Karen Oberhauser was mountaineering about 100 kilometers northwest of Mexico City when she began to worry about the future of the monarch butterfly. It was wintertime 1996-1997, and Oberhauser, an ecologist who was working at the University of Minnesota at the time and more accustomed to the American flat and lower Midwest, blew and puffed throughout the steep hike and at an excessive altitude. His head was injured in the air. But when she stopped to look around, she noticed that tens of millions of monarchs draped like home earrings on fir wood were embracing the slopes.
Almost all of the monarch population was once crammed into this area and some nearby forests, about 18 hectares in total value. Scientists analyzing the butterfly knew the place, but it was Oberhauser's first visit. An ordinary storm or illegal logging, she thought, might want to wipe out the place. "It made me realize how exceptionally vulnerable they are," she recalls.
This forest is the beginning of an impressive annual migration that sends monarchs to northern Canada during the summer and brings them back to Mexico each winter. Along the way, they breed and feed in the agricultural fields of the Midwest, near Oberhauser's house. And in the years following his departure for the forest, Oberhauser began to suspect that his place had become another vulnerability of the monarch. Farmers sprayed corn and soybean fields with Roundup weedkiller to control many weeds. But the chemical also kills a plant that is very valuable to monarchs: milkweed, on which adult butterflies lay their eggs, and the only plant that monarch caterpillars eat. Oberhauser and his colleagues began counting the flora and eggs. They concluded that less milkweed flora in agricultural fields meant fewer eggs, which meant fewer adults returning to Mexico. In 2012, she co-wrote an article affirming this "milkweed dilemma hypothesis" and its alarming implications: Roundup threatened the migration of the wonderful monarch butterfly.
The public and many monarch scientists have been galvanized by the usefulness of this idea. It allowed us to experiment - a fundamental supply of ingredients that disappeared permanently as soon as the Mexican butterfly population collapsed. During the winter climate of Oberhauser's visit, there had been about 300 million butterflies, but no doubt, more than a decade later, there were far less than a hundred million. Oberhauser and others mentioned that the remedy used to be to plant milkweed in large quantities to compensate for the losses. Thousands of inexperienced residents answered the call. Michelle Obama planted milkweed in a White House garden. Environmental companies have asked the U.S. Fish and Wildlife Service to list the monarch butterfly, Danaus plexippus, as an endangered species to ensure better habitat protection.
However, if we consider this situation, some scientific cracks have appeared in the case of milkweed. Censuses of monarchs in the United States during and after the summer breeding season did not show a steady decline, although Mexican numbers declined. And many Mexican butterflies have arrived here from American regions, with the exception of many fields of cultivation soaked in Roundup, as suggested by different registers. Skeptical scientists have claimed that insects reproduce correctly in northern climates, but that something is taking them to Mexico. "Migration is like a marathon," said Andrew Davis, an ecologist at the University of Georgia. "If the variety of humans starting the marathon has not really changed in 20 years, but the variety of humans reaching the finish line has decreased, you cannot conclude that the variety of humans is decreasing. You would conclude that something was going on for the duration of the race. "
The identification of this something, however, remains an elusive and boring mystery. Some facts confirm that the landscapes have misplaced the nectar-giving vegetation that adult monarchs feed on at some point in their day trip south and that the very vital forests from the migratory route have been degraded. Scientists have also hypothesized that parasitic contamination should reduce the number of migrants. (A smaller population of monarchs wintering on the California coast has also recently crashed. Entomologists are concerned about this group, however, their habitat no longer overlaps with that of the Japanese population, so scientists believe the reasons may be different).
Almost everyone believes that, overall, despite 12-month-to-year peaks and troughs, Mexico's winter climate population has declined for most of the past three decades. This is not accurate information for monarchs. The question of what to do, however, depends on the cause. Oberhauser and his allies argue, however, that the loss of milkweed is the most important enemy variety. But the various evidence brings heavy and complicated twists to what, from the start, seemed like an easy story with a villain quite. In addition, the ability to help insects has become more complicated.
North to South
The first trace of monarchs moving in droves dates back to 1857, when a naturalist described butterflies acting in the Mississippi Valley "in numbers as they obscure the air with their clouds."
