Where have all the insects gone?

As many of Wilson’s colleagues soon realized, the significance of the theory extended well beyond the actual islands. Logging and mining and widespread sprawl have increasingly divided the world into “islands” of habitat. The smaller and more isolated these islands are, be they patches of forest, tundra or grassland, the fewer species they would eventually contain. Wilson had moved on to new research questions and was initially not much concerned with the implications of his own work. When the first accounts of deforestation in the Amazon emerged, he was, in his words, “tipped into active engagement”. In an article in Scientific AmericanIn 1989, he combined data on deforestation with his and MacArthur theory’s predictions to estimate that as many as 6,000 species per year were fading into oblivion. “That, in turn, is on the order of 10,000 times greater than the naturally occurring background extinction rate that existed before the appearance of humans,” he wrote.

The same year that Wilson published his article in Scientific American, a group of insect enthusiasts installed so-called malaise traps in several nature reserves in Germany. Malaise traps look like tents overturned on their sides, and they’re designed to catch just about anything that flies into them. The group, the Krefeld Entomological Society, was interested in how insects fared in different types of parks and protected areas. From then on, members of society set out new traps every summer, usually in different reservations. In 2013, they resampled some of the sites they originally sampled in 1989. The contents of the traps were a fraction of what they had been the first time.

Over the next three summers, the group members resampled more sites. The results were similar. In 2017, with the help of some outside experts, they published a paper documenting a seventy-five percent decline in “total flying insect biomass” in the areas surveyed. These areas were exactly the kind of habitat fragments that, according to Wilson’s theory, were destined to lose species. Still, the findings were shocking. In 2019, a second group of researchers published a more rigorous and comprehensive study, and the findings were even more dire. Over the course of the previous decade, grasslands in Germany had lost an average of one-third of their arthropod species and two-thirds of their arthropod biomass. (Terrestrial arthropods include spiders and centipedes in addition to insects.) In forests, the number of arthropod species had fallen by more than a third and biomass by 40 percent. “This is frightening,” said one of the authors of the article, Wolfgang Weisser, a biologist at the Technical University of Munich.

In the years since, many more articles have appeared with similar findings. Significant declines have been found in mayfly populations in the American Midwest, butterfly numbers in the Sierra Nevadas, and caterpillar diversity in northern Costa Rica. While many species seem to be doing just fine, for example the spotted lanternfly, an invasive species from Asia, which was first discovered in Pennsylvania around 2014 and has since spread to at least ten other states, including New York, such as was noted in the introduction to a recent special issue of the procedure from the National Academy of Sciences devoted to the state of the insect world, “enough cause for concern”.

Dave Goulson, an entomologist at the University of Sussex, is one of the experts the Krefeld group has reached out to to understand the data. Like Wilson, Goulson can be described as a naturalist turned post-naturalist; he decided to study insects because he found them fascinating, and now he’s studying why they’re in trouble.

“I’ve seen clouds of butterfly wings sip on the muddy banks of a river in Borneo, and thousands of fireflies flashing in sync with their luminous bottom at night in the swamps of Thailand,” he writes in “Silent Earth: Averting the Insect Apocalypse.” (vintage). “I had a lot of fun. But I was haunted by the knowledge that these creatures are in decline.”

Goulson laments the fact that many people consider insects to be pests. Wanting readers to appreciate how wonderful they really are, he begins his chapters with profiles of six-legged creatures. Males of many earwig species have two penises; if disturbed while mating, they break down the one they are using and make a quick escape. Female jewel wasps sting their prey — large cockroaches — to induce a zombie-like trance. Then they chew off the tips of the roaches’ antennae, use the stumps to guide the stunned creatures back to their burrows, and lay their eggs in them. Aging termites of the species Neocapritermes taracua develop pouches around their abdomen that are filled with copper-rich proteins. If an invader gains the upper hand — or leg — in a fight, the older termites blow themselves up to protect the colony, a practice known as suicidal altruism. The proteins react with chemicals stored in their salivary glands to become highly toxic compounds.

