EXPERT REACTION: Has there been a global insect apocalypse?

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Many insect populations around the world are decreasing by 1-2 per cent every year, but this may not be as simple as an insect 'apocalypse' across the board, according to a series of 12 research papers being published in PNAS. For example, in the United Kingdom, butterfly numbers have declined by around 50 per cent since 1976, while at the same time, several papers identify other insect species that are increasing in numbers, especially in temperate and Arctic areas, where insects have been historically limited by winter conditions.

Journal/conference: PNAS

Link to research (DOI): 10.1073/pnas.2023989118

Organisation/s: University of Connecticut, USA

Funder: Various - see papers for funding details

Media release

From: PNAS

Global decline of insects                                                  

With more than a million described species and a history of terrestrial abundance dating back more than 400 million years, insects might appear as a group to be indestructible, but recent studies documenting striking patterns of decline have raised concerns about their future in a world profoundly altered by human activities. The 12 papers in the Global Decline of Insects in the Anthropocene Special Feature examine losses of insect biodiversity from multiple perspectives. The 56 authors evaluate threats to insect biodiversity across three main dimensions of declines—insect biomass, abundance, and species numbers. Many insect populations are decreasing at annual rates of 1-2% a year—a dangerous clip when extended over even a few decades. In a perspective Raven and Wagner place these declines in the context of human population growth, currently at 7.8 billion and already exploiting most of the planet’s arable land for agriculture. Two articles document worrying declines of butterflies and moths in the Neotropics, both linked to climate changes and harbingers of the broader fate of Earth’s tropical forests, home to the vast majority of insect species. At the same time, several papers identify species that are increasing in abundance and geographic distribution, especially in temperate and Arctic areas, where insects have been historically limited by winter conditions. The collection exposes many of the challenges associated with documenting insect diversity. Schowalter et al., for example, provide new data that contradicts an earlier study of catastrophic losses of insects in a Puerto Rican forest. Janzen and Hallwachs describe an ambitious effort by Costa Rica to bioinventory its entire biota to advance national bioliteracy and the long-term protection of its wild biodiversity. Many of the articles suggest ways forward—short- and long-term actions, ranging from the individual to the national level—to protect insects and sustain the ecosystem services that they provide.


Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr David Yeates is Director of the Australian National Insect Collection, CSIRO National Facilities and Collections

Several studies over recent years have documented declines in insect abundance, biomass, distribution and diversity.  The best evidence comes from Europe and North America, areas that combine high human population density and widespread agriculture with the scientific infrastructure to sustain detailed insect abundance studies over decades. Evidence from other parts of the world, including Australia, is limited, at best.

The most likely common explanation for insect declines is the range of effects that agricultural intensification has in simplifying landscapes and ecosystems. It would be sensible to conclude that Australian insects are not immune to these effects, including land clearing, increased fertilizer and insecticide application, and the gradual removal of non-crop areas in these landscapes. About 75% of Australian arable land has been either cleared of native vegetation or disturbed and modified. 

Australian insect declines are likely occurring in the areas of the country that have experienced the greatest agricultural intensification, areas such as the Murray-Darling Basin,  the wheat belt of southern Australia, and the peri-urban areas around our major cities.

The magnitude, rate and geographic extent of the declines are not well understood.  There is evidence of a number of species in decline over relatively small spatial scales during the last 40 years.  Climate change often acts through intermediary drivers like fire to impact insect populations negatively.  Insects restricted to cooler areas at the summits of mountains in eastern Australia are likely to suffer population declines and possibly extinction as the weather warms and their habitats shrink as they move higher in altitude.

Last updated: 14 Jan 2021 3:28pm
Declared conflicts of interest:
None declared.
Associate Professor Greg Holwell, Te Kura Mātauranga Koiora | School of Biological Sciences, Te Whare Wānanga o Tāmaki Makaurau | University of Auckland

For Aotearoa New Zealand, the most important message is that we need to invest in assessing and monitoring our precious insect communities, because we simply don't know if most of our native insects are in decline as in other parts of the world. One positive note is that there are now more people taking notice of our extraordinary insects, and this might lead to a greater appreciation of their inherent value, and greater conservation effort. I think it is an exciting time for those of us who love insects. From kids adding pictures of their backyard insects to iNaturalist to those working to protect our iconic insect fauna and their habitats, everyone can make a difference.

Last updated: 12 Jan 2021 12:14pm
Declared conflicts of interest:
No conflicts of interest
Professor Saul Cunningham, Director of the Fenner School of Environment & Society at the Australian National University

Insects are hugely important to ecological processes that humans rely on, including the provision of food and recycling of nutrients into the soil. That is why they have been described as the little things that run the world. These latest studies confirm that serious declines in insect diversity and abundance are happening in a number of well-studied locations around the world, including some agricultural landscapes and alpine areas affected by climate warming.

They also show that insect declines are not universal, with losses not apparent for some other regions. The studies add significant urgency to the case that we need to develop agricultural practices that support healthy and diverse insect populations. We can learn from those places that are not witnessing dramatic insect declines. Globally we are not monitoring insect populations in a widespread or systematic way, which limits our power to respond. For this reason, it is very difficult to know if Australian insect populations are among those in decline, and it would pay to monitor trends especially in agricultural areas and at high elevations.

Last updated: 12 Jan 2021 11:14am
Declared conflicts of interest:
Philip Batterham is Professor Emeritus, School of BioSciences and the Bio21 Institute, University of Melbourne

Insects are like the canaries once used to warn miners of the presence of toxic gases and the urgent need to flee to safety.  The demise of insects alerts us to our abuse of this planet through habitat destruction, climate change and excessive use of pesticides.  My own research has caused me to be concerned about insecticide use and the way in which it may synergize with these other stressors, particularly climate change, to harm beneficial insects. Agricultural productivity and ecosystem health are both absolutely dependent on insects.  Like the miners of old, we need to heed the warning.  Unlike the miners of old, we cannot afford to let the ‘canaries’ die.
Two world clocks are ticking. With every passing minute the global human population is increasing, while the available land useful for agriculture is decreasing.  We need to intensively research how human activity is impacting insects and find sustainable ways to produce our food.

Last updated: 12 Jan 2021 11:12am
Declared conflicts of interest:
Phillip has declared he has no conflict of interest.

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