atoms with three hydrogens attached) are involved. Like Dana, Simon will be collecting samples this year to test her hypothesis.A terrifying fungusAlthough the prime-number trick seems to help cicadas evade predators, it hasn’t fooled a certain parasite. Massospora cicadina fungus infects 13- and 17-year cicadas as they crawl out of the ground, eating through their abdomens and replacing their tissue with plugs of spores. Psychoactive chemicals released by the spores turn the infected cicadas into ‘zombies’, driving them to mate manically to pass spores on to others.
    Do insects have an inner life? Animal consciousness needs a rethink
    The spores remain dormant in soil for periods matching the prime-numbered cicada cycles, and become activated during an emergence year. But researchers have questions about how this works.Has the fungus evolved its own internal way of tracking 13- and 17-year cycles to keep up with the cicadas? Or is it simply activated by chemical cues released by cicada nymphs as they are about to emerge? To find out, Sierra Raglin, a soil microbial ecologist at the University of Illinois Urbana-Champaign, will locate and collect infected cicadas this year, as well as look for spores in the nearby soil. The soil and its microbiome haven’t been studied much in this context, Raglin says.Cicada emergences are a bolt out of the blue for people and wildlife alike. “Swarms of shrimp-like nymphs crawl out of the ground and cover the trees and the car tyres and the mailboxes,” says Weiss, along with “the legs of passers-by”. Weiss studied her first cicada emergence in 2004; she is now in Illinois to record how brood XIII affects the surrounding ecosystem, including animals such as birds and ants. Piles of cicada carcasses, left behind after the mating is over, offer a feast. This time around, Weiss plans to use ant colonies as an indicator of how nature reacts to this bounty, by studying their foraging patterns and interspecies relationships before, during and after the emergence.“It’s a new experiment every single time,” she says. More

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    Baobab trees’ evolutionary history could inform conservation efforts

    29 May 2024

    The genomes of all eight living species of baobab tree (Adansonia sp.) reveal the group’s origin and diversification history. Ecological analyses were incorporated to characterize the baobabs’ past population dynamics and were used to propose protection measures for these iconic species, including the reassessment of their conservation status and the close monitoring of several of Madagascar’s baobab species. More