Insects are of course also vital. They are by far the largest class of animals on Earth, with about a million named species and probably four times as many pending identification. (Robert May, an Australian scientist who contributed to the development of the field of theoretical ecology, once noted, “Initially, all species are insects.”) They support most terrestrial food webs, serving as the planet’s primary pollinators. and act as crucial decomposers. Goulson quotes Wilson’s observation: “If all of humanity disappeared, the world would return to the rich equilibrium state that existed 10,000 years ago. If insects disappeared, the environment would collapse into chaos.”

Like insects themselves, the threats to them are many and diverse. First, there is habitat loss. Since Wilson’s article in Scientific American appeared, South America lost at least 300 million hectares of tropical forest in 1989, and Southeast Asia suffered similar losses. In places like the US and Britain, which were deforested generations ago, the hedges and weed patches that were once a refuge for insects are disappearing as a result of increasingly intensive agricultural practices. From an insect’s perspective, Goulson points out, even using fertilizers is a form of habitat destruction. Fertilizer leaching from fields promotes the growth of certain plants over others, and many insects depend on these others.

Climate change, light pollution and introduced species pose even more dangers. The Varroa destructor mite evolved to feed on (and consume the body fat of) Asian honeybees, which are smaller than their European counterparts. When European honeybees were imported to East Asia, the mites jumped off hosts, and when European bees were brought to new places, the mites hitched a ride. Varroa mites carry diseases such as misshapen wing virus, and they have had a devastating effect on European honeybees, probably losing hundreds of thousands of colonies. In the US (and in many other countries), European honeybees are treated like small livestock. They are driven around to pollinate crops such as apples and almonds, and their health is closely monitored. But what is the impact of imported parasites and pathogens on other bees, not to mention ants, beetles, crickets, dragonflies, moths, thrips and wasps? “We just don’t know anything about 99.9 percent of insect species,” Goulson complains.

Then there are pesticides. Since the Fire Ant Wars, which featured prominently in Rachel Carson’s ‘Silent Spring’, many have been taken off the market. However, they replaced new ones. Goulson is particularly concerned about a class of chemicals known as neonicotinoids. Neonics, as they are often called, are in some ways even more toxic than Mirex and chlordane. They were first marketed in the 1990s; in 2010, more than three million pounds a year was applied to crops in the US and nearly two hundred thousand pounds to crops in Britain. Neonics are water soluble, meaning they can leach into soil and ponds and potentially be absorbed by other plants. There is much controversy about the dangers they pose to non-target insects, especially bees; in 2018, the European Union found the evidence of damage compelling enough to ban three key neonics from outdoor use. (The chemicals are still used in many European countries under ’emergency permits’.) Meanwhile, their use in the rest of the world, including the US, continues to grow rapidly. “Carson may have won a battle, but not the war,” notes Goulson.

In the final chapter of “Silent Earth,” Goulson offers dozens of actions we can take to “change our relationship with the tiny creatures that live all around us.” Some involve tending one’s own garden, for example, trying to rethink ‘weeds’ such as dandelion as ‘wild flowers’. Others are regional or national in scope: “plant streets and parks with flowering, native trees” or “introduce pesticide and fertilizer taxes.” The list is long enough that almost anyone who wants to can find a recommendation to follow, but it focuses heavily on reducing pesticide use, which, as “Silent Earth” makes clear, is just one of many dangers. is what insects face.

Wilson, who has been called the ‘father of biodiversity’, has a bigger idea. In “Half-Earth: Our Planet’s Fight for Life” (2016), he argues that the only way to conserve insects in the world — and everything else, for that matter — is to set aside fifty percent of them in “inviolable reserves.” .” He came to the figure, he explains, using the principles of island biogeography; on fifty percent of the globe, he calculates, about eighty-five percent of the species on Earth could be saved. The task of preserving — or, in many places, restoring, half of the world’s habitat — is, he admits, daunting. The alternative, however, is to grow dandelions while the world burns: “The only hope for the species still alive is human effort commensurate with the magnitude of the problem.”

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