Over time, biologists have discovered that when spring arrives in the valley, as well as in the various components of North America, the monarch ladies descend on more than 70 species of milkweed flora (genus Asclepias) for feed and lay eggs. A lady can lay up to five hundred eggs. When this work is finished, she dies. From its eggs hatch caterpillars that turn into butterflies; the cycle repeats 4 to 5 times a year.
Monarchs living in Winter in Mexico fly north and lay eggs near the Texas border in the spring. Their offspring remained for two to six weeks and gave birth to generations passing through the Midwest and South and eventually to the Great Lakes states, New England and Canada. As the days get shorter in the fall, the fashionable butterfly technology, called "super generation," is emerging. These insects can stay for up to eight months because their metabolism slows down and they no longer spend valuable electricity to reproduce. Instead, they travel south from the great latitudes to Mexico, traveling up to a hundred and sixty kilometers a day. In December, the insects that survived this day of release gathered on the Mexican fir trees. They stay there until early spring, when they begin their own experience in the north, and their youth continue the odyssey.
In the late 1970s, after extensive research, biologists determined the tiny mountainside forests where monarchs wintered in Mexico. The late Lincoln Brower, who worked as a biologist at Amherst College and then the University of Florida, helped persuade Mexican authorities to put the forests under protection, launching the monarch's conservation motion.
In the early 2000s, Oberhauser and John Pleasants, an ecologist at Iowa State University, located all other key habitats for the monarch: the agricultural fields of Iowa and various Midwestern states, where milkweeds frequent growing between rows of plants were dotted with monarch eggs. Apparently, the agricultural fields were a large hatchery. "It used to be a revelation," says Oberhauser. He said that "how vital agriculture can be, even if we consider it a wild area of biodiversity."
Subsequent visits by the two researchers revealed that milkweed flora in these agricultural fields contained up to four times as many eggs as milkweed in grasslands and agricultural conservation lands. "They seemed to be magnets to monarchs," says Pleasants.
American agricultural fields, however, had been on the verge of an extraordinary ecological clean-up. Agricultural chemical company Monsanto had designed corn and soybean flowers with a gene that allowed them to live on the basis of advertising for the herbicide glyphosate, better known by its name of change, Roundup. The Roundup had to be sprayed generously, leaving the useful plants unscathed while killing almost everything else in a field. For farmers, Roundup Ready corn and soybeans have been benefits. For the different flowers that occupied the house between the harvest rows, it was once a death sentence. In 2007, almost all soybeans grown and more than half of U.S. corn was Roundup Ready.
Monarch butterflies want milkweed to breed again. Adult butterflies lay their eggs on the flora (1). The caterpillars of these eggs consume only milkweed (2). Credit: Ingo Arndt Nature Picture Library (1); Doug Wechsler Nature Photo Library (2)
Based on their Iowa data, Pleasants and Oberhauser estimated that between 1999 and 2010, the total amount of milkweed plants in the Midwest decreased by 58%. Brower and his colleagues stated that throughout this period, wintering monarch populations declined sharply. In fact, at some point in the icy period of 2009-2010, the occupied area of Mexico's forests declined too little (less than half of what it was the previous year) and fell below two hectares for the first time, since maintenance document began in the early 1990s. As the link between the two developments was considered inevitable, he asked Pleasants and Oberhauser to set their historical record from 2012, arguing that the loss of Midwest milkweed killed the monarch. Oberhauser is known as a "smoking gun".
If the article had focused on one insect out of two, only a handful of professional scientists should have taken note. But the monarch butterfly has a specific region in the hearts of the inhabitants of three North American nations. The bright orange color of the insect and its giant size, the soft curls of its flight and, above all, its amazing migration have made the monarch an extremely popular celebrity.
Also, the story had a miscreant that the general population was once prepared to loathe. Gathering's maker, Monsanto (presently part of the Bayer combination), typified the feelings of trepidation of numerous people identified with hereditary designing and the administration of agrarian endeavors. The possibility that Monsanto's lead item once murdered the American leader creepy-crawly stood out as truly newsworthy. Hypothesis by Oberhauser and Pleasants was generally resuscitated with the assistance of the US media, comprising of it.
