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Insects around the world are in crisis, according to a limited but growing number of long-term studies showing a dramatic decline in the invertebrate population. A new report suggests that the problem is more prevalent than scientists have understood. One study found that very many insects were lost in a virgin Puerto Rican national forest and that insectivorous animals in the forest also disappeared.
In 2014, an international team of biologists estimated that "in the past 35 years, the abundance of invertebrates such as beetles and bees had decreased by 45%. Where long-term data on insects are available, mainly in Europe, the number of insects is in free fall. A study from last year showed a 76% decrease in flying insects in recent decades in German nature reserves.
The latest report, published Monday in the Proceedings of the National Academy of Sciences, shows that the problem is spreading to the Americas. The authors of the study implicate climate change in the loss of tropical invertebrates.
"This study in PNAS is a real alarm call – a clarion call – to say that the phenomenon could be much larger and encompass many more ecosystems," said David Wagner, expert in invertebrate conservation at University of Connecticut. not involved in this research. He added, "This is one of the most disturbing articles I have ever read."
A biologist at the Rensselaer Polytechnic Institute in New York, Bradford Lister has been studying the insects of the rainforest in Puerto Rico since the 1970s. If Puerto Rico is the island of enchantment – "the isla del encanto" – its rainforest is "the enchanted forest of the enchanted island," he said. Birds and mongrels trill under an emerald canopy 50 feet high. The forest, named El Yunque, is well protected. The Spanish king Alfonso XII claimed the jungle as a royal reserve of the nineteenth century. Decades later, Theodore Roosevelt made it a national reserve and El Yunque remains the only rainforest in the national forest system.
"We went down in '76, '77 specifically to measure the resources: insects and insectivores in the rainforest, birds, frogs, lizards," Lister said.
He returned nearly 40 years later with his colleague Andres Garcia, an ecologist at the National Autonomous University of Mexico. What the scientists did not see on their return troubled them. "Boy, it was immediately obvious when we went to this forest," Lister said. Fewer birds flew overhead. The butterflies, once abundant, had practically disappeared.
Garcia and Lister once again measured insects and other invertebrates of the forest, a group called arthropods that includes spiders and centipedes. The researchers trapped arthropods on the floor in plates covered with sticky glue and raised several other plates about three feet into the canopy. They also spent hundreds of times on brush, picking up creatures that crawled through the vegetation.
Each technique revealed that biomass (the dry weight of all captured invertebrates) had decreased significantly from 1976 to the present day. The biomass of the swept sample decreased by a quarter or one eighth of what it had been. Between January 1977 and January 2013, the catch rate in sticky traps was divided by 60.
"Everything is falling," Lister said. The most common invertebrates in the tropical rainforest – moths, butterflies, grasshoppers, spiders and others – are all much less abundant.
The University of Louisiana entomologist, Timothy Schowalter, who is not the author of this recent report, has been studying this forest since the 1990s. This research is consistent with its data as well as with European biomass studies. "These sites need long-term, consistent sampling over a long period, to document these trends," he said. "I find their data quite convincing."
The authors of the study also trapped anemic lizards, who eat arthropods, in the rainforest. They compared these figures with the figures of the 1970s. Anole biomass dropped by more than 30%. Some anole species have completely disappeared from the interior forest.
Frogs and insectivorous birds also fell. Another research team used Japanese nets to catch birds in 1990 and again in 2005. Catch dropped by about 50%. Garcia and Lister analyzed the data with an eye on insectivores. The red quail dove, which eats fruits and seeds, has not changed population. A brilliant green bird called the Puerto Rican tody, which eats almost exclusively insects, has disappeared by 90%.
The food web seems to have been torn from the bottom. It is credible that the authors associate the cascade with the loss of arthropods, Schowalter said, because "all these different taxa show the same trends – insectivorous birds, frogs and lizards – but you do not see them among the birds that feed the seeds. "
Lister and Garcia attribute this accident to the climate. During the same 40-year period as that of the arthropod accident, the average high temperature in the tropical rainforest increased by 4 degrees Fahrenheit. Temperatures in the tropics are limited to a narrow band. Likewise, the invertebrates that live there are adapted to these temperatures and come out badly; Insects can not regulate their internal heat.
A recent analysis of climate change and insects, published in the journal Science in August, predicts a decline in tropical insect populations, according to the author of this study, Scott Merrill, who studies crop pests at the University of Vermont. In temperate regions farther away from the equator, where insects can survive in a wider temperature range, agricultural pests will devour more food as their metabolism increases, warned Merrill and his co-authors. But after a certain thermal threshold, insects will no longer lay eggs, he said, and their internal chemistry breaks down.
The authors of a study conducted in 2017 on missing flying insects in Germany suggested other possible causes, including the loss of pesticides and habitat. Arthropods around the world must also fight pathogens and invasive species.
"It's staggering, and I'm so scared that it's death by a thousand cuts," Wagner said. "One of the scariest aspects about this is that we have no obvious smoking gun here." In his opinion, the danger for these arthropods was not the temperature but the drought and the lack of rainfall.
Lister pointed out that since 1969, the use of pesticides has dropped more than 80% in Puerto Rico. He does not know what else could be to blame. The study's authors used a recent analytical method, invented by an economics professor at Fordham University, to evaluate the role of heat. "This allows you to place a probability on the variable X causing the variable Y," said Lister. "So we did and five of our six populations got the most powerful support against heat, which resulted in a decrease in the abundance of frogs and insects."
The authors analyzed the effects of weather conditions, such as hurricanes, and again found a consistent trend, according to Schowalter, who argues convincingly for the climate.
"I think their results and warnings are minimized, and the gravity of their discoveries and ramifications for other animals, particularly vertebrates, is hyper-armorizing," said Wagner. But he is not convinced that climate change is the global driver of insect loss. "The decline of insects in Northern Europe precedes that of climate change in this country," he said. "Similarly, in New England, tangible declines began in the 1950s."
No matter the cause, all scientists agreed that more people should pay attention to the bugpocalypse.
"It's a very scary thing," said Merill, which follows a "dark and dark" American report that said there was still a decade left in the world to deal with climate change. But "we can all go ahead," he said using more fuel-efficient cars and turning off unused electronics. The company Xerces Society, based in Portland Oregon, a nonprofit environmental group that promotes insect conservation, recommends planting a garden with native plants that bloom throughout the year.
"Unfortunately, we have a deaf ear in Washington," said Schowalter. But these ears will listen at some point, he said, because our food supply will be threatened.
Thirty-five percent of the world's crop plants require pollination by bees, wasps and other animals. And arthropods are not just pollinators. These are the little guardians of the planet who work in unseen or avoided nooks. They chew decaying wood and eat carrion. "And none of us wants to have more carcasses," said Schowalter. According to a 2006 estimate, wild insects provide the United States with a six-legged labor of $ 57 billion.
The loss of insects and arthropods could further wipe out the food web of the virgin forest, Lister warned, resulting in the disappearance of plant species without pollinators. "If the rainforests disappear, it will be another catastrophic failure of the entire Earth system," he said, "which would be passed on to man in an almost unimaginable way."
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