Questions and Answers: Global Insect Declines Due to “Death From A Thousand Cuts”


W.When a handful of long-term studies reported dramatic declines in insects in Germany and Puerto Rico in 2017 and 2018, global headlines with the title “The Insect Apocalypse” or “Insectageddon” were imminent. Like the media, researchers were alarmed by the results, but some wondered if these trends were expanding globally.

“There were a lot of questions,” says David Wagner, entomologist and professor of ecology and evolutionary biology at the University of Connecticut. “We decided to hold a symposium with some of the best insect experts in the world to find out what we knew, to find out what we didn’t know, and to find out what we could do in the future and what the data gaps were, and if we knew enough to actually recommend action by individuals, communities, and national and international politics. ”

This week a special edition of PNAS Based on this symposium, 11 studies on the decline of insects will be presented. The scientist spoke to Wagner, who wrote the introduction to the collection and co-authored two of the studies, to learn more about threats to insect biodiversity and the importance of insect protection.

David Wagner

Courtesy of David Wagner

The scientist:: In the introductory paper you say that insects suffer from death from a thousand cuts. Can you explain what you mean by that?

David Wagner: There were about two or three large studies [on insect declines] that got a lot of attention. In each case – and in others – we have not been able to pinpoint the causal factor. . . . And I think it’s death by a thousand cuts in the sense that there are often a variety of factors at work and it’s a different amount in different places, which makes it a very difficult problem. But I think where there is a lot of anthropogenic activity, people cutting forests, areas of high urbanization or a lot of agriculture, there will be multiplicative factors associated with everyone’s decline [taxon]. And the honey bee or the monarch [butterfly] would be a great example of things where we believe there are six or seven main factors that really challenge these animals.

TS:: What are some of the biggest threats to insects?

DW: I think globally what I’m most concerned about is habitat destruction, especially deforestation in the tropics, and essentially so is agriculture in the sense that we often cut down the rainforest to plant soybeans or other crops. And climate change. Climate change is the great unknown. . . . In the temperate zone there are often only a large number of people. These declines in North America and Western Europe are often due to areas of very high human density. . . . We’re pushing Mother Nature in the corners and fragmenting and marginalizing her, applying pesticides and doing what we can to push nature back. That does not surprise me. But some of the reports coming out of the Neotropic really make me afraid of climate change. And then I am very concerned that the cloud forests and rainforests will dry up – sometimes only for a few days, but it is devastating to dry up a rainforest and expose these plants and animals to physiological conditions that they have never experienced. But there are other stressors too: there are pesticides, there are exotic species and suburbanization.

TS:: What is the current understanding of what insect populations look like around the world, and how do these studies in the collection contribute to this image?

DW: I think the most important thing we are doing is to point out that it is much more complex than originally reported and we did point out to draw attention to many instances where insects are on the increase. It’s not that there is a single rate of decline that is ubiquitous across the planet. We don’t believe that anymore. And so some of the early reports suggested it. For example, the review by Sánchez-Bayo and Wyckhuys claimed that we would lose 40 percent of all insects within decades. But with climate change and global warming, more and more species, or at least new ones, will clearly appear in areas where winter temperatures have limited their distribution. Here in New England, where I am, we see a number of new butterflies that were southern and that were never established or lived here. Still, in cases where you restore habitat, we can restore numbers and bring back populations from the fringes for a number of insects. . . . There is hope in our personal actions.

But we have also found that in areas with high levels of human activity, species decline by one to two percent [annually] . . . and that is really disastrous. It’s hard to get people across the importance of one to two percent. It doesn’t sound like a lot, but that’s ten to twenty percent per decade. In a couple of decades, you could lose a third of your insects. . . . But it’s not uniform around the world, and there are places where they are losing weight much faster than a percent or two, and we are particularly concerned about the tropics.

TS:: How would you like to apply the results of this study collection?

DW: I think at least five of the posts mentioned things we might do in the future. . . . The collection of Akito Kawahara and his co-authors has a really nice paper that lists eight things that individuals can do to help the insect plight. So that was an important piece in the collection. But other writers have talked about maybe making agriculture a little friendlier, and the introduction to the collection also mentions things that are funding and policy-looking for insects. One [idea] I love it when children and parents meet in a small part of the yard that they leave “wild”. [to] Create a nature observatory or a small nature reserve just big enough for lots of insects.

TS:: Was there one study in the special that you found the most prominent, and why?

DW: I thought one of the key studies in the collection was Matt Forister’s study of the role of climate change in insect decline. He had some very good data from the west [in the US] and some surprising results on one of the drivers that was completely new and that no one had talked about. Warm night temperatures and drier conditions in autumn are a challenge for mountain butterflies. . . . When so many people think of climate change, they think of global warming and they almost synonymize climate change with global warming. But . . . Climate change also means more droughts of longer intensity, climate change means more fires like in Australia and the Amazon and terrible fires in California, climate change means less snow to isolate these animals over winter, and climate change means the soils dry out. The place where these things may have diapaused or retained for the winter now doesn’t have enough moisture to keep them up. So there are all sorts of aspects of climate change that haven’t even been measured that affect biodiversity, and I think that message comes across very strongly in Matt’s paper, and that’s hugely important.

One of the studies that is really exciting and new is Dan Janzen’s article; It is actually in the interest of the Costa Rican government to barcode every organism in Costa Rica. Basically, they want to get DNA from every single organism in the country. I think it is a hundred million dollar effort over a decade to map the tree of life and make that knowledge available to every citizen, school child, and weekend naturalist in the country to raise awareness of the vast biodiversity in in their forests and in their mountains and let them be stakeholders and owners of this tree of life. So this is a very new concept. Basically, it’s about creating bioliterate so that people know and care for these creatures with whom they share their land.

TS:: What are some of the challenges in researching insect diversity and answering that question about global insect decline?

DW: The big challenge is that we don’t know enough. This is especially true for the tropics. I think maybe eighty percent of all insects are in the tropics, most of which haven’t even been named, and it’s difficult to protect things that are unknown and unexamined. There is just so much diversity and so little data that we don’t know what’s going on there. This is actually a pretty scary unknown.

Insects are very difficult to study in the tropics because they are very diverse and are usually small and we don’t even have the taxonomy to really start there. Another thing that makes it hard to understand how fast they are gaining or losing weight, or whether they are fine or not, is that they go through these wild population cycles from year to year, they have these boom-and-bust life cycles. That makes it really difficult to see one to two percent annual erosion.

TS:: What do you see as a promising technology or initiative for understanding these insect decline questions?

DW: Much of wildlife biology is moving towards automated data collection. And then move on to molecular methods of identifying insects because there are so many [species] and it takes experts [to identify them] If we just move it into molecules, we can collect data on anything, even in a rainforest. One of the things that I find really exciting is that the phone apps are getting so good at identifying insects that now even a fourth grader can make very important discoveries and get the name of something and upload that information into a database. So we have a lot more engagement in the community, orders of magnitude greater than in the last decade than ever before, because there are so many really good identification guides out there for people who only have a little weekend time or know about the outdoors in their backyard want or they are grounded because of COVID. . . . I think there is a new group that was formed two years ago to identify caterpillars together. They all talk to each other on Facebook and now have 13,000 people. I mean, this is a new human culture or a new phenomenon that didn’t even exist ten years ago. So we’re going to see huge amounts of community-collected data from kids and weekend naturalists and backyard biologists, as well as lawyers and doctors, and gardeners.

Editor’s Note: This interview has been edited for brevity.



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