A navy of conservationists has mobilized to store the situation. In 2014, greater than 10,000 "monarch stations" had sprouted throughout the country, thanks to a milkweed planting software led by using insect scientist Orley "Chip" Taylor at the University of Kansas. Over the subsequent few years, President Barack Obama and his Mexican and Canadian counterparts all promised to guard the butterfly, and a few months later, cameras clicked when the First Lady joined the youngsters as they planted milkweed in a one of a kind pollinator garden.
Number that has now not been added
But even though speculation about the milkweed dilemma has won public support, some scientists have suspected that it was once built on fragile foundations. Davis, the Georgian environmentalist, was one of the first to express specific doubts. He had analyzed the number of monarchs whose late-summer trips to Mexico had led them through a handful of funnel points: Peninsula Point, which sinks into the northern facet of Lake Michigan, and Cape May in New Jersey, a small strip of land bounded by the Atlantic Ocean and Delaware Bay. For decades, volunteers have been tracking insects and birds from the south to late summer in each of these areas. For monarchs, Davis noted, numbers have not declined steadily, but have rebounded by 12 months in a year, as is usually the case with insect populations.
Davis' report attracted little interest when it was published in 2012, and Oberhauser and Pleasants indicated that funnel factors had been north and east of the corn belt, so they would no longer present the consequences of losses in agricultural fields in the Midwest. "No one wanted to hear that the monarchs weren't declining, as crazy as it sounds," Davis says.
Credit: Nigel Hawtin; Sources: "The Mechanisms Behind the Decline of the Monarch," by Anurag A. Agrawal and Hidetoshi Inamine, in Science, Vol. 360; June 2018; World Wildlife Fund, Mexico (population facts in winter 2018); Citizen Science Project Journey North, University of Wisconsin - Madison Arboretum (Annual Cycle)
Not everyone welcomed this prospect, says Agrawal. At a 2012 meeting held through Oberhauser at the University of Minnesota, he asked a team of participants what they think of Davis' latest article. Agrawal recalls that Chip Taylor grabbed his arm and asked him not to advocate now that a monarch's decline could be inflated as it would undermine conservation efforts. "I was incredulous before," says Agrawal. "For someone to enter your non-public space, grab your hand and say, " Don't let me hear you say that - I will not neglect it in any way. Taylor said he would not pay attention to the meeting and doubted that this had happened.
But others shared Agrawal's and Davis's doubts. Leslie Ries, an environmentalist from Georgetown University, who also attended the meeting, became a statistic from a surveillance app run with the help of the North American Butterfly Association, or NABA. The team recruits volunteers to visit selected websites and document all the butterflies they see in a circle 24 km in diameter in a single day. In a 2015 article, Ries suggested that their information set, as correct as Illinois-specific, did not confirm any evidence that the northern monarch population had declined in 21 years.
Number that has now not been added
But even though speculation about the milkweed dilemma has won public support, some scientists have suspected that it was once built on fragile foundations. Davis, the Georgian environmentalist, was one of the first to express specific doubts. He had analyzed the number of monarchs whose late-summer trips to Mexico had led them through a handful of funnel points: Peninsula Point, which sinks into the northern facet of Lake Michigan, and Cape May in New Jersey, a small strip of land bounded by the Atlantic Ocean and Delaware Bay. For decades, volunteers have been tracking insects and birds from the south to late summer in each of these areas. For monarchs, Davis noted, numbers have not declined steadily, but have rebounded by 12 months in a year, as is usually the case with insect populations.
Davis' report attracted little interest when it was published in 2012, and Oberhauser and Pleasants indicated that funnel factors had been north and east of the corn belt, so they would no longer present the consequences of losses in agricultural fields in the Midwest. "No one wanted to hear that the monarchs weren't declining, as crazy as it sounds," Davis says.
Credit: Nigel Hawtin; Sources: "The Mechanisms Behind the Decline of the Monarch," by Anurag A. Agrawal and Hidetoshi Inamine, in Science, Vol. 360; June 2018; World Wildlife Fund, Mexico (population facts in winter 2018); Citizen Science Project Journey North, University of Wisconsin - Madison Arboretum (Annual Cycle)
His paper attracted the interest of Anurag Agrawal, an evolutionary ecologist at Cornell University who had studied how monarchs use chemical compounds produced from milkweed. He too began to suspect that the story of Pleasants and Oberhauser, although clear and convincing, was too easy to explain the dynamics of insect populations crossing a substantial and different landscape. In the land of Agrawal, New York, for example, agricultural fields are nestled among grasslands, pastures and various ecosystems. It became apparent to him that even if milkweed disappeared from the ranks of crops, there would be many different places where monarchs would discover plants .
