Is this a new Silent Spring?

Entomologists have united to take stock of growing warnings about an “insect apocalypse” in a special feature published in the journal PNAS.

These teeny little critters, some of which have been around for about 475 million years, provide vital ecosystem services yet have received relatively little attention compared to other animals as the Earth faces a sixth mass extinction.

And while awareness is rising, the emerging picture is far more nuanced than initial reports suggested, according to David Wagner from the University of Connecticut, US, and his co-authors in the feature’s introductory overview.

The feature arose from a perceived need to provide a critical evaluation of the research and understand these complexities to help address the issue – which it confirms is serious.

“Nature is under siege,” Wagner and his colleagues warn, noting that millions of acres of tropical forest – home to around half the world’s insects – are cleared every year, a predicament compounded by insecticides, herbicides, human-caused climate change and light and sound pollution.

Of the dozen papers, more than half focus on these stressors, with erratic and warming weather emerging as major contributors, along with agriculture and habitat destruction.

Across Europe, a review of butterfly populations reports up to an 80% decline, attributed largely to habitat loss and degradation as well as chemical pollution.

Not to be overlooked, moths have also received considerable attention, with “an alarming record of decreases in moth abundance and diversity from across Europe,” write Wagner and others in a separate paper.

In reviewing the plight of moths, which they say are considerably more diverse than butterflies ecologically and taxonomically, they find multiple stressors are at play including habitat destruction, pesticides and light pollution.

The worst declines are from the Northern Hemisphere, attributed to human population density and intensive agriculture.

In the latter regard, Peter Raven, also from the University of Connecticut, and Wagner write that the industrialisation of agriculture created large expanses of monocrops, increased use of pesticides and fertilisers, and removal of hedgerows and other wildlife refuges.

Bees have been major casualties of modern farming, they add, noting increasing reports of population declines in Europe that ironically compromise bees’ contribution to food crop pollination valued at USD$518 billion per year.

As previously noted, improving agricultural practices appears vital in order to mitigate insect declines, although Raven and Wagner note regional differences need to be considered in working out the best approaches.

Christopher Halsch, from the University of Nevada, US, and co-authors, review the effects of climate change on insect populations. While they find the declines to be “staggering” overall, they note that the impacts are variable and that some species even benefit.

Evidence of insect resilience in extenuating conditions offers a glimmer of hope, they say, noting that if some stressors can be addressed, certain species could survive.

“Unlike animals with larger home ranges and greater per-individual resource requirements, insects are remarkable in the speed with which they respond to a bit of hedgerow improvement or even a backyard.”

Indeed, a few of the papers report that some insect numbers have not dropped and others have even increased. Some freshwater insects, for instance, have benefited from clean water legislation in Europe and North America, while some native insects thrived by sourcing nectar and food from non-native plants.

While we can take heart from such successes and learn from them, the overall message adds to an urgent wake-up call that is embraced by other scientists.

“These latest studies confirm that serious declines in insect diversity and abundance are happening in a number of well-studied locations around the world,” says Saul Cunningham from the Australian National University, “including some agricultural landscapes and alpine areas affected by climate warming.”

Philip Batterham, from Australia’s University of Melbourne, underscores the urgency of the situation, warning that insects are like canaries in a coal mine. “The demise of insects alerts us to our abuse of this planet through habitat destruction, climate change and excessive use of pesticides,” he says. “Like the miners of old, we need to heed the warning. Unlike the miners of old, we cannot afford to let the ‘canaries’ die.”

Identifying challenges with documenting insect populations and diversity, the special series highlights the need for further research and analysis of untapped public datasets, writes Wagner.

But, he adds, “[T]ime is not on our side,” urging for multifaceted action to address anthropogenic stressors and increase public education to “find ways to integrate insects and other arthropods into the fabric of daily human life”.