Insects around the world are in crisis, following a small but growing number of long-term studies showing dramatic declines in invertebrate populations. A new report suggests that the problem is more widespread than scientists have realized. The study found that huge amounts of vermin have been lost in an untouched national forest in Puerto Rico, and the insectivorous animals in the forest have also disappeared.
In 2014, an international team of biologists estimated that in the past 35 years, the incidence of invertebrates such as beetles and bees had dropped by 45 percent. In places where long-term infectious data are available, especially in Europe, insect numbers are falling. A study from last year showed in German nature reserves in recent decades, a decline in flying insects by 76 percent.
The most recent report recently published in the Proceedings of the National Academy of Sciences shows that this surprising loss of insect wealth continues to America. The authors of the study point to climate change in the loss of tropical invertebrates.
"This study in PNAS is a true wake-up call ̵
Bradford Lister, a biologist at the Rensselaer Polytechnic Institute in New York, has studied rainforest insects in Puerto Rico since the 1970s. If Puerto Rico is the island of enchantment – "la isla del encanto" – then its rainforest is "the enchanted forest on the enchanted island," he said. Birds and coqui frogs trill under a 50-foot emerald-green canopy. The forest called El Yunque is well protected. The Spanish King Alfonso XII. Claimed the jungle as a royal domain from the 19th century. Decades later, Theodore Roosevelt made it a national reserve, and El Yunque remains the only tropical rainforest in the National Forest System.
"In 1976, we descended to explicitly measure the resources: the insects and the insectivores in the rainforest, the birds, the frogs, the lizards," said Lister.
He returned almost 40 years later with his colleague Andrés García, an ecologist at the National Autonomous University of Mexico. What the scientists did not see on their return worried them. "Boy, it was obvious when we went to this forest," Lister said. Fewer birds darted over their heads. The once abundant butterflies were almost gone.
García and Lister again measured the insects and other invertebrates of the forest, a group called arthropods, including spiders and centipedes. The researchers captured the arthropods in plates covered with sticky glue on the ground and lifted several more plates about three feet into the canopy. The researchers also swept nets hundreds of times over the brush and collected the critters that crawled through the vegetation.
Each technique showed that the biomass (the dry weight of all trapped invertebrates) declined significantly from 1976 until today. The sweep-sample biomass dropped to a quarter or an eighth of what it had been. Between January 1977 and January 2013, the catch rate in traps with sticky soil fell 60-fold.
"Everything falls," said Lister. The most common invertebrates in the rainforest – the moths, the butterflies, the grasshoppers, the spiders and others – are all far less numerous.
"Holy crap," Wagner said about 60-fold loss.
Louisiana Timothy Schowalter, the entomologist of the state university, who is not the author of the most recent report, has been investigating this forest since the 1990s. The new research is in line with its data and European biomass studies. "To document these trends, it takes those long-term locations with a consistent sample over a long period of time," he said. "I think your data is pretty convincing."
The study authors have also caught anole lizards eating arthropods in the rainforest. They compared these numbers with counts from the 1970s. Anolis biomass fell more than 30 percent. Some anole species have completely disappeared from the inner forest.
Insectivorous frogs and birds also collapsed. Another research team used fishing nets again in 1990 and 2005 to catch birds. The fishing gear fell by about 50 percent. Garcia and Lister analyzed the data with regard to the insectivores. The reddish quail pigeon eating fruits and seeds had no population change. A bright green bird named Puerto Rican Tody, which almost exclusively eats beetles, has dropped by 90 percent.
The food web seems to have been obliterated from below. 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 – the insect-eating birds, frogs and lizards – but you do not see them among the seed-bearing birds."
Lister and Garcia attribute this crash to the climate. In the same 40-year period as the collapse of the arthropods, the average rainforest temperature rose 4 degrees Fahrenheit. The temperatures in the tropics remain at a narrow band. The invertebrates that live there are also used to these temperatures and are bad outside; 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 author of the study, Scott Merrill, who studies plant pests at the University of Vermont. Far away from the equator in temperate regions, where insects can survive a wider range of temperatures, agricultural pests will devour more food as their metabolism increases, Merrill and his co-authors warned. But after a certain temperature threshold, insects will no longer lay eggs, he said, and their internal chemistry collapses.
The authors of a study on vanished flying insects in Germany in 2017 suggested other possible perpetrators, including pesticides and habitat loss. Arthropods around the globe are also struggling with pathogens and invasive species.
"It's confusing, and I'm scared to death that it's actually death by a thousand cuts," said Wagner. "One of the scariest parts of this is that we have no obvious smoking gun here." A particular danger for these arthropods in his view was not the temperature, but droughts and rainfall.
Lister pointed out Since 1969, the use of pesticides in Puerto Rico has fallen by more than 80 percent. He does not know what else could be to blame. The authors of the study used a more recent analytical method, which was invented by a professor of economics at Fordham University to evaluate the role of heat. "It allows you to set a probability on variable X that causes variable Y," said Lister. "So we did that, and then we got the strongest support for heat from five of our six populations, which led to a drop in frogs and insects."
The authors have sorted out the effects of weather such as hurricanes and yet have seen a consistent trend, Schowalter said, which represents a compelling argument for the climate.
"I think their results and reservations are understated, and the severity of their findings and consequences for other animals, especially vertebrates, is hyperactive," Wagner said. But he is not convinced that climate change is the global engine for the loss of insects. "The decline of insects in northern Europe is ahead of climate change," he said. "In New England, there were some noticeable declines in the 1950s."
Regardless of the cause, all scientists agreed that more people should pay attention to the Bug Pokemon.
"It's a very scary thing". Merrill said this follows on the heels of a "bleak, bleak" UN report, which estimates that the world has barely more than a decade to bring climate change under control. But "we can all climb up," he said, using more fuel-efficient cars and shutting down unused electronics. The Portland, Oregon-based Xerces Society, a non-profit environmental organization dedicated to protecting insects, recommends planting a garden of native plants that bloom year-round.
"Unfortunately we have deaf ears in Washington," said Schowalter. But those ears will eventually come, he said, because our food supply is in danger.
Thirty-five percent of the world's crops require pollination by bees, wasps and other animals. And arthropods are more than just pollinators. They are the little guardians of the planet who are in unnoticed corners or corners. They chew rotting wood and eat carrion. "And none of us wants more carcasses," said Schowalter. According to 2006 estimates, wild insects in the United States provide $ 57 billion in six-legged labor every year.
The loss of insects and arthropods could further tear the rainforest's food web, Lister warned, causing plant species to disappear without pollinators. "If the tropical forests go away, it will be another catastrophic failure of the entire Earth system," he said, "that will repercuss people in an almost unimaginable way."