But others shared Agrawal's and Davis's doubts. Leslie Ries, an environmentalist from Georgetown University, who also attended the meeting, became a statistic from a surveillance app run with the help of the North American Butterfly Association, or NABA. The team recruits volunteers to visit selected websites and document all the butterflies they see in a circle 24 km in diameter in a single day. In a 2015 article, Ries suggested that their information set, as correct as Illinois-specific, did not confirm any evidence that the northern monarch population had declined in 21 years.
Agrawal went further, collecting several long-term counts of monarch populations at particular times in the life cycle, which include wintering data, NABA data and funnel factor counts. Together with many colleagues, he wanted to see if population estimates at a given factor over time should allow for predicting estimates at the next stage - a chain of fundamental links to the argument that the decrease in milkweed vegetation from the summer season in the Midwest has resulted in a decrease in winter butterflies in Mexico. Scientists mentioned in 2016 in the journal Oikos and once again in 2018 in Science that there was a giant hole in the direction of stopping this chain: late summer counts did not predict ice populations. As mentioned using the Ries, the summer season's counts remained additional or much less stable even as winter counts decreased. In agreement with Davis, Agrawal and his co-authors recommended that something considered to shoot down monarchs at some point in their southward migration in the fall, which seemed more vital than the occasions of the summer breeding season.
After about 10 days in a pupa, an adult butterfly emerges. It deforms against the thin container (1). Then the insect withdraws (2). Finally, the new butterfly spreads its wings (3, 4). There are four to five generations of butterflies each year. Credit: National Geographic Image Collection
Different suspects
At Agrawal and Davis, Flockhart had provided more overwhelming evidence against the milkweed limitation hypothesis. If less than two in five monarchs come from the corn belt to begin with, they asked, how could the loss of milkweed explain the dramatic losses in Mexico?
Flockhart himself is more careful. Although there may be enough total milkweed in North America to support a healthy population of monarchs, he suspects that the use of Roundup may have changed the distribution of milkweed in a way that could adversely affect . If the effect of the chemical has been to concentrate milkweeds in smaller areas outside of agricultural fields, female monarchs may need to lay all of their eggs closest to each other, forcing more caterpillars to compete for the same food and stressing people, he suggests.
Flockhart's speculation points to a dilemma faced by milkweed opponents like Agrawal and Davis. It is not enough to dig holes in the limitation hypothesis. They needed a different culprit to convince scientists that something else was going on, and they didn't really have one.
Then, in the spring of 2019, a separate team of researchers found two likely suspects: damage to nectar-producing plants along the migration route and changes in the density of forests in Mexico. In an article published in the Proceedings of the National Academy of Sciences USA, a team led by Elise Zipkin, a quantitative ecologist at Michigan State University, examined the statistical correlations between the sizes of monarch populations at different times of the year and a wide range of environmental data. It was the first investigation to divide the winter monarchs into their 19 individual colonies rather than grouping all the wooded areas together. It turned out that colonies with denser forest cover were home to more butterflies. "It is shocking that no one has done this before," said Zipkin.
The Zipkin team also used satellite imagery to quantify the amount of living plant matter in a given landscape. When the southern United States was greener in the fall, more monarchs arrived in Mexico; when it was darker, like drought, less did. This pattern appeared because greener, healthier plants produce more nectar capable of supporting migrating monarchs, Zipkin and his coauthors suspect. And indeed, a powerful drought hit the southern United States between 2010 and 2013, when the population of Mexican monarchs reached its lowest level.
According to Agrawal and Davis, the study highlighted the real and unrelated causes of the problems of the milkweed population at the end of the migration. "It's the document that deals most quantitatively," says Agrawal. There are also other, more vague suspects. Davis believes that a protozoan parasite that infects monarchs could be on the rise. According to research by environmentalist Davis Sonia Altizer of the University of Georgia (she and Davis are married), levels of Ophryocystis elektroscirrha, which can weaken or kill monarchs, could reach higher levels in insects southern United States. Also, Davis and other researchers have suggested that habitat modification increases the physiological stress of migrating monarchs, reducing their endurance during the long fall hike.
A new case
New evidence may also show that there may be many culprits in the decline of the monarch, not just one. This prospect even partially conquered Oberhauser, the first defender of milkweed. "I was probably too strong in my argument that there was once nothing going on in the migration zone," said the scientist, now director of the University of Wisconsin - Madison Arboretum. Others have described the fate of monarchs as "the loss of a thousand human lives".
But she still believes that the loss of milkweed is the deepest cut. "I recognize Andy and Anurag very well. I love them both very much," says Oberhauser. "But I am a little tired of this argument" which, unlike the removal of milkweed vegetation, is notably responsible for the decimating of ice numbers. How can something that has managed to get rid of so many monarchs in transit to Mexico remain hidden, she asks? Only milkweed availability and climate change strongly affect the number of monarchs, according to a laptop dummy she and a few colleagues used in a 2017 study.
Oberhauser and Pleasants further assert that the DST counts which show no decline - the figures on which Agrawal, Ries and Davis are mainly based - have had problems: they were carried out with the help of volunteers who do not almost never ventured into agricultural fields, so they ignored the massive population declines in these places. Logically, she insists, there must be abandonments at daylight saving time. If the winter populations of monarchs decline from year to year, how could the offspring of this reduced crew want to jump again to reach the equal and excessive number of the summer season for many years? "It really doesn't make any organic sense," she says.
Zipkin also believes that speculation about the milkweed dilemma remains at stake. With Oberhauser, she determined the evidence in the Illinois statistics that the use of glyphosate, in conjunction with changes in the weather in the spring, can additionally affect the abundance of the monarch butterfly in the vicinity in the summer. "It's hard to consider ... that the amount of milkweed in the panorama has no impact on monarchs. My question is: How important is this amount? Zipkin said.
Indeed, it is everyone's question. To get an answer, the scientists launched a series of information called the Integrated Monarch Surveillance Program, which aims to perform statistically reliable counts of monarchs correlated with habitat in heaps of areas across the American continent. Program officials randomly selected websites and invited each expert and scientific citizen to post them and send information using well-known tips so researchers could search for trends. Volunteers have accumulated records as 2017 and one hundred and twenty human beings reveal 235 sites. "We get a little energy, using acceleration," says Oberhauser.
All events agree that the resource for the monarch cannot wait for the science to be settled. The region of the Mexican forest occupied by the monarchs fell in 2013 in a region barely larger than a fashionable football field, a level of ratio. Although the migrant population has rebounded rather because, at the time, most researchers still reflect on the precariousness of their popularity. The U.S. Fish and Wildlife Service said it would vote on the Endangered Species petition later this year.
To improve butterfly habitat areas in general, Oberhauser would like the U.S. Department of Agriculture to increase the hectares of its conservation reserve software - the largest federal software to help areas of flora and fauna on farmland - which has fallen to much less than 9.3 million since 2007. nearly 15 million.
At Agrawal and Davis, Flockhart had provided more overwhelming evidence against the milkweed limitation hypothesis. If less than two in five monarchs come from the corn belt to begin with, they asked, how could the loss of milkweed explain the dramatic losses in Mexico?
Flockhart himself is more careful. Although there may be enough total milkweed in North America to support a healthy population of monarchs, he suspects that the use of Roundup may have changed the distribution of milkweed in a way that could adversely affect . If the effect of the chemical has been to concentrate milkweeds in smaller areas outside of agricultural fields, female monarchs may need to lay all of their eggs closest to each other, forcing more caterpillars to compete for the same food and stressing people, he suggests.
Flockhart's speculation points to a dilemma faced by milkweed opponents like Agrawal and Davis. It is not enough to dig holes in the limitation hypothesis. They needed a different culprit to convince scientists that something else was going on, and they didn't really have one.
Then, in the spring of 2019, a separate team of researchers found two likely suspects: damage to nectar-producing plants along the migration route and changes in the density of forests in Mexico. In an article published in the Proceedings of the National Academy of Sciences USA, a team led by Elise Zipkin, a quantitative ecologist at Michigan State University, examined the statistical correlations between the sizes of monarch populations at different times of the year and a wide range of environmental data. It was the first investigation to divide the winter monarchs into their 19 individual colonies rather than grouping all the wooded areas together. It turned out that colonies with denser forest cover were home to more butterflies. "It is shocking that no one has done this before," said Zipkin.
The Zipkin team also used satellite imagery to quantify the amount of living plant matter in a given landscape. When the southern United States was greener in the fall, more monarchs arrived in Mexico; when it was darker, like drought, less did. This pattern appeared because greener, healthier plants produce more nectar capable of supporting migrating monarchs, Zipkin and his coauthors suspect. And indeed, a powerful drought hit the southern United States between 2010 and 2013, when the population of Mexican monarchs reached its lowest level.
According to Agrawal and Davis, the study highlighted the real and unrelated causes of the problems of the milkweed population at the end of the migration. "It's the document that deals most quantitatively," says Agrawal. There are also other, more vague suspects. Davis believes that a protozoan parasite that infects monarchs could be on the rise. According to research by environmentalist Davis Sonia Altizer of the University of Georgia (she and Davis are married), levels of Ophryocystis elektroscirrha, which can weaken or kill monarchs, could reach higher levels in insects southern United States. Also, Davis and other researchers have suggested that habitat modification increases the physiological stress of migrating monarchs, reducing their endurance during the long fall hike.
A new case
New evidence may also show that there may be many culprits in the decline of the monarch, not just one. This prospect even partially conquered Oberhauser, the first defender of milkweed. "I was probably too strong in my argument that there was once nothing going on in the migration zone," said the scientist, now director of the University of Wisconsin - Madison Arboretum. Others have described the fate of monarchs as "the loss of a thousand human lives".
But she still believes that the loss of milkweed is the deepest cut. "I recognize Andy and Anurag very well. I love them both very much," says Oberhauser. "But I am a little tired of this argument" which, unlike the removal of milkweed vegetation, is notably responsible for the decimating of ice numbers. How can something that has managed to get rid of so many monarchs in transit to Mexico remain hidden, she asks? Only milkweed availability and climate change strongly affect the number of monarchs, according to a laptop dummy she and a few colleagues used in a 2017 study.
Oberhauser and Pleasants further assert that the DST counts which show no decline - the figures on which Agrawal, Ries and Davis are mainly based - have had problems: they were carried out with the help of volunteers who do not almost never ventured into agricultural fields, so they ignored the massive population declines in these places. Logically, she insists, there must be abandonments at daylight saving time. If the winter populations of monarchs decline from year to year, how could the offspring of this reduced crew want to jump again to reach the equal and excessive number of the summer season for many years? "It really doesn't make any organic sense," she says.
Zipkin also believes that speculation about the milkweed dilemma remains at stake. With Oberhauser, she determined the evidence in the Illinois statistics that the use of glyphosate, in conjunction with changes in the weather in the spring, can additionally affect the abundance of the monarch butterfly in the vicinity in the summer. "It's hard to consider ... that the amount of milkweed in the panorama has no impact on monarchs. My question is: How important is this amount? Zipkin said.
Indeed, it is everyone's question. To get an answer, the scientists launched a series of information called the Integrated Monarch Surveillance Program, which aims to perform statistically reliable counts of monarchs correlated with habitat in heaps of areas across the American continent. Program officials randomly selected websites and invited each expert and scientific citizen to post them and send information using well-known tips so researchers could search for trends. Volunteers have accumulated records as 2017 and one hundred and twenty human beings reveal 235 sites. "We get a little energy, using acceleration," says Oberhauser.
All events agree that the resource for the monarch cannot wait for the science to be settled. The region of the Mexican forest occupied by the monarchs fell in 2013 in a region barely larger than a fashionable football field, a level of ratio. Although the migrant population has rebounded rather because, at the time, most researchers still reflect on the precariousness of their popularity. The U.S. Fish and Wildlife Service said it would vote on the Endangered Species petition later this year.
To improve butterfly habitat areas in general, Oberhauser would like the U.S. Department of Agriculture to increase the hectares of its conservation reserve software - the largest federal software to help areas of flora and fauna on farmland - which has fallen to much less than 9.3 million since 2007. nearly 15 